JP2010250193A - Image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an image signal representing correct gradation by reducing the change in gradation between sub-fields thereby shortening a response time of liquid crystal up to a desired gradation value. <P>SOLUTION: In a field sequential image display device, features of image signals of respective colors supplied to a display panel in one frame are detected, and the sequence of emission colors of a backlight and the sequence of colors of image signals supplied to a display panel in at least one frame are controlled on the basis of the detected features of image signals. Concretely, as features of image signals, the number of pixels having maximum gradation is detected with respect to each color of image signals, and the sequence of emission colors of the backlight and the sequence of colors of image signals supplied to the display panel in one frame are controlled so that they are rearranged in the ascending or descending order of the number of pixels having the maximum gradation. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a video display device configured to display video by a field sequential method.

  Unlike a liquid crystal display device using a field sequential method, in which one pixel is composed of sub-pixels having color filters of, for example, red (R), green (G), and blue (B), one pixel is RGB3. It is configured to display color images by sequentially switching in time. More specifically, one frame of an image is divided into three subfields corresponding to each RGB color (or four if one color other than RGB (for example, white or interpolated color) is included), and each subfield is divided. In addition, any image data of RGB (including white and interpolated colors in the case of four divisions) is written to all the pixels of the liquid crystal panel, and the color of the image data is changed by the backlight on the back surface of the liquid crystal display panel. By emitting corresponding light, a color image is displayed by visual mixing of each color. Such a field sequential method has an advantage that the liquid crystal panel can have high transmittance and high resolution as compared with a method in which one pixel is composed of three sub-pixels having RGB color filters.

  However, in the field sequential method, switching of R, G, and B (including white and interpolated colors in the case of four divisions) for each subfield is easily recognized visually, and so-called color breakage occurs.

  As a conventional technique for eliminating such color breakup, for example, one described in Patent Document 1 is known. In Patent Document 1, a liquid crystal display device and a backlight are divided into three regions, and unit color images of different colors are displayed in the first, second, and third divided regions, respectively, for each divided region, It is disclosed that color breakup is difficult to visually recognize.

Japanese Patent Laying-Open No. 2005-316092

  By the way, in the field sequential method, in order to sequentially display each color for each subfield, it is necessary to write image data to the pixel at a speed three times or more than that of a normal liquid crystal display device. Therefore, if the gradation difference of the image displayed between adjacent subfields is large, the response of the liquid crystal element may not be in time and the correct gradation corresponding to the image signal may not be expressed. For example, the gradation of a pixel in the first subfield is 10 (here, the gradation is expressed in 8 bits and takes a value of 0 to 255), and the same pixel level in the subsequent second subfield. When the tone is 220, the liquid crystal element of the pixel cannot follow the rapid and large gradation change from 10 to 220, and the pixel in the second subfield has a transmittance that expresses, for example, 180 gradations. Can only be obtained. Therefore, the color of the second subfield, which should originally be expressed with 220 gradations, can only be expressed with 180 gradations, and color reproducibility is degraded.

  The technique described in Patent Document 1 does not take into consideration the problem relating to the response speed of the liquid crystal element, and in each of the first, second, and third divided regions, R is used regardless of the characteristics and state of the video signal. , G, and B emit light in a certain order. For this reason, for example, when the gradation difference between R and G or G and B is large in a certain divided area, a good color cannot be expressed in the divided area as described above, and an image including color unevenness in the entire screen is displayed. May be displayed.

  The present invention has been made in view of the above-described problems, and provides a technique for improving color reproducibility in a field sequential method. Another object of the present invention is to provide a technique capable of improving color reproducibility while preventing color breakage in a field sequential method.

  According to the present invention, in a field sequential video display device, the characteristics of the video signals of the respective colors supplied to the display panel are detected in one frame, and at least the one frame is detected based on the detected characteristics of the video signal. The order of the colors emitted from the backlight and the order of the colors of the video signals supplied to the display panel are controlled.

  Specifically, as a feature of the video signal, the number of pixels having the maximum gradation is detected for each color of the video signal, and the difference between the maximum gradation numbers is reduced, that is, the maximum gradation is provided. Control is performed so that the order of the emission color of the backlight and the order of the colors of the video signals supplied to the display panel in one frame are rearranged in the order of the color having the largest number of pixels or the color having the smallest number.

  Here, the order of the emission color of the backlight and the order of the color of the video signal supplied to the display panel in a certain frame is the order of the color having the largest number of pixels having the maximum gradation or the order of the few colors. On the other hand, when rearranged, the subsequent frames may be rearranged in the other order.

  Further, the display area of the display panel is divided into a plurality of areas, and the order of the light emission color of the backlight and the color order of the video signal supplied to the display panel is controlled for each of the plurality of areas. You may make it do.

  According to the present invention, in the field sequential video display device, for each of a plurality of areas obtained by dividing the display area of the display panel, the characteristics of the video signals of the respective colors supplied to the display panel in one frame are detected, and this detection is performed. According to the characteristics of each region, the order of the color of light emitted from the backlight and the display panel are reduced so that the change in the light control amount of the display panel between subfields in each region is reduced. The color sequence of the supplied video signal is controlled.

  The video display device may further include a video signal processing unit for correcting the video signal of each color supplied to the display panel in each subfield. The video signal processing unit calculates a coefficient k based on the detected gradation value of the video signal, and corrects the video signal by multiplying the coefficient k by the gradation value of each pixel in the region. May be offensive. More specifically, the coefficient k may be obtained by a quotient of a predetermined gradation upper limit value and the detected maximum gradation value of the video signal, or a predetermined gradation value. May be equal to or less than the quotient of the detected upper limit value and the maximum gradation value of the detected video signal, and may have a value of 1 or more.

  According to the configuration of the present invention, in a video display device using a field sequential method, the light emission order and the video signal supply order are controlled so that the gradation change between the subfields is small, so that a desired display panel can be obtained. The response time to the light control amount (light transmittance) can be shortened, and a high-quality image having gradation corresponding to each image signal can be obtained.

The figure for demonstrating the operation | movement principle figure of this invention. The figure which shows a mode that the display area was divided | segmented into the several area | region. 1 is an overall block diagram of a video display apparatus according to a first embodiment of the present invention. The figure which shows the flow of operation | movement by the area | region feature detection part (303). The figure which shows an example of the pixel structure of each area | region. The figure which shows the mode of the rearrangement control by a present Example. The figure which shows the example which inserted the black period in each subfield. The figure which shows the mode of the gradation conversion which concerns on 2nd Example of this invention. The figure which shows the mode of the rearrangement control which concerns on 2nd Example of this invention. The figure which shows the other example of the rearrangement control which concerns on 2nd Example of this invention.

  Embodiments of the present invention will be described below with reference to the drawings. First, the concept of the embodiment of the present invention will be described with reference to FIG. In FIG. 1, it is assumed that one frame is divided into three sub-frames corresponding to RGB. FIG. 1A shows the state of a video signal in a certain region (or one pixel) in two consecutive frames (frame I and frame II). In the frame I, as shown in the left diagram of FIG. 1A, the gradation of the video signal G is the highest, the gradation of the video signal B is the next highest, and the gradation of the video signal R is the lowest. And In the frame II, as shown in the right diagram of FIG. 1A, the gradation of the video signal G is the highest, the gradation of the video signal B is the next highest, and the gradation of the video signal R is the lowest. Shall.

  In the present embodiment, the feature (here, maximum gradation) of the video signal of each color is detected by a feature detection unit, which will be described later, for each frame of such video. Then, according to the characteristics of the video, the order of the colors of the display video in one frame period is rearranged so that the change in gradation between the subfields is minimized. Hereinafter, rearranging the order of the colors of the display video may be simply referred to as “reordering control”.

  For example, as shown in FIG. 1B, the frames I are rearranged in order of increasing gradation, that is, G → B → R. Accordingly, in the frame I, in the first subfield f11, the backlight emits light of G color and the video signal G is supplied to the transmissive display panel (hereinafter simply referred to as “liquid crystal panel”). In the second subfield f12, the backlight emits light of B color and the video signal B is supplied to the liquid crystal panel. In the last (third) subfield f13, the backlight emits light of R color. Light is emitted and the video signal R is supplied to the liquid crystal panel.

  On the other hand, the frame II is rearranged in the order of decreasing gradation, that is, G → R → B, contrary to the frame I. This is to reduce the difference in gradation between frames (that is, subfield f13 of frame I and subfield f21 of frame II). That is, since the frame I is rearranged in the descending order and the gradation of the subfield f13 of the frame I is the smallest, the gradation of the subfield f21 of the frame II is the smallest in the frame II. This is because the gradation difference between the two is reduced. Note that when the frame I is rearranged in the descending order of the gradation, the frame II is rearranged in the descending order of the gradation.

  In the frame II, in the first subfield f21, the backlight emits light of G color and the video signal G is supplied to the liquid crystal panel. In the second subfield f22, the backlight is light of R color. And the video signal R is supplied to the liquid crystal panel. In the last (third) subfield f23, the backlight emits light of B color and the video signal B is supplied to the liquid crystal panel.

  As a result, as shown in FIG. 1B, the transmittance of the liquid crystal panel (liquid crystal transmittance) reduces the difference in transmittance between adjacent subfields and between adjacent frames. Reduction in color reproducibility due to response delay is prevented.

  On the other hand, in the prior art as described in Patent Document 1, for example, the order of the colors of the display video is fixed, for example, in the order of RGB regardless of the characteristics of the video signal, so the signal shown in FIG. 1 is input, for example, as shown in FIG. 1C, the gradation difference between subfield f11 and subfield f12 of frame I and subfield f22 and subfield f23 of frame II is large. Thus, the color reproducibility is degraded in the subfield f12 and the subfield f22.

  In the present embodiment, as described above, the control is performed to rearrange the order of the colors of the display video according to the characteristics of the video, for example, the gradation level of each color in one frame. It suppresses a rapid change in the liquid crystal transmittance during the period and prevents a decrease in color reproducibility. In the above example, when the colors of the display image of frame I are rearranged in order of increasing (smaller) gradation, frame II is rearranged in order of decreasing (larger) gradation. You may unify them in either the order of large or small.

  Next, examples of the present invention will be described.

  In the first embodiment, as shown in FIG. 2, the display area of the liquid crystal panel is divided into a plurality of areas, and the color order of the display video is rearranged for each of the divided areas. Prevention of color degradation and reduction of color breakup. In this embodiment, one frame is divided into three sub-fields corresponding to RGB three colors, and R, G, B three-color images are displayed in each sub-field. That is, the backlight according to the present embodiment has three types of light sources (LEDs) that emit three colors of R, G, and B.

  FIG. 2 shows an example in which the display area of the liquid crystal panel is divided into a total of 16 areas (area 0 to area 15) of 4 areas in the horizontal direction (horizontal direction) and 4 areas in the vertical direction (vertical direction). Hereinafter, the divided areas are simply referred to as “areas” or “divided areas”. This region is determined according to the division of the backlight that emits light from the back surface of the liquid crystal panel. In other words, the backlight is divided corresponding to the 16 divided display areas, and the color and the amount of light can be individually controlled in each area. For example, the backlight corresponding to each region is configured by providing a plurality of sets of light emitting diodes (LEDs) of three colors of R, G, and B, and the light emitting diodes of each color are switched and emitted in units of subfields. The In addition, the liquid crystal panel is configured so that the supply of video signals can be individually controlled in units of subfields for each of the 16 regions. This can be realized, for example, by providing a liquid crystal driver (not shown) for supplying a video signal corresponding to each area and individually controlling each driver.

  For example, when a red video is displayed in area 0 and a green video is displayed in area 10 in a certain subfield, the backlight corresponding to area 0 turns on only the R LED and the video signal to the liquid crystal driver corresponding to area 0 is displayed. Control is performed so that R is supplied to the liquid crystal panel, and the backlight corresponding to area 10 turns on only the G LED and controls the liquid crystal driver corresponding to area 10 to supply the video signal G to the liquid crystal panel. .

  The configuration of such control will be described with reference to FIG. FIG. 3 is a block diagram of the liquid crystal display device according to the first embodiment of the present invention. As shown in the figure, the liquid crystal display device of this embodiment includes a main control unit (301), an LED control unit (305) as a backlight control unit, an LED driver (306), and an LED backlight unit (307). A liquid crystal control unit (308), an H-driver (309), a V-driver (310), and a liquid crystal panel (311).

  The main control unit (301) further includes a video signal processing unit (302), a region feature detection unit (303), and a control signal generation unit (304). The video signal processing unit (302) performs various video corrections such as contrast correction, gamma correction, and brightness correction on the input video signal, and the corrected video data is input to the region feature detection unit (303). Send it out. The region feature detection unit (303) detects the video feature of the region from the video data for one frame corresponding to each of the plurality of divided regions, and determines the display video color order of the subfields. The order is output to the control signal generation unit (304). The control signal generation unit (304) sequentially changes the color of the backlight and the color of the video data supplied to the liquid crystal panel (311) according to the order from the region feature detection unit (303). Backlight control signal for designating the color of light emitted by the backlight, video data corresponding to the color designated by the backlight control signal, synchronization signal, and area for designating the area to be controlled The designation signal is output to the LED control unit (305) and the liquid crystal control unit (308).

  In the LED control unit (305), the region designated by the region designation signal from the control signal generation unit (304) is changed to the color (and / or designated by the backlight control signal from the control signal generation unit (304)). Alternatively, the color of the LED backlight unit (307) is partially controlled for each region by controlling the light emission color of the LED driver (306) corresponding to the region so as to emit light with intensity. That is, the LED control unit (305) controls the intensity of the LED driver (306) corresponding to the designated area by lighting only the LED (for example, R) corresponding to the color designated by the backlight control signal. LED drive signal for output. At this time, LEDs of other colors (G, B) are turned off. The LED drive signal is PWM (Pulse Width Modulation) or amplitude modulation. In the case of PWM, the PWM frequency is fixed, and the ratio (duty ratio) between the ON period and the OFF period is changed according to the light emission intensity, so that the LED driver (306) performs PWM control. The PWM frequency is preferably higher than the frame frequency of the liquid crystal display device. As a result, among the three color LEDs driven by the LED driver (306) corresponding to the designated region, the LED of the color designated by the backlight control signal is selectively driven to emit light.

  Note that the signal may be transmitted from the control signal generation unit (304) to the LED control unit (305) in any form as long as the region designation signal, the backlight control signal, and the like can be transmitted. For example, the various signals may be transmitted using a dedicated bus line, or an interface conforming to various interface standards may be used. Further, the region designation signal and the backlight control signal may be inserted and transmitted during the blanking period of the video signal.

  On the other hand, the liquid crystal control unit (308) is a horizontal (H) − that is a liquid crystal driver provided corresponding to each region based on the video data, the synchronization signal, and the region designation signal from the control signal generation unit (304). The driver (309) and vertical (V) -driver (310) are controlled. At this time, the color of the video data is the same as the color specified by the backlight control signal output simultaneously with the child video data. That is, the liquid crystal control unit (305) synchronizes the video data with the H-driver (309) and the V-driver (310) corresponding to the region designated by the region designation signal from the control signal generation unit (304). Based on the signal, a liquid crystal driving signal to be supplied to the liquid crystal panel (311) is output. The liquid crystal drive signal is generated based on the display signal applied to the data electrode of the liquid crystal panel (311) and the synchronization signal generated based on the video data to control the transmittance of the liquid crystal panel (311). The scanning signal applied to the scanning electrode of the liquid crystal panel (311) is included. In the liquid crystal panel (311), by driving each scanning electrode and each data electrode, a gradation voltage corresponding to a display signal is applied to the pixels in the designated region, and the pixels (liquid crystal elements) in the designated region are applied. The response of the liquid crystal is controlled. Further, the liquid crystal control unit (308) may output a timing signal (30) to the LED control unit (305), and the timing of changing the emission color and the color of the video data in each region is matched by this timing signal. Is possible.

  Next, an example of video feature detection in the region feature detection unit (303) and rearrangement control based on the detection result will be described with reference to FIGS. FIG. 4 is a flowchart showing the flow of the detection and rearrangement control process, and FIG. 5 shows one pixel configuration of the divided area shown in FIG. 2 and the state of gradation of each pixel. Further, the process shown in FIG. 4 is repeatedly performed in one frame period of the video.

  In FIG. 4, first, in step 401, the area feature detection unit (303) detects the gradation value and the maximum gradation color of each color for each pixel included in each area for each divided area. The state of this detection is shown in FIG. As shown in FIG. 5, each region is configured by a total of 16 pixels of 4 pixels in the horizontal direction and 4 pixels in the vertical direction. In the following, it is assumed that the gradation has a value of 0 to 255 in 8-bit expression and the maximum gradation length is 255.

  In FIG. 5A, for example, the gradation values of each color in the pixel Pixel A at the upper left are R (50), G (60), and B (70), respectively, as a result of detection by the region feature detection unit (303). It shall be. Further, the region feature detection unit (303) extracts the color having the maximum gradation by comparing the detected gradation values of the respective colors with each other. Here, since the gradation value of B (blue) is 70 and has the maximum value, “B” is extracted as the maximum gradation color of the Pixel A. The detection or extraction of the gradation value of each color and the maximum gradation color is performed for all the pixels included in the region. As a result, for example, it is assumed that a detection result as shown in FIG. 5B is obtained. When two colors having the same maximum gradation exist in one pixel as in Pixel B, the color is selected according to an arbitrary order (for example, R → G → B) determined in advance for each area. Or the corresponding pixel is treated as having no maximum gradation color. At this time, it is not necessary to set the same priority order in all the areas, and the order may be different for each area (for example, area 0 is R → G → B and area 1 is B → G → R). In FIG. 5B, since the priority order is R → G → B, “R” is selected as the maximum gradation color for Pixel B.

  Note that the detected maximum gradation value itself may be used as the maximum gradation value of each color, but the representable gradation range 0 to 255 is divided into, for example, eight, and the divided gradation ranges DR1 to DR8 are preliminarily set. A divided gradation range (any one of DR1 to DR8) to which the detected maximum gradation value belongs may be set as the maximum gradation value. For example, when the detected maximum gradation value is 240 and this belongs to the divided gradation range DR8 indicating the gradation range of 224 to 255, this DR8 may be used instead of the detected maximum gradation value 240. Good.

  Next, in step 402, the number of pixels having the maximum gradation of each color (R, G, B) in the region is counted for each color (R, G, B) to obtain the maximum gradation pixel number of each color. In the example of FIG. 5B, the maximum number of grayscale pixels N (Rmax) = 6, the maximum number of grayscale pixels N (Gmax) = 7, and the maximum number of grayscale pixels N (Bmax) = 3. Is required. In step 402, simultaneously with the calculation of the maximum number of gradation pixels, a total sum of gradation values for each color (R, G, B) in the region is obtained. In the example of FIG. 5B, the sum of R gradation values R (SUM) = 920, the sum of G gradation values G (SUM) = 980, and the sum of G gradation values G (SUM) = 750. Is required.

  Subsequently, in step 403, it is determined whether there is a pixel having the same number of maximum gradation pixels of each color, that is, N (Rmax), N (Gmax), and N (Bmax). If there is no match in the number of maximum gradation pixels in the region, the process proceeds to step 404.

  In step 404, the order of the colors of the display video is determined according to the maximum number of gradation pixels of each color in the area. Here, it is assumed that the order of colors of the display video is determined in descending order of the maximum gradation pixel number. In the example of FIG. 5, since the maximum number of gradation pixels has a relationship of N (Gmax)> N (Rmax)> N (Bmax), the first subfield (for example, f11 in FIG. 1) of the frame is used. G, the second subfield (eg, f12 in FIG. 1) is R, and the third subfield (eg, f13 in FIG. 1) is B. When the frame preceding the frame is rearranged in the order of colors having the largest number of maximum gradation pixels, the frames are rearranged in the order of colors having the smallest number of maximum gradation colors.

  In step 403, if there is a pixel having the same maximum gradation pixel number for each color, the process proceeds to step 405. In this step 405, it is determined whether or not there is a matching sum of gradation values for each color.

  If there is no match, the process proceeds to step 406, and the order of the colors of the display video is determined according to the sum of the gradation values for each color. Here, it is assumed that the order of the colors of the display video is determined in the order of the color having the largest sum of the gradation values. In the example of FIG. 5B, since the sum of the gradation values has a relationship of G (SUM)> R (SUM)> B (SUM), the first subfield (for example, FIG. 1) Let f11) be G, the second subfield (eg, f12 in FIG. 1) be R, and the third subfield (eg, f13 in FIG. 1) be B. When the previous frame is rearranged in the order of the color having the largest sum of the gradation values, the frames are rearranged in the order of the color having the smallest sum of the gradation values.

  In step 405, if there is a match in the sum of the gradation values for each color, the process proceeds to step 407, where the display video is displayed in an arbitrary order (for example, R → G → B) predetermined for each region. Determine the color order. At this time, it is not necessary to use the same order for all the areas, and the order may be different for each area (for example, area 0 is R → G → B, area 1 is G → B → R, etc.).

  The order determined by the region feature detection unit (303) as described above is input to the control signal generation unit (304) as described above. As described above, the control signal generation unit (304) controls the color of the backlight and the color of the video data supplied to the liquid crystal panel so as to switch the color of the display video in units of subfields according to the determined order. To do. Thereby, the rearrangement control described above is performed.

  FIG. 6 shows how rearrangement control is performed by the region feature detection unit (303) and the control signal generation unit (304) according to the present embodiment. Here, for simplification of explanation, it is assumed that the order of the display video colors is determined only by the determination in step 404 of FIG. FIG. 6A shows the maximum number of gradation pixels of each color in each region detected by the region feature detection unit (303). For example, in area 0 of FIG. 2, it is assumed that the maximum gradation pixel number is larger in the order of R, G, and B in frame I, and larger in the order of B, R, and G in frame II. On the other hand, in area 10, the maximum gradation pixel number is large in the order of G, B, and R in frame I, and is large in the order of R, G, and B in frame II.

  At this time, the display video color of each subfield in area 0, that is, the order of the display video color, is as shown in FIG. 6B, in order of increasing the maximum gradation pixel number in frame I, that is, the subfield (SF). The video of f11 is R, the subfield f12 is G, and the subfield f12 is B. On the contrary, in the frame II, the image of the maximum gradation pixel number is ascending order, that is, the subfield f21 is displayed as G, the subfield f22 is displayed as R, and the subfield f23 is displayed as B. On the other hand, as shown in FIG. 6C, the display video color of each subfield in area10, that is, the order of the display video color is the order in which the maximum gradation pixel number is large in frame I, that is, the subfield f11 is G, The subfield f12 is displayed as B, and the subfield f12 is displayed as R. On the contrary, in the frame II, in order of decreasing maximum gradation pixel number, the subfield f21 is displayed as B, the subfield f22 as G, and the subfield f23 as R.

  In this embodiment, the video signal processing unit (302) shown in FIG. 3 may have a function for converting the gradation values of the respective colors (R, G, B). This gradation value conversion function detects the maximum gradation value in the frame of each color of the input video signal for each of a plurality of areas, and converts the maximum gradation value and the upper limit value of the gradation (for example, 255 for 8 bits). Based on this, the gradation value of each pixel in the region is converted. Here, the maximum gradation value of each color may be detected by the video signal processing unit (302) itself, or the maximum gradation value detected by the region feature detection unit (303) is fed back to the video signal processing unit (302). You may use what you did.

  For example, when the 8-bit R signal is taken as an example, the tone conversion has the tone upper limit value 255 as the brightest tone in the region i (where i is 0 to 15 in the example of FIG. 2). The coefficient k (= 255 / Rmax) obtained by dividing by the value Rmax is multiplied by the gradation value Rj of each pixel in the area. Such gradation conversion may be performed with non-linear processing in consideration of the gamma characteristic of the video signal.

  In the above gradation conversion, depending on the maximum gradation value of the area, the difference of the gradation value for each color in the area may be larger than the input video signal, and the transmittance change of the liquid crystal panel between subfields may occur. May be larger than the input video signal. Accordingly, one or more coefficients slightly smaller than the coefficient k may be substituted for the coefficient k to be multiplied by the gradation value Rj of each pixel in each region. Thus, by selecting an optimum coefficient value for each color and converting the gradation value of each pixel in each region, the change in transmittance of the liquid crystal panel between subfields can be reduced. In addition to this, the LED backlight unit (307) has an advantage that power consumption can be reduced by turning on the LED with a duty corresponding to the maximum transmittance of the liquid crystal panel in the region. The effect of reducing the transmittance change will be described in detail below.

For example, in a region i composed of 4 pixels expressed by 8-bit gradation, (R, G, B) = (40, 50, 60) is 3 pixels, and (R, G, B) = (100, 150, 200) is an image of one pixel, the difference Δi of all gradation values in the input video signal is as follows.
Δi = ((60−50) + (50−40)) × 3 + ((200−150) + (150−100)) × 1 = 160
In this region i, the coefficients of each color are kr, kg, kb, kr = 1.5 (<255/100), kg = 1.2 (<255/150), kb = 1.0. When gradation conversion is performed by multiplying the video signal of each color by this coefficient, (R, G, B) = (60, 60, 60) is 3 pixels, and (R, G, B) = (150, 180, 200) is one pixel. Accordingly, the difference Δi ′ of all gradation values is as follows.
Δi = ((60−60) + (60−60)) × 3 + ((200−180) + (180−150)) × 1 = 50
That is, according to the gradation conversion according to the present embodiment, the gradation difference between the subfields is reduced from 160 to 50, and the change in the transmittance of the liquid crystal panel is reduced accordingly. By performing gradation conversion in this way, the change in transmittance of the liquid crystal panel between subfields can be reduced, and the LED is turned on with a duty corresponding to the transmittance of the largest transmissive display panel in that region. Power consumption can be reduced.

  In the present embodiment, a so-called black insertion technique can be applied. That is, as shown in FIG. 7, a black period 71 in which no video is displayed may be inserted at the head of each subfield (f11 to f13, f21 to f23) in FIG. Thereby, while ensuring the response time of a liquid crystal element, the sharpness of an image | video can be acquired. The order of display video colors and rearrangement control are the same as those described above.

  In this way, in this embodiment, the order of the colors of the video displayed in each subfield is determined, and rearrangement control is performed based on this, so that the change in the transmittance of the liquid crystal panel between each subfield is small. Thus, the above-described deterioration in color reproducibility can be reduced. In this embodiment, since the rearrangement control is performed for each divided area of the liquid crystal panel, it is possible to reduce color breakup. Furthermore, if the gradation value of each color in each region is converted using the maximum gradation value, the change in the transmittance of the liquid crystal panel can be further reduced, and the deterioration of color reproducibility is more suitably reduced. can do.

  In the description of the above embodiment, the region feature detection unit (303) also determines the order of display video colors (that is, performs the processing of steps 403 to 407 in FIG. 4). 303) obtains only the maximum number of gradation pixels of each color and the sum of gradation values of each color, and the control signal generation unit (304) performs the subsequent processing, that is, the processing of steps 403 to 407 in FIG. Also good.

  Next, a second embodiment of the present invention will be described with reference to FIG. 3 and FIGS. Unlike the first embodiment described above, the second embodiment divides one frame into four subfields, and each of the subfields has three colors of R, G, and B, and white (W). A specific example of rearrangement control in the case of displaying a video is shown. That is, in the present embodiment, the backlight is configured to include white LEDs in addition to the RGB three-color LEDs. 8 and 9 show an example in which one backlight unit corresponds to one pixel, as in FIG. 1, for the sake of simplicity. In the present embodiment, the same circuit block as that in FIG. 3 is used.

  The area feature detection unit (303) in FIG. 3 performs, based on the video data output from the video signal processing unit (302), for example, as shown in FIG. The gradation value is detected, and the darkest gradation (minimum gradation value: Pmin) among the detected gradation values of each color is determined. In the example of the video data of the frame I shown in the left diagram in FIG. 8, since R is the minimum gradation value, the gradation value of R = Pmin. Further, in the example of the video data of the frame II shown in the right diagram in FIG. 8, since G is the minimum gradation value, it is assumed that G gradation value = Pmin. Then, as shown in the lower part of FIG. 8, a value (Pmin / 2) obtained by halving the minimum gradation value of each frame is assigned as a white gradation value, and each of the R, G, and B gradation values in the area is assigned. Converts the original gradation value (detected gradation value) into a value obtained by subtracting a value (Pmin / 2) obtained by halving the minimum gradation value. Thus, in this embodiment, the video data shown in FIG. 8 is converted into the data shown in the lower part of FIG. Here, the converted gradation value data Rt, Bt, Gt, and W of each color are expressed as follows when the detected gradation value data (before conversion) are Rd, Bd, and Gt, respectively. It is represented by

Rt = Rd−Pmin / 2
Gt = Gd−Pmin / 2
Bt = Bd−Pmin / 2
W = Pmin / 2
Here, since Rt is the minimum gradation value in frame I, Rt = Pmin, and in frame II, Gt = Pmin because Gt is the minimum gradation value.

  Subsequently, the area feature detection unit (303) performs the maximum for each area in each frame, as shown in FIG. 9, based on the gradation data of each color after gradation conversion as shown in the lower part of FIG. The order of display image colors is determined in the order of colors with the smallest gradation value (when there are a plurality of pixels in each region, the maximum number of gradation pixels is used as described in FIG. 4). White (W) is assigned to the last (fourth) subfield in any frame. That is, in the frame I, the order is such that the first subfield f11 is R, the second subfield f12 is B, the third subfield f13 is G, and the fourth subfield f14 is W. In the frame II, the first subfield f21 is displayed in the order of G, the second subfield f22 is displayed in R, the third subfield f23 is displayed in B, and the fourth subfield f24 is displayed in W.

  The region feature detection unit (303) transmits the order determined as described above to the control signal generation unit (304). As in the first embodiment, the control signal generation unit (304) transmits the emission color and emission intensity of each region to the LED control unit (305) and generates a video signal corresponding to the emission color of each region. To the liquid crystal control unit (308).

  As described above, in this embodiment, RGB except W is rearranged in order of increasing or decreasing the maximum gradation value (or the maximum number of gradation pixels) of each color, but the display order of white images is within the frame. It is going to be the last. As a result, white is displayed at a constant period (for example, 60 Hz when one field is 60 Hz), so that the frame frequency for each color can be set high. However, in this case, as shown in FIG. 9, the change in gradation value from the subfields f13 to f14 and from the subfields f23 to f24 becomes large. Therefore, for example, the display of the white image may be started after a certain period from the start of the subfield without displaying the white image in the entire subfield period. Alternatively, a display timing table corresponding to the change in the gradation value may be stored in the ROM, and the display timing of the white image may be determined by referring to the ROM.

  Further, in order to suppress the gradation difference between the frames, the subfields for displaying the W video may be adjacent to each other between consecutive frames. For example, as shown in FIG. 10, the last subfield f14 may be W in frame I, and the first subfield f21 may be W in frame 2. At this time, it is preferable that the display image order of each RGB color is in the order of the largest gradation value or the largest number of gradation pixels in the frame I and the order of the largest gradation value or the largest number of gradation pixels in the frame II. Also in this embodiment, as in FIG. 7, a black period in which no video is displayed may be inserted at the head of each subfield (f11 to f14 and f21 to f24 in this embodiment).

  As described above, according to the second embodiment, rearrangement control according to the gradation of each color is performed even in the field sequential method in which one frame is divided into four subfields and RGB and W images are respectively displayed. Therefore, even in such a method, the change in the transmittance of the liquid crystal panel can be reduced, and the above-described decrease in color reproducibility can be suppressed. Further, if the rearrangement control is performed for each divided area obtained by dividing the display area into a plurality of areas, color breakup can be suppressed. In the above example, white is used in addition to RGB, but other colors such as an interpolation color (for example, yellow) may be used.

  In the above embodiments, the liquid crystal display panel has been described as the display panel. However, if it is used in combination with a backlight, a display panel such as an electrophoretic type or MEMS (Micro Electro Mechanical Systems) is used. The same effect can be obtained. Moreover, although LED was mentioned as an example as a backlight, fluorescent tubes, such as HCFL (Hot Cathode Fluorescent Lamp), CCFL (Cold Cathode Fluorescent Lamp), EEFL (External Electrode Fluorescent Lamp), EL (Electro-Luminescence), OLED A light source capable of emitting light by color such as (Organic light-emitting diode) may be used.

  The present invention can be applied to a video display device using a field sequential system, such as a liquid crystal television or a portable display, which can divide and control a backlight into a plurality of regions.

301 Video Signal Processing Unit 302 Video Signal Processing Unit 303 Region Feature Detection Unit 304 Control Signal Generation Unit 305 LED Control Unit 306 LED Driver 307 LED Backlight Unit 308 Liquid Crystal Control Unit 309 H-Driver 310 V-Driver 311 Liquid Crystal Panel

Claims (16)

A backlight that sequentially switches and emits light of different colors for each of a plurality of subfields obtained by dividing one frame into a plurality of subfields;
The light emitted from the backlight is irradiated and a video signal of a color corresponding to the color of the light from the backlight is sequentially supplied, and the light from the backlight is supplied according to the supplied video signal. A display panel that controls each pixel;
In a field sequential video display device having
A detecting unit for detecting characteristics of the video signals of the respective colors supplied to the display panel in the one frame;
A control unit that controls the order of the emission colors of the backlight and the order of the colors of the video signals supplied to the display panel in at least the one frame based on the characteristics of the video signal detected by the detection unit; ,
A video display device comprising:   2. The video display device according to claim 1, wherein the detection unit detects the number of pixels having a maximum gradation for each color of the video signal as a characteristic of the video signal of each color. apparatus.   3. The video display device according to claim 2, wherein the control unit is configured to control the backlight of the one frame in the order of colors having the largest number of pixels having the maximum gradation detected by the detection unit or in order of colors having a small number. An image display apparatus, wherein control is performed to rearrange the order of light emission colors and the order of colors of video signals supplied to the display panel.   4. The video display device according to claim 3, wherein the control unit is configured to change the order of the emission color of the backlight and the order of the color of the video signal supplied to the display panel in a certain frame to a pixel having the maximum gradation. An image display device characterized in that when the number of images is rearranged in one of the order of colors having the largest number or the order of colors having the smallest number, the images are rearranged in the order of the other in subsequent frames.   2. The video display device according to claim 1, wherein a display area of the display panel is divided into a plurality of areas, and the detection unit is configured to supply each color supplied to the display panel in each subfield for each of the plurality of areas. In addition, the control unit detects the order of the light emission color of the backlight and the order of the color of the video signal supplied to the display panel for each of the plurality of areas. An image display device characterized by controlling.   3. The video display device according to claim 2, wherein a display area of the display panel is divided into a plurality of areas, and the control unit is a pixel having the maximum gradation detected by the detection unit for each of the plurality of areas. A video display device that controls the order of the light emission color of the backlight and the color of the video signal supplied to the display panel in the order of the color with the largest number or the color with the smallest number .   The video display device according to claim 6, wherein the control unit determines the order of the emission color of the backlight and the color order of the video signal supplied to the display panel in an area of a certain frame as the maximum gradation. An image display device characterized in that when rearranged in the order of colors with the largest number of pixels or in the order of few colors, the same area of the subsequent frame is rearranged in the other order.   2. The video display device according to claim 1, wherein the backlight includes three-color light emitting diodes that respectively emit light of red, blue, and green as the plurality of colors. A backlight that sequentially switches and emits light of different colors for each of a plurality of subfields obtained by dividing one frame into a plurality of subfields;
The light emitted from the backlight is irradiated and a video signal of a color corresponding to the color of the light from the backlight is sequentially supplied, and the light from the backlight is supplied according to the supplied video signal. A display panel that controls each pixel;
In a field sequential video display device having
A detection unit for detecting a feature of the video signal of each color supplied to the display panel in the one frame for each of a plurality of areas obtained by dividing the display area of the display panel;
The order of the colors of light emitted from the backlight so that the change in light control amount of the display panel between subfields in each region is reduced according to the characteristics of each region detected by the detection unit. And a control unit for controlling the color order of video signals supplied to the display panel;
A video display device comprising: The video display device according to claim 9, wherein
And a video signal processing unit for correcting the video signal of each color supplied to the display panel in each subfield,
The detection unit detects a gradation value of the video signal as a feature of the video signal,
The video signal processing unit calculates a coefficient k based on the gradation value of the video signal detected by the detection unit, and multiplies the gradation value of each pixel in the region by the coefficient k. A video display device which corrects a video signal.   11. The video display device according to claim 10, wherein the video signal processing unit calculates the coefficient k as a quotient of a predetermined upper limit value of gradation and a maximum gradation value of the video signal detected by the detection unit. A video display device characterized by calculating by calculating.   11. The video display device according to claim 10, wherein the coefficient k is equal to or less than a quotient between a predetermined upper limit value of gradation and a maximum gradation value of the video signal detected by the detection unit, and is equal to or more than one. A video display device characterized by having a value.   10. The video display device according to claim 9, wherein the detection unit has, as a feature of the video signal, a color having a maximum gradation in each region and / or a pixel included in the region for each color. An image display device that detects a sum of gradation values.   The video display device according to claim 9, wherein the light control amount change direction of the display panel between the subfields is changed for each of the adjacent regions.   10. The video display device according to claim 9, wherein the backlight includes three color light emitting diodes that emit light of at least red, blue, and green. A field-sequential video display comprising a backlight, in which one frame is composed of a plurality of subfields, and a backlight that sequentially switches the emission color in the field unit, and a transmissive display panel in which the transmittance is controlled in the field unit. In the device
A feature detector for detecting features of the video signal for each of a plurality of display areas from the input video signal of one frame;
In accordance with the characteristics of each display area detected by the detection unit, the emission color and brightness of the backlight are set so that the change in transmittance of the transmissive display panel between subfields in each display area is reduced. A video display device comprising: a control unit that controls each region and controls the transmissive display panel.

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