JP4622900B2 - Image processing apparatus, image processing method, program, and recording medium - Google Patents

Description

  The present invention relates to an image processing apparatus capable of controlling a video signal so as to improve its visibility according to the ambient illuminance, input signal, and display image content used, and a processing method therefor.

  Conventionally, in mobile display devices, in-vehicle display devices, television receivers, etc., in order to improve the visibility of images according to the display contents of input signals and the brightness of the surrounding environment used, Techniques for adaptively controlling signal contrast, brightness, color signals, display brightness of display devices, γ characteristics, and the like have been developed.

  For example, in the case of a liquid crystal display, a specific example is shown in Patent Document 1, and based on the brightness control signal of the sensor, the amplitude of the video signal applied to the liquid crystal panel and the operation reference level are automatically controlled. It controls the brightness and contrast of the liquid crystal display screen.

  On the other hand, in the example of the signal processing of the display device, a specific example is shown in Patent Document 2, and the character information of the input signal for character broadcasting is detected, and the contour emphasis control and the threshold value of the character part are detected according to the illuminance information. Based on this, processing such as changing the character color and the background color is performed.

Also, in-vehicle display devices need to improve visibility in a wide illuminance range from direct sunlight to darkness, and dimming control of display devices according to ambient illuminance (backlight dimming control for liquid crystal displays) A function called dimmer has been widely adopted.
JP-A-6-83287 JP 11-352950 A

  However, in the case of the liquid crystal display device disclosed in Patent Document 1, the signal contrast is increased, the brightness (operation reference level) set point is increased to make it brighter, and the γ characteristic is controlled. However, it is possible to improve the visibility to some extent in an AV natural image such as a TV or DVD video, but display of a video signal having a wide dynamic range of a so-called computer graphics image such as a map image in a car navigation system. Can be said to be insufficient in some cases because of its visual characteristics.

  In the case of the display device shown in Patent Document 2, the display device is for character broadcasting and has a character information detection unit and an image generation unit as shown in FIG. In order to improve the performance, processing is performed so that the color of the character and the background has a complementary color relationship, but it requires a character detection unit and an image generation unit, and also for objects other than characters It will not be improved.

  In addition, in the case of only backlight dimming control (dimmer) for liquid crystal displays or the like as is done in conventional in-vehicle display devices, the maximum brightness of the backlight is adjusted in the case of extremely high illuminance such as direct sunlight. Visibility cannot be improved beyond light control.

  The object of the present invention is to improve the above-described problems. Even in the case where the illuminance environment changes drastically in a wide range such as an in-vehicle display, the display is simultaneously performed according to the illuminance change. In consideration of the video characteristics of the video, an image processing apparatus capable of always improving the image quality and improving the visibility optimally over the entire illuminance range.

  In particular, when displaying maps in car navigation, the signal source (drawing data recorded on a DVD disc or hard disk in the case of car navigation) can be faithfully reproduced and displayed under normal illumination conditions. Basically, in an extremely bright environment where direct sunlight shines, priority should be given to making it easier to see from the standpoint of safety, such as high instantaneous readability by the driver. It is an object of the present invention to be able to automatically adjust the display color so as to enhance visibility in an environmental situation.

  In order to solve the above problem, an image processing apparatus according to a first aspect of the present invention includes a brightness correction unit that corrects a brightness signal of the input video signal in accordance with a level of a saturation signal of the input video signal, and the brightness The correction means corrects the gain of the lightness signal to be decreased when the level of the saturation signal is low and to increase the gain of the lightness signal when the level of the saturation signal is high. This improves the visibility of the image when displayed on the screen.

  An image processing apparatus according to a second aspect of the present invention includes a luminance correction unit that corrects a luminance signal of the input video signal in accordance with a level of the color difference signal of the input video signal, and the luminance correction unit includes the color difference signal. The visibility of the image when displayed on the display device is reduced by reducing the gain of the luminance signal when the level of the color signal is low, and increasing the gain of the luminance signal when the level of the color difference signal is high. Is to improve.

  An image processing apparatus according to a third aspect of the present invention includes an illuminance detection unit that detects illuminance around the display device, and a table that represents a relationship between illuminance and a correction coefficient. By providing RGB correction means for correcting each of the RGB signals based on the correction coefficient selected by the illuminance signal from the detection means, the visibility of the image when displayed on the display device is improved.

  According to the present invention, an object extraction process of an input video signal is performed in an image processing apparatus that corrects and displays an input video signal for the purpose of improving visibility when the illuminance state of the usage environment is very bright or dark. Therefore, an image processing apparatus that effectively performs color correction control of a video signal can be obtained.

  In particular, in the case of a computer graphics image such as a map image display in a car navigation system or a vehicle information display in an in-vehicle display device, there is little chromaticity difference between an object such as a road or character on the map and the background, and color contrast is low. Even for a low image, color control can be performed to appropriately increase the color contrast, and the visibility in a bright illuminance environment can be effectively improved.

  Hereinafter, an image processing apparatus and a processing method thereof according to the present invention will be described with reference to the drawings. In the following embodiments, description will be made as an example in which each processing means is configured by hardware, but similar processing can also be performed by software. It is also possible to realize the above hardware by an integrated circuit integrated on one or a plurality of semiconductors. An example in which the display device is connected to a liquid crystal display device will be described. However, the image processing device to which the present invention is applied is not limited to this example, and an organic EL (electroluminescence) display device or a PDP (plasma display) is used. Connection to a panel) display device or the like is also applicable.

(Embodiment 1)
FIG. 1 is a block diagram showing the configuration of the image processing apparatus according to the first embodiment of the present invention. The image processing apparatus of FIG. 1 includes a color space conversion unit 1, a lightness correction processing unit 2, a lightness control coefficient calculation unit 3, a color space inverse conversion unit 4, and an illuminance detection unit 5, and an output signal is sent to the display panel 6. It is connected. Here, the thing including the brightness correction processing means 2 and the brightness control coefficient calculation means 3 is called brightness correction means. Hereinafter, the case where the display panel 6 is an in-vehicle display device which is a liquid crystal display will be described.

  The color space conversion means 1 receives an input video signal in the RGB signal format, and converts the RGB signal into signal components of a hue signal, a saturation signal, and a brightness signal. This signal conversion is performed by the following arithmetic expression.

Lightness signal V = MAX (R, G, B)
Hue signal H = {MID (R, G, B) −MIN (R, G, B)} / {MAX (R, G, B) −MIN (R, G, B)}
Saturation signal S = {MAX (R, G, B) −MIN (R, G, B)} / MAX (R, G, B)
Where MAX (R, G, B) is the maximum value of each RGB signal
MID (R, G, B) is the intermediate value of RGB signals
MIN (R, G, B) represents the minimum value among the RGB signals.

  At the time of this conversion, it is determined which of MAX, MID, and MIN each corresponds to RGB.

  After the conversion, the brightness signal is sent to the brightness correction processing means 2, the saturation signal is sent to the brightness control coefficient calculating means 3 and the color space inverse transform means 4, and the hue signal is sent to the brightness control coefficient calculating means 3 and the color space. It is output to the inverse conversion means 4. In the lightness correction processing means 2, lightness gain control is performed on the lightness signal using the lightness correction control coefficient calculated by the lightness control coefficient calculation means 3, and the result is output to the color space inverse conversion means 4. The lightness control coefficient calculation means 3 calculates a lightness correction control coefficient from the input saturation signal and hue signal and the illuminance signal detected by the illuminance detection means 5, and outputs it to the lightness correction processing means 2. In the color space reverse conversion means 4, the input hue signal and saturation signal and the lightness signal after the correction processing are converted into RGB signals by an operation reverse to that of the color space conversion means 1, and the display panel 6 Is output.

  In the image processing apparatus configured as described above, the content of the lightness correction coefficient calculation calculation that is adaptively controlled by the lightness control coefficient calculation unit 3 will be described.

  The lightness correction control coefficient is a contrast gain value for contrast control of the lightness component with respect to the lightness correction processing means 2 in the present embodiment. This is because the video signal is divided into hue, saturation, and lightness components, and only the lightness component is subjected to variable processing according to the hue and the saturation value, and then returned to the RGB signal, whereby a specific color (hue and hue) is obtained. It is possible to change to a color with a specific amount of lightness changed only for (saturation level), and this is a control value for intentionally changing the lightness value in order to improve visibility.

In particular, the present application is characterized in that the control characteristic is calculated with the saturation signal level as an input for this control value. Specifically, the saturation signal level as shown in FIG. It is a gain characteristic that outputs a control gain value. In the characteristic example shown in this embodiment, as shown in FIG. 3, when the saturation signal level is low (that is, when the color is light and light), the lightness is lowered to darken, and conversely, the saturation signal level. When the value is high (that is, when the color is dark and the color is good), brightness control is performed so that the brightness is increased and the brightness is increased. That is, as shown in FIG. 3, when the level of the saturation signal having a brightness gain of 1.0 with respect to the brightness signal is defined as the first saturation level, the level of the saturation signal is higher than that of the first saturation level. In a large range, the lightness gain is increased as the level of the saturation signal is larger, and in a range where the level of the saturation signal is smaller than the first saturation level, the lightness gain is decreased as the level of the saturation signal is smaller. Thus, the correction processing of the brightness correction means is controlled. FIG. 4 shows the concept of correction in the HSV color space for this brightness correction control.

  In general, in order to improve the visibility of the image processing apparatus in situations such as when the illuminance of the usage environment is extremely high, the screen brightness is increased and the chromaticity difference between colors is increased. Is known to be effective.

  By using the gain characteristics as described above, the light color is changed to a darker tone, and the dark color is changed to a lighter tone, resulting in an increase in the chromaticity difference between the two different colors. Therefore, the color contrast is improved, and the color is changed to a color that improves the visibility in a bright place with very high illuminance.

  In FIG. 3, the gain is not lowered when the saturation level is very low near 0. The lightness is near 0 (that is, an achromatic color or a color close to it) where the saturation level is very low. This is to prevent the lightness from being lowered, especially when the lightness is originally high (white or light gray). As a result, for example, in the case of a map image or the like having a white line road or character in the background portion of a relatively low color, the original image has low color contrast between the white line road and character and the background, and visibility in a bright place is low. What was bad is that the low-saturation color portion of the background (for example, the color indicated by “original color” in FIG. 4) is changed to a dark tone (the color indicated by “corrected color” in FIG. 4). The white lines and white characters can be clearly seen, and the visibility in the bright place is improved.

  This gain characteristic is sufficiently effective even if it is a uniform characteristic regardless of the hue, but for each predetermined hue, for example, the hue ring can be set independently for each hue divided into 12 (12 axes). More optimal control can be realized by selecting an optimum gain characteristic for the hue according to the signal input and outputting it as a brightness correction coefficient. For example, the characteristics are changed so as to be enhanced in hues where color contrast due to brightness differences is difficult to be applied, or application to Purkinje compensation described later. In addition, if the characteristics of the display panel used, for example, if the display panel is a liquid crystal display, the color reproduction characteristics of RGB are biased depending on the characteristics of the color filter used in the device. Thus, by setting different characteristics for each hue, it becomes possible to make the effect of providing a brightness difference uniform regardless of the hue.

Next, illumination adaptive control will be described. The brightness correction coefficient (gain characteristic) described above is adapted to achieve more optimal control by adjusting the control state in accordance with the environmental illuminance where the display device is located. Specifically, as shown in FIG. 5, control is performed so that the characteristics are adaptively changed with a predetermined control intensity in a predetermined illuminance region by an input illuminance signal. The control intensity characteristics shown in FIG. 5 are characteristics that increase the control intensity as the distance from the standard illuminance increases in the illuminance region where the illuminance environment on the bright side and the dark side is not good. That is, as shown in FIG. 5, in the high illuminance range where the ambient illuminance is 3000 lx or more, the correction process is emphasized as the illuminance increases, and in the low illuminance range where the ambient illuminance is 200 lx or less, the illuminance decreases. The brightness correction unit is controlled to emphasize the correction process, and the brightness gain is controlled to be fixed to 1.0 in a standard illuminance range where the ambient illuminance exceeds 200 lx and less than 3000 lx. This is for seamlessly switching between the visibility improvement effect and the uncomfortable feeling because the uncomfortable feeling with respect to the color design of the original image occurs as a trade-off although the visibility is improved by the brightness correction control.

  The purpose of the visibility improving process described in the present embodiment is to improve the visibility in a bright place, so that the brightness correction control itself is weakened on the dark side.

  In the middle standard illuminance state, brightness correction control is not necessary and only the color design of the original image is changed meaninglessly. Therefore, the brightness control is turned off. In the present embodiment, the final brightness correction coefficient shown in FIG. 6 is obtained by multiplying the gain characteristic calculated in FIG. 3 as the illuminance correction coefficient by a coefficient obtained from the control intensity characteristic as shown in FIG. 5 based on the detected illuminance. As shown in FIG. In this embodiment, the illuminance detection means is provided and the illuminance adaptive control is performed with the characteristics shown in FIG. 5 by the illuminance signal. However, even if the illuminance detection means is not provided, the user However, it may be possible to select ON / OFF of brightness correction according to the illuminance by a switch.

  Here, the Purkinje phenomenon, which is a visual feature in the case of dark illuminance, will be described.

  The visual feature is that the rod, which is a photoreceptor cell that mainly works in dark vision of about 10 lx or less, reacts well in light and dark, but does not react to light of long wavelength components, so that red ones appear dark and blue color Is called the Purkinje phenomenon. As shown in FIG. 7, this means that the relative visibility curve shifts to the short wavelength side from 555 nm to about 507 nm in dark place vision. Therefore, as compensation for this phenomenon, when the illuminance is below a predetermined illuminance (approximately 10 lx), control for each hue is such that the gain characteristic of the R hue is emphasized as in bright illuminance and conversely the gain characteristic of the B hue is suppressed. It is what. In the case of the illuminance condition, this can be realized by changing the lightness gain characteristic in this way in accordance with the hue signal input in the lightness control coefficient calculating means.

  In this way, the brightness control characteristic with respect to the saturation is calculated by adapting to the illuminance and hue, and is input to the brightness correction processing means 2 to control the gain of brightness, thereby controlling the color in the direction in which the chromaticity difference is enlarged. It can be changed to increase the color contrast and improve the visibility.

  This is particularly effective in the case of so-called computer graphics images such as car navigation map images. In addition, by performing illuminance adaptive control, the original color reproduction of the signal source is performed under a standard illuminance environment, and the color display is changed to expand the color contrast in a light environment, etc. Even in a state, it is possible to achieve natural control so as to produce a seamless effect.

(Embodiment 2)
FIG. 2 is a block diagram showing the configuration of the image processing apparatus according to the second embodiment of the present invention. The difference between the image processing apparatus shown in FIG. 2 and the image processing apparatus shown in FIG. 1 is that a brightness feature detection means 7 and a saturation feature detection means 8 are added, and the internal operation of the brightness control coefficient calculation means 3a. Is a change. Since the other points are the same as those of the image processing apparatus shown in FIG.

  In the brightness feature detection means 7, the input brightness signal is passed through a low-pass filter, and then the minimum value, maximum value, and average of the brightness signal for a predetermined detection area within one screen of the input video signal. Each integrated value for calculating the value is obtained, and each detected value is input to the brightness control coefficient calculating means 3a. In the saturation feature detection means 8, an integrated value for calculating the minimum value, maximum value, and average value of the saturation signal is obtained by a similar circuit with the saturation signal as an input, and the brightness control coefficient calculation means 3a. Is input.

  The feature of this embodiment is that it is necessary from the total of six parameters of the lightness control coefficient calculation means 3a, that is, the average value calculated from the minimum value, maximum value, and integrated value of the lightness signal and the saturation signal. The brightness gain characteristic with respect to the saturation shown in FIG. 3 is optimally corrected according to the input video characteristics using various parameters, and the operation for improving the visibility more effectively is performed. It is.

  Hereinafter, a specific example of video feature adaptive correction of brightness gain characteristics will be described. First, an example of adaptive control based on lightness characteristics. When lightness is distributed with high levels of bias, control is performed to reduce the lightness gain enhancement, and when lightness is distributed with low levels of lightness. In this method, the characteristic is controlled so as to enhance the enhancement of the brightness gain.

  The lightness level distribution is performed by a method of detecting a simple lightness distribution state as shown in FIG. FIG. 8a is an example of a very wide dynamic range where the minimum value is close to 0 and the maximum value is close to the maximum range, but the overall lightness level is an example with many low lightness signals. In such a case, the average value is inevitably close to the minimum value. On the contrary, FIG. 8b shows the same minimum and maximum levels in a wide dynamic range as in FIG. 8a, but the overall brightness level is an example in which there are many signals with relatively high brightness. In some cases, the average value is relatively close to the maximum value. By calculating the average value in this way and comparing it with the maximum and minimum values (calculating which position is between the maximum and minimum values), the peak level (appearance) of the distribution state is simplified. It is possible to roughly detect the degree of the frequency peak value) or the distribution state. In this embodiment, a simple distribution state detection method is described. However, it is more desirable to detect a more accurate distribution state by using a configuration in which a histogram is counted.

  Then, in an image in which the lightness distribution is concentrated at a relatively low lightness level in consideration of this distribution state, the lightness correction is performed strongly, for example, close to the light place in the correction by the illuminance described in the first embodiment. As in the case of time, the brightness gain characteristic is corrected in the direction of widening the variation range of the brightness gain. Conversely, for an image in which the lightness distribution is concentrated at a relatively high lightness level, the correction is made in the direction of narrowing the change width. Alternatively, in the former case, the gain characteristic shown in FIG. 3 may be offset in the direction of increasing the gain as a whole, and conversely in the latter case, the gain characteristic may be offset in the direction of decreasing the gain. FIG. 9 shows a setting example of the correction amount of the gain characteristic according to such a brightness distribution state. In FIG. 9, the distribution state calculated by the method as described above is shown on the horizontal axis (in this example, the value obtained by dividing “maximum brightness value−average brightness value” by the maximum brightness value is on the horizontal axis. In the case of many distributions, the value on the horizontal axis becomes large), and the vertical axis represents the offset amount for correcting the characteristics of FIG. As described above, when the gain characteristic is corrected with the change width as shown in FIG. 6, the vertical axis corresponds to the change width.

  In this way, when the original image feature is a bright image having a high overall brightness, the brightness is not saturated by the brightness correction process, and in the case of a dark image having a low overall brightness, a sufficient effect is obtained. By emphasizing the brightness correction process, the brightness correction process adapted to the image feature can be performed.

  Next, there is an example of adaptive control using saturation features. This is also the case when the distribution state of saturation is simply detected in the same way as in the case of brightness features, and the distribution is biased to a high saturation level. If the brightness gain characteristic is controlled so that the range for suppressing the brightness gain characteristic is widened, and the saturation is distributed with a bias in a low level, the characteristic is set so that the range for emphasizing the lightness gain characteristic (gain of 1 or more) is widened. It is something to control. That is, in an image in which the saturation distribution is concentrated at a relatively high saturation level in consideration of the saturation distribution state, the solid line of FIG. 10 shows the characteristics of FIG. 3 in order to increase the color contrast improvement effect. Set the point to suppress the gain to the high saturation side. Thereby, it is possible to suppress the saturation of saturation and make it easy to add a brightness difference to an image having a generally high saturation level and good color. On the other hand, in an image where the saturation distribution is concentrated at a relatively low saturation level, the characteristic is switched to a characteristic such that the gain on the high saturation side is sufficiently increased as shown by the dotted line in FIG. As a result, it is possible to effectively make a difference in brightness effectively for images with generally low saturation levels and light colors.

  As another correction method, in the case where the minimum value and the maximum value of the saturation are significantly biased, the saturation level range is shown in FIG. It is also effective to change the gain characteristic so that a sufficient brightness difference can be provided.

  As explained above, the gain correction gain characteristics are adjusted to match the image characteristics of the lightness and saturation of the input signal, and the lightness correction processing is performed, so that the effects suitable for the image features can be reduced. Color correction is performed, and visibility can be effectively improved.

(Embodiment 3)
FIG. 12 is a block diagram showing the configuration of the image processing apparatus according to the third embodiment of the present invention.

  When the input video signal is a luminance signal and a color difference, the image processing apparatus in FIG. 12 uses the luminance signal and the color difference signal as they are, replaces the luminance signal with a lightness signal, and replaces the color difference signal with a saturation signal. It is an example of embodiment which performs the process similar to the form 1 and 2, and obtains the same effect.

  The difference between the image processing apparatus shown in FIG. 2 and the image processing apparatus shown in FIG. 12 is that the color space conversion means 1 is the signal conversion means 1a, the lightness correction processing means 2 is the brightness correction processing means 2a, and the brightness control coefficient is calculated. Means 3a is changed to luminance control coefficient calculation means 3b, color space inverse conversion means 4 is changed to RGB conversion means 4a, and brightness feature detection means 7 is changed to brightness feature detection means 7a, and saturation feature detection means 8a The internal operation has been changed. The operation of the illuminance detection means 5 is the same as that of the image processing apparatus shown in FIG. Here, a unit including the luminance correction processing unit 2a and the luminance control coefficient calculation unit 3b is referred to as a luminance correction unit. Hereinafter, the changes will be described in order.

  The signal conversion means 1a receives a luminance signal and a color difference signal, creates a hue signal from the luminance signal and the color difference signal by calculation, and outputs a luminance signal, a hue signal, and a color difference signal, respectively. When the individual processing according to the hue signal is omitted as described in the first and second embodiments, the signal conversion unit 1a can be omitted, but the luminance control coefficient calculation unit 3b as described later. Since a process for each hue is necessary, it is desirable to create a hue signal and perform the process for each hue. The luminance correction processing means 2a uses a luminance signal as an input, and performs the same correction processing as the brightness correction processing means 2 described in the first and second embodiments. The brightness control coefficient calculation means 3b uses the brightness input of the brightness control coefficient calculation means 3a described in the second embodiment as a brightness input, performs the same adaptive control processing as the brightness control coefficient calculation means 3a, and performs brightness correction processing. A luminance correction coefficient is calculated for the means 2a. The basic configuration of the luminance control coefficient calculating unit 3b is the same as that of the lightness control coefficient calculating unit 3a. However, in order to control the luminance component by the luminance in the same manner as in the first and second embodiments, it is shown in FIG. Regarding the characteristic diagram, the characteristic value for each hue, etc., it is necessary to set values different from those in the case of performing processing depending on the brightness. In particular, correction processing is necessary for hues that have high brightness values but do not have high brightness values, or hues that tend to be reversed. Accordingly, as processing for each hue, it is necessary to perform an operation so as to appropriately change the luminance correction characteristic for such a hue.

  The RGB conversion means 4a converts the luminance signal and color difference signal after correction processing into an RGB signal and outputs the converted signal to the display device. The luminance feature detection means 7a uses the input signal of the lightness feature detection means 7 described in Embodiment 2 as a luminance signal, and performs the same operation to detect the characteristic value of the luminance signal. The saturation feature detection unit 8a uses the input signal of the saturation feature detection unit 8 described in the second embodiment as a color difference signal, calculates a saturation component from the color difference signal, and implements the feature value of the saturation component. This is detected in the same manner as in the second mode.

  As described above, even when a luminance signal and a color difference signal are input signals, the luminance signal is replaced with a lightness signal, and the color difference signal is replaced with a saturation signal, and the same processing as in the first and second embodiments is performed. Therefore, substantially the same effect can be realized.

  Further, as is understood from the configuration in which the first and second embodiments receive the RGB signal and output the processed RGB signal to the display device as the RGB signal in the HSV space, It is also possible to adopt a configuration in which the processing in the HSV space described is converted into a corresponding RGB signal after the direct correction processing without changing the RGB signal. For example, a plurality of correction coefficient lookup tables created by calculating the correction calculation process described in Embodiment 1 in advance for each predetermined illuminance are provided, and an RGB signal based on the correction coefficient selected from the table by the illuminance signal RGB-RGB conversion is performed by RGB correction means for correcting the above.

  In this way, not the color correction in the HSV color space described in the first and second embodiments, but the image processing that achieves the same effect in the case of the luminance signal and the color difference signal, or even in the RGB signal form. Can do.

  An image processing apparatus and a processing method thereof according to the present invention are video display devices in applications where the illuminance range of an environment used for a vehicle-mounted display or the like can change widely and drastically, particularly for map images and vehicle information display of a car navigation system. The present invention is useful when applied to a visibility improving process in a bright place when a so-called computer graphics image is displayed.

1 is a block diagram showing the configuration of an image processing apparatus according to a first embodiment of the present invention. The block diagram which shows the structure of the image processing apparatus by 2nd Embodiment of this invention. FIG. 1 is a characteristic diagram for explaining an example of lightness control characteristics with respect to saturation in the lightness control coefficient calculating means shown in FIG. Schematic diagram illustrating the concept of color correction by brightness control for saturation in the present invention FIG. 3 is a characteristic diagram for explaining an example of a control intensity characteristic depending on illuminance in the brightness control coefficient calculation unit shown in FIG. FIG. 1 is a characteristic diagram for explaining an example of illuminance adaptive control of a brightness control characteristic with respect to saturation in the brightness control coefficient calculation means shown in FIG. Characteristic diagram showing specific visibility curves in photopic and scotopic vision as human visual characteristics Schematic diagram illustrating an example of a lightness signal level distribution state detection method in the lightness control coefficient calculation means shown in FIG. FIG. 2 is a characteristic diagram showing a setting example of a lightness gain correction amount according to a lightness distribution state in the lightness control coefficient calculating unit shown in FIG. FIG. 2 is a characteristic diagram for explaining an example of correction for the lightness gain characteristic by the saturation feature in the lightness control coefficient calculating means shown in FIG. FIG. 2 is a characteristic diagram for explaining an example of correction for the lightness gain characteristic by the saturation level range in the lightness control coefficient calculation means shown in FIG. The block diagram which shows the structure of the image processing apparatus by 3rd Embodiment of this invention. Block diagram showing schematic configuration of conventional example

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Color space conversion means 2 Lightness correction processing means 3 Lightness control coefficient calculation means 4 Color space reverse conversion means 5 Illuminance detection means 6 Display panel

Claims (10)

An image processing device for improving the visibility of an image when displayed on a display device with respect to an input video signal including each signal component of a hue signal, a saturation signal, and a brightness signal,
Brightness correction means for correcting the brightness signal of the input video signal according to the level of the saturation signal of the input video signal;
Illuminance detection means for detecting illuminance around the display device;
Assuming that the level of the saturation signal having a brightness gain of 1.0 with respect to the brightness signal is a first saturation level, the saturation signal is within a range where the level of the saturation signal is greater than the first saturation level. The brightness correction is performed such that the brightness gain is increased as the level of the color signal increases, and the brightness gain is decreased as the level of the saturation signal decreases in a range where the level of the saturation signal is smaller than the first saturation level. Control means for controlling the correction processing of the means,
The control means emphasizes the correction process as the illuminance increases in the high illuminance range where the ambient illuminance is 3000 lx or more, and the correction process as the illuminance decreases in the low illuminance range where the ambient illuminance is 200 lx or less. An image processing apparatus configured to control the brightness correction unit so as to emphasize the brightness and to control the brightness gain to be fixed to 1.0 in a standard illuminance range in which the ambient illuminance is greater than 200 lx and less than 3000 lx . In the range where the level of the saturation signal is smaller than the second saturation level smaller than the first saturation level, the control means increases the lightness gain as the level of the saturation signal is smaller. The image processing apparatus according to claim 1, wherein a correction process of the brightness correction unit is controlled . The image processing apparatus according to claim 1, wherein the brightness correction unit is configured to perform correction independently for each hue signal of the input video signal. The control means emphasizes the correction process when the hue signal is red and compensates the correction process when the hue signal is blue so as to compensate for Purkinje phenomenon of scotopic vision when the illuminance is less than or equal to a predetermined illuminance. The image processing apparatus according to claim 3, wherein the brightness correction unit is controlled to be suppressed. The image processing apparatus according to claim 1 , wherein the brightness correction unit is capable of selecting ON / OFF of correction processing . Further comprising a brightness characteristic detecting means for detecting a brightness feature information representing a distribution of the level of the brightness signal of one screen from the brightness signal of the input video signal, said control means, based on said brightness characteristic information, the lightness The image processing apparatus according to claim 1, wherein the brightness correction unit is controlled so that the correction process is emphasized as the signal level is distributed more in the lower side. Saturation feature detection means for detecting saturation feature information representing the distribution status of the saturation signal level for one screen from the saturation signal of the input video signal is further provided , and the control means includes the saturation feature information in the saturation feature information. Based on the configuration, the correction processing of the lightness correction means is controlled so that the range in which the lightness signal is increased with respect to the saturation signal level becomes wider as the saturation signal level is distributed more in the lower side. The image processing apparatus according to claim 1. An image processing method for improving the visibility of an image when displayed on a display device with respect to an input video signal including each signal component of a hue signal, a saturation signal, and a brightness signal,
A lightness correction step of correcting the lightness signal of the input video signal in accordance with the level of the saturation signal of the input video signal, wherein the level of the saturation signal having a lightness gain of 1.0 for the lightness signal is set to a first level. When the saturation signal level is greater than the first saturation level, the lightness gain is increased as the saturation signal level is increased, and the saturation signal level is A lightness correction step for correcting the lightness gain to decrease as the level of the saturation signal is smaller when the saturation level is smaller than the first saturation level;
An illuminance detection step of detecting ambient illuminance of the display device ,
The brightness correction step emphasizes the correction process as the illuminance increases in the high illuminance range where the ambient illuminance is 3000 lx or more, and the illuminance decreases as the illuminance decreases in the low illuminance range where the ambient illuminance is 200 lx or less. An image processing method for controlling the correction process to be emphasized and for controlling the brightness gain to be 1.0 in a standard illuminance range in which the ambient illuminance exceeds 200 lx and less than 3000 lx . The program for making a computer perform each step of the image processing method of Claim 8 . A computer-readable recording medium on which the program according to claim 9 is recorded.

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