WO2017163685A1 - Video processing device, display apparatus, video processing method, control program, and recording medium - Google Patents

Video processing device, display apparatus, video processing method, control program, and recording medium Download PDF

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Publication number
WO2017163685A1
WO2017163685A1 PCT/JP2017/005763 JP2017005763W WO2017163685A1 WO 2017163685 A1 WO2017163685 A1 WO 2017163685A1 JP 2017005763 W JP2017005763 W JP 2017005763W WO 2017163685 A1 WO2017163685 A1 WO 2017163685A1
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gradation value
value
luminance level
gradation
maximum luminance
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PCT/JP2017/005763
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French (fr)
Japanese (ja)
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下田　裕紀
神田　貴史
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シャープ株式会社
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Priority claimed from JP2016181002A external-priority patent/JP2017184220A/en
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Publication of WO2017163685A1 publication Critical patent/WO2017163685A1/en

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N7/00—Television systems
    • H04N7/01—Conversion of standards, e.g. involving analogue television standards or digital television standards processed at pixel level

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  • the present invention relates to a video processing device or the like that converts a gradation value of an HDR signal.
  • HDR High Dynamic Range
  • SDR Standard Dynamic Range
  • the SDR signal is produced on the premise of reproduction in a reproduction environment (hereinafter referred to as “SDR environment”) having an EOTF (Electro-Optical Transfer Function) equivalent to ⁇ 2.2, while the HDR signal is , And SMPTE-ST2084 (hereinafter abbreviated as “ST2084”), etc., are manufactured on the premise of reproduction in a reproduction environment (hereinafter referred to as “SDR environment”) having an EOTF. For this reason, when the HDR signal is reproduced in the SDR environment, the luminance of the obtained video is different from the luminance intended by the manufacturer.
  • Patent Document 1 discloses a liquid crystal display device that performs dimming control of a backlight by changing a change width of an average luminance level before and after dynamic range expansion by an average luminance level and a ⁇ adjustment value of an input video signal. Has been.
  • a scan conversion unit that scan-converts an input video signal into a signal having a predetermined number of scanning lines, a gamma correction unit that gamma-corrects a signal from the scan conversion unit, and a signal level from the input video signal.
  • a plasma display that includes a level detection unit that detects and controls a gamma correction unit based on the detection signal, and controls the average luminance in accordance with the input signal level.
  • Japanese Patent Publication Japanese Patent Publication “Japanese Laid-Open Patent Publication No. 2002-108305 (published on April 10, 2002)” Japanese Patent Publication “Japanese Laid-Open Patent Publication No. 2002-354378 (Released on Dec. 6, 2002)”
  • the EOTF of the HDR signal is different from that of the SDR signal. Therefore, when converting the gradation value taken by each pixel by the HDR signal, if the entire domain of the HDR signal EOTF is mapped to the domain of the SDR signal EOTF, the gradation value is reduced (different levels). The tone value is mapped to the same tone value).
  • the number of gradations per unit luminance difference is particularly large in a low luminance region in order to express a slight difference in brightness in a dark part. For this reason, when the gradation value taken by each pixel is converted by the HDR signal by such mapping, the gradation value is likely to be degenerated in the low luminance region.
  • a range corresponding to a luminance level equal to or lower than the maximum luminance level of content in the EOTF definition region for HDR signals is mapped to the EOTF definition region for SDR signals.
  • a method is conceivable.
  • each pixel can take a gradation value corresponding to a luminance of 10000 cd / m 2 or less, but not all of these gradation values are used in actual content. For this reason, if pixel values taken by each pixel with the HDR signal are converted by such mapping, it is possible to suppress black crushing and gradation value degeneration.
  • the HDR signal includes metadata representing the maximum luminance of content called MAX_CLL (Maximum Content Light Level). The maximum brightness of the content can be specified by referring to this metadata.
  • the maximum luminance level of the content is the luminance level of a specific pixel in a specific frame of a specific scene. Therefore, in a frame other than this specific frame or in a scene other than this specific scene, a gradation value that is not actually used is mapped to the definition area of the SDR signal EOTF. That is, in the method of mapping the range corresponding to the luminance level equal to or lower than the maximum luminance level of the content in the EOTF definition area for the HDR signal to the EOTF definition area for the SDR signal, the level that can occur in the low luminance area There remains room for further suppression of degeneration of the tone value.
  • the present invention has been made in view of the above problems, and an object of the present invention is to provide a gradation value conversion apparatus for converting gradation values of HDR signals, which can reduce gradation values that can occur in a low luminance region. Is to realize a gradation value conversion apparatus in which the above is further suppressed.
  • a video processing device converts a gradation value taken by each pixel in a video signal according to a second video format having a wider luminance range than the first video format.
  • a virtual maximum that sets a virtual maximum luminance level lower than a maximum luminance level indicated by metadata included in the video signal by referring to a gradation value taken by each pixel in the video signal.
  • a luminance level setting unit; and a gradation value conversion unit that converts a gradation value corresponding to each luminance level equal to or lower than the virtual maximum luminance level among gradation values taken by each pixel in the video signal.
  • a video processing method is a video processing method for converting a gradation value taken by each pixel in a video signal according to a second video format having a wider luminance range than the first video format.
  • a virtual maximum luminance level setting step for setting a virtual maximum luminance level lower than a maximum luminance level indicated by metadata included in the video signal by referring to a gradation value taken by each pixel in the video signal;
  • a gradation value conversion apparatus that further suppresses gradation value degeneration that may occur in a low luminance region.
  • Embodiment 1 (Display device 1) A display device 1 including a gradation value conversion device (video processing device) 2 according to a first embodiment of the present invention will be described with reference to FIGS.
  • FIG. 1 is a block diagram illustrating a configuration of a display device 1 including a gradation value conversion device 2 according to the present embodiment.
  • FIG. 2 is a perspective view showing the appearance of the display device 1.
  • the display device 1 includes a gradation value conversion device 2, a panel control unit 6, and a display panel 7.
  • the gradation value conversion device 2 is a device that converts the gradation value of each pixel of the HDR signal (video signal according to the second video format), and includes a video data acquisition unit 3, a virtual maximum luminance level setting unit 4, and a floor.
  • a tone value conversion unit 5 is provided.
  • the video data acquisition unit 3 acquires an HDR signal.
  • the HDR signal acquired by the video data acquisition unit 3 is an HDMI signal based on the HDMI (registered trademark) (High-Definition Multimedia Interface) standard, a Tuner signal (a signal received by the tuner), and a CVBS. (Composite Video, Blanking, and Sync: composite video signal) signal or the like.
  • the HDR signal includes metadata such as MAX_CLL indicating the maximum luminance level of content in addition to the gradation value taken by each pixel.
  • the virtual maximum luminance level setting unit 4 refers to the gradation value or metadata included in the HDR signal acquired by the video data acquisition unit 3, and sets a virtual maximum luminance level having a value smaller than the maximum luminance level indicated by MAX_CLL for each frame. Or set for each scene.
  • the gradation value conversion unit 5 refers to the virtual maximum luminance level set by the virtual maximum luminance level setting unit 4, and converts the gradation value taken by each pixel in the HDR signal from the first gradation value to the second gradation. Convert to value.
  • the gradation value converting unit 5 corresponds to each luminance level equal to or lower than the virtual maximum luminance level set by the virtual maximum luminance level setting unit 4 among the gradation values that each pixel can take in the HDR signal. Is used for mapping each tone value in the EOTF domain for the SDR signal (video signal according to the first video format).
  • the panel control unit 6 controls the luminance of each pixel of the display panel 7 to a luminance value corresponding to the gradation value obtained by the gradation value conversion unit 5 in the SDR EOTF. As a result, the video represented by the HDR signal is displayed on the display panel 7 with the original luminance.
  • the display panel 7 may be realized by any device as long as it is capable of displaying images. Specific examples include a liquid crystal display, an organic EL (Electro Luminescence) display, a plasma display, and the like. Is mentioned.
  • FIG. 3 is a flowchart showing the flow of gradation conversion processing.
  • FIG. 4 is a graph showing the content of the gradation conversion process.
  • the gradation value conversion apparatus 2 performs the steps S0 to S4 described below for each frame, thereby changing the gradation value of each pixel constituting the HDR signal from the first gradation value. Conversion to the second gradation value.
  • the video data acquisition unit 3 acquires an HDR signal (step S0).
  • the video data acquisition unit 3 supplies the virtual maximum luminance level setting unit 4 and the gradation value conversion unit 5 with the gradation values taken by each pixel constituting the processing target frame in the acquired HDR signal.
  • the virtual maximum luminance level setting unit 4 acquires the gradation value taken by each pixel constituting the processing target frame from the video data acquisition unit 3, and acquires the maximum value of the acquired gradation value (the maximum gradation value in the frame). ) (The maximum luminance value in the frame) corresponding to) is set as the virtual maximum luminance level (step S1).
  • FIG. 4A shows a correspondence relationship (OETF) between the luminance value and the gradation value in the HDR signal.
  • the maximum luminance value in the frame corresponding to the maximum gradation value in the frame is lower than the maximum luminance level of the content indicated by MAC_CLL. Therefore, the virtual maximum brightness level set in this step is lower than the maximum brightness level of the content indicated by MAC_CLL.
  • the virtual maximum luminance level setting unit 4 supplies the set virtual maximum luminance level to the gradation value conversion unit 5.
  • the gradation value conversion unit 5 acquires the gradation value taken by each pixel constituting the processing target frame from the video data acquisition unit 3, and acquires the acquired gradation value from the first gradation value to the second value. Conversion into gradation values (step S2). For this conversion, the gradation value conversion unit 5 acquires the virtual maximum luminance level from the virtual maximum luminance level setting unit 4, and among the gradation values that each pixel can take for the HDR signal, the acquired virtual maximum luminance level A mapping is used in which the gradation value x corresponding to each luminance level y below the level is associated with each gradation value X in the definition area of the EOTF for the SDR signal.
  • MAX_y represents a virtual maximum brightness level
  • MAX_Y represents a maximum value of the EOTF value range for the SDR signal (corresponding to the maximum brightness level of the display device).
  • 4B is a graph showing the relationship between the luminance value x before conversion and the gradation value y (HETF signal OETF), and FIG. 4C shows the luminance value X after conversion. It is a graph showing the relationship with the gradation value Y (OETF for SDR signal).
  • the gradation value conversion unit 5 supplies the converted gradation value taken by each pixel constituting the processing target frame to the panel control unit 6.
  • the panel control unit 6 acquires the converted gradation value taken by each pixel constituting the processing target frame from the gradation value conversion unit 5, and converts the acquired gradation value into a luminance value (step S3). ).
  • the panel control unit 6 uses an EOTF for SDR, for example, an EOTF equivalent to ⁇ 2.2. This conversion is also called tone mapping, and the correspondence between the gradation value and the luminance value in this conversion is also called a tone curve.
  • the panel control unit 6 controls the luminance of each pixel constituting the display panel 7 to the luminance value obtained by tone mapping. As a result, the processing target frame is displayed on the display panel 7 (step S4).
  • the range corresponding to the luminance value equal to or lower than the virtual maximum luminance level is defined as the EOTF definition region for the SDR signal in the definition region of the HDR signal EOTF.
  • Use mapping to associate Since the virtual maximum luminance level is lower than the maximum luminance level indicated by MAC_CLL, the range corresponding to the luminance value equal to or lower than the maximum luminance level indicated by MAX_CLL is defined in the EOTF definition region for HDR signal. Compared with the case of using the mapping associated with the area, it is possible to suppress the black crushing and the gradation value degeneration.
  • the gradation value conversion process is executed for each frame, and the maximum luminance value in each frame is set as the virtual maximum luminance level.
  • the present embodiment is not limited to this.
  • gradation value conversion processing is executed for each scene, and the maximum in-scene luminance value of each scene (the maximum in-frame of all the frames constituting the scene). It is also possible to adopt a configuration in which the maximum luminance value) is set to the virtual maximum luminance level. In this case, before starting the gradation value conversion of the first frame constituting the processing target scene, the gradation values taken by the pixels constituting all the frames constituting the processing target scene are acquired, and the maximum luminance value in the scene is obtained.
  • the HDR signal includes metadata indicating the in-scene maximum luminance value of each scene
  • a configuration in which the virtual maximum luminance level is set with reference to the metadata may be employed. With such a configuration, gradation value conversion processing can be performed not only on HDR signals recorded on a recorder or the like but also on HDR signals received by a tuner or the like.
  • a configuration in which the temporal average value of the maximum luminance value in each frame is the virtual maximum luminance level may be adopted.
  • a known time average filter may be used.
  • the display device 1 including the gradation value conversion device 2 shown in FIG. 1 is used as in the first embodiment.
  • FIG. 5 is a flowchart showing the flow of the gradation value conversion process executed by the gradation value conversion apparatus according to the present embodiment. Note that the processing executed in steps S10 and S13 to S15 shown in FIG. 5 is the same as the processing executed in steps S0 and S2 to S4 shown in FIG. 3, respectively. For this reason, the processing executed in steps S11 to S12 will be described below.
  • step S11 the virtual maximum luminance level setting unit 4 generates a histogram of luminance values corresponding to the gradation values taken by each pixel constituting the processing target frame, and obtains the maximum histogram value from the generated histogram.
  • step S12 the virtual maximum luminance level setting unit 4 sets the virtual maximum luminance level to the maximum histo value obtained in step S11.
  • the maximum histogram value is a maximum value of luminance values excluding a specifically large luminance value among luminance values corresponding to gradation values taken by pixels constituting the processing target frame, and is an average value M of the histogram.
  • the standard deviation ⁇ is a typical example of the maximum histo value.
  • FIG. 6 shows an example of the histogram generated in step S11.
  • some pixels take a specifically large luminance value close to the maximum luminance level indicated by MAX_CLL.
  • the gradation value conversion step In S13 the region between the specifically large luminance value and the maximum value of the luminance value excluding the specifically large luminance value is unnecessarily associated with the SDR EOTF value range.
  • the luminance value excluding the large luminance value is specifically determined.
  • the SDR EOTF value range can be associated without waste.
  • a configuration has been described in which a histogram of luminance values is created for each frame, and the maximum value within the frame of each frame is a virtual maximum luminance level, but the present embodiment is not limited to this.
  • a histogram of luminance values is executed for each scene and the maximum value of the in-scene hist of each scene is set as a virtual maximum luminance level. It is.
  • a histogram of luminance values corresponding to the gradation values taken by the pixels constituting all the frames constituting the processing target scene is created.
  • the maximum value of the hist in the scene is set to the virtual maximum luminance level.
  • the HDR signal includes metadata indicating the in-scene maximum value of each scene, it is possible to adopt a configuration in which the virtual maximum luminance level is set with reference to this metadata. With such a configuration, gradation value conversion processing can be performed not only on HDR signals recorded on a recorder or the like but also on HDR signals received by a tuner or the like.
  • a configuration in which the time average value of the in-frame maximum value of each frame is the virtual maximum luminance level may be adopted.
  • a known time average filter may be used in calculating the time average value of the intra-frame maximum value of each frame.
  • FIG. 7 is a flowchart showing the flow of the gradation value conversion process executed by the gradation value conversion apparatus according to this embodiment.
  • the processes executed in step S100 and steps S106 to S108 shown in FIG. 7 are the same as the processes executed in steps S0 and S2 to S4 shown in FIG. 3, respectively. For this reason, the processing executed in steps S101 to S105 will be described below.
  • step S101 the virtual maximum luminance level setting unit 4 generates a histogram of luminance values corresponding to the gradation values taken by each pixel constituting the processing target frame, and obtains a maximum histogram value from the generated histogram.
  • the definition of the maximum hysteresis value is the same as that given in the second embodiment.
  • the virtual maximum brightness level setting unit 4 sets a limit value that is lower than the maximum brightness level indicated by MAC_CLL by a predetermined value.
  • the predetermined value is an arbitrary value and may be set at the time of shipment from the factory, or may be set by the user after shipment from the factory.
  • step S103 the virtual maximum luminance level setting unit 4 determines whether or not the maximum histogram value calculated in step S101 is lower than the limit value calculated in step S102.
  • step S104 when the maximum histo value is lower than the limit value, in step S104, the virtual maximum luminance level setting unit 4 sets the virtual maximum luminance level to the limit value.
  • step S106 the range below the limit value in the definition area of the HDR signal OETF is mapped to the whole definition area of the ODR for SDR signal.
  • the virtual maximum luminance level setting unit 4 sets the virtual maximum luminance level to the maximum histogram value in step S105.
  • step S106 the range below the maximum histogram value in the HDR signal EOTF value range is mapped to the entire SDR signal EOTF value range.
  • the virtual maximum luminance that can occur when the maximum value of the histogram becomes extremely small by providing a limit value for the virtual maximum luminance level. It is possible to prevent a decrease in image quality due to a large level fluctuation.
  • the flow of the gradation value conversion process executed by the gradation value conversion apparatus 2 according to the present embodiment is similar to the gradation conversion process executed by the gradation value conversion apparatus 2 according to the third embodiment, as shown in FIG. Is expressed by the flowchart shown in FIG.
  • the limit value setting process S102 in the third embodiment is replaced with a limit value setting process S109 described below.
  • the virtual maximum luminance level setting unit 4 has a predetermined ratio between the difference obtained by subtracting the limit value from the maximum luminance level indicated by MAX_CLL and the difference obtained by subtracting the maximum histogram value in the luminance histogram from the limit value.
  • the predetermined ratio is an arbitrary ratio, and may be set at the time of shipment from the factory, or may be set by the user after shipment from the factory.
  • step S104 when the maximum histo value is lower than the limit value, in step S104, the virtual maximum luminance level setting unit 4 sets the virtual maximum luminance level to the limit value.
  • step S106 the range below the limit value in the definition area of the HDR signal OETF is mapped to the whole definition area of the SDR signal OETF.
  • the virtual maximum luminance level setting unit 4 sets the virtual maximum luminance level to the maximum histogram value in step S105.
  • step S106 the range below the maximum value of the histories of the EOTF for the HDR signal is mapped to the entire range of the EOTF for the SDR signal.
  • the virtual maximum luminance that can occur when the maximum value of the histogram becomes extremely small by providing a limit value for the virtual maximum luminance level. It is possible to prevent a decrease in image quality due to a large level fluctuation.
  • the virtual maximum luminance level setting unit 4 has a luminance value (maximum intra-frame luminance value) corresponding to the maximum gradation value (maximum intra-frame gradation value) taken by each pixel constituting the processing target frame. It was explained that is set to the virtual maximum luminance level. With this configuration, gradation values can be converted according to peak luminance, which is the greatest advantage of HDR.
  • the gradation value in the low gradation value region with respect to the luminance value is relatively lowered (blackout).
  • blackout the area in the image displayed with the gradation value in the low gradation value area becomes completely dark, resulting in insufficient expression.
  • the gradation value conversion apparatus 11 has the gradation value in the low gradation value region among the gradation values converted by the gradation value conversion unit 5.
  • the gradation value taken by each pixel constituting each frame or each scene is adjusted so as to have a lifting portion.
  • the low gradation value region indicates a gradation value region near the origin (a point where the gradation value and the corresponding luminance value are zero) in the converted gradation value.
  • the low gradation value area indicates an area having a gradation value of about one fifth when the gradation value is quantized with 8 bits (256 gradations (0 to 255)). (A region where the gradation value is 0 to 51).
  • the gradation value area having the gradation value larger than the maximum gradation value in the low gradation value area as the lowest gradation value is defined as the intermediate gradation value area, and the largest gradation in the intermediate gradation value area.
  • a region of gradation values having a gradation value larger than the tone value as the lowest gradation value is defined as a high gradation value region.
  • “having a lifting portion in the gradation value of the low gradation value region” means a low-order image generated by converting the gradation value by the gradation value conversion method described in the first embodiment. This means that the gradation value in the low gradation area is increased in order to improve the relative decrease (blackout) in the gradation value area.
  • FIG. 10 is a block diagram illustrating a configuration of the display device 10 including the gradation value conversion device (video processing device) 11 according to the present embodiment. As shown in FIG. 10, the gradation value conversion apparatus 11 further includes a gradation value adjustment unit 12 in addition to the configuration of the gradation value conversion apparatus 2 according to the first embodiment.
  • the gradation value adjustment unit 12 adjusts the gradation value converted by the gradation value conversion unit 5 to have a lifting unit in the gradation value in the low gradation value region.
  • FIG. 11 is a flowchart showing the flow of gradation value conversion processing.
  • the gradation value conversion process is executed for each frame, and the maximum luminance value in each frame is set as the virtual maximum luminance level.
  • the gradation value conversion process is executed for each scene, The same applies to the configuration in which the in-scene maximum luminance value of each scene is set as the virtual maximum luminance level.
  • the video data acquisition unit 3 acquires an HDR signal (step S20).
  • the video data acquisition unit 3 sets a gradation value taken by each pixel constituting the processing target frame in the acquired HDR signal as a virtual maximum luminance level setting unit. 4 and the gradation value converter 5.
  • the virtual maximum luminance level setting unit 4 acquires the gradation value taken by each pixel constituting the processing target frame from the video data acquisition unit 3, and acquires the maximum value of the acquired gradation value (the maximum gradation value in the frame). ) (The maximum luminance value in the frame) corresponding to) is set as the virtual maximum luminance level (step S21).
  • the gradation value conversion unit 5 acquires the gradation value taken by each pixel constituting the processing target frame from the video data acquisition unit 3, and among the acquired gradation values, the virtual maximum luminance level setting unit 4 The gradation value corresponding to each luminance level below the set virtual maximum luminance level is converted from the first gradation value to the second gradation value (step S22).
  • the gradation value adjustment unit 12 adjusts the gradation value converted by the gradation value conversion unit 5 to have a lifting unit in the gradation value in the low gradation value region (step S23).
  • a specific example of how the gradation value adjusting unit 12 adjusts the gradation value will be described later.
  • the gradation value adjusted by the gradation value adjustment unit 12 is preferably larger than the gradation value indicated by the predetermined format in the low gradation value region.
  • An example of the predetermined format is ST2084.
  • the panel control unit 6 acquires the adjusted gradation value taken by each pixel constituting the processing target frame from the gradation value adjustment unit 12, and converts the acquired gradation value into a luminance value (step S24). ) (Tone mapping).
  • the panel control unit 6 controls the luminance of each pixel constituting the display panel 7 to the luminance value obtained by tone mapping. Thereby, the processing target frame is displayed on the display panel 7 (step S25).
  • FIG. 12 is a graph showing the relationship between the converted gradation value and the corresponding luminance value.
  • a region A in FIG. 12 represents the above-described low gradation value region, a dotted line represents a curve before adjustment, and a solid line represents a curve after adjustment.
  • the gradation value adjustment unit 12 adjusts the converted gradation value so that the gradation value in the region A has a lifting part (adjusts from the dotted curve to the solid curve).
  • the gradation value adjusting unit 12 adjusts the gradation value in the low gradation value region by adding a value of about 10% of the gradation value.
  • the gradation value adjustment unit 12 graphs the gradation value corresponding to the gradation value with respect to the gradation value in the low gradation value region. In this case, adjustment is made so that the curve in the graph is equivalent to the curve of ⁇ 2.2.
  • the gradation value adjustment unit 12 may change the low gradation value region with reference to the average value of the luminance level corresponding to the gradation value converted by the gradation value conversion unit 5. Thereby, since the low gradation value region can be set according to the distribution of the luminance level, the gradation value can be adjusted according to the distribution of the luminance level.
  • the average value of the luminance levels referred to by the gradation value adjustment unit 12 may be calculated by the gradation value adjustment unit 12 itself or may be acquired from the outside.
  • the gradation value adjustment unit 12 has a gradation value in the low gradation value region and a gradation value in the high gradation value region in the graph of the gradation value converted by the gradation value conversion unit and the corresponding luminance level. Further, the gradation value in the middle gradation value region may be further adjusted so that “and” continuously change. As a result, in the image displayed with the adjusted gradation value, unnaturalness due to the difference between the gradation value in the low gradation value area and the gradation value in the high gradation value area can be eliminated.
  • the gradation value conversion apparatus 11 sets the virtual maximum luminance level to the maximum value of the luminance level, converts the gradation value with reference to the set virtual maximum luminance level, Of the converted gradation values, the gradation values in the low gradation value region are adjusted to have a lifting portion.
  • the virtual maximum luminance level to the maximum value of the luminance level, it is possible to maintain the fidelity of the peak feeling included in the video signal, and among the converted gradation values, the low gradation value
  • the gradation value of the region By adjusting the gradation value of the region so as to have a raised portion, it is possible to prevent black crushing due to a decrease in the gradation value of the low gradation value region, and to improve the gradation expressing ability of the low gradation value region.
  • the control block (particularly the video data acquisition unit 3, the virtual maximum luminance level setting unit 4 and the gradation value conversion unit 5) of the gradation value conversion device 2 is a logic circuit (hardware) formed in an integrated circuit (IC chip) or the like. ) Or by software using a CPU (Central Processing Unit).
  • the gradation value conversion device 2 includes a CPU that executes instructions of a program that is software that realizes each function, and a ROM (Read Only) in which the program and various data are recorded so as to be readable by a computer (or CPU). Memory) or a storage device (these are referred to as “recording media”), a RAM (Random Access Memory) for expanding the program, and the like. And the objective of this invention is achieved when a computer (or CPU) reads the said program from the said recording medium and runs it.
  • a “non-temporary tangible medium” such as a tape, a disk, a card, a semiconductor memory, a programmable logic circuit, or the like can be used.
  • the program may be supplied to the computer via an arbitrary transmission medium (such as a communication network or a broadcast wave) that can transmit the program.
  • a transmission medium such as a communication network or a broadcast wave
  • the present invention can also be realized in the form of a data signal embedded in a carrier wave in which the program is embodied by electronic transmission.
  • a video processing device (2, 11) converts a gradation value taken by each pixel in a video signal according to a second video format having a wider luminance range than the first video format.
  • a virtual maximum luminance level setting unit that sets a virtual maximum luminance level lower than the maximum luminance level indicated by the metadata included in the video signal by referring to the gradation value taken by each pixel in the video signal.
  • the gradation value conversion unit (5) is a level that each pixel can take in the second video format that the video signal follows.
  • a mapping is used in which tone values corresponding to each luminance level equal to or lower than the virtual maximum luminance level among tone values correspond to the tone values that each pixel can take in the first video format. The gradation value taken by each pixel is converted.
  • the video display quality can be further improved.
  • the first video format is an EOTF equivalent to ⁇ 2.2
  • the second format is an EOTF of SMPTE.
  • the format is ST2084.
  • the display quality of the video in the SDR playback environment can be improved.
  • the virtual maximum luminance level setting unit is a floor taken by each pixel constituting each frame or each scene in the video signal.
  • the virtual maximum luminance level is set by referring to the tone value.
  • the gradation value can be efficiently converted in accordance with the gradation value included in the video signal.
  • the virtual maximum luminance level setting unit (4) sets the virtual maximum luminance level in each frame or each scene in the video signal. Is set to the maximum value of the luminance level corresponding to the gradation value taken by each pixel.
  • the gradation value can be efficiently converted in accordance with the gradation value included in the video signal.
  • the video processing apparatus (11) according to aspect 6 of the present invention has a lifting unit in the gradation value of the low gradation value region among the gradation values converted by the gradation value conversion part in the aspect 5. Further, a gradation value adjusting unit (12) for adjusting to the above is further provided.
  • the gradation value adjustment unit refers to an average value of luminance levels corresponding to the gradation values converted by the gradation value conversion unit. Then, the low gradation value region is changed.
  • the gradation value region can be set according to the luminance level distribution, the gradation value can be adjusted according to the luminance level distribution.
  • the gradation value adjustment unit is a graph of the gradation value converted by the gradation value conversion unit and the corresponding luminance level. , The gradation value in the middle gradation value region is further adjusted so that the gradation value in the low gradation value region and the gradation value in the high gradation value region change continuously.
  • the gradation value adjusted by the gradation value adjustment unit is the gradation indicated by a predetermined format in the low gradation value region. Greater than the value.
  • the video conversion devices according to aspects 6 to 8 can be suitably used.
  • the virtual maximum luminance level setting unit (4) takes each pixel constituting each frame or each scene in the video signal.
  • a virtual maximum luminance level is set by creating a histogram of luminance levels corresponding to gradation values and referring to the histogram.
  • the gradation value can be more efficiently converted in accordance with the gradation value included in the video signal.
  • the virtual maximum luminance level setting unit (4) configures the virtual maximum luminance level and each frame or each scene in the video signal.
  • the effective maximum value of the luminance level corresponding to the gradation value taken by each pixel is set to the effective maximum value defined by a constant multiple of the standard deviation of the histogram.
  • the gradation value can be more efficiently converted in accordance with the gradation value included in the video signal.
  • the virtual maximum luminance level setting unit (4) sets a limit value lower than the maximum luminance level by a predetermined value, and the effective maximum luminance If the value is lower than the limit value, the virtual maximum brightness level is set to the limit value, and if the effective maximum value is greater than or equal to the limit value, the virtual maximum brightness level is set to the effective maximum value. To do.
  • the virtual maximum luminance level setting unit (4) is configured to subtract the limit value from the maximum luminance level, When the effective maximum value is lower than the limit value, the virtual maximum luminance level is set to the limit value when the effective maximum value is lower than the limit value. If the effective maximum value is greater than or equal to the limit value, the virtual maximum luminance level is set to the effective maximum value.
  • the limit value can be set to a desired value.
  • the video processing device (2) according to aspect 14 of the present invention is the image processing apparatus (2) according to aspect 14, wherein the virtual maximum luminance level is a luminance corresponding to a gradation value taken by each pixel constituting each frame or each scene in the HDR signal.
  • the effective maximum value of the level is set to the time average value of the effective maximum value defined by a constant multiple of the standard deviation of the histogram.
  • the video quality can be improved.
  • the display device (1, 10) according to the aspect 15 of the present invention includes any one of the video processing apparatuses according to the above aspects 1 to 14.
  • the display device can obtain the effects that the video processing device has in each aspect.
  • a video processing method is a video processing method for converting a gradation value taken by each pixel in a video signal according to a second video format having a luminance range wider than that of the first video format,
  • a virtual maximum luminance level setting step for setting a virtual maximum luminance level lower than a maximum luminance level indicated by metadata included in the video signal by referring to a gradation value taken by each pixel in the video signal;
  • the display device may be realized by a computer.
  • the display device is realized by the computer by operating the computer as each unit (software element) included in the display device.
  • a control program for the display device and a computer-readable recording medium on which the control program is recorded also fall within the scope of the present invention.

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Abstract

Even in a display apparatus supporting an SDR signal, the present invention efficiently converts gradation characteristics indicated by an HDR signal to gradation characteristics suitable for the display apparatus, and thereby, improves display quality. A video processing device (2) is provided with: a virtual maximum luminance level setting unit (4) that sets a virtual maximum luminance level that is lower than a maximum luminance level indicated by metadata included in a video signal; and a gradation value converting unit (5) that converts gradation values corresponding to respective luminance levels equal to or lower than the virtual maximum luminance level, among the gradation values taken by respective pixels in the video signal.

Description

映像処理装置、表示装置、映像処理方法、制御プログラム、および記録媒体VIDEO PROCESSING DEVICE, DISPLAY DEVICE, VIDEO PROCESSING METHOD, CONTROL PROGRAM, AND RECORDING MEDIUM
　本発明は、ＨＤＲ信号の階調値を変換する映像処理装置等に関する。 The present invention relates to a video processing device or the like that converts a gradation value of an HDR signal.
　近年、高画質化技術の１つとして、ＳＤＲ（Standard Dynamic Range）信号よりも、階調数（取り得る階調値の個数）が多く、かつ、より高輝度の情報を含むＨＤＲ（High Dynamic Range）信号が注目を集めている。ＨＤＲ信号を用いることより、従来よりも高輝度かつ高コントラストな迫力のある映像を得ることができる。 In recent years, as one of the high image quality technologies, HDR (High Dynamic Range) has more gradations (number of possible gradation values) and higher brightness information than SDR (Standard Dynamic Range) signals. ) The signal is getting attention. By using the HDR signal, it is possible to obtain a powerful image with higher brightness and higher contrast than before.
　ＳＤＲ信号は、γ２．２相当等のＥＯＴＦ（Electro-Optical Transfer Function）を有する再生環境（以下、「ＳＤＲ環境」と記載）での再生を前提として製作されているのに対して、ＨＤＲ信号は、ＳＭＰＴＥ－ＳＴ２０８４（以下、「ＳＴ２０８４」と略記）等のＥＯＴＦを有する再生環境（以下、「ＳＤＲ環境」と記載）での再生を前提として製作されている。このため、ＳＤＲ環境でＨＤＲ信号を再生すると、得られる映像の輝度が製作者の意図した輝度と異なってしまう。 The SDR signal is produced on the premise of reproduction in a reproduction environment (hereinafter referred to as “SDR environment”) having an EOTF (Electro-Optical Transfer Function) equivalent to γ2.2, while the HDR signal is , And SMPTE-ST2084 (hereinafter abbreviated as “ST2084”), etc., are manufactured on the premise of reproduction in a reproduction environment (hereinafter referred to as “SDR environment”) having an EOTF. For this reason, when the HDR signal is reproduced in the SDR environment, the luminance of the obtained video is different from the luminance intended by the manufacturer.
　このような問題を回避するための方法としては、例えば、ＳＤＲ環境でＨＤＲ信号を表示する前に、ＨＤＲ信号で各画素が取る階調値を、ＨＤＲ環境において作成者の意図した輝度に対応する第１の階調値から、ＳＤＲ環境において作成者の意図した輝度に対応する第２の階調値に変換することなどが考えられる。例えば、ＨＤＲ環境におけるＥＯＴＦをｆ、ＳＤＲ環境におけるＥＯＴＦをｇとすると、この変換は、第１の階調値ｘを、第２の階調値ｙ＝ｇ－１（ｆ（ｘ））に対応させるマッピングとなる。 As a method for avoiding such a problem, for example, before displaying the HDR signal in the SDR environment, the gradation value taken by each pixel in the HDR signal corresponds to the brightness intended by the creator in the HDR environment. It is conceivable to convert the first gradation value into a second gradation value corresponding to the brightness intended by the creator in the SDR environment. For example, if the EOTF in the HDR environment is f and the EOTF in the SDR environment is g, this conversion corresponds to the first gradation value x and the second gradation value y = g −1 (f (x)). Mapping.
　再生環境のＥＯＴＦ又はガンマカーブに関連する技術を開示した文献としては、例えば、特許文献１～２が挙げられる。特許文献１には、入力映像信号の平均輝度レベル及びγ調整値によりダイナミックレンジ拡大前後の平均輝度レベルの変化幅を毎フレーム変化させることにより、バックライトの調光制御を行う液晶表示装置が開示されている。 Examples of documents disclosing technologies related to EOTF or gamma curve in the reproduction environment include, for example, Patent Documents 1 and 2. Patent Document 1 discloses a liquid crystal display device that performs dimming control of a backlight by changing a change width of an average luminance level before and after dynamic range expansion by an average luminance level and a γ adjustment value of an input video signal. Has been.
　特許文献２には、入力映像信号を所定の走査線数を有する信号に走査変換する走査変換部と、この走査変換部からの信号をガンマ補正するガンマ補正部と、入力映像信号から信号レベルを検出し、この検出信号によりガンマ補正部を制御するレベル検出部とを備え、入力信号レベルに応じて平均輝度を制御するプラズマディスプレイが開示されている。 In Patent Document 2, a scan conversion unit that scan-converts an input video signal into a signal having a predetermined number of scanning lines, a gamma correction unit that gamma-corrects a signal from the scan conversion unit, and a signal level from the input video signal. There is disclosed a plasma display that includes a level detection unit that detects and controls a gamma correction unit based on the detection signal, and controls the average luminance in accordance with the input signal level.
日本国公開特許公報「　特開２００２－１０８３０５号公報（２００２年４月１０日公開）」Japanese Patent Publication “Japanese Laid-Open Patent Publication No. 2002-108305 (published on April 10, 2002)” 日本国公開特許公報「　特開２００２－３５４３７８号公報（２００２年１２月６日公開）」Japanese Patent Publication “Japanese Laid-Open Patent Publication No. 2002-354378 (Released on Dec. 6, 2002)”
　上述したように、ＨＤＲ信号は、ＳＤＲ信号よりも高輝度の情報を含むように構成されているため、ＨＤＲ信号のＥＯＴＦは、ＳＤＲ信号のものと異なる。したがって、ＨＤＲ信号で各画素が取る階調値を変換する際に、ＨＤＲ信号用のＥＯＴＦの定義域全体をＳＤＲ信号用のＥＯＴＦの定義域にマッピングしようとすると、階調値の縮退（異なる階調値が同一の階調値にマッピングされることを指す）が生じることがある。特に、ＳＭＰＴＥ－ＳＴ２０８４等のＨＤＲ用のＥＯＴＦでは、暗部における僅かな明暗の違いを表現するべく、単位輝度差あたり階調数が低輝度領域において特に大きくなっている。このため、このようなマッピングによりＨＤＲ信号で各画素が取る階調値を変換すると、低輝度領域において階調値の縮退が生じ易い。 As described above, since the HDR signal is configured to include information with higher luminance than the SDR signal, the EOTF of the HDR signal is different from that of the SDR signal. Therefore, when converting the gradation value taken by each pixel by the HDR signal, if the entire domain of the HDR signal EOTF is mapped to the domain of the SDR signal EOTF, the gradation value is reduced (different levels). The tone value is mapped to the same tone value). In particular, in HDR EOTF such as SMPTE-ST2084, the number of gradations per unit luminance difference is particularly large in a low luminance region in order to express a slight difference in brightness in a dark part. For this reason, when the gradation value taken by each pixel is converted by the HDR signal by such mapping, the gradation value is likely to be degenerated in the low luminance region.
　このような問題を解決するための方法としては、ＨＤＲ信号用のＥＯＴＦの定義域のうち、コンテンツの最大輝度レベル以下の輝度レベルに対応する範囲を、ＳＤＲ信号用のＥＯＴＦの定義域にマッピングする方法が考えられる。ＨＤＲ信号で各画素は１００００ｃｄ/ｍ２以下の輝度に対応する階調値を取り得るが、これらの階調値の全部が実際のコンテンツで使われるわけではない。このため、このようなマッピングによりＨＤＲ信号で各画素が取る画素値を変換すれば、黒潰れの抑制、階調値の縮退の抑制を行うことができる。なお、ＨＤＲ信号には、ＭＡＸ＿ＣＬＬ（Maximum Content Light Level）と呼ばれる、コンテンツの最大輝度を表すメタデータが含まれている。コンテンツの最大輝度は、このメタデータを参照することにより特定することが可能である。 As a method for solving such a problem, a range corresponding to a luminance level equal to or lower than the maximum luminance level of content in the EOTF definition region for HDR signals is mapped to the EOTF definition region for SDR signals. A method is conceivable. In the HDR signal, each pixel can take a gradation value corresponding to a luminance of 10000 cd / m 2 or less, but not all of these gradation values are used in actual content. For this reason, if pixel values taken by each pixel with the HDR signal are converted by such mapping, it is possible to suppress black crushing and gradation value degeneration. Note that the HDR signal includes metadata representing the maximum luminance of content called MAX_CLL (Maximum Content Light Level). The maximum brightness of the content can be specified by referring to this metadata.
　しかしながら、コンテンツの最大輝度レベルは、ある特定のシーンの、ある特定のフレームの、ある特定の画素の輝度レベルである。したがって、この特定のフレーム以外のフレーム、あるいは、この特定のシーン以外のシーンでは、実際に使われない階調値がＳＤＲ信号用のＥＯＴＦの定義域にマッピングされてしまっていることになる。すなわち、ＨＤＲ信号用のＥＯＴＦの定義域のうち、コンテンツの最大輝度レベル以下の輝度レベルに対応する範囲を、ＳＤＲ信号用のＥＯＴＦの定義域にマッピングする方法には、低輝度領域において生じ得る階調値の縮退を更に抑制する余地が残されている。 However, the maximum luminance level of the content is the luminance level of a specific pixel in a specific frame of a specific scene. Therefore, in a frame other than this specific frame or in a scene other than this specific scene, a gradation value that is not actually used is mapped to the definition area of the SDR signal EOTF. That is, in the method of mapping the range corresponding to the luminance level equal to or lower than the maximum luminance level of the content in the EOTF definition area for the HDR signal to the EOTF definition area for the SDR signal, the level that can occur in the low luminance area There remains room for further suppression of degeneration of the tone value.
　本発明は、前記の問題点に鑑みてなされたものであり、その目的は、ＨＤＲ信号の階調値を変換する階調値変換装置であって、低輝度領域において生じ得る階調値の縮退を更に抑制された階調値変換装置を実現することである。 The present invention has been made in view of the above problems, and an object of the present invention is to provide a gradation value conversion apparatus for converting gradation values of HDR signals, which can reduce gradation values that can occur in a low luminance region. Is to realize a gradation value conversion apparatus in which the above is further suppressed.
　上記の課題を解決するために、本発明の一態様に係る映像処理装置は、第１の映像フォーマットよりも輝度範囲の広い第２の映像フォーマットに従う映像信号において各画素が取る階調値を変換する映像処理装置であって、上記映像信号において各画素が取る階調値を参照することによって、上記映像信号に含まれるメタデータが示す最大輝度レベルよりも低い仮想最大輝度レベルを設定する仮想最大輝度レベル設定部と、上記映像信号において各画素が取る階調値のうち、上記仮想最大輝度レベル以下の各輝度レベルに対応する階調値を変換する階調値変換部と、を備えている。 In order to solve the above problem, a video processing device according to an aspect of the present invention converts a gradation value taken by each pixel in a video signal according to a second video format having a wider luminance range than the first video format. A virtual maximum that sets a virtual maximum luminance level lower than a maximum luminance level indicated by metadata included in the video signal by referring to a gradation value taken by each pixel in the video signal. A luminance level setting unit; and a gradation value conversion unit that converts a gradation value corresponding to each luminance level equal to or lower than the virtual maximum luminance level among gradation values taken by each pixel in the video signal. .
　また、本発明の一態様に係る映像処理方法は、第１の映像フォーマットよりも輝度範囲の広い第２の映像フォーマットに従う映像信号において各画素が取る階調値を変換する映像処理方法であって、上記映像信号において各画素が取る階調値を参照することによって、上記映像信号に含まれるメタデータが示す最大輝度レベルよりも低い仮想最大輝度レベルを設定する仮想最大輝度レベル設定ステップと、上記映像信号において各画素が取る階調値のうち、上記仮想最大輝度レベル以下の各輝度レベルに対応する階調値を変換する階調値変換ステップと、を含んでいる。 A video processing method according to an aspect of the present invention is a video processing method for converting a gradation value taken by each pixel in a video signal according to a second video format having a wider luminance range than the first video format. A virtual maximum luminance level setting step for setting a virtual maximum luminance level lower than a maximum luminance level indicated by metadata included in the video signal by referring to a gradation value taken by each pixel in the video signal; A gradation value conversion step of converting a gradation value corresponding to each luminance level equal to or lower than the virtual maximum luminance level among gradation values taken by each pixel in the video signal.
　本発明によれば、低輝度領域において生じ得る階調値の縮退を更に抑制された階調値変換装置を実現することができる。 According to the present invention, it is possible to realize a gradation value conversion apparatus that further suppresses gradation value degeneration that may occur in a low luminance region.
本発明の実施形態１、２および３に係る階調値変換装置を備えた表示装置の構成を示すブロック図である。It is a block diagram which shows the structure of the display apparatus provided with the gradation value converter which concerns on Embodiment 1, 2, and 3 of this invention. 上記表示装置の外観を示す図である。It is a figure which shows the external appearance of the said display apparatus. 本発明の実施形態１に係る階調値変換方法を説明するフローチャートである。It is a flowchart explaining the gradation value conversion method which concerns on Embodiment 1 of this invention. 本発明の実施形態１に係る階調値変換方法を説明するための図である。It is a figure for demonstrating the gradation value conversion method which concerns on Embodiment 1 of this invention. 本発明の実施形態２に係る階調値変換方法を説明するフローチャートである。It is a flowchart explaining the gradation value conversion method which concerns on Embodiment 2 of this invention. 本発明の実施形態２に係る階調値変換方法を説明するための図である。It is a figure for demonstrating the gradation value conversion method which concerns on Embodiment 2 of this invention. 本発明の実施形態３に係る階調値変換方法を説明するフローチャートである。It is a flowchart explaining the gradation value conversion method which concerns on Embodiment 3 of this invention. 本発明の実施形態３に係る階調値変換方法を説明するための図である。It is a figure for demonstrating the gradation value conversion method which concerns on Embodiment 3 of this invention. 本発明の実施形態４に係る階調値変換方法を説明するための図である。It is a figure for demonstrating the gradation value conversion method which concerns on Embodiment 4 of this invention. 本発明の実施形態５に係る階調値変換装置を備えた表示装置の構成を示すブロック図である。It is a block diagram which shows the structure of the display apparatus provided with the gradation value converter which concerns on Embodiment 5 of this invention. 本発明の実施形態５に係る階調値変換方法を説明するフローチャートである。It is a flowchart explaining the gradation value conversion method which concerns on Embodiment 5 of this invention. 本発明の実施形態５に係る階調値変換方法を説明するための図である。It is a figure for demonstrating the gradation value conversion method which concerns on Embodiment 5 of this invention.
　以下、本発明の実施形態について、詳細に説明する。ただし、本実施形態に記載されている構成は、特に特定的な記載がない限り、この発明の範囲をそれのみに限定する趣旨ではなく、単なる説明例に過ぎない。 Hereinafter, embodiments of the present invention will be described in detail. However, unless otherwise specified, the configuration described in the present embodiment is merely an illustrative example, and is not intended to limit the scope of the present invention.
　〔実施形態１〕
　（表示装置１）
　本発明の第１の実施形態に係る階調値変換装置（映像処理装置）２を備えた表示装置１について、図１および図２を参照して説明する。図１は、本実施形態に係る階調値変換装置２を備えた表示装置１の構成を示すブロック図である。また、図２は、表示装置１の外観を示す斜視図である。図１が示すように、表示装置１は、階調値変換装置２、パネル制御部６、および表示パネル７を備えている。 Embodiment 1
(Display device 1)
A display device 1 including a gradation value conversion device (video processing device) 2 according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram illustrating a configuration of a display device 1 including a gradation value conversion device 2 according to the present embodiment. FIG. 2 is a perspective view showing the appearance of the display device 1. As shown in FIG. 1, the display device 1 includes a gradation value conversion device 2, a panel control unit 6, and a display panel 7.
　（階調値変換装置２）
　階調値変換装置２は、ＨＤＲ信号（第２の映像フォーマットに従う映像信号）の各画素の階調値を変換する装置であり、映像データ取得部３、仮想最大輝度レベル設定部４、および階調値変換部５を備えている。映像データ取得部３は、ＨＤＲ信号を取得する。なお、映像データ取得部３が取得するＨＤＲ信号は、ＨＤＭＩ（登録商標）（High-Definition Multimedia Interface：高精細度マルチメディアインターフェース）規格に基づくＨＤＭＩ信号、Ｔｕｎｅｒ信号（チューナーによって受信した信号）およびＣＶＢＳ（Composite Video, Blanking, and Sync：コンポジット映像信号）信号等であり得る。また、ＨＤＲ信号には、各画素が取る階調値の他に、コンテンツの最大輝度レベルを示すＭＡＸ＿ＣＬＬ等のメタデータとして含まれる。仮想最大輝度レベル設定部４は、映像データ取得部３が取得したＨＤＲ信号に含まれる階調値またはメタデータを参照し、ＭＡＸ＿ＣＬＬが示す最大輝度レベルよりも値の小さい仮想最大輝度レベルをフレーム毎またはシーン毎に設定する。階調値変換部５は、仮想最大輝度レベル設定部４が設定した仮想最大輝度レベルを参照し、ＨＤＲ信号において各画素が取る階調値を、第１の階調値から第２の階調値に変換する。この際、階調値変換部５は、ＨＤＲ信号において各画素が取り得る階調値のうち、仮想最大輝度レベル設定部４が設定した仮想最大輝度レベル以下の各輝度レベルに対応する階調値を、ＳＤＲ信号（第１の映像フォーマットに従う映像信号）用のＥＯＴＦの定義域内の各階調値に対応させるマッピングが用いられる。 (Tone value converter 2)
The gradation value conversion device 2 is a device that converts the gradation value of each pixel of the HDR signal (video signal according to the second video format), and includes a video data acquisition unit 3, a virtual maximum luminance level setting unit 4, and a floor. A tone value conversion unit 5 is provided. The video data acquisition unit 3 acquires an HDR signal. The HDR signal acquired by the video data acquisition unit 3 is an HDMI signal based on the HDMI (registered trademark) (High-Definition Multimedia Interface) standard, a Tuner signal (a signal received by the tuner), and a CVBS. (Composite Video, Blanking, and Sync: composite video signal) signal or the like. The HDR signal includes metadata such as MAX_CLL indicating the maximum luminance level of content in addition to the gradation value taken by each pixel. The virtual maximum luminance level setting unit 4 refers to the gradation value or metadata included in the HDR signal acquired by the video data acquisition unit 3, and sets a virtual maximum luminance level having a value smaller than the maximum luminance level indicated by MAX_CLL for each frame. Or set for each scene. The gradation value conversion unit 5 refers to the virtual maximum luminance level set by the virtual maximum luminance level setting unit 4, and converts the gradation value taken by each pixel in the HDR signal from the first gradation value to the second gradation. Convert to value. At this time, the gradation value converting unit 5 corresponds to each luminance level equal to or lower than the virtual maximum luminance level set by the virtual maximum luminance level setting unit 4 among the gradation values that each pixel can take in the HDR signal. Is used for mapping each tone value in the EOTF domain for the SDR signal (video signal according to the first video format).
　（その他の部材）
　パネル制御部６は、表示パネル７の各画素の輝度を、ＳＤＲ用のＥＯＴＦにおいて階調値変換部５が得た階調値に対応する輝度値に制御する。これにより、ＨＤＲ信号が表す映像が本来の輝度で表示パネル７に表示される。表示パネル７は、映像の表示が可能な表示装置であればどのような装置によって実現されてもよいが、具体的な例としては、液晶ディスプレイ、有機ＥＬ（Electro Luminescence）ディスプレイ、およびプラズマディスプレイ等が挙げられる。 (Other parts)
The panel control unit 6 controls the luminance of each pixel of the display panel 7 to a luminance value corresponding to the gradation value obtained by the gradation value conversion unit 5 in the SDR EOTF. As a result, the video represented by the HDR signal is displayed on the display panel 7 with the original luminance. The display panel 7 may be realized by any device as long as it is capable of displaying images. Specific examples include a liquid crystal display, an organic EL (Electro Luminescence) display, a plasma display, and the like. Is mentioned.
　（階調値変換方法）
　本実施形態に係る階調値変換装置２により実行される階調変換処理（映像処理方法）の流れを、図３及び図４を参照して説明する。図３は、階調変換処理の流れを示すフローチャートである。図４は、階調変換処理の内容を示すグラフである。 (Tone value conversion method)
A flow of gradation conversion processing (video processing method) executed by the gradation value conversion apparatus 2 according to the present embodiment will be described with reference to FIGS. FIG. 3 is a flowchart showing the flow of gradation conversion processing. FIG. 4 is a graph showing the content of the gradation conversion process.
　本実施形態に係る階調値変換装置２は、以下に説明するステップＳ０～Ｓ４をフレーム毎に実効することによって、ＨＤＲ信号を構成する各画素の階調値を、第１の階調値から第２の階調値に変換する。 The gradation value conversion apparatus 2 according to the present embodiment performs the steps S0 to S4 described below for each frame, thereby changing the gradation value of each pixel constituting the HDR signal from the first gradation value. Conversion to the second gradation value.
　まず、映像データ取得部３は、ＨＤＲ信号を取得する（ステップＳ０）。映像データ取得部３は、取得したＨＤＲ信号において処理対象フレームを構成する各画素が取る階調値を仮想最大輝度レベル設定部４及び階調値変換部５に供給する。 First, the video data acquisition unit 3 acquires an HDR signal (step S0). The video data acquisition unit 3 supplies the virtual maximum luminance level setting unit 4 and the gradation value conversion unit 5 with the gradation values taken by each pixel constituting the processing target frame in the acquired HDR signal.
　次に、仮想最大輝度レベル設定部４は、処理対象フレームを構成する各画素が取る階調値を映像データ取得部３から取得し、取得した階調値の最大値（フレーム内最大階調値）に対応する輝度値（フレーム内最大輝度値）を仮想最大輝度レベルに設定する（ステップＳ１）。図４の（ａ）に、ＨＤＲ信号における輝度値と階調値との対応関係（ＯＥＴＦ）を示す。図４の（ａ）に示すように、フレーム内最大階調値に対応するフレーム内最大輝度値は、ＭＡＣ＿ＣＬＬが示すコンテンツの最大輝度レベルよりも低くなる。したがって、本ステップにおいて設定される仮想最大輝度レベルは、ＭＡＣ＿ＣＬＬが示すコンテンツの最大輝度レベルよりも低くなる。仮想最大輝度レベル設定部４は、設定した仮想最大輝度レベルを階調値変換部５に供給する。 Next, the virtual maximum luminance level setting unit 4 acquires the gradation value taken by each pixel constituting the processing target frame from the video data acquisition unit 3, and acquires the maximum value of the acquired gradation value (the maximum gradation value in the frame). ) (The maximum luminance value in the frame) corresponding to) is set as the virtual maximum luminance level (step S1). FIG. 4A shows a correspondence relationship (OETF) between the luminance value and the gradation value in the HDR signal. As shown in FIG. 4A, the maximum luminance value in the frame corresponding to the maximum gradation value in the frame is lower than the maximum luminance level of the content indicated by MAC_CLL. Therefore, the virtual maximum brightness level set in this step is lower than the maximum brightness level of the content indicated by MAC_CLL. The virtual maximum luminance level setting unit 4 supplies the set virtual maximum luminance level to the gradation value conversion unit 5.
　次に、階調値変換部５は、処理対象フレームを構成する各画素が取る階調値を映像データ取得部３から取得し、取得した階調値を第１の階調値から第２の階調値に変換する（ステップＳ２）。この変換のために、階調値変換部５は、仮想最大輝度レベルを仮想最大輝度レベル設定部４から取得し、ＨＤＲ信号用において各画素が取り得る階調値のうち、取得した仮想最大輝度レベル以下の各輝度レベルｙに対応する階調値ｘを、ＳＤＲ信号用のＥＯＴＦの定義域内の各階調値Ｘに対応させるマッピングを用いる。より具体的に言うと、仮想最大輝度レベル以下の各輝度レベルｙに対応する階調値ｘを、ＳＤＲ信号用のＥＯＴＦにおいて輝度レベルＹ＝（ＭＡＸ＿Ｙ／ＭＡＸ＿ｙ）ｙに対応する階調値Ｘに対応させるマッピングを用いる。ここで、ＭＡＸ＿ｙは、仮想最大輝度レベルを表し、ＭＡＸ＿Ｙは、ＳＤＲ信号用のＥＯＴＦの値域の最大値（表示装置の最大輝度レベルに相当）を表す。図４の（ｂ）は、変換前の輝度値ｘと階調値ｙとの関係（ＨＤＲ信号用のＯＥＴＦ）を表すグラフであり、図４の（ｃ）は、変換後の輝度値Ｘと階調値Ｙとの関係（ＳＤＲ信号用のＯＥＴＦ）を表すグラフである。階調値変換部５は、処理対象フレームを構成する各画素が取る変換後の階調値をパネル制御部６に供給する。 Next, the gradation value conversion unit 5 acquires the gradation value taken by each pixel constituting the processing target frame from the video data acquisition unit 3, and acquires the acquired gradation value from the first gradation value to the second value. Conversion into gradation values (step S2). For this conversion, the gradation value conversion unit 5 acquires the virtual maximum luminance level from the virtual maximum luminance level setting unit 4, and among the gradation values that each pixel can take for the HDR signal, the acquired virtual maximum luminance level A mapping is used in which the gradation value x corresponding to each luminance level y below the level is associated with each gradation value X in the definition area of the EOTF for the SDR signal. More specifically, the gradation value x corresponding to each luminance level y below the virtual maximum luminance level is changed to the gradation value X corresponding to the luminance level Y = (MAX_Y / MAX_y) y in the EOTF for the SDR signal. Use the corresponding mapping. Here, MAX_y represents a virtual maximum brightness level, and MAX_Y represents a maximum value of the EOTF value range for the SDR signal (corresponding to the maximum brightness level of the display device). 4B is a graph showing the relationship between the luminance value x before conversion and the gradation value y (HETF signal OETF), and FIG. 4C shows the luminance value X after conversion. It is a graph showing the relationship with the gradation value Y (OETF for SDR signal). The gradation value conversion unit 5 supplies the converted gradation value taken by each pixel constituting the processing target frame to the panel control unit 6.
　次に、パネル制御部６は、処理対象フレームを構成する各画素が取る変換後の階調値を階調値変換部５から取得し、取得した階調値を輝度値に変換する（ステップＳ３）。この変換のために、パネル制御部６は、ＳＤＲ用のＥＯＴＦ、例えば、γ２．２相当のＥＯＴＦを用いる。この変換は、トーンマッピングとも呼ばれ、この変換における階調値と輝度値との対応関係は、トーンカーブとも呼ばれる。パネル制御部６は、表示パネル７を構成する各画素の輝度を、トーンマッピングにより得られた輝度値に制御する。これにより、処理対象フレームが表示パネル７に表示される（ステップＳ４）。 Next, the panel control unit 6 acquires the converted gradation value taken by each pixel constituting the processing target frame from the gradation value conversion unit 5, and converts the acquired gradation value into a luminance value (step S3). ). For this conversion, the panel control unit 6 uses an EOTF for SDR, for example, an EOTF equivalent to γ2.2. This conversion is also called tone mapping, and the correspondence between the gradation value and the luminance value in this conversion is also called a tone curve. The panel control unit 6 controls the luminance of each pixel constituting the display panel 7 to the luminance value obtained by tone mapping. As a result, the processing target frame is displayed on the display panel 7 (step S4).
　以上のように、本実施形態に係る階調値変換処理では、ＨＤＲ信号用のＥＯＴＦの定義域のうち、仮想最大輝度レベル以下の輝度値に対応する範囲をＳＤＲ信号用のＥＯＴＦの定義域に対応付けるマッピングを用いる。仮想最大輝度レベルは、ＭＡＣ＿ＣＬＬが示す最大輝度レベルよりも低いので、ＨＤＲ信号用のＥＯＴＦの定義域のうち、ＭＡＸ＿ＣＬＬが示す最大輝度レベル以下の輝度値に対応する範囲をＳＤＲ信号用のＥＯＴＦの定義域に対応付けるマッピングを用いる場合と比べて、黒潰れの抑制、階調値の縮退の抑制を行うことができる。 As described above, in the gradation value conversion processing according to the present embodiment, the range corresponding to the luminance value equal to or lower than the virtual maximum luminance level is defined as the EOTF definition region for the SDR signal in the definition region of the HDR signal EOTF. Use mapping to associate. Since the virtual maximum luminance level is lower than the maximum luminance level indicated by MAC_CLL, the range corresponding to the luminance value equal to or lower than the maximum luminance level indicated by MAX_CLL is defined in the EOTF definition region for HDR signal. Compared with the case of using the mapping associated with the area, it is possible to suppress the black crushing and the gradation value degeneration.
　なお、ここでは、階調値変換処理をフレーム毎に実行し、各フレームのフレーム内最大輝度値を仮想最大輝度レベルとする構成について説明したが、本実施形態はこれに限定されない。例えば、レコーダ等に記録されたＨＤＲ信号を再生する場合には、階調値変換処理をシーン毎に実行し、各シーンのシーン内最大輝度値（そのシーンを構成する全てのフレームのフレーム内最大輝度値の最大値）を仮想最大輝度レベルとする構成を採用することも可能である。この場合、処理対象シーンを構成する最初のフレームの階調値変換を開始する前に、処理対象シーンを構成する全てのフレームを構成する画素が取る階調値を取得し、シーン内最大輝度値を仮想最大輝度レベルに設定することになる。また、各シーンのシーン内最大輝度値を示すメタデータがＨＤＲ信号に含まれている場合は、このメタデータを参照して仮想最大輝度レベルを設定する構成を採用することもできる。このような構成であれば、レコーダ等に記録されたＨＤＲ信号のみならず、チューナ等で受信したＨＤＲ信号に対しても階調値変換処理を施すことが可能である。 In addition, here, the gradation value conversion process is executed for each frame, and the maximum luminance value in each frame is set as the virtual maximum luminance level. However, the present embodiment is not limited to this. For example, when reproducing an HDR signal recorded on a recorder or the like, gradation value conversion processing is executed for each scene, and the maximum in-scene luminance value of each scene (the maximum in-frame of all the frames constituting the scene). It is also possible to adopt a configuration in which the maximum luminance value) is set to the virtual maximum luminance level. In this case, before starting the gradation value conversion of the first frame constituting the processing target scene, the gradation values taken by the pixels constituting all the frames constituting the processing target scene are acquired, and the maximum luminance value in the scene is obtained. Is set to the virtual maximum luminance level. Further, when the HDR signal includes metadata indicating the in-scene maximum luminance value of each scene, a configuration in which the virtual maximum luminance level is set with reference to the metadata may be employed. With such a configuration, gradation value conversion processing can be performed not only on HDR signals recorded on a recorder or the like but also on HDR signals received by a tuner or the like.
　また、各フレームのフレーム内最大輝度値そのものを仮想最大輝度レベルとする構成の代わりに、各フレームのフレーム内最大輝度値の時間平均値を仮想最大輝度レベルとする構成を採用してもよい。これにより、各フレームのフレーム内最大輝度値そのものを仮想最大輝度レベルとする構成を採用した場合に生じ得る画面のちらつきを効果的に抑制することが可能である。なお、各フレームのフレーム内輝度値の時間平均値の算出にあたっては、例えば公知の時間平均フィルタなどを用いればよい。 Further, instead of the configuration in which the maximum luminance value in each frame is the virtual maximum luminance level, a configuration in which the temporal average value of the maximum luminance value in each frame is the virtual maximum luminance level may be adopted. Thereby, it is possible to effectively suppress the flickering of the screen that may occur when the configuration in which the maximum luminance value in each frame is the virtual maximum luminance level is adopted. In calculating the time average value of the in-frame luminance value of each frame, for example, a known time average filter may be used.
　〔実施形態２〕
　本発明の第２の実施形態について、図面に基づいて説明すれば、以下のとおりである。なお、本実施形態では、図１に示す階調値変換装置２を備える表示装置１を、第１の実施形態と同様に用いる。 [Embodiment 2]
The following describes the second embodiment of the present invention with reference to the drawings. In the present embodiment, the display device 1 including the gradation value conversion device 2 shown in FIG. 1 is used as in the first embodiment.
　図５は、本実施形態に係る階調値変換装置により実行される階調値変換処理の流れを示すフローチャートである。なお、図５に示すステップＳ１０およびステップＳ１３～Ｓ１５において実行される処理は、それぞれ、図３に示すステップＳ０およびステップＳ２～Ｓ４において実行される処理と同様である。このため、以下では、ステップＳ１１～Ｓ１２にて実行される処理について説明する。 FIG. 5 is a flowchart showing the flow of the gradation value conversion process executed by the gradation value conversion apparatus according to the present embodiment. Note that the processing executed in steps S10 and S13 to S15 shown in FIG. 5 is the same as the processing executed in steps S0 and S2 to S4 shown in FIG. 3, respectively. For this reason, the processing executed in steps S11 to S12 will be described below.
　ステップＳ１１において、仮想最大輝度レベル設定部４は、処理対象フレームを構成する各画素が取る階調値に対応する輝度値のヒストグラム生成し、生成したヒストグラムからヒスト最大値を求める。そして、ステップＳ１２において、仮想最大輝度レベル設定部４は、仮想最大輝度レベルをステップＳ１１にて求めたヒスト最大値に設定する。 In step S11, the virtual maximum luminance level setting unit 4 generates a histogram of luminance values corresponding to the gradation values taken by each pixel constituting the processing target frame, and obtains the maximum histogram value from the generated histogram. In step S12, the virtual maximum luminance level setting unit 4 sets the virtual maximum luminance level to the maximum histo value obtained in step S11.
　ここで、ヒスト最大値とは、処理対象フレームを構成する画素が取る階調値に対応する輝度値のうち、特異的に大きな輝度値を除く輝度値の最大値であり、ヒストグラムの平均値Ｍと標準偏差σとから算出できる量である。例えば、Ｍ＋３σは、ヒスト最大値の典型例である。 Here, the maximum histogram value is a maximum value of luminance values excluding a specifically large luminance value among luminance values corresponding to gradation values taken by pixels constituting the processing target frame, and is an average value M of the histogram. And the standard deviation σ. For example, M + 3σ is a typical example of the maximum histo value.
　ステップＳ１１に生成されるヒストグラムの例を図６に示す。図６に示す例では、幾つかの画素がＭＡＸ＿ＣＬＬが示す最大輝度レベルに近い特異的に大きな輝度値を取る。このような場合、処理対象フレームを構成する画素が取る階調値に対応する輝度値の最大値を仮想最大輝度レベルとする構成（第１の実施形態参照）を採用すると、階調値変換ステップＳ１３において特異的に大きな輝度値と特異的に大きな輝度値を除く輝度値の最大値との間の領域が、ＳＤＲ用のＥＯＴＦの値域に無駄に対応付けられることになる。これに対して、処理対象フレームを構成する画素が取る階調値に対応する輝度値のヒスト最大値を仮想最大輝度レベルとする構成を採用すれば、特異的に大きな輝度値を除く輝度値を、階調値変換ステップＳ１３においてＳＤＲ用のＥＯＴＦの値域に無駄なく対応付けることができる。 FIG. 6 shows an example of the histogram generated in step S11. In the example shown in FIG. 6, some pixels take a specifically large luminance value close to the maximum luminance level indicated by MAX_CLL. In such a case, when a configuration (see the first embodiment) in which the maximum value of the luminance value corresponding to the gradation value taken by the pixels constituting the processing target frame is the virtual maximum luminance level is employed, the gradation value conversion step In S13, the region between the specifically large luminance value and the maximum value of the luminance value excluding the specifically large luminance value is unnecessarily associated with the SDR EOTF value range. On the other hand, if a configuration is adopted in which the maximum value of the luminance value corresponding to the gradation value taken by the pixels constituting the processing target frame is set as the virtual maximum luminance level, the luminance value excluding the large luminance value is specifically determined. In the gradation value conversion step S13, the SDR EOTF value range can be associated without waste.
　なお、ここでは、輝度値のヒストグラムをフレーム毎に作成し、各フレームのフレーム内ヒスト最大値を仮想最大輝度レベルとする構成について説明したが、本実施形態はこれに限定されない。例えば、レコーダ等に記録されたＨＤＲ信号を再生する場合には、輝度値のヒストグラムをシーン毎に実行し、各シーンのシーン内ヒスト最大値を仮想最大輝度レベルとする構成を採用することも可能である。この場合、処理対象シーンを構成する最初のフレームの階調値変換を開始する前に、処理対象シーンを構成する全てのフレームを構成する画素が取る階調値に対応する輝度値のヒストグラムを作成し、シーン内ヒスト最大値を仮想最大輝度レベルに設定することになる。また、各シーンのシーン内ヒスト最大値を示すメタデータがＨＤＲ信号に含まれている場合は、このメタデータを参照して仮想最大輝度レベルを設定する構成を採用することもできる。このような構成であれば、レコーダ等に記録されたＨＤＲ信号のみならず、チューナ等で受信したＨＤＲ信号に対しても階調値変換処理を施すことが可能である。 Note that, here, a configuration has been described in which a histogram of luminance values is created for each frame, and the maximum value within the frame of each frame is a virtual maximum luminance level, but the present embodiment is not limited to this. For example, when reproducing an HDR signal recorded on a recorder or the like, it is possible to adopt a configuration in which a histogram of luminance values is executed for each scene and the maximum value of the in-scene hist of each scene is set as a virtual maximum luminance level. It is. In this case, before starting the gradation value conversion of the first frame constituting the processing target scene, a histogram of luminance values corresponding to the gradation values taken by the pixels constituting all the frames constituting the processing target scene is created. Then, the maximum value of the hist in the scene is set to the virtual maximum luminance level. In addition, when the HDR signal includes metadata indicating the in-scene maximum value of each scene, it is possible to adopt a configuration in which the virtual maximum luminance level is set with reference to this metadata. With such a configuration, gradation value conversion processing can be performed not only on HDR signals recorded on a recorder or the like but also on HDR signals received by a tuner or the like.
　また、各フレームのフレーム内ヒスト最大値そのものを仮想最大輝度レベルとする構成の代わりに、各フレームのフレーム内ヒスト最大値の時間平均値を仮想最大輝度レベルとする構成を採用してもよい。これにより、各フレームのフレーム内ヒスト最大値そのものを仮想最大輝度レベルとする構成を採用した場合に生じ得る画面のちらつきを効果的に抑制することが可能である。なお、各フレームのフレーム内ヒスト最大値の時間平均値の算出にあたっては、例えば公知の時間平均フィルタなどを用いればよい。 In addition, instead of the configuration in which the in-frame maximum value itself of each frame is the virtual maximum luminance level, a configuration in which the time average value of the in-frame maximum value of each frame is the virtual maximum luminance level may be adopted. Thereby, it is possible to effectively suppress the flickering of the screen that can occur when the configuration in which the in-frame maximum value of each frame is the virtual maximum luminance level is adopted. It should be noted that, for example, a known time average filter may be used in calculating the time average value of the intra-frame maximum value of each frame.
　〔実施形態３〕
　本発明の第３の実施形態について、図面に基づいて説明すれば、以下のとおりである。なお、本実施形態では、図１に示す階調値変換装置２を備える表示装置１を第１の実施形態と同様に用いる。 [Embodiment 3]
A third embodiment of the present invention will be described below with reference to the drawings. In the present embodiment, the display device 1 including the gradation value conversion device 2 shown in FIG. 1 is used in the same manner as in the first embodiment.
　図７は、本実施形態に係る階調値変換装置により実行される階調値変換処理の流れを示すフローチャートである。なお、図７に示すステップＳ１００およびステップＳ１０６～Ｓ１０８において実行される処理は、それぞれ、図３に示すステップＳ０およびステップＳ２～Ｓ４において実行される処理と同様である。このため、以下では、ステップＳ１０１～Ｓ１０５にて実行される処理について説明する。 FIG. 7 is a flowchart showing the flow of the gradation value conversion process executed by the gradation value conversion apparatus according to this embodiment. The processes executed in step S100 and steps S106 to S108 shown in FIG. 7 are the same as the processes executed in steps S0 and S2 to S4 shown in FIG. 3, respectively. For this reason, the processing executed in steps S101 to S105 will be described below.
　まず、ステップＳ１０１において、仮想最大輝度レベル設定部４は、処理対象フレームを構成する各画素が取る階調値に対応する輝度値のヒストグラム生成し、生成したヒストグラムからヒスト最大値を求める。ヒスト最大値の定義は、第２の実施形態において与えたものと同様である。 First, in step S101, the virtual maximum luminance level setting unit 4 generates a histogram of luminance values corresponding to the gradation values taken by each pixel constituting the processing target frame, and obtains a maximum histogram value from the generated histogram. The definition of the maximum hysteresis value is the same as that given in the second embodiment.
　次に、ステップＳ１０２において、仮想最大輝度レベル設定部４は、ＭＡＣ＿ＣＬＬが示す最大輝度レベルよりも所定の値だけ低いリミット値を設定する。ここで、所定の値は、任意の値であり、工場出荷時に設定されたものであってもよいし、工場出荷後にユーザが設定したものであってもよい。 Next, in step S102, the virtual maximum brightness level setting unit 4 sets a limit value that is lower than the maximum brightness level indicated by MAC_CLL by a predetermined value. Here, the predetermined value is an arbitrary value and may be set at the time of shipment from the factory, or may be set by the user after shipment from the factory.
　次に、ステップＳ１０３において、仮想最大輝度レベル設定部４は、ステップＳ１０１で算出したヒスト最大値がステップＳ１０２で算出したリミット値よりも低いか否かを判定する。 Next, in step S103, the virtual maximum luminance level setting unit 4 determines whether or not the maximum histogram value calculated in step S101 is lower than the limit value calculated in step S102.
　図８の（ａ）に示すように、ヒスト最大値がリミット値よりも低い場合、ステップＳ１０４において、仮想最大輝度レベル設定部４は、仮想最大輝度レベルをリミット値に設定する。このとき、図８の（ｂ）に示すように、ステップＳ１０６において、ＨＤＲ信号用のＯＥＴＦの定義域のうち、リミット値以下の範囲がＳＤＲ信号用のＯＥＴＦの定義域全体にマッピングされる。 As shown in FIG. 8A, when the maximum histo value is lower than the limit value, in step S104, the virtual maximum luminance level setting unit 4 sets the virtual maximum luminance level to the limit value. At this time, as shown in FIG. 8B, in step S106, the range below the limit value in the definition area of the HDR signal OETF is mapped to the whole definition area of the ODR for SDR signal.
　一方、図８の（ｃ）に示すように、ヒスト最大値がリミット値以上である場合、仮想最大輝度レベル設定部４は、ステップＳ１０５において、仮想最大輝度レベルをヒスト最大値に設定する。このとき、図８の（ｄ）に示すように、ステップＳ１０６において、ＨＤＲ信号用のＥＯＴＦの値域のうち、ヒスト最大値以下の範囲がＳＤＲ信号用のＥＯＴＦの値域全体にマッピングされる。 On the other hand, as shown in (c) of FIG. 8, when the maximum histogram value is equal to or greater than the limit value, the virtual maximum luminance level setting unit 4 sets the virtual maximum luminance level to the maximum histogram value in step S105. At this time, as shown in FIG. 8 (d), in step S106, the range below the maximum histogram value in the HDR signal EOTF value range is mapped to the entire SDR signal EOTF value range.
　本実施形態に係る階調値変換装置２の階調値変換方法によれば、仮想最大輝度レベルにリミット値を設けることにより、ヒスト最大値が極端に小さくなった場合に生じ得る、仮想最大輝度レベルの大きな変動に伴う映像品位の低下を防ぐことができる。 According to the gradation value conversion method of the gradation value conversion apparatus 2 according to the present embodiment, the virtual maximum luminance that can occur when the maximum value of the histogram becomes extremely small by providing a limit value for the virtual maximum luminance level. It is possible to prevent a decrease in image quality due to a large level fluctuation.
　〔実施形態４〕
　本発明の第４の実施形態について、図面に基づいて説明すれば、以下のとおりである。なお、本実施形態では、図１に示す階調値変換装置２を備える表示装置１を第１の実施形態と同様に用いる。 [Embodiment 4]
The following describes the fourth embodiment of the present invention with reference to the drawings. In the present embodiment, the display device 1 including the gradation value conversion device 2 shown in FIG. 1 is used in the same manner as in the first embodiment.
　本実施形態に係る階調値変換装置２により実行される階調値変換処理の流れは、第３の実施形態に係る階調値変換装置２により実行される階調変換処理と同様、図７に示すフローチャートにより表現される。ただし、本実施形態においては、第３の実施形態におけるリミット値設定処理Ｓ１０２は、以下に説明するリミット値設定処理Ｓ１０９に置き換えられる。 The flow of the gradation value conversion process executed by the gradation value conversion apparatus 2 according to the present embodiment is similar to the gradation conversion process executed by the gradation value conversion apparatus 2 according to the third embodiment, as shown in FIG. Is expressed by the flowchart shown in FIG. However, in the present embodiment, the limit value setting process S102 in the third embodiment is replaced with a limit value setting process S109 described below.
　すなわち、ステップＳ１０９において、仮想最大輝度レベル設定部４は、ＭＡＸ＿ＣＬＬが示す最大輝度レベルからリミット値を減算した差と、リミット値から輝度ヒストグラムにおけるヒスト最大値を減算した差とが所定の比になるようリミット値を設定する。ここで、所定の比は、任意の比であり、工場出荷時に設定されたものであってもよいし、工場出荷後にユーザが設定したものであってもよい。 That is, in step S109, the virtual maximum luminance level setting unit 4 has a predetermined ratio between the difference obtained by subtracting the limit value from the maximum luminance level indicated by MAX_CLL and the difference obtained by subtracting the maximum histogram value in the luminance histogram from the limit value. Set the limit value. Here, the predetermined ratio is an arbitrary ratio, and may be set at the time of shipment from the factory, or may be set by the user after shipment from the factory.
　図９の（ａ）に示すように、ヒスト最大値がリミット値よりも低い場合、ステップＳ１０４において、仮想最大輝度レベル設定部４は、仮想最大輝度レベルをリミット値に設定する。このとき、図９の（ｂ）に示すように、ステップＳ１０６において、ＨＤＲ信号用のＯＥＴＦの定義域のうち、リミット値以下の範囲がＳＤＲ信号用のＯＥＴＦの定義域全体にマッピングされる。 As shown in FIG. 9A, when the maximum histo value is lower than the limit value, in step S104, the virtual maximum luminance level setting unit 4 sets the virtual maximum luminance level to the limit value. At this time, as shown in FIG. 9B, in step S106, the range below the limit value in the definition area of the HDR signal OETF is mapped to the whole definition area of the SDR signal OETF.
　一方、図９の（ｃ）に示すように、ヒスト最大値がリミット値以上である場合、仮想最大輝度レベル設定部４は、ステップＳ１０５において、仮想最大輝度レベルをヒスト最大値に設定する。このとき、図９の（ｄ）に示すように、ステップＳ１０６において、ＨＤＲ信号用のＥＯＴＦの値域のうち、ヒスト最大値以下の範囲がＳＤＲ信号用のＥＯＴＦの値域全体にマッピングされる。 On the other hand, as shown in (c) of FIG. 9, when the maximum histogram value is equal to or greater than the limit value, the virtual maximum luminance level setting unit 4 sets the virtual maximum luminance level to the maximum histogram value in step S105. At this time, as shown in FIG. 9 (d), in step S106, the range below the maximum value of the histories of the EOTF for the HDR signal is mapped to the entire range of the EOTF for the SDR signal.
　本実施形態に係る階調値変換装置２の階調値変換方法によれば、仮想最大輝度レベルにリミット値を設けることにより、ヒスト最大値が極端に小さくなった場合に生じ得る、仮想最大輝度レベルの大きな変動に伴う映像品位の低下を防ぐことができる。 According to the gradation value conversion method of the gradation value conversion apparatus 2 according to the present embodiment, the virtual maximum luminance that can occur when the maximum value of the histogram becomes extremely small by providing a limit value for the virtual maximum luminance level. It is possible to prevent a decrease in image quality due to a large level fluctuation.
　〔実施形態５〕
　本発明の第５の実施形態について、図面に基づいて説明すれば、以下のとおりである。なお、説明の便宜上、実施形態１にて説明した部材と同じ機能を有する部材については、同じ符号を付記し、その説明を省略する。 [Embodiment 5]
The following describes the fifth embodiment of the present invention with reference to the drawings. For convenience of explanation, members having the same functions as those described in the first embodiment are denoted by the same reference numerals and description thereof is omitted.
　実施形態１において、仮想最大輝度レベル設定部４が、処理対象フレームを構成する各画素が取る階調値の最大値（フレーム内最大階調値）に対応する輝度値（フレーム内最大輝度値）を仮想最大輝度レベルに設定することを説明した。当該構成により、ＨＤＲの最大の利点であるピーク輝度に応じて、階調値を変換することができる。 In the first embodiment, the virtual maximum luminance level setting unit 4 has a luminance value (maximum intra-frame luminance value) corresponding to the maximum gradation value (maximum intra-frame gradation value) taken by each pixel constituting the processing target frame. It was explained that is set to the virtual maximum luminance level. With this configuration, gradation values can be converted according to peak luminance, which is the greatest advantage of HDR.
　しかし、このように階調値を変換すると、輝度値に対する低階調値領域の階調値が相対的に低下してしまう（黒つぶれ）。これにより、画像を表示したときに、低階調値領域内の階調値で表示された画像内の領域は、真っ暗になり、表現不足となってしまう。 However, when the gradation value is converted in this way, the gradation value in the low gradation value region with respect to the luminance value is relatively lowered (blackout). As a result, when an image is displayed, the area in the image displayed with the gradation value in the low gradation value area becomes completely dark, resulting in insufficient expression.
　上記のような問題を解決するために、本実施形態に係る階調値変換装置１１は、階調値変換部５が変換した後の階調値のうち、低階調値領域の階調値に持ち上げ部を有するように、映像信号において各フレーム又は各シーンを構成する各画素が取る階調値を調整する。 In order to solve the above-described problem, the gradation value conversion apparatus 11 according to the present embodiment has the gradation value in the low gradation value region among the gradation values converted by the gradation value conversion unit 5. In the video signal, the gradation value taken by each pixel constituting each frame or each scene is adjusted so as to have a lifting portion.
　なお、本願明細書において、低階調値領域とは、変換後の階調値において、原点（階調値および対応する輝度値がゼロの点）近傍の階調値領域を示す。例えば、低階調値領域とは、階調値が８ビットで量子化されている場合（２５６階調（０～２５５））、その５分の１程度の階調値の領域のことを示す（階調値が０～５１である領域）。また、低階調値領域における最大の階調値よりも大きい階調値を最低の階調値として有する階調値の領域を、中階調値領域とし、中階調値領域における最大の階調値よりも大きい階調値を最低の階調値として有する階調値の領域を、高階調値領域として定義する。 In the present specification, the low gradation value region indicates a gradation value region near the origin (a point where the gradation value and the corresponding luminance value are zero) in the converted gradation value. For example, the low gradation value area indicates an area having a gradation value of about one fifth when the gradation value is quantized with 8 bits (256 gradations (0 to 255)). (A region where the gradation value is 0 to 51). In addition, the gradation value area having the gradation value larger than the maximum gradation value in the low gradation value area as the lowest gradation value is defined as the intermediate gradation value area, and the largest gradation in the intermediate gradation value area. A region of gradation values having a gradation value larger than the tone value as the lowest gradation value is defined as a high gradation value region.
　また、本願明細書において、「低階調値領域の階調値に持ち上げ部を有する」とは、実施形態１で説明した階調値変換方法によって階調値を変換することにより生じる、低階調値領域の階調値の相対的な低下（黒つぶれ）を改善するために、低階調領域の階調値を上昇させることを意味する。 In the specification of the present application, “having a lifting portion in the gradation value of the low gradation value region” means a low-order image generated by converting the gradation value by the gradation value conversion method described in the first embodiment. This means that the gradation value in the low gradation area is increased in order to improve the relative decrease (blackout) in the gradation value area.
　（階調値変換装置１１）
　図１０は、本実施形態に係る階調値変換装置（映像処理装置）１１を備えている表示装置１０の構成を示すブロック図である。図１０が示すように、階調値変換装置１１は、実施形態１に係る階調値変換装置２の構成に加えて、階調値調整部１２をさらに備えている。 (Tone value converter 11)
FIG. 10 is a block diagram illustrating a configuration of the display device 10 including the gradation value conversion device (video processing device) 11 according to the present embodiment. As shown in FIG. 10, the gradation value conversion apparatus 11 further includes a gradation value adjustment unit 12 in addition to the configuration of the gradation value conversion apparatus 2 according to the first embodiment.
　階調値調整部１２は、階調値変換部５が変換した階調値のうち、低階調値領域の階調値に持ち上げ部を有するように調整する。 The gradation value adjustment unit 12 adjusts the gradation value converted by the gradation value conversion unit 5 to have a lifting unit in the gradation value in the low gradation value region.
　（階調値変換方法）
　本実施形態に係る階調値変換装置１１により実行される階調値変換処理の流れを、図１１を参照して説明する。図１１は、階調値変換処理の流れを示すフローチャートである。なお、以下では、階調値変換処理をフレーム毎に実行し、各フレームのフレーム内最大輝度値を仮想最大輝度レベルとする構成について説明するが、階調値変換処理をシーン毎に実行し、各シーンのシーン内最大輝度値を仮想最大輝度レベルとする構成についても同様である。 (Tone value conversion method)
A flow of gradation value conversion processing executed by the gradation value conversion apparatus 11 according to the present embodiment will be described with reference to FIG. FIG. 11 is a flowchart showing the flow of gradation value conversion processing. In the following description, the gradation value conversion process is executed for each frame, and the maximum luminance value in each frame is set as the virtual maximum luminance level. However, the gradation value conversion process is executed for each scene, The same applies to the configuration in which the in-scene maximum luminance value of each scene is set as the virtual maximum luminance level.
　まず、映像データ取得部３は、ＨＤＲ信号を取得する（ステップＳ２０）映像データ取得部３は、取得したＨＤＲ信号において処理対象フレームを構成する各画素が取る階調値を仮想最大輝度レベル設定部４及び階調値変換部５に供給する。 First, the video data acquisition unit 3 acquires an HDR signal (step S20). The video data acquisition unit 3 sets a gradation value taken by each pixel constituting the processing target frame in the acquired HDR signal as a virtual maximum luminance level setting unit. 4 and the gradation value converter 5.
　次に、仮想最大輝度レベル設定部４は、処理対象フレームを構成する各画素が取る階調値を映像データ取得部３から取得し、取得した階調値の最大値（フレーム内最大階調値）に対応する輝度値（フレーム内最大輝度値）を仮想最大輝度レベルに設定する（ステップＳ２１）。 Next, the virtual maximum luminance level setting unit 4 acquires the gradation value taken by each pixel constituting the processing target frame from the video data acquisition unit 3, and acquires the maximum value of the acquired gradation value (the maximum gradation value in the frame). ) (The maximum luminance value in the frame) corresponding to) is set as the virtual maximum luminance level (step S21).
　次に、階調値変換部５は、処理対象フレームを構成する各画素が取る階調値を映像データ取得部３から取得し、取得した階調値のうち、仮想最大輝度レベル設定部４が設定した仮想最大輝度レベル以下の各輝度レベルに対応する階調値を、第１の階調値から第２の階調値に変換する（ステップＳ２２）。 Next, the gradation value conversion unit 5 acquires the gradation value taken by each pixel constituting the processing target frame from the video data acquisition unit 3, and among the acquired gradation values, the virtual maximum luminance level setting unit 4 The gradation value corresponding to each luminance level below the set virtual maximum luminance level is converted from the first gradation value to the second gradation value (step S22).
　次に、階調値調整部１２は、階調値変換部５が変換した階調値のうち、低階調値領域の階調値に持ち上げ部を有するように調整する（ステップＳ２３）。階調値調整部１２が階調値を調整する方法の具体的な例は後述する。なお、階調値調整部１２が調整した階調値は、低階調値領域において、所定のフォーマットが示す階調値よりも大きいことが好ましい。当該所定のフォーマットの例として、ＳＴ２０８４が挙げられる。 Next, the gradation value adjustment unit 12 adjusts the gradation value converted by the gradation value conversion unit 5 to have a lifting unit in the gradation value in the low gradation value region (step S23). A specific example of how the gradation value adjusting unit 12 adjusts the gradation value will be described later. Note that the gradation value adjusted by the gradation value adjustment unit 12 is preferably larger than the gradation value indicated by the predetermined format in the low gradation value region. An example of the predetermined format is ST2084.
　次に、パネル制御部６は、処理対象フレームを構成する各画素が取る調整後の階調値を階調値調整部１２から取得し、取得した階調値を輝度値に変換する（ステップＳ２４）（トーンマッピング）。 Next, the panel control unit 6 acquires the adjusted gradation value taken by each pixel constituting the processing target frame from the gradation value adjustment unit 12, and converts the acquired gradation value into a luminance value (step S24). ) (Tone mapping).
　次に、パネル制御部６は、表示パネル７を構成する各画素の輝度を、トーンマッピングにより得られた輝度値に制御する。これにより、処理対象フレームが表示パネル７に表示される（ステップＳ２５）。 Next, the panel control unit 6 controls the luminance of each pixel constituting the display panel 7 to the luminance value obtained by tone mapping. Thereby, the processing target frame is displayed on the display panel 7 (step S25).
　（階調値調整部１２が階調値を調整する方法の例）
　図１２は、変換後の階調値と対応する輝度値との関係を示すグラフである。図１２の領域Ａは、上述の低階調値領域を示し、点線は調整前のカーブ、実線は調整後のカーブを示す。階調値調整部１２は、変換後の階調値を、領域Ａにおける階調値に持ち上げ部を有するように調整する（点線のカーブから実線のカーブに調整する）。 (Example of method in which the gradation value adjusting unit 12 adjusts the gradation value)
FIG. 12 is a graph showing the relationship between the converted gradation value and the corresponding luminance value. A region A in FIG. 12 represents the above-described low gradation value region, a dotted line represents a curve before adjustment, and a solid line represents a curve after adjustment. The gradation value adjustment unit 12 adjusts the converted gradation value so that the gradation value in the region A has a lifting part (adjusts from the dotted curve to the solid curve).
　例えば、階調値調整部１２は、低階調値領域の階調値に対して、当該階調値の１０％程度の値を付加することによって調整する。または、調整する階調値がＳＴ２０８４に従う階調値である場合、階調値調整部１２は、低階調値領域の階調値に対して、当該階調値と対応する輝度値とをグラフにした場合、当該グラフにおけるカーブがγ２．２のカーブと同等になるように調整する。 For example, the gradation value adjusting unit 12 adjusts the gradation value in the low gradation value region by adding a value of about 10% of the gradation value. Alternatively, when the gradation value to be adjusted is a gradation value according to ST 2084, the gradation value adjustment unit 12 graphs the gradation value corresponding to the gradation value with respect to the gradation value in the low gradation value region. In this case, adjustment is made so that the curve in the graph is equivalent to the curve of γ2.2.
　また、階調値調整部１２は、階調値変換部５が変換した階調値に対応する輝度レベルの平均値を参照して、上記低階調値領域を変更してもよい。これにより、輝度レベルの分布に応じて、低階調値領域を設定することができるため、輝度レベルの分布に応じた階調値の調整が可能となる。なお、階調値調整部１２が参照する輝度レベルの平均値は、階調値調整部１２自体が算出してもよいし、外部から取得してもよい。 Also, the gradation value adjustment unit 12 may change the low gradation value region with reference to the average value of the luminance level corresponding to the gradation value converted by the gradation value conversion unit 5. Thereby, since the low gradation value region can be set according to the distribution of the luminance level, the gradation value can be adjusted according to the distribution of the luminance level. Note that the average value of the luminance levels referred to by the gradation value adjustment unit 12 may be calculated by the gradation value adjustment unit 12 itself or may be acquired from the outside.
　また、階調値調整部１２は、階調値変換部が変換した階調値と対応する輝度レベルとのグラフにおいて、低階調値領域の階調値と、高階調値領域の階調値とが連続的に変化するように、中階調値領域の階調値をさらに調整してもよい。これにより、調整後の階調値で表示した画像において、低階調値領域の階調値と高階調値領域の階調値との差異による不自然さを解消することができる。 In addition, the gradation value adjustment unit 12 has a gradation value in the low gradation value region and a gradation value in the high gradation value region in the graph of the gradation value converted by the gradation value conversion unit and the corresponding luminance level. Further, the gradation value in the middle gradation value region may be further adjusted so that “and” continuously change. As a result, in the image displayed with the adjusted gradation value, unnaturalness due to the difference between the gradation value in the low gradation value area and the gradation value in the high gradation value area can be eliminated.
　（実施形態５のまとめ）
　以上のように、本実施形態に係る階調値変換装置１１は、仮想最大輝度レベルを、輝度レベルの最大値に設定し、設定した仮想最大輝度レベルを参照して階調値を変換し、変換した階調値のうち、低階調値領域の階調値に持ち上げ部を有するように調整する。当該構成では、仮想最大輝度レベルを輝度レベルの最大値に設定することにより、映像信号が含むピーク感の忠実性を保持することができ、また、変換した階調値のうち、低階調値領域の階調値に持ち上げ部を有するように調整することにより、低階調値領域の階調値の低下による黒つぶれを防ぎ、低階調値領域の階調表現力を改善することができる。 (Summary of Embodiment 5)
As described above, the gradation value conversion apparatus 11 according to the present embodiment sets the virtual maximum luminance level to the maximum value of the luminance level, converts the gradation value with reference to the set virtual maximum luminance level, Of the converted gradation values, the gradation values in the low gradation value region are adjusted to have a lifting portion. In this configuration, by setting the virtual maximum luminance level to the maximum value of the luminance level, it is possible to maintain the fidelity of the peak feeling included in the video signal, and among the converted gradation values, the low gradation value By adjusting the gradation value of the region so as to have a raised portion, it is possible to prevent black crushing due to a decrease in the gradation value of the low gradation value region, and to improve the gradation expressing ability of the low gradation value region. .
　〔ソフトウェアによる実現例〕
　階調値変換装置２の制御ブロック（特に映像データ取得部３、仮想最大輝度レベル設定部４および階調値変換部５）は、集積回路（ＩＣチップ）等に形成された論理回路（ハードウェア）によって実現してもよいし、ＣＰＵ（Central Processing Unit）を用いてソフトウェアによって実現してもよい。 [Example of software implementation]
The control block (particularly the video data acquisition unit 3, the virtual maximum luminance level setting unit 4 and the gradation value conversion unit 5) of the gradation value conversion device 2 is a logic circuit (hardware) formed in an integrated circuit (IC chip) or the like. ) Or by software using a CPU (Central Processing Unit).
　後者の場合、階調値変換装置２は、各機能を実現するソフトウェアであるプログラムの命令を実行するＣＰＵ、上記プログラムおよび各種データがコンピュータ（またはＣＰＵ）で読み取り可能に記録されたＲＯＭ（Read Only Memory）または記憶装置（これらを「記録媒体」と称する）、上記プログラムを展開するＲＡＭ（Random Access Memory）などを備えている。そして、コンピュータ（またはＣＰＵ）が上記プログラムを上記記録媒体から読み取って実行することにより、本発明の目的が達成される。上記記録媒体としては、「一時的でない有形の媒体」、例えば、テープ、ディスク、カード、半導体メモリ、プログラマブルな論理回路などを用いることができる。また、上記プログラムは、該プログラムを伝送可能な任意の伝送媒体（通信ネットワークや放送波等）を介して上記コンピュータに供給されてもよい。なお、本発明は、上記プログラムが電子的な伝送によって具現化された、搬送波に埋め込まれたデータ信号の形態でも実現され得る。 In the latter case, the gradation value conversion device 2 includes a CPU that executes instructions of a program that is software that realizes each function, and a ROM (Read Only) in which the program and various data are recorded so as to be readable by a computer (or CPU). Memory) or a storage device (these are referred to as “recording media”), a RAM (Random Access Memory) for expanding the program, and the like. And the objective of this invention is achieved when a computer (or CPU) reads the said program from the said recording medium and runs it. As the recording medium, a “non-temporary tangible medium” such as a tape, a disk, a card, a semiconductor memory, a programmable logic circuit, or the like can be used. The program may be supplied to the computer via an arbitrary transmission medium (such as a communication network or a broadcast wave) that can transmit the program. The present invention can also be realized in the form of a data signal embedded in a carrier wave in which the program is embodied by electronic transmission.
　〔まとめ〕
　本発明の態様１に係る映像処理装置（２、１１）は、第１の映像フォーマットよりも輝度範囲の広い第２の映像フォーマットに従う映像信号において各画素が取る階調値を変換する映像処理装置であって、上記映像信号において各画素が取る階調値を参照することによって、上記映像信号に含まれるメタデータが示す最大輝度レベルよりも低い仮想最大輝度レベルを設定する仮想最大輝度レベル設定部（４）と、上記映像信号において各画素が取る階調値のうち、上記仮想最大輝度レベル以下の各輝度レベルに対応する階調値を変換する階調値変換部（５）と、を備えている。 [Summary]
A video processing device (2, 11) according to an aspect 1 of the present invention converts a gradation value taken by each pixel in a video signal according to a second video format having a wider luminance range than the first video format. A virtual maximum luminance level setting unit that sets a virtual maximum luminance level lower than the maximum luminance level indicated by the metadata included in the video signal by referring to the gradation value taken by each pixel in the video signal. (4) and a gradation value conversion unit (5) for converting a gradation value corresponding to each luminance level equal to or lower than the virtual maximum luminance level among gradation values taken by each pixel in the video signal. ing.
　上記の構成によれば、上記映像信号が表す映像を、上記映像信号が従う第２の映像フォーマットよりも輝度のダイナミックレンジの狭い第１の映像フォーマットに対応した表示装置に表示する際に、低輝度領域において生じ得る階調値の縮退を抑制することができる。これにより、映像の表示品位を向上することができる。 According to the above configuration, when the video represented by the video signal is displayed on a display device corresponding to the first video format having a narrower dynamic range of luminance than the second video format followed by the video signal, It is possible to suppress gradation value degeneration that may occur in the luminance region. Thereby, the display quality of a video can be improved.
　本発明の態様２に係る映像処理装置（２、１１）は、上記態様１において、上記階調値変換部（５）は、上記映像信号が従う第２の映像フォーマットにおいて各画素が取り得る階調値のうち、上記仮想最大輝度レベル以下の各輝度レベルに対応する階調値を、上記第１の映像フォーマットにおいて各画素が取り得る階調値に対応させるマッピングを用いて、上記映像信号において各画素が取る階調値を変換する。 In the video processing device (2, 11) according to aspect 2 of the present invention, in the aspect 1, the gradation value conversion unit (5) is a level that each pixel can take in the second video format that the video signal follows. In the video signal, a mapping is used in which tone values corresponding to each luminance level equal to or lower than the virtual maximum luminance level among tone values correspond to the tone values that each pixel can take in the first video format. The gradation value taken by each pixel is converted.
　上記の構成によれば、映像の表示品位をさらに向上することができる。 According to the above configuration, the video display quality can be further improved.
　本発明の態様３に係る映像処理装置（２、１１）は、上記態様２において、上記第１の映像フォーマットは、ＥＯＴＦがγ２．２相当のフォーマットであり、上記第２フォーマットは、ＥＯＴＦがＳＭＰＴＥ－ＳＴ２０８４であるフォーマットである。 In the video processing device (2, 11) according to aspect 3 of the present invention, in the aspect 2, the first video format is an EOTF equivalent to γ2.2, and the second format is an EOTF of SMPTE. -The format is ST2084.
　上記の構成によれば、上記映像信号がＨＤＲ信号であるときに、ＳＤＲ再生環境における映像の表示品位を向上することができる。 According to the above configuration, when the video signal is an HDR signal, the display quality of the video in the SDR playback environment can be improved.
　本発明の態様４に係る映像処理装置（２、１１）は、上記態様１～３において、上記仮想最大輝度レベル設定部は、上記映像信号において各フレーム又は各シーンを構成する各画素が取る階調値を参照することによって、上記仮想最大輝度レベルを設定する。 In the video processing devices (2, 11) according to aspect 4 of the present invention, in the above-described aspects 1 to 3, the virtual maximum luminance level setting unit is a floor taken by each pixel constituting each frame or each scene in the video signal. The virtual maximum luminance level is set by referring to the tone value.
　上記の構成によれば、映像信号が含む階調値に即して、効率的に階調値を変換することができる。 According to the above configuration, the gradation value can be efficiently converted in accordance with the gradation value included in the video signal.
　本発明の態様５に係る映像処理装置（２、１１）は、上記態様４において、上記仮想最大輝度レベル設定部（４）は、上記仮想最大輝度レベルを、上記映像信号において各フレーム又は各シーンを構成する各画素が取る階調値に対応する輝度レベルの最大値に設定する。 In the video processing device (2, 11) according to aspect 5 of the present invention, in the aspect 4, the virtual maximum luminance level setting unit (4) sets the virtual maximum luminance level in each frame or each scene in the video signal. Is set to the maximum value of the luminance level corresponding to the gradation value taken by each pixel.
　上記の構成によれば、映像信号が含む階調値に即して、効率的に階調値を変換することができる。 According to the above configuration, the gradation value can be efficiently converted in accordance with the gradation value included in the video signal.
　本発明の態様６に係る映像処理装置（１１）は、上記態様５において、上記階調値変換部が変換した階調値のうち、低階調値領域の階調値に持ち上げ部を有するように調整する階調値調整部（１２）をさらに備えている。 The video processing apparatus (11) according to aspect 6 of the present invention has a lifting unit in the gradation value of the low gradation value region among the gradation values converted by the gradation value conversion part in the aspect 5. Further, a gradation value adjusting unit (12) for adjusting to the above is further provided.
　上記の構成によれば、低階調値領域の階調値の低下による黒つぶれを防ぎ、低階調値領域の階調表現力を改善することができる。 According to the above configuration, it is possible to prevent blackout due to a decrease in the gradation value in the low gradation value region, and to improve the gradation expressing ability in the low gradation value region.
　本発明の態様７に係る映像処理装置（１１）は、上記態様６において、上記階調値調整部は、上記階調値変換部が変換した階調値に対応する輝度レベルの平均値を参照して、上記低階調値領域を変更する。 In the video processing device (11) according to aspect 7 of the present invention, in the aspect 6, the gradation value adjustment unit refers to an average value of luminance levels corresponding to the gradation values converted by the gradation value conversion unit. Then, the low gradation value region is changed.
　上記の構成によれば、輝度レベルの分布に応じて、低階調値領域を設定することができるため、輝度レベルの分布に応じた階調値の調整が可能となる。 According to the above configuration, since the low gradation value region can be set according to the luminance level distribution, the gradation value can be adjusted according to the luminance level distribution.
　本発明の態様８に係る映像処理装置（１１）は、上記態様５または６において、上記階調値調整部は、上記階調値変換部が変換した階調値と対応する輝度レベルとのグラフにおいて、低階調値領域の階調値と、高階調値領域の階調値とが連続的に変化するように、中階調値領域の階調値をさらに調整する。 In the video processing apparatus (11) according to the eighth aspect of the present invention, in the fifth or sixth aspect, the gradation value adjustment unit is a graph of the gradation value converted by the gradation value conversion unit and the corresponding luminance level. , The gradation value in the middle gradation value region is further adjusted so that the gradation value in the low gradation value region and the gradation value in the high gradation value region change continuously.
　上記の構成によれば、調整後の階調値で表示した画像において、低階調値領域の階調値と高階調値領域の階調値との差異による不自然さを解消することができる。 According to the above configuration, unnaturalness due to the difference between the gradation value in the low gradation value region and the gradation value in the high gradation value region can be eliminated in the image displayed with the adjusted gradation value. .
　本発明の態様９に係る映像処理装置（１１）は、上記態様６～８において、上記階調値調整部が調整した階調値は、低階調値領域において、所定のフォーマットが示す階調値よりも大きい。 In the video processing device (11) according to aspect 9 of the present invention, in the above aspects 6 to 8, the gradation value adjusted by the gradation value adjustment unit is the gradation indicated by a predetermined format in the low gradation value region. Greater than the value.
　上記の構成によれば、上記態様６～８の映像変換装置を好適に用いることができる。 According to the above configuration, the video conversion devices according to aspects 6 to 8 can be suitably used.
　本発明の態様１０に係る映像処理装置（２）は、上記態様１～４において、上記仮想最大輝度レベル設定部（４）は、上記映像信号において各フレーム又は各シーンを構成する各画素が取る階調値に対応する輝度レベルのヒストグラムを作成し、上記ヒストグラムを参照することによって、上記仮想最大輝度レベルを設定することを特徴とする。 In the video processing device (2) according to the tenth aspect of the present invention, in the first to fourth aspects, the virtual maximum luminance level setting unit (4) takes each pixel constituting each frame or each scene in the video signal. A virtual maximum luminance level is set by creating a histogram of luminance levels corresponding to gradation values and referring to the histogram.
　上記の構成によれば、映像信号が含む階調値に即して、さらに効率的に階調値を変換することができる。 According to the above configuration, the gradation value can be more efficiently converted in accordance with the gradation value included in the video signal.
　本発明の態様１１に係る映像処理装置（２）は、上記態様１０において、上記仮想最大輝度レベル設定部（４）は、上記仮想最大輝度レベルを、上記映像信号において各フレーム又は各シーンを構成する各画素が取る階調値に対応する輝度レベルの実効最大値であって、上記ヒストグラムの標準偏差の定数倍により定義される実効最大値に設定する。 In the video processing device (2) according to aspect 11 of the present invention, in the aspect 10, the virtual maximum luminance level setting unit (4) configures the virtual maximum luminance level and each frame or each scene in the video signal. The effective maximum value of the luminance level corresponding to the gradation value taken by each pixel is set to the effective maximum value defined by a constant multiple of the standard deviation of the histogram.
　上記の構成によれば、映像信号が含む階調値に即して、さらに効率的に階調値を変換することができる。 According to the above configuration, the gradation value can be more efficiently converted in accordance with the gradation value included in the video signal.
　本発明の態様１２に係る映像処理装置（２）は、上記態様１０において、上記仮想最大輝度レベル設定部（４）は、上記最大輝度レベルから所定値低いリミット値を設定すると共に、上記実効最大値が上記リミット値よりも低い場合、上記仮想最大輝度レベルを上記リミット値の値に設定し、上記実効最大値が上記リミット値以上である場合、上記仮想最大輝度レベルを上記実効最大値に設定する。 In the video processing device (2) according to aspect 12 of the present invention, in the aspect 10, the virtual maximum luminance level setting unit (4) sets a limit value lower than the maximum luminance level by a predetermined value, and the effective maximum luminance If the value is lower than the limit value, the virtual maximum brightness level is set to the limit value, and if the effective maximum value is greater than or equal to the limit value, the virtual maximum brightness level is set to the effective maximum value. To do.
　上記の構成によれば、仮想最大輝度レベルにリミット値を設けることにより、仮想最大輝度レベルの大きな変動を防ぎ、輝度およびヒストグラムの大きな変動による映像品位の低下を防ぐことができる。 According to the above configuration, by providing a limit value for the virtual maximum luminance level, it is possible to prevent a large variation in the virtual maximum luminance level and to prevent a reduction in video quality due to a large variation in luminance and histogram.
　本発明の態様１３に係る映像処理装置（２）は、上記態様１０において、上記仮想最大輝度レベル設定部（４）は、リミット値を、上記最大輝度レベルから当該リミット値を減算した差と、当該リミット値から上記実効最大値を減算した差とが所定の比になるように設定すると共に、上記実効最大値が上記リミット値よりも低い場合、上記仮想最大輝度レベルを上記リミット値の値に設定し、上記実効最大値が上記リミット値以上である場合、上記仮想最大輝度レベルを上記実効最大値に設定する。 In the video processing device (2) according to aspect 13 of the present invention, in the aspect 10, the virtual maximum luminance level setting unit (4) is configured to subtract the limit value from the maximum luminance level, When the effective maximum value is lower than the limit value, the virtual maximum luminance level is set to the limit value when the effective maximum value is lower than the limit value. If the effective maximum value is greater than or equal to the limit value, the virtual maximum luminance level is set to the effective maximum value.
　上記の構成によれば、リミット値を所望の値に設定することができる。 According to the above configuration, the limit value can be set to a desired value.
　本発明の態様１４に係る映像処理装置（２）は、上記態様１０において、上記仮想最大輝度レベルを、上記ＨＤＲ信号において各フレーム又は各シーンを構成する各画素が取る階調値に対応する輝度レベルの実効最大値であって、上記ヒストグラムの標準偏差の定数倍により定義される実効最大値の時間平均値に設定する。 The video processing device (2) according to aspect 14 of the present invention is the image processing apparatus (2) according to aspect 14, wherein the virtual maximum luminance level is a luminance corresponding to a gradation value taken by each pixel constituting each frame or each scene in the HDR signal. The effective maximum value of the level is set to the time average value of the effective maximum value defined by a constant multiple of the standard deviation of the histogram.
　上記の構成によれば、映像品位を向上させることができる。 According to the above configuration, the video quality can be improved.
　本発明の態様１５に係る表示装置（１、１０）は、上記態様１～１４の何れか１つの映像処理装置を備えている。 The display device (1, 10) according to the aspect 15 of the present invention includes any one of the video processing apparatuses according to the above aspects 1 to 14.
　上記の構成によれば、上記映像処理装置が上記各態様において奏する効果を上記表示装置において得ることができる。 According to the above configuration, the display device can obtain the effects that the video processing device has in each aspect.
　本発明の態様１６に係る映像処理方法は、第１の映像フォーマットよりも輝度範囲の広い第２の映像フォーマットに従う映像信号において各画素が取る階調値を変換する映像処理方法であって、上記映像信号において各画素が取る階調値を参照することによって、上記映像信号に含まれるメタデータが示す最大輝度レベルよりも低い仮想最大輝度レベルを設定する仮想最大輝度レベル設定ステップと、上記映像信号において各画素が取る階調値のうち、上記仮想最大輝度レベル以下の各輝度レベルに対応する階調値を変換する階調値変換ステップと、を含んでいる。 A video processing method according to a sixteenth aspect of the present invention is a video processing method for converting a gradation value taken by each pixel in a video signal according to a second video format having a luminance range wider than that of the first video format, A virtual maximum luminance level setting step for setting a virtual maximum luminance level lower than a maximum luminance level indicated by metadata included in the video signal by referring to a gradation value taken by each pixel in the video signal; The tone value conversion step of converting the tone value corresponding to each brightness level below the virtual maximum brightness level among the tone values taken by each pixel in FIG.
　上記の構成によれば、上記態様１の映像処理装置と同様の効果を奏することができる。 According to the above configuration, the same effects as those of the video processing device according to aspect 1 can be obtained.
　本発明の各態様に係る表示装置は、コンピュータによって実現してもよく、この場合には、コンピュータを上記表示装置が備える各部（ソフトウェア要素）として動作させることにより上記表示装置をコンピュータにて実現させる表示装置の制御プログラム、およびそれを記録したコンピュータ読み取り可能な記録媒体も、本発明の範疇に入る。 The display device according to each aspect of the present invention may be realized by a computer. In this case, the display device is realized by the computer by operating the computer as each unit (software element) included in the display device. A control program for the display device and a computer-readable recording medium on which the control program is recorded also fall within the scope of the present invention.
　本発明は上述した各実施形態に限定されるものではなく、請求項に示した範囲で種々の変更が可能であり、異なる実施形態にそれぞれ開示された技術的手段を適宜組み合わせて得られる実施形態についても本発明の技術的範囲に含まれる。さらに、各実施形態にそれぞれ開示された技術的手段を組み合わせることにより、新しい技術的特徴を形成することができる。 The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention. Furthermore, a new technical feature can be formed by combining the technical means disclosed in each embodiment.
　１、１０　表示装置　
　２、１１　階調値変換装置　
　３　映像データ取得部　
　４　仮想最大輝度レベル設定部　
　５　階調値変換部　
　６　パネル制御部　
　７　表示パネル　
　１２　階調値調整部 1, 10 display device
2,11 gradation value converter
3 Video data acquisition unit
4 Virtual maximum brightness level setting part
5 Tone value converter
6 Panel controller
7 Display panel
12 Tone value adjustment unit

Claims (18)

  1. 　第１の映像フォーマットよりも輝度範囲の広い第２の映像フォーマットに従う映像信号において各画素が取る階調値を変換する映像処理装置であって、
    　上記映像信号において各画素が取る階調値を参照することによって、上記映像信号に含まれるメタデータが示す最大輝度レベルよりも低い仮想最大輝度レベルを設定する仮想最大輝度レベル設定部と、
    　上記映像信号において各画素が取る階調値のうち、上記仮想最大輝度レベル以下の各輝度レベルに対応する階調値を変換する階調値変換部と、を備えていることを特徴とする、映像処理装置。     A video processing device for converting a gradation value taken by each pixel in a video signal according to a second video format having a wider luminance range than the first video format,
    A virtual maximum luminance level setting unit that sets a virtual maximum luminance level lower than the maximum luminance level indicated by the metadata included in the video signal by referring to the gradation value taken by each pixel in the video signal;
    A gradation value conversion unit that converts a gradation value corresponding to each luminance level equal to or lower than the virtual maximum luminance level among gradation values taken by each pixel in the video signal, Video processing device.
  2. 　上記階調値変換部は、上記映像信号が従う第２の映像フォーマットにおいて各画素が取り得る階調値のうち、上記仮想最大輝度レベル以下の各輝度レベルに対応する階調値を、上記第１の映像フォーマットにおいて各画素が取り得る階調値に対応させるマッピングを用いて、上記映像信号において各画素が取る階調値を変換する、
    ことを特徴とする請求項１に記載の映像処理装置。     The gradation value converter converts gradation values corresponding to each luminance level equal to or lower than the virtual maximum luminance level among gradation values that can be taken by each pixel in the second video format followed by the video signal. Converting the gradation value taken by each pixel in the video signal using mapping that corresponds to the gradation value that each pixel can take in one video format;
    The video processing apparatus according to claim 1.
  3. 　上記第１の映像フォーマットは、ＥＯＴＦがγ２．２相当のフォーマットであり、
    　上記第２の映像フォーマットは、ＥＯＴＦがＳＭＰＴＥ（Ｓｏｃｉｅｔｙ　ｏｆ　Ｍｏｔｉｏｎ　Ｐｉｃｔｕｒｅ　ａｎｄ　Ｔｅｌｅｖｉｓｉｏｎ　Ｅｎｇｉｎｅｅｒｓ）－ＳＴ２０８４であるフォーマットである、
    ことを特徴とする請求項２に記載の映像処理装置。     The first video format is a format in which EOTF is equivalent to γ2.2,
    The second video format is a format in which the EOTF is SMPTE (Society of Motion Picture and Television Engineers) -ST2084.
    The video processing apparatus according to claim 2.
  4. 　上記仮想最大輝度レベル設定部は、上記映像信号において各フレーム又は各シーンを構成する各画素が取る階調値を参照することによって、上記仮想最大輝度レベルを設定することを特徴とする請求項１～３の何れか１項に記載の映像処理装置。 2. The virtual maximum luminance level setting unit sets the virtual maximum luminance level by referring to a gradation value taken by each pixel constituting each frame or each scene in the video signal. 4. The video processing apparatus according to any one of items 1 to 3.
  5. 　上記仮想最大輝度レベル設定部は、上記仮想最大輝度レベルを、上記映像信号において各フレーム又は各シーンを構成する各画素が取る階調値に対応する輝度レベルの最大値に設定する、ことを特徴とする請求項４に記載の映像処理装置。 The virtual maximum luminance level setting unit sets the virtual maximum luminance level to a maximum value of a luminance level corresponding to a gradation value taken by each pixel constituting each frame or each scene in the video signal. The video processing apparatus according to claim 4.
  6. 　上記階調値変換部が変換した階調値のうち、低階調値領域の階調値に持ち上げ部を有するように調整する階調値調整部をさらに備えていることを特徴とする、請求項５に記載の映像処理装置。 The apparatus further comprises a gradation value adjustment unit that adjusts the gradation value converted by the gradation value conversion unit so that the gradation value in the low gradation value region has a lifting part. Item 6. The video processing device according to Item 5.
  7. 　上記階調値調整部は、上記階調値変換部が変換した階調値に対応する輝度レベルの平均値を参照して、上記低階調値領域を変更することを特徴とする、請求項６に記載の映像処理装置。 The said gradation value adjustment part changes the said low gradation value area | region with reference to the average value of the brightness | luminance level corresponding to the gradation value which the said gradation value conversion part converted. 6. The video processing apparatus according to 6.
  8. 　上記階調値調整部は、上記階調値変換部が変換した階調値と対応する輝度レベルとのグラフにおいて、低階調値領域の階調値と、高階調値領域の階調値とが連続的に変化するように、中階調値領域の階調値をさらに調整することを特徴とする、請求項６または７に記載の映像処理装置。 In the graph of the gradation value converted by the gradation value conversion unit and the corresponding luminance level, the gradation value adjustment unit includes a gradation value in a low gradation value region and a gradation value in a high gradation value region. The video processing apparatus according to claim 6, wherein the gradation value of the middle gradation value region is further adjusted so that the value continuously changes.
  9. 　上記階調値調整部が調整した階調値は、低階調値領域において、所定のフォーマットが示す階調値よりも大きいことを特徴とする、請求項６～８の何れか１項に記載の映像処理装置。 The gradation value adjusted by the gradation value adjustment unit is larger than the gradation value indicated by a predetermined format in the low gradation value region. Video processing equipment.
  10. 　上記仮想最大輝度レベル設定部は、上記映像信号において各フレーム又は各シーンを構成する各画素が取る階調値に対応する輝度レベルのヒストグラムを作成し、上記ヒストグラムを参照することによって、上記仮想最大輝度レベルを設定することを特徴とする請求項１～４の何れか１項に記載の映像処理装置。 The virtual maximum luminance level setting unit creates a histogram of luminance levels corresponding to gradation values taken by each pixel constituting each frame or each scene in the video signal, and refers to the histogram to thereby determine the virtual maximum luminance level. 5. The video processing apparatus according to claim 1, wherein a luminance level is set.
  11. 　上記仮想最大輝度レベル設定部は、上記仮想最大輝度レベルを、上記映像信号において各フレーム又は各シーンを構成する各画素が取る階調値に対応する輝度レベルの実効最大値であって、上記ヒストグラムの標準偏差の定数倍により定義される実効最大値に設定する、ことを特徴とする請求項１０に記載の映像処理装置。 The virtual maximum luminance level setting unit is an effective maximum value of a luminance level corresponding to a gradation value taken by each pixel constituting each frame or each scene in the video signal, wherein the virtual maximum luminance level is the histogram. The video processing apparatus according to claim 10, wherein an effective maximum value defined by a constant multiple of a standard deviation of the image is set.
  12. 　上記仮想最大輝度レベル設定部は、上記最大輝度レベルから所定値低いリミット値を設定すると共に、上記映像信号において各フレーム又は各シーンを構成する各画素が取る階調値に対応する輝度レベルの実効最大値であって、上記ヒストグラムの標準偏差の定数倍により定義される実効最大値が上記リミット値よりも低い場合、上記仮想最大輝度レベルを上記リミット値の値に設定し、上記実効最大値が上記リミット値以上である場合、上記仮想最大輝度レベルを上記実効最大値に設定することを特徴とする請求項１０に記載の映像処理装置。 The virtual maximum luminance level setting unit sets a limit value that is lower than the maximum luminance level by a predetermined value, and also executes an effective luminance level corresponding to a gradation value taken by each pixel constituting each frame or each scene in the video signal. If the effective maximum value defined by a constant multiple of the standard deviation of the histogram is lower than the limit value, the virtual maximum luminance level is set to the limit value, and the effective maximum value is The video processing apparatus according to claim 10, wherein the virtual maximum luminance level is set to the effective maximum value when it is equal to or greater than the limit value.
  13. 　上記仮想最大輝度レベル設定部は、リミット値を、上記最大輝度レベルから当該リミット値を減算した差と、上記映像信号において各フレーム又は各シーンを構成する各画素が取る階調値に対応する輝度レベルの実効最大値であって、上記ヒストグラムの標準偏差の定数倍により定義される実効最大値を上記リミット値から減算した差とが所定の比になるように設定すると共に、上記実効最大値が上記リミット値よりも低い場合、上記仮想最大輝度レベルを上記リミット値の値に設定し、上記実効最大値が上記リミット値以上である場合、上記仮想最大輝度レベルを上記実効最大値に設定することを特徴とする請求項１０に記載の映像処理装置。 The virtual maximum luminance level setting unit is a luminance corresponding to a difference between a limit value obtained by subtracting the limit value from the maximum luminance level and a gradation value taken by each pixel constituting each frame or each scene in the video signal. The effective maximum value of the level, which is set so that the effective maximum value defined by a constant multiple of the standard deviation of the histogram is subtracted from the limit value to be a predetermined ratio, and the effective maximum value is When the value is lower than the limit value, the virtual maximum luminance level is set to the value of the limit value. When the effective maximum value is equal to or greater than the limit value, the virtual maximum luminance level is set to the effective maximum value. The video processing apparatus according to claim 10.
  14. 　上記仮想最大輝度レベル設定部は、上記仮想最大輝度レベルを、上記映像信号において各フレーム又は各シーンを構成する各画素が取る階調値に対応する輝度レベルの実効最大値であって、上記ヒストグラムの標準偏差の定数倍により定義される実効最大値の時間平均値に設定する、ことを特徴とする請求項１０に記載の映像処理装置。 The virtual maximum luminance level setting unit is an effective maximum value of a luminance level corresponding to a gradation value taken by each pixel constituting each frame or each scene in the video signal, wherein the virtual maximum luminance level is the histogram. The video processing apparatus according to claim 10, wherein a time average value of an effective maximum value defined by a constant multiple of the standard deviation is set.
  15. 　請求項１～１４の何れか１項に記載の映像処理装置を備えている表示装置。 A display device comprising the video processing device according to any one of claims 1 to 14.
  16. 　第１の映像フォーマットよりも輝度範囲の広い第２の映像フォーマットに従う映像信号において各画素が取る階調値を変換する映像処理方法であって、
    　上記映像信号において各画素が取る階調値を参照することによって、上記映像信号に含まれるメタデータが示す最大輝度レベルよりも低い仮想最大輝度レベルを設定する仮想最大輝度レベル設定ステップと、
    　上記映像信号において各画素が取る階調値のうち、上記仮想最大輝度レベル以下の各輝度レベルに対応する階調値を変換する階調値変換ステップと、を含んでいることを特徴とする、映像処理方法。     A video processing method for converting a gradation value taken by each pixel in a video signal according to a second video format having a wider luminance range than the first video format,
    A virtual maximum luminance level setting step for setting a virtual maximum luminance level lower than the maximum luminance level indicated by the metadata included in the video signal by referring to the gradation value taken by each pixel in the video signal;
    A gradation value converting step of converting a gradation value corresponding to each luminance level equal to or lower than the virtual maximum luminance level among gradation values taken by each pixel in the video signal, Video processing method.
  17. 　請求項１に記載の映像処理装置としてコンピュータを機能させるための制御プログラムであって、上記仮想最大輝度レベル設定部および上記階調値変換部としてコンピュータを機能させるための制御プログラム。 A control program for causing a computer to function as the video processing apparatus according to claim 1, wherein the control program causes the computer to function as the virtual maximum luminance level setting unit and the gradation value conversion unit.
  18. 　請求項１７に記載の制御プログラムを記録したコンピュータ読み取り可能な記録媒体。 A computer-readable recording medium on which the control program according to claim 17 is recorded.
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