Color compensation for panel display device in which light source array is used for back light illumination

Abstract

To provide various techniques which can relax coloring of an undesired display image which may be caused by a change of a color of a light source with a brightness level which may be generated in a local dimming technique.SOLUTION: A display device comprises: a display panel; a back light device; and a display driver. The back light device has multiple light sources, each light source being configured so that, according to a brightness level, a color of light emitted from the light source is varied. The display driver is configured to determine, a first output gradation of a first color, about a target pixel, by processing on the basis of a designated brightness level of the corresponding light source, a first input gradation of a first color about the target pixel, and process a second input gradation of a second color about the target pixel on the basis of the designated brightness level for determining a second output gradation of the second color about the target pixel. The first output gradation and second output gradation are determined to compensate, the change of the color of the light emitted from the corresponding light source.SELECTED DRAWING: Figure 8

Description

[Technical field]

[0001] The disclosed technology relates generally to displays, and more specifically to color compensation for panel displays that use an array of light sources for backlight illumination. [Background technology]

[0002] Display devices that include a light-transmissive display panel, such as a light-transmissive liquid crystal display (LCD) panel, incorporate a backlight illumination system that illuminates the light-transmissive display panel. Modern backlight illumination systems (e.g., direct backlight illumination, full array backlight illumination, etc.) may illuminate the display panel with an array of light sources (e.g., light-emitting diodes (LEDs)) located directly behind the display panel. The use of an array of light sources for backlight illumination allows for local dimming, which provides brightness and darkness for the displayed image, enhancing the contrast of the displayed image. Summary of the Invention

[0003] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to limit the scope of the claimed subject matter.

[0004] In general, in one aspect, one or more embodiments relate to a display device including a display panel, a backlight device, and a display driver. The backlight device includes a plurality of light sources configured to illuminate the display panel. The plurality of light sources are configured such that a color of light emitted from the plurality of light sources varies with a luminance level of the plurality of light sources. The display driver is configured to process a first input grey level of a first color of a target pixel of the display panel based at least in part on a designated luminance level of a corresponding light source of the plurality of light sources to determine a first output grey level of the first color of the target pixel. The display driver is further configured to process a second input grey level of a second color of the target pixel based at least in part on a designated luminance level of the corresponding light source to determine a second output grey level of the second color of the target pixel. The first output grey level and the second output grey level are determined to compensate for changes in color of light emitted from the corresponding light source. The display driver is further configured to update the target pixel based on the first output grey level and the second output grey level.

[0005] In general, in one aspect, one or more embodiments relate to a display driver including a color compensation block and driver circuitry. The color compensation block is configured to process a first input grey level of a first color of a target pixel of a display panel to determine a first output grey level of the first color of the target pixel. The display panel is illuminated by a backlight device including a plurality of light sources, where the plurality of light sources are configured such that a color of light emitted from the plurality of light sources varies with a luminance level of the plurality of light sources. The processing of the first input grey level is based at least in part on a designated luminance level of a corresponding light source of the plurality of light sources. The color compensation block is further configured to process a second input grey level of a second color of the target pixel to determine a second output grey level of the second color of the target pixel based at least in part on the designated luminance level of the corresponding light source. The first output grey level and the second output grey level are determined to compensate for the change in color of the light emitted from the corresponding light source. The driver circuitry is further configured to update the target pixel based on the first output grey level and the second output grey level.

[0006] In general, in one aspect, one or more embodiments relate to a method for color compensation for a display device including a display panel illuminated by a backlight device including a plurality of light sources, the plurality of light sources being configured such that a color of light emitted from the plurality of light sources varies with a luminance level of the plurality of light sources. The method includes processing a first input grayscale of a first color of a target pixel of the display panel to determine a first output grayscale of the first color of the target pixel. The processing of the first input grayscale is based at least in part on a designated luminance level of a corresponding light source of the plurality of light sources. The method further includes processing a second input grayscale of a second color of the target pixel to determine a second output grayscale of the second color of the target pixel based at least in part on the designated luminance level of the corresponding light source. The first output grayscale and the second output grayscale are determined to compensate for the variation in color of the light emitted from the corresponding light source. The method further includes updating the target pixel based on the first output grayscale and the second output grayscale.

[0007] Other aspects of the embodiments will be apparent from the following description and the appended claims. [Brief description of the drawings]

[0008] So that the above-mentioned features of the present disclosure can be understood in detail, a more particular description of the present disclosure briefly summarized above may be made with reference to embodiments, some of which are illustrated in the accompanying drawings. However, it should be noted that the accompanying drawings only illustrate exemplary embodiments, and therefore should not be considered as limiting the scope of the invention, since the present disclosure may admit of other equally effective embodiments.

[0009] [Figure 1] FIG. 1 illustrates an example of a display device that includes a display panel illuminated by an array of light sources, according to one or more embodiments.

[0010] [Figure 2A] FIG. 2A illustrates an example of a display image displayed on a display panel in accordance with one or more embodiments.

[0011] [Figure 2B] FIG. 2B illustrates an example distribution of light source brightness levels determined by "local dimming" for the displayed image shown in FIG. 2A, in accordance with one or more embodiments.

[0012] [Diagram 3] FIG. 3 illustrates an example of LED color changing in accordance with one or more embodiments.

[0013] [Figure 4] FIG. 4 illustrates an example display device configuration according to one or more embodiments.

[0014] [Diagram 5] FIG. 5 illustrates an example side view configuration of the display device shown in FIG. 4 according to one or more embodiments.

[0015] [Figure 6] FIG. 6 illustrates an example display driver configuration according to one or more embodiments.

[0016] [Figure 7] FIG. 7 illustrates example zone definitions for a display panel in accordance with one or more embodiments.

[0017] [Figure 8] FIG. 8 illustrates an example configuration of the backlight control circuitry and color compensation block according to one or more embodiments.

[0018] [Figure 9] FIG. 9 illustrates an example of the relationship between red (R), green (G) and blue (B) compensation levels and specified luminance levels, according to one or more embodiments.

[0019] [Figure 10A] FIG. 10A illustrates an example of a definition of a "magnified" panel area in accordance with one or more embodiments.

[0020] [Figure 10B] FIG. 10B illustrates an example of a definition of a "neighborhood zone" for a target pixel, according to one or more embodiments.

[0021] [Figure 10C] FIG. 10C illustrates an example of interpolation for determining a compensation level for a target pixel in accordance with one or more embodiments.

[0022] [Figure 11] FIG. 11 illustrates an example of interpolation for determining a compensation level for red (R) in accordance with one or more embodiments.

[0023] [Figure 12] FIG. 12 illustrates zones where the brightness of the displayed image may decrease.

[0024] [Figure 13] FIG. 13 illustrates an example of the configuration of a backlight control circuit according to another embodiment.

[0025] [Figure 14] FIG. 14 illustrates an example of the relationship between red (R), green (G) and blue (B) compensation levels and specified luminance levels, in accordance with one or more embodiments.

[0026] [Figure 15] FIG. 15 illustrates an example of interpolation for determining a compensation level for red (R) in accordance with one or more embodiments.

[0027] [Figure 16] FIG. 16 is a flowchart illustrating an example method for color compensation in accordance with one or more embodiments.

[0028] For ease of understanding, the same reference numbers are used, where possible, to designate identical elements common to the figures. It is anticipated that elements disclosed in one embodiment may be beneficially used in other embodiments without specific mention. Reference numbers may be subscripted to distinguish identical elements from one another. The drawings referred to herein should not be understood to be drawn to scale unless specifically noted. Also, for clarity of presentation and explanation, the drawings are often simplified, omitting details or components. The drawings and discussion serve to explain the principles discussed below, with like numbers indicating like elements. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] The following detailed description is merely exemplary in nature and is not intended to be limiting of the disclosed technology or the application and uses of the disclosed technology, nor is it intended to be bound by any expressed or implied theory presented in the preceding technical field, background, or description below.

[0030] In the following detailed description of the embodiments, many specific details are presented to provide a deeper understanding of the disclosed technology. However, it will be apparent to those skilled in the art that the disclosed technology can be implemented without using these specific details. In other instances, well-known configurations are not described in detail to avoid unnecessarily complicating the description.

[0031] The term "coupled" as used herein means directly connected or connected via one or more intervening components or circuits. Additionally, ordinal numbers (e.g., first, second, third, etc.) may be used throughout the application as adjectives of elements (i.e., any nouns in the application). The use of ordinal numbers is not intended to imply or create a particular ordering of any elements, nor is it intended to limit any element to only a single element, unless expressly disclosed, for example, by the use of "before," "after," "single," and other similar terms. Rather, the use of ordinal numbers is intended to distinguish elements. For example, a first element is distinct from a second element, and a first element may include more than one element and may follow (or precede) a second element in the ordering of elements.

[0032] Display devices that include a light-transmissive display panel, such as a light-transmissive liquid crystal display (LCD) panel, may be configured to illuminate the display panel using an array of light sources (e.g., light-emitting diodes (LEDs)) located directly behind the display panel. Such backlight illumination techniques may be referred to as direct backlight illumination or full-array backlight illumination. Each of the light sources may be configured to illuminate a corresponding area or zone of the display panel.

[0033] In some implementations, the brightness levels of the light sources may be individually controlled to perform "local dimming," which is a technique for increasing image contrast by individually controlling the brightness level of each light source to provide brightness and darkness in a displayed image. For example, when a dark image is desired in a particular zone of a display panel, the brightness level of the light source illuminating that zone may be reduced. The brightness levels of the light sources may be controlled based on image data, which may specify shades of each color (e.g., red (R), green (G), and blue (B)) for each pixel of the display panel.

[0034] A possible problem with local dimming is that the color of the light emitted from the light source may change with the brightness level, which may result in undesirable coloration in the displayed image. LEDs, which are widely used as light sources to illuminate display panels, may exhibit color changes with brightness levels depending on the manufacturing process and / or driving technology of the LEDs. For example, the emitted light of some LEDs may become reddish with decreasing brightness levels. When such LEDs are used as light sources to illuminate display panels, using local dimming techniques in which the brightness of the light sources is individually adjusted may result in undesirable coloration in the displayed image due to the change in the light emitted from the light sources.

[0035] The present disclosure provides various techniques for mitigating undesirable coloration of a displayed image that may result from a change in color of a light source with luminance level. In one or more embodiments, a display device includes a display panel, a backlight device, and a display driver. The backlight device includes a plurality of light sources that illuminate the display panel. The plurality of light sources may be configured such that a color of light emitted from the light sources changes with a luminance level of the light sources. The display driver may process a first input grayscale of a first color of a target pixel of the display panel based at least in part on a designated luminance level of a corresponding light source of the plurality of light sources to determine a first output grayscale of the first color of the target pixel. The display driver may further process a second input grayscale of a second color of the target pixel based at least in part on a designated luminance level of the corresponding light source to determine a second output grayscale of the second color of the target pixel. The first output grayscale and the second output grayscale are determined to compensate for the change in color of light emitted from the corresponding light source. The display driver may further be configured to update the target pixel based on the first output grayscale and the second output grayscale. Below is a detailed description of various embodiments of the present disclosure.

[0036] FIG. 1 illustrates an exemplary display device 100 comprising a display panel 110 illuminated by an array of light sources 120. Note that the light sources 120 are illustrated with dashed lines because they are actually located behind the display panel 110. Also note that the array of light sources 120 comprises multiple rows, but only the first row is labeled. To achieve local dimming, the brightness levels of the light sources 120 may be individually controlled adaptively to the displayed image. The light sources 120 illuminating areas or zones of the display panel 110 where light portions of the displayed image are displayed may be controlled to emit light at a high brightness level. Similarly, the light sources 120 illuminating areas or zones of the display panel 110 where dark portions of the displayed image are displayed may be controlled to emit light at a low brightness level.

[0037] FIG. 2A illustrates an example display image displayed on the display panel 110, and FIG. 2B illustrates an example distribution of the luminance levels of the light sources 120 determined by "local dimming" for the display image illustrated in FIG. 2A. The display image illustrated in FIG. 2A includes light and dark areas, and the luminance level of each light source 120 is adjusted based on the luminance level of the corresponding area. In FIG. 2B, the luminance level of each light source 120 is indicated by the shading of each zone. A light shaded zone indicates that the light source illuminating that zone is emitting light at a high luminance level, and a dark shaded zone indicates that the light source illuminating that zone is emitting light at a low luminance level. The "local dimming" technique dynamically adjusts the luminance level of each light source 120 according to the luminance level of each zone of the display panel.

[0038] One problem with local dimming techniques is that some light sources, including LEDs, may exhibit color changes with luminance, which may result in undesirable coloring of portions of a displayed image depending on the luminance of the portion. FIG. 3 illustrates an example of color change of an LED, according to one or more embodiments. In FIG. 3, the horizontal axis represents the luminance level of the LED, and the vertical axis represents the xy color coordinates of the color of the light emitted by the LED in the Yxy color space. Note that the Yxy color space is a standard color space defined in 1931 by the International Commission on Illumination (CIE). In the example illustrated in FIG. 3, both the x and y coordinates of the light emitted by the LED increase as the luminance level of the LED decreases in the practical range 122, except for the unstable behavior in the low luminance range 124. Due to the change in the xy coordinates illustrated in FIG. 3, the light emitted by the LED becomes redder as the luminance level of the LED decreases. Note that an increase in the x coordinate in the Yxy color space means an increase in the red component of the color. Variation in color with the brightness level of the light source 120 can result in undesirable coloration in the displayed image on the display panel 110 .

[0039] 4 illustrates an example configuration of a display device 1000 configured to mitigate undesired coloration of a displayed image in accordance with one or more embodiments. The display device 1000 includes a display panel 200 and is configured to display a desired image on the display panel 200. The display panel 200 may be a light-transmissive display panel, such as an LCD panel. Although the illustrated embodiment has a rectangular shape, the display panel 200 may have different shapes (e.g., a rectangular shape with one or more notches, an elliptical shape, a hexagonal shape, an octagonal shape, etc.).

[0040] The display device 1000 further comprises a display driver 300, a backlight device 400, and a backlight driver 500. The display driver 300 is configured to receive image data from an image source 600 and drive the display panel 200 to display an image corresponding to the image data. The image source 600 may be a processor, such as an application processor, a host, a central processing unit (CPU), a microprocessor unit (MPU), or a different type of processor configured to provide image data.

[0041] The backlight device 400 and the backlight driver 500 form a backlight system. The backlight device 400 is configured to illuminate the display panel 200 with an array of light sources 420. The light sources 420 are shown in dashed lines in FIG. 4 because the light sources 420 are located behind the display panel 200 as shown in FIG. 5. The light sources 420 are disposed directly behind the display panel 200 facing the display panel 200 and configured to illuminate corresponding areas or zones of the display panel 200. In the illustrated embodiment, the light sources 420 are spaced apart to illuminate the display panel 200 as uniformly as possible. In one implementation, each light source 420 comprises one or more LEDs. In other implementations, each light source 420 may comprise different types of light sources. Although FIG. 4 illustrates 128 (=16×8) light sources 420, one skilled in the art will understand that the backlight device 400 may comprise more than 128 light sources 420 or less than 128 light sources 420. The backlight driver 500 is configured to drive the light sources 420 of the backlight device 400 under the control of the display driver 300 so that each light source 420 emits light at a luminance level specified by the display driver 300 .

[0042] 6 illustrates an example configuration of a display driver 300 according to one or more embodiments. In the illustrated embodiment, the display driver 300 includes an image memory 310, image processing circuitry 320, driver circuitry 330, image analysis circuitry 340, and backlight control circuitry 350.

[0043] The image memory 310 is configured to receive image data from an image source 600 (shown in FIG. 4) corresponding to a display image to be displayed on the display panel 200 and store the received image data. In one implementation, the image data includes original pixel data for each pixel of the display panel 200. In one implementation, the original pixel data for each pixel may include a gradation of each primary color (e.g., red (R), green (G), and blue (B)). In one implementation, each pixel of the display panel 200 includes R, G, and B sub-pixels configured to display red, green, and blue, respectively, and the original pixel data for each pixel includes R, G, and B gradations that specify the luminance levels of the R, G, and B sub-pixels, respectively. In other embodiments, the image memory 310 may be omitted and the current pixel data may be provided directly to the image processing circuitry 320.

[0044] The image processing circuitry 320 is configured to perform image processing on the original pixel data read from the image memory 310 to generate processed pixel data. The image processing circuitry 320 includes a color compensation block 360 configured to perform color compensation to mitigate undesirable coloration that may occur due to color changes in the light emitted by the light source 420. Details of color compensation will be described in detail later. The image processing performed by the image processing circuitry 320 may further include color adjustment, demurration correction, deburn correction, image scaling, gamma conversion, or other image processing.

[0045] The driver circuitry 330 is configured to receive the processed pixel data from the image processing circuitry 320 and drive or update pixels of the display panel 200 based at least in part on the processed pixel data. The driver circuitry 330 may include a source driver (also called a data driver) configured to generate data voltages based on the processed pixel data and drive source lines (also called data lines) of the display panel 200 to program or update pixels of the display panel 200 with the generated data voltages. In one implementation, each pixel of the display panel 200 may include R, G, and B sub-pixels, and the processed pixel data may specify respective gray levels for the R, G, and B sub-pixels of each pixel. The driver circuitry 330 may be configured to program or update the R, G, and B sub-pixels of each pixel based at least in part on the processed pixel data to control the luminance levels of the R, G, and B sub-pixels.

[0046] The image analysis circuitry 340 and the backlight control circuitry 350 are collectively configured to generate and provide backlight control commands based at least in part on the image data to the backlight driver 500 to control the brightness levels of each light source 420 (shown in FIGS. 4 and 5 ) of the backlight device 400. In one embodiment, raw pixel data is provided to the image analysis circuitry 340. In another embodiment, processed pixel data generated by the image processing circuitry 320 may be provided to the image analysis circuitry 340 instead of the raw pixel data, as indicated by the dashed arrow from the image processing circuitry 320 to the image analysis circuitry 340. The image analysis circuitry 340 is configured to analyze the raw pixel data or the processed pixel data to generate image analysis data. The image analysis data may indicate a brightness distribution of a display image to be displayed on the display panel 200. The backlight control circuitry 350 is configured to control the brightness of each light source 420 based at least in part on the image analysis data. The image analysis data may also be provided to the image processing circuitry 320. In such embodiments, the image processing performed by image processing circuitry 320 may be based on the image analysis data.

[0047] In one or more embodiments, the image analysis performed by the image analysis circuitry 340 may be based on a number of "zones" defined for the display panel 200. FIG. 7 illustrates an example of the definition of zones 220 for the display panel 200, in accordance with one or more embodiments. In the illustrated embodiment, the zones 220 are defined by partitioning the display panel 200. In embodiments in which the display panel 200 is not rectangular, the zones 220 may be defined by partitioning a rectangular area circumscribing the display panel 200. In the illustrated embodiment, all of the zones 220 are square shaped. In other embodiments, the zones 220 may be defined to have other shapes. Each zone 220 is defined such that one light source 420 faces the zone 220 at the center (e.g., geometric center) of the zone 220. A light source 420 faces a zone 220 if the projection of the light source 420 on the display panel 200 falls within the zone 220.

[0048] In one or more embodiments, the image analysis data generated by the image analysis circuitry 340 includes an average picture level (APL) for each zone 220 calculated based on the original pixel data or the processed pixel data. The APL for a particular zone 220 may be calculated based on the original pixel data or the processed pixel data for the image located in that zone 220. In one implementation, the APL for a particular zone 220 may be an average of the luminance of the pixels located in that zone 220. In an embodiment in which the original pixel data (or the processed pixel data) for each pixel includes R, G, and B gradations that specify the luminance of the R, G, and B sub-pixels, respectively, the luminance level of each pixel may be calculated based on the R, G, and B gradations. The luminance level of each pixel may be calculated as a weighted sum of the R, G, and B sub-pixels of each pixel. The backlight control circuitry 350 may be configured to control the luminance level of each light source 420 based on the APL of the zone 220 that each light source 420 faces.

[0049] 8 illustrates an example configuration of the backlight control circuitry 350 and the color compensation block 360 in accordance with one or more embodiments. In the illustrated embodiment, the backlight control circuitry 350 is configured to determine a designated brightness level for each light source 420 based on the image analysis data received from the image analysis circuitry 340 and provide the designated brightness level to the backlight driver 500. The backlight driver 500 is configured to control the brightness level of each light source 420 according to the designated brightness level of each light source 420. The backlight control circuitry 350 is further configured to provide the designated brightness level of each light source 420 to the color compensation block 360.

[0050] In the illustrated embodiment, the backlight control circuitry 350 includes a base luminance level determination circuit 352, a light source luminance memory 354, and a correction circuit 356. The base luminance level determination circuit 352 is configured to determine a base luminance level for each light source 420 based on the image analysis data received from the image analysis circuitry 340. In an embodiment in which the image analysis data includes the APL of each zone 220, the base luminance level determination circuit 352 may be configured to determine a base luminance level for each light source 420 based on the APL of each zone 220 that each light source 420 faces. In one implementation, the base luminance level of a particular light source 420 may increase with an increase in the APL of the corresponding zone 220 that faces the particular light source 420. The base luminance level determination circuit 352 is further configured to transfer the determined base luminance level of each light source 420 to be stored in the light source luminance memory 354.

[0051] The correction circuit 356 is configured to read the base luminance level of each light source 420 from the light source luminance memory 354, and determine the designated luminance level of each light source 420 by correcting the base luminance level of each light source 420 based on a display luminance value (DBV). The DBV specifies a desired display luminance level. Here, the display luminance level may be an overall desired luminance level of a display image displayed on the display panel 200. The correction circuit 356 may be configured to determine a correction coefficient based on the DBV, and determine the designated luminance level of each light source 420 by applying the correction coefficient to the base luminance level of each light source 420. In one implementation, the correction circuit 356 may be configured to determine the designated luminance level of each light source 420 by multiplying the base luminance level of each light source 420 by the correction coefficient. The correction circuit 356 is further configured to provide the designated luminance level of each light source 420 to the backlight driver 500 and also to the color compensation block 360.

[0052] In one implementation, the DBV may be generated by the image source 600 (shown in FIG. 4) and provided to the correction circuit 356 in the display driver 300. The DBV may be generated based on a user operation. For example, if a command to adjust the brightness level of a display image displayed on the display device 1000 is manually input to an input device (not shown), the image source 600 may generate the DBV to adjust the display brightness level based on the command. The input device may include a touch panel, a cursor control device, and mechanical and / or non-mechanical buttons disposed on at least a portion of the display panel 200. In other implementations, a different processor or controller may generate and provide the DBV to the display driver 300.

[0053] The color compensation block 360 is configured to receive input pixel data and perform color compensation on the input pixel data for each pixel to generate output pixel data for each pixel. The input pixel data may be original pixel data or may be generated by performing one or more other image processing (e.g., color adjustment, demurra correction, deburn correction, image scaling, etc.) on the original pixel data by the image processing circuitry 320 (shown in FIG. 6). The output image data may be used as processed pixel data provided to the driver circuitry 330, which is configured to update the pixels of the display panel 200 based on the processed pixel data. Alternatively, the output pixel data may be further processed (e.g., color adjustment, demurra correction, deburn correction, image scaling, gamma conversion, or other image processing) and then provided to the driver circuitry 330 as processed pixel data.

[0054] The color compensation performed by the color compensation block 360 is based on the designated brightness level of each light source 420 received from the backlight control circuitry 350. In one implementation, the color compensation block 360 may be configured to process input pixel data of a target pixel located in a particular zone 220 based on the designated brightness level of a light source 420 corresponding to or facing the particular zone 220 to generate output pixel data of the target pixel located in the particular zone 220. The processing of the input pixel data of the target pixel located in the particular zone 220 may be further based on the designated brightness level of one or more light sources 420 facing one or more zones 220 adjacent to the particular zone 220.

[0055] Color compensation is performed by subtracting the R, G, and B gradations of the input pixel data. IN , G IN and B. IN are processed individually to obtain the R, G and B gradations of the output pixel data. OUT , G OUT and B. OUT For simplicity, the R, G and B gradations of the input pixel data are determined as R IN , G IN and B. IN are R, G and B input gradations R IN, G IN and B. IN Also called the R, G and B gradations of the output pixel data, R OUT , G OUT and B. OUT are R, G and B output gradations R OUT , G OUT and B. OUT In various implementations, the output grayscale for a given luminance level is called R OUT , G OUT and B. OUT The first change in tone is the input tone R IN , G IN and B. IN For the same value of R, G, and B output gradations for a specified luminance level, R OUT , G OUT and B. OUT For example, the change in the R output grey level R for a specified luminance level may be different from the change in the second grey level R for a specified luminance level to compensate for a coloration that causes the displayed image to have an undesirable reddish tint. OUT The change in the input gradation R IN , G IN and B. IN G and B output gradations for a specified luminance level for the same value of G OUT and B. OUT The change in R, G, and B output gradations for a specified luminance level may be different from that of OUT , G OUT and B. OUT By varying the variation of the different values, the desired color compensation can be achieved.

[0056] In some embodiments, as described in relation to FIG. 3, the x coordinate of the color of light emitted from the light source 420 in the Yxy color space may increase as the designated luminance level of each light source 420 decreases in the practical use range 122. Note that an increase in the x coordinate in the Yxy color space means an increase in the red component of the color. In such an embodiment, the R output gradation may be determined to be smaller than the R input gradation. By determining the R output gradation to be smaller than the R input gradation, undesirable reddish coloring of the displayed image may be mitigated.

[0057] In the illustrated embodiment, the color compensation block 360 includes an R compensation block 362R, a G compensation block 362G, and a B compensation block 362B that process R, G, and B input gradations, respectively. The R compensation block 362R includes a compensation level register 364, a compensation level determination circuit 366, and a correction circuit 368. Although not illustrated, the G compensation block 362G and the B compensation block 362B may have the same configuration as the R compensation block 362R. The G compensation block 362G and the B compensation block 362B may each include a compensation level register, a compensation level determination circuit, and a correction circuit corresponding to the compensation level register 364, the compensation level determination circuit 366, and the correction circuit 368 of the R compensation block 362R.

[0058] The compensation level register 364 of the R compensation block 362R is configured to store compensation level correspondence information indicating a correspondence between a specified luminance level and a compensation level to be applied to the R input gradation of each pixel. The compensation level determination circuit 366 is configured to determine a compensation level for the R input gradation of each pixel based on the specified luminance level of the light source 420 according to the compensation level correspondence information. In some embodiments, the compensation level correspondence information stored in the compensation level register 364 may include compensation levels for some, but not all, of the allowed specified luminance levels. In one implementation, the compensation level correspondence information may include compensation levels for a minimum specified luminance level, a maximum specified luminance level, and one or more intermediate specified luminance levels. The compensation level determination circuit 366 may be configured to determine the compensation levels for all the allowed specified luminance levels by interpolating the compensation levels included in the compensation level correspondence information. The correction circuit 368 may be configured to apply the compensation levels to the R input gradation of each pixel to determine the R output gradation of each pixel.

[0059] In one implementation, the R output grayscale of a target pixel located in a particular zone 220 may be determined as follows: The R compensation block 362R may receive a designated luminance level of the light source 420 facing the particular zone 220 in which the target pixel is located. The compensation level determination circuit 366 may determine a compensation level for the target pixel according to the compensation level correspondence information stored in the compensation level register 364. The correction circuit 368 may determine the R output grayscale of the target pixel by applying the determined compensation level to the R input grayscale of the target pixel. In some embodiments, the correction circuit 368 may determine the R output grayscale of the target pixel by multiplying the R input grayscale of the target pixel by the determined compensation level. In other embodiments, the correction circuit 368 may determine the R output grayscale of the target pixel by performing different arithmetic operations (e.g., addition, subtraction, etc.) on the R input grayscale of the target pixel based on the determined compensation level.

[0060] The G compensation block 362G and the B compensation block 362B, which process the G input gradation and the B input gradation to determine the G output gradation and the B output gradation, respectively, are configured to operate in the same manner as the R compensation block 362R, except that the contents of the compensation level correspondence relationship information stored in the compensation level register are different. Each of the G compensation block 362G and the B compensation block 362B includes a compensation level register, a compensation level determination circuit, and a correction circuit configured to operate in the same manner as the compensation level register 364, the compensation level determination circuit 366, and the correction circuit 368 of the R compensation block 362R, respectively. However, in order to realize color compensation, the compensation level correspondence relationship information stored in the compensation level registers of the G compensation block 362G and the B compensation block 362B may indicate a relationship between the designated luminance level and the compensation level that is different from the compensation level correspondence relationship information stored in the compensation level register 364 of the R compensation block 362R.

[0061] 9 illustrates an example of a relationship between compensation levels for red (R), green (G) and blue (B) and specified luminance levels, according to one or more embodiments. The compensation levels for red, green and blue may hereinafter be referred to as the R compensation level, the G compensation level and the B compensation level, respectively. The embodiment illustrated in FIG. 9 may be used when the color of the light emitted by the light source becomes reddish as the luminance level decreases. In the illustrated embodiment, the specified luminance level for the light source facing zone 220a is a low luminance level L L and the designated luminance level for the light sources facing the zones 220b, 220c, and 220d is the low luminance level L L Higher brightness level than L H The specified luminance level L H The compensation level for R is “100%” while the compensation level for L is “100%”. L R compensation level for a given luminance level L H 9 is lower than the designated luminance level, i.e., “70%”. Meanwhile, the G compensation level and the B compensation level are “100%” regardless of the designated luminance level. The compensation levels determined as shown in FIG. 9 can prevent the image displayed in the zone illuminated by the light source at the low designated luminance level from being reddish.

[0062] In some embodiments, the compensation level for a target pixel located in a particular zone may be determined by interpolating the compensation levels determined based on the designated luminance levels of the light source facing the particular zone and one or more zones adjacent to the particular zone. An example of the operation of the compensation level determination circuit 366 of the R compensation block 362R according to such an embodiment is described below. It should be noted that the compensation level determination circuits of the G compensation block 362G and the B compensation block 362B may operate in a similar manner to the compensation level determination circuit 366 of the R compensation block 362R.

[0063] 10A, the compensation level determination circuit 366 may be configured to use an "extended" panel area 230 defined as the total area of ​​the display panel 200 plus a series of "copy" zones 225 surrounding the display panel 200. Note that the extended panel area 230 is determined virtually only for the purpose of facilitating the calculation of the compensation level, including interpolation. The copy zone 225 is defined as a copy of the outermost zone 220 of the display panel 200, assuming that a virtual light source 425 faces the copy zone 225 and emits light at the same specified luminance level as the light source 420 facing an adjacent one of the outermost zones 220.

[0064] 10B, in one implementation, the compensation level determination circuit 366 may be further configured to identify four "neighborhood zones" 220-1, 220-2, 220-3, and 220-4 from among the zones 220 and the copy zones 225 for the target pixel when determining the compensation level for the target pixel P. The identification of the "neighborhood zones" 220-1 to 220-4 may be based on a pixel address of the target pixel, where the pixel address indicates the location of the target pixel in the display panel 200. One of the "neighborhood zones" 220-1 to 220-4 is the zone 220 in which the target pixel is located, and the other three neighboring zones are the three zones in the zones 220 and the copy zones 225 that are closest to the target pixel. In the illustrated embodiment, the "neighborhood zones" 220-1 to 220-4 for the target pixel P are defined using a reference region 240. Here, the reference region 240 has the same dimensions as the zone 220, and the geometric center of the reference region 240 is located at the target pixel. The neighborhood zones 220-1 to 220-4 may be defined as four of the zones 220 and the copy zone 225 that at least partially overlap the reference region 240. Note that if the target pixel is located in one of the outermost zones 220, then one or more of the neighborhood zones 220-1 to 220-4 may be the copy zone 225.

[0065] The compensation level determination circuit 326 may further determine a compensation level for a pixel located at the center (e.g., geometric center) of the neighborhood zone based on a specified luminance level for the light source 420 (or virtual light source 425) according to the compensation level correspondence information stored in the compensation level register 364. The compensation level determination circuit 326 may further determine a compensation level for the target pixel P by interpolating the compensation levels for the pixels located at the center of the neighborhood zone based on the position of the target pixel P.

[0066] 10C illustrates an example of an interpolation for determining a compensation level for a target pixel P, according to one or more embodiments. In FIG. 10C, (x, y) are the coordinates of the target pixel P. Furthermore, (x1, y1) are the coordinates of the geometric center of the neighborhood zone 220-1, (x2, y1) are the coordinates of the geometric center of the neighborhood zone 220-2, (x1, y2) are the coordinates of the geometric center of the neighborhood zone 220-3, and (x2, y2) are the coordinates of the geometric center of the neighborhood zone 220-4. CL1, CL2, CL3, and CL4 are the compensation levels of the pixels located at the centers of the neighborhood zones 220-1, 220-2, 220-3, and 220-4, respectively.

[0067] In one or more embodiments, horizontal interpolation is first performed to obtain horizontal interpolation compensation values ​​L for intermediate points P1(x,y1) and P2(x,y2). P1 and L P2 Then, vertical interpolation is performed to obtain the compensation level L for the target pixel P. P In one implementation, the horizontal interpolation compensation level CL P1 and C.L. P2 may be calculated according to the following formulas (1a) and (1b):

number

number

[0068] 11 illustrates an example of an interpolation for determining an R compensation level, according to one or more embodiments. Note that the G compensation level and the B compensation level may be determined in a similar manner. In the embodiment illustrated in FIG. 11, the low luminance level L L is specified for the light source facing the zone 220a, and the high luminance level L H are specified for light sources facing the zones 220b, 220c, and 220d. The R compensation level for pixel Pa located at the center of the zone 220a is "70%", and the R compensation levels for pixels Pb, Pc, and Pd located at the centers of the zones 220b, 220c, and 220d are "100%". The dashed-dotted line 222 represents an interpolation for determining the R compensation level for a pixel located between pixel Pa and pixel Pd. As a result of the interpolation, the R interpolation level for a pixel located between pixel Pa and pixel Pb approaches "70%" as the pixel is located closer to pixel Pa, and approaches "100%" as the pixel is located closer to pixel Pb. Since both the R compensation levels for pixel Pb and pixel Pd are "100%, the R compensation level for a pixel located between pixel Pb and pixel Pd is "100%".

[0069] 12, the brightness level of the displayed image may be lower near the edge of the display panel 200, especially when the light sources 420 are arranged in a regular array with a certain interval. In FIG. 12, hatching indicates zones 220 where the brightness of the displayed image may be lower. Since the light emitted from the light sources 420 spreads as it travels toward the display panel 200, each zone 220 may receive light not only from the light source 420 facing the zone 220, but also from one or more light sources 420 facing one or more zones 220 located around the zone 220. Therefore, the number of light sources 420 from which each zone 220 receives light may differ depending on the location of the zone 220. For example, the zones 220 at the edge of the display panel 200 may receive light from fewer light sources than the zones 220 located inside the display panel 200. The zones 220 located at the corners of the display panel 200 may receive light from fewer light sources 420. The difference in the number of light sources 420 from which each zone 220 receives light is due to the difference in the arrangement of the light sources 420 around the periphery of the zone 220 depending on the location of the zone 220. Such difference in the number of light sources 420 from which each zone 220 receives light can result in lower brightness levels at the periphery of the display panel 200, resulting in non-uniform image brightness.

[0070] To mitigate the effect of differences in the number of light sources 420 from which each zone 220 receives light, in one or more embodiments, the designated brightness level of each light source 420 may be determined based on the placement of one or more light sources 420 around the zone 220 that each light source 420 faces. In one implementation, the designated brightness level of a light source 420 facing a particular zone 220 may be adjusted based on the number of light sources 420 positioned around that particular zone 220.

[0071] 13 illustrates an example configuration of a backlight control circuitry 1350 for adjusting the designated brightness level of each light source 420 to compensate for non-uniformity in image brightness near the edges of the display panel 200, according to another embodiment. The backlight control circuitry 1350 is configured to determine the designated brightness level of each light source 420 based on the location of the light source 420 (e.g., an edge, a corner, or the interior of the display panel 200).

[0072] In the illustrated embodiment, the backlight control circuit section 1350 includes a base luminance level determination circuit 1352, a light source luminance memory 1354, a light source compensation memory 1356, a first correction circuit 1358, and a second correction circuit 1360. The base luminance level determination circuit 1352 and the light source luminance memory 1354 are configured to operate in the same manner as the base luminance level determination circuit 352 and the light source luminance memory 354 illustrated in FIG. 8. The base luminance level determination circuit 1352 is configured to determine a base luminance level of each light source 420 based on the image analysis data received from the image analysis circuit section 340. In an embodiment in which the image analysis data includes the APL of each zone 220, the base luminance level determination circuit 1352 may be configured to determine a base luminance level of each light source 420 based on the APL of each zone 220 that each light source 420 faces. The base luminance level determination circuit 1352 is further configured to transfer and store the determined base luminance level of each light source 420 in the light source luminance memory 1354.

[0073] The light source compensation memory 1356 is configured to store, for each light source 420, a luminance compensation value to be applied to the base luminance level of each light source 420. The luminance compensation value of each light source 420 is pre-determined based on the position of each light source 420 to compensate for the above-mentioned image luminance non-uniformity. In one implementation, the luminance compensation value of a particular light source 420 may be determined based on the arrangement of one or more light sources 420 around the particular light source 420. For example, the luminance compensation value of a light source 420 facing a particular zone 220 may be determined based on whether the particular zone 220 is located at an edge of the display panel 200, at a corner of the display panel 200, or inside the display panel 200. Using the luminance compensation value determined in this manner, the non-uniformity of the display panel 200 that may be caused by a decrease in the luminance level of the peripheral portion of the edge 00 of the display panel 200 may be effectively compensated.

[0074] The first correction circuit 1358 and the second correction circuit 1360 are collectively configured to determine a designated brightness level for each light source 420 based on the base brightness level stored in the light source brightness memory 1354, the brightness compensation value stored in the light source compensation memory 1356, and the DBV.

[0075] The first correction circuit 1358 is configured to read the base luminance level of each light source 420 from the light source luminance memory 1354 and read the luminance compensation value of each light source 420 from the light source compensation memory 1356. The first correction circuit 1358 is further configured to correct the base luminance level of each light source 420 based on the luminance compensation value for each light source 420 and provide the corrected base luminance level of each light source 420 to the second correction circuit 1360. In one implementation, the first correction circuit 1358 may be configured to correct the base luminance level of each light source 420 by multiplying the base luminance level of each light source 420 by the luminance correction value for each light source 420. In other implementations, the first correction circuit 1358 may be configured to correct the base luminance level of each light source 420 by applying other arithmetic operations (e.g., addition or subtraction) based on the luminance correction value for each light source 420.

[0076] The second correction circuit 1360 is configured to determine the designated luminance level of each light source 420 by further correcting the corrected base luminance level of each light source 420 based on the DBV that specifies the desired display luminance level. The second correction circuit 1360 may be configured to determine the designated luminance level of each light source 420 by determining a correction coefficient based on the DBV and applying the correction coefficient to the base luminance level of each light source 420. In one implementation, the second correction circuit 1360 may be configured to determine the designated luminance level of each light source 420 by multiplying the base luminance level of each light source 420 by the correction coefficient. The second correction circuit 1360 further provides the designated luminance level of each light source 420 to the backlight driver 500 and also to the color compensation block 360. The color compensation block 360 is configured to apply color compensation to the input pixel data of each pixel based on the designated luminance level of each light source 420 to generate output pixel data of each pixel.

[0077] 14 illustrates an example of the relationship between the compensation levels of red (R), green (G) and blue (B) and the designated luminance level in an embodiment in which the designated luminance level is determined to mitigate the reduction in the luminance level of the displayed image near the edge of the display panel. In the illustrated embodiment, the designated luminance level of the light source facing the zone 220e located at a position inside the display panel 200 is the low luminance level L L The designated luminance level of the light source facing the zones 220f and 220g, which are also located at positions inside the display panel 200, is the low luminance level L L Higher brightness level than L H1 In order to compensate for the drop in the luminance level near the edge of the display panel 200, the designated luminance level of the light source facing the zone 220h located at the edge of the display panel 200 is set to a high luminance level L H1 Higher brightness level than L H2 It is.

[0078] In the illustrated embodiment, the specified brightness level L L The R compensation level is “70%” and the specified luminance level L H1 and L H2The compensation levels for red for each of the four colors are "95%" and "100%", respectively. Meanwhile, the compensation levels for green (G) and blue (B) are "100%" regardless of the specified luminance level. The compensation levels determined as shown in Fig. 14 can prevent the image displayed in the zone illuminated by the light source at a low specified luminance level from being reddish.

[0079] FIG. 15 illustrates an example of an interpolation for determining a compensation level for red (R) for the case illustrated in FIG. 14, according to one or more embodiments. Note that compensation levels for green (G) and blue (B) can be determined in a similar manner. In the illustrated embodiment, the R compensation level for pixel Pe located at the center of zone 220e is "70%", the R compensation level for pixels Pf and Pg located at the centers of zones 220f and 220g is "95%", and the R compensation level for pixel Ph located at the center of zone 220h is "100%". The dashed and dotted line 224 represents the interpolation for determining the R compensation level of a pixel located between pixel Pe and pixel Ph. As a result of the interpolation, the R compensation level for a pixel located between pixel Pe and pixel Pf approaches "70%" the closer the pixel is to pixel Pe, and approaches "95%" the closer the pixel is to pixel Pf. Since the R compensation levels for pixel Pf and pixel Pg located at the center of zones 220f and 220g are both "95%", the compensation level of the pixel located between pixel Pf and pixel Pg is "95%". The R compensation level of the pixel located between pixel Pg and pixel Ph approaches "95%" the closer the pixel is to pixel Pg, and approaches "100%" the closer the pixel is to pixel Ph.

[0080] 16 is a flow chart illustrating an example method 1600 for color compensation, according to one or more embodiments. Although various steps in the flow chart are presented and described sequentially, one skilled in the art will appreciate that some or all of the steps may be performed in a different order, combined, or omitted, and some or all of the steps may be performed in parallel. Additional steps may also be performed. Thus, the scope of the present disclosure should not be considered limited to the particular sequence of steps illustrated in FIG.

[0081] In one or more embodiments, the method 1600 performs color compensation for a display device that includes a display panel illuminated by a backlight device that includes multiple light sources configured such that the color of light emitted from the multiple light sources varies with the luminance level of the multiple light sources. Figures 4 and 5 illustrate an example of such a display device, in accordance with one or more embodiments. In the display device 1000 illustrated in Figures 4 and 5, a display panel 200 is illuminated by a backlight device 400 that includes an array of light sources 420. The x and y coordinates in the Yxy color space of the color of light emitted from the light sources 420 may vary with the luminance level, as illustrated in Figure 3.

[0082] The method 1600 shown in Figure 16 includes, at step 1602, processing a first input grey level of a first color for a target pixel of a display panel to determine a first output grey level of the first color for the target pixel. The processing of the first input grey level is based at least in part on a designated luminance level of a corresponding light source of a plurality of light sources. The method 1600 further includes, at step 1604, processing a second input grey level of a second color for the target pixel based at least in part on the designated luminance level of the corresponding light source to determine a second output grey level of the second color for the target pixel. The first output grey level and the second output grey level are determined to compensate for changes in color of light emitted from the corresponding light source.

[0083] Steps 1602 and 1604 may be performed by a color compensation block 360 illustrated in FIG. 8. An R compensation block 362R of the color compensation block 360 processes an R input grayscale (which may correspond to a first input grayscale) for the target pixel to determine an R output grayscale (which may correspond to a first output grayscale). A G compensation block 362G of the color compensation block 360 processes a G input grayscale (which may correspond to a second input grayscale) for the target pixel to determine a G output grayscale (which may correspond to a second output grayscale). A B compensation block 362B of the color compensation block 360 processes a B input grayscale for the target pixel to determine a B output grayscale. In one implementation, the R, G, and B output grayscales for the target pixel are determined to compensate for changes in color of light emitted from corresponding light sources as illustrated in FIG. 3.

[0084] Returning to Figure 16, the method 1600 further includes updating the target pixel based on the first output grayscale and the second output grayscale at step 1606. In one embodiment, the updating of the target pixel may be performed by the driver circuitry 330 shown in Figure 6.

[0085] While a number of embodiments have been described, those skilled in the art, having the benefit of this disclosure, will appreciate that other embodiments may be devised which do not depart from the scope of the present invention. Accordingly, the scope of the present invention should be limited only by the scope of the appended claims.

Claims

1. A display panel; a backlight device comprising a plurality of light sources for illuminating the display panel, the plurality of light sources being configured such that a color of light emitted from the plurality of light sources changes with a luminance level of the plurality of light sources; processing a first input grey level of a first color for a target pixel of the display panel based at least in part on a designated luminance level of a corresponding light source of the plurality of light sources to determine a first output grey level of the first color for the target pixel; processing a second input grey level of a second color for the target pixel based at least in part on the designated luminance level of the corresponding light source to determine a second output grey level of the second color for the target pixel; a display driver configured to update the target pixel based on the first output greyscale and the second output greyscale; Equipped with The first output grayscale and the second output grayscale are determined to compensate for changes in color of the light emitted from the corresponding light source. Display device.

2. the corresponding light source is configured to illuminate the target pixel. The display device according to claim 1 .

3. For the same value of the first input grayscale and the second input grayscale, a change in the first output grayscale with respect to the designated luminance level is different from a change in the second output grayscale with respect to the designated luminance level. The display device according to claim 1 .

4. the first color is red; an x coordinate in a Yxy color space of a color of light emitted from the corresponding light source increases as the designated luminance level of the corresponding light source decreases in an actual use range of the designated luminance level; The first output gray level of the first color is smaller than the first input gray level of the first color. The display device according to claim 1 .

5. Processing the first input tone of the first color comprises: determining a first compensation level based on the designated brightness level of the corresponding light source; determining the first output grey level of the first color by applying the first compensation level to the first input grey level of the first color; Includes The display device according to claim 1 .

6. Processing the second input tone of the second color comprises: determining a second compensation level based on the designated brightness level of the corresponding light source; determining the second output grey level of the second color by applying the second compensation level to the second input grey level of the second color; Including, The second compensation level is different from the first compensation level. The display device according to claim 5 .

7. The display driver is further configured to determine the designated luminance level based on pixel data of pixels located in a zone opposite the corresponding light source. The display device according to claim 1 .

8. Determining the designated brightness level is based on a placement of one or more light sources around the zone. The display device according to claim 7.

9. processing a first input grey level of a first color for a target pixel of a display panel illuminated by a backlight device comprising a plurality of light sources, the plurality of light sources being configured such that a color of light emitted from the plurality of light sources varies with a luminance level of the plurality of light sources, based at least in part on a designated luminance level of a corresponding light source of the plurality of light sources to determine a first output grey level of the first color for the target pixel; a color compensation block configured to process a second input grey level of a second color for the target pixel based at least in part on the designated luminance level of the corresponding light source to determine a second output grey level of the second color for the target pixel; a driver circuit configured to update the target pixel based on the first output grayscale and the second output grayscale; Equipped with The first output grayscale and the second output grayscale are determined to compensate for changes in color of the light emitted from the corresponding light source. Display driver.

10. the corresponding light source is configured to illuminate the target pixel.

10. A display driver as claimed in claim 9.

11. For the same value of the first input grayscale and the second input grayscale, a change in the first output grayscale with respect to the designated luminance level is different from a change in the second output grayscale with respect to the designated luminance level.

10. A display driver as claimed in claim 9.

12. the first color is red; an x coordinate in a Yxy color space of a color of light emitted from the corresponding light source increases as the designated luminance level of the corresponding light source decreases in an actual use range of the designated luminance level; The first output gray level of the first color is smaller than the first input gray level of the first color.

10. A display driver as claimed in claim 9.

13. Processing the first input tone of the first color comprises: determining a first compensation level based on the designated brightness level of the corresponding light source; determining the first output grey level of the first color by applying the first compensation level to the first input grey level of the first color; Includes 10. A display driver as claimed in claim 9.

14. Processing the second input tone of the second color comprises: determining a second compensation level based on the designated brightness level of the corresponding light source; determining the second output grey level of the second color by applying the second compensation level to the second input grey level of the second color; Including, The second compensation level is different from the first compensation level. A display driver as claimed in claim 13.

15. a backlight control circuitry configured to determine the designated luminance level based on pixel data of pixels located in a zone opposite the corresponding light source; 10. A display driver as claimed in claim 9.

16. Determining the designated brightness level is based on a placement of one or more light sources around the zone.

16. A display driver as claimed in claim 15.

17. processing a first input grey level of a first color for a target pixel of a display panel illuminated by a backlight device comprising a plurality of light sources, the plurality of light sources being configured such that a color of light emitted from the plurality of light sources varies with a luminance level of the plurality of light sources, based at least in part on a designated luminance level of a corresponding light source of the plurality of light sources to determine a first output grey level of the first color for the target pixel; processing a second input grey level of a second color for the target pixel based at least in part on the designated luminance level of the corresponding light source to determine a second output grey level of the second color for the target pixel; updating the target pixel based on the first output grayscale and the second output grayscale; Including, The first output grayscale and the second output grayscale are determined to compensate for changes in color of the light emitted from the corresponding light source. method.

18. the corresponding light source is configured to illuminate the target pixel.

20. The method of claim 17.

19. For the same value of the first input grayscale and the second input grayscale, a change in the first output grayscale with respect to the designated luminance level is different from a change in the second output grayscale with respect to the designated luminance level.

20. The method of claim 17.

20. the first color is red; an x coordinate in a Yxy color space of a color of light emitted from the corresponding light source increases as the designated luminance level of the corresponding light source decreases in an actual use range of the designated luminance level; The first output gray level of the first color is smaller than the first input gray level of the first color.

20. The method of claim 17.

Images