System and method for adjusting display based on detected environment

In one embodiment the present invention includes a method that adjusts a display device according to a display environment. The method includes sensing the display environment of the display device and generating environment data that corresponds to the display environment. The environment data includes color data. The method further includes adjusting a color appearance model according to the color data, generating a control signal according to the color appearance model having been adjusted, and controlling a backlight of the display device according to the control signal. In this manner, a viewer perceives the images displayed by the display device in the manner intended by the content creator, because the adjustments to the color appearance model compensate for the viewer's physiological response to the display environment.

BACKGROUND

The present invention relates to display devices, and in particular, to reconfiguration of display devices according to their current environment.

A color appearance model (CAM, which may also be referred to as a “color model”) is an abstract mathematical model describing the way colors can be represented as tuples of numbers, typically as three or four values or color components. When this model is associated with a precise description of how the components are to be interpreted (viewing conditions, etc.), the resulting set of colors is called color space. Examples of color spaces include the tristimulus color space, the XYZ color space (developed by the International Commission on Illumination [CIE], and which may also be referred to as the “CIE 1931 color space”), the red-green-blue (RGB) color space, the hue-saturation-value (HSV) color space, the hue-saturation-lightness (HSL) color space, the long-medium-short (LMS) color space, and the cyan-magenta-yellow (CMY) color space.

CAMs are useful to match colors under different environment conditions that otherwise might be perceived to be different, according to the human visual system (HVS). In particular, a color captured (e.g., in an image) under one set of conditions may be perceived as a different color by an observer viewing that color in another set of conditions. The following are examples of factors that can contribute to perceptible color mismatches: the different chromacities and/or luminance levels of different illuminants, different types of devices used to display the color, the relative luminance of the background, different conditions of the surrounding environment, as well as other factors. Conventional CAMs aim to compensate for these factors by adjusting an image viewed with a destination set of conditions so that it appears to be the same color at which it was captured with a source set of conditions. Thus, CAMs can be used to convert a patch of color seen in one environment (e.g., the source environment) to an equivalent patch of color as it would be observed in a different environment (e.g., the target environment).

As an example, consider the most recent CAM ratified by CIE, which is referred to as CIECAM02. CIECAM02 provides a limited ability to modify a color appearance model based on the environment of the display device. Three surround conditions (namely Average, Dim and Dark) provide the parameters given in TABLE 1:

In TABLE 1, the surround ratio SRtests whether the surround luminance is darker or brighter than medium gray (0.2). The parameter F is a factor that determines a degree of adaptation. The parameter c is a factor that determines the impact of the surroundings. The parameter Ncis a chromatic induction factor. The color appearance model may be modified according to the parameters corresponding to the appropriate surround conditions.

SUMMARY

An embodiment of the present invention improves a color appearance model beyond a basic color appearance model. As discussed above, many basic CAMs (such as the CIECAM02 model as understood) provide only a limited ability to modify the CAM based on the environment of the display device. Furthermore, many basic CAMs (such as the CIECAM02 model as understood) do not define how various sensor results may be used to determine which of the three surround conditions is appropriate for a particular environment. In addition, many basic CAMs (such as the CIECAM02 model as understood) do not consider the interaction between a back modulator and a front modulator in a dual modulator display device.

According to an embodiment, a method adjusts a display device according to a display environment. The method includes sensing the display environment of the display device and generating environment data that corresponds to the display environment. The environment data includes color data. The method further includes adjusting a color appearance model according to the color data, generating a control signal according to the color appearance model having been adjusted, and controlling a backlight of the display device according to the control signal. In this manner, a viewer perceives the images displayed by the display device in the manner intended by the content creator, because the adjustments to the color appearance model compensate for the viewer's physiological response to the display environment.

The color appearance model may be adjusted according to the luminance of the display environment. Various parameters of the color appearance model may be adjusted, including the whitepoint achromatic response (Aw), the degree of adaptation (D), the induction factor (n), and the luminance level adaptation factor (Fl).

The display environment may be sensed with more than one sensor, and the color appearance model may be adjusted according to a weighted distance to the sensors.

A front modulator may be controlled by input video data such that the backlight and the front modulator display an image corresponding to the input video data. The backlight may be a back modulator that is also controlled by the input video data.

According to an embodiment, an apparatus includes a control circuit that implements the above-described method.

According to an embodiment, a display device includes a backlight, a sensor, and a control circuit that work together to implement the above-described method.

The following detailed description and accompanying drawings provide a further understanding of the nature and advantages of the present invention.

DETAILED DESCRIPTION

In the following description, various methods, processes and procedures are detailed. Although particular steps may be described in a certain order, such order is mainly for convenience and clarity. A particular step may be repeated more than once, may occur before or after other steps (even if those steps are otherwise described in another order), and may occur in parallel with other steps. A second step is required to follow a first step only when the first step must be completed before the second step is begun. Such a situation will be specifically pointed out when not clear from the context.

The following description uses the term “display device.” In general, this term refers to device that displays visual information (such as video data or image data). An embodiment of the present invention is directed toward a display device that includes two elements that, in combination, control the display of the visual information. One example embodiment includes a backlight and a front panel. In general, the backlight may be implemented with LEDs, and the front panel may be implemented with LCDs. Another example embodiment includes a back modulator and a front modulator. In general, the back modulator may be implemented with LEDs, and the front modulator may be implemented with LCDs. Controlling the back modulator and front modulator together may be referred to as dual modulation. (When the distinction is unimportant, the terms backlight and back modulator may be used interchangeably, and the terms front panel and front modulator may be used interchangeably.)

The following description uses the term “backlight”. In general, this term refers to a light generating element that, in combination with the front panel, generates the output image.

In a dual modulation device, the term “back modulator” may be used to more precisely refer to the backlight.

Note that in the video display arts, the term “backlight” may be used to refer to a different feature than the term “backlight” is to be understood according to embodiments of the present invention. This different “backlight” refers to a light that illuminates the wall behind a display, to improve viewer depth perception, to reduce viewer eye strain, etc. This different “backlight” does not relate to the generation of the output image. This different “backlight” is not related to the CAM. This different “backlight” is to be understood to be excluded from the term “backlight” in the following description of embodiments of the present invention.

FIG. 1is a block diagram of a control circuit100that is configured to adjust the color appearance model of a display device according to the environment in which the display device is located, according to an embodiment. The control circuit100includes a sensor interface102, a memory circuit104, a processor circuit106, and a video interface108. A bus110interconnects the sensor interface102, the memory104, the processor106, and the video interface108. The control circuit100may be implemented as a single circuit device, as shown, such as with a programmable logic device. Such a programmable logic device may include functions beyond the described functions of embodiments of the present invention. Alternatively, the functions of the control circuit100may be implemented by multiple circuit devices that are interconnected by, for example, an external bus.

The sensor interface102connects to a sensor (not shown). The sensor interface102receives environment data120from the sensor. The environment data120corresponds to the display environment. The display environment may include information such as the color and brightness of the light in the display environment. Specific details of the environment data are provided in subsequent paragraphs.

The memory circuit104stores a color appearance model (CAM). In general, the CAM is used to modify the characteristics of the display device so that the output video appears as intended by the creator of the video data input into the display device. More specifically as related to an embodiment of the present invention, the CAM is used to control the color of the backlight of the display device according to the display environment, as further described below. As further detailed below, the CAM may be implemented as a memory that contains lookup tables that were generated according to environmental parameters, and circuitry (e.g., a processor) that manipulates the data in the lookup tables. According to a further embodiment, when the backlight is modulated according to the input video data, the display environment modifies the CAM.

According to an embodiment, the CAM corresponds to a modified CIECAM02 color appearance model (International Commission on Illumination 2002 CAM). Other embodiments may implement with modifications other CAMs as desired according to design preferences. Examples of such CAMs include CIECAM97 and a revised CIECAM97s by Mark Fairchild. In addition, embodiments of the present invention may also be applied to chromatic adaptation transforms (CATs) or lookup tables of color appearance information. Specific details of the CAMs are provided in subsequent paragraphs.

The second interface circuit108generates control signals124. The control signals124control the display elements of the display device (seeFIGS. 2A-2B).

The processor circuit106adjusts the CAM according to the color data. According to an embodiment, the data in the lookup tables used by the CAM is regenerated based on the color data. The processor circuit106generates the control signals124that control a back modulator (or backlight) of the display device (seeFIGS. 2A-2B) according to the CAM having been adjusted. According to another embodiment, the control signals124may also control the front panel (or front modulator). The details of these adjustments are given in subsequent sections.

As an example, if the display environment is more orange than normal (e.g., sunset light via a window into a room with the display device), the color appearance model is adjusted to take this information into account. When images are displayed, their color is adjusted so that a viewer perceives the images as intended, and does not perceive them in an unintended manner due to the excess orange color in the viewing environment. As another example, artificial light and daylight produce different viewing environments; an embodiment adjusts the CAM so that the backlight takes the environment into account, and the viewer perceives the images as intended.

Although the sensor interface102and the video interface108are shown as separate interfaces, such separation is shown mainly for ease in understanding and explanation. According to another embodiment, the functions of these two interfaces may be implemented with a single interface. According to another embodiment, the functions of these interfaces may be implemented with more than two interfaces (e.g., a sensor control interface, a sensor input interface, a video input interface, and a video output interface). The number and type of interfaces may be made according to design considerations such as the speed and amount of data to be processed. According to an embodiment, the control circuit100may include additional interfaces to implement additional functionality beyond the functionality described in the present disclosure. According to an embodiment, the control circuit100may be arranged to follow the other processing elements of a display device (e.g., the upscaler, the deinterlacer, etc.).

FIGS. 2A-2Bprovide more details of embodiments that include the control circuit100.FIG. 2Ashows an embodiment that includes a backlight, andFIG. 2Bshows an embodiment that includes a back modulator. More generally, in the embodiment ofFIG. 2A, the operation of the backlight is independent of the input video data; in the embodiment ofFIG. 2B, the back modulator uses the input video data.

FIG. 2Ais a block diagram of a display device200aaccording to an embodiment. The display device200aincludes a backlight202a, a front panel204a, the control circuit100a(seeFIG. 1), and a sensor206. The control circuit100aoperates as described above regardingFIG. 1(with additional details as described below). The display device200amay include other components (not shown) in order to implement the additional functionality of a display device; a description of these other components is omitted for brevity. The display device200amay be a television, a video monitor, a computer monitor, a video display, a telephone screen, etc. As discussed above regardingFIG. 1, the control circuit100areceives the environment data120and generates the control signals124.

The backlight202areceives the control signals124and generates backlight output signals210a. The backlight output signals210agenerally correspond to light having a color that has been adjusted according to the environment. The backlight202amay be implemented by light emitting diodes (LEDs). Each LED element may be implemented as one or more LED devices; for example, each LED element may include a red LED, a green LED and a blue LED that are controlled together to generate a particular color of light. The LEDs may be organic LEDs (OLEDs). According to an embodiment, the backlight202amay be implemented by a field emission display (FED). According to an embodiment, the backlight202amay be implemented by a surface-conduction electron-emitter display (SED).

The front panel204afurther modifies the backlight output signals210aaccording to the video input signal122to produce front panel output signals212. The front panel output signals212generally correspond to the image that is displayed by the device200a. As a more specific example, the front panel selectively blocks the backlight output signals210ato produce the front panel output signals212. The front panel204amay be implemented by liquid crystal elements of a liquid crystal display (LCD).

The sensor206senses the display environment220and generates the environment data120. As discussed above, the environment data120may include information such as the color and brightness of the light in the display environment220. Additional details of the environment data120are provided in subsequent paragraphs.

FIG. 2Bis a block diagram of a display device200baccording to an embodiment. The display device200bincludes a back modulator202b, a front modulator204b, the control circuit100b(seeFIG. 1), and a sensor206. The control circuit100boperates as described above regardingFIG. 1(with additional details as described below). The display device200bmay include other components (not shown) in order to implement the additional functionality of a display device; a description of these other components is omitted for brevity. The display device200bmay be a television, a video monitor, a computer monitor, a video display, a telephone screen, etc.

The control circuit100breceives the environment data120and input video data122, and generates the control signals124. The input video data122may be still image data (e.g., pictures) in various formats, such as JPEG (Joint Photographic Experts Group) data, GIF (graphics interchange format) data, etc. The input video data122may be moving image data (e.g., television) in various formats, such as MPEG (Moving Picture Experts Group) data, WMV (Windows media video) data, etc. The input video data122may include metadata, for example Exif (Exchangeable image file format) data.

More specifically, the control signals124are based on both the input video data122and the environment data120. According to an embodiment, the color appearance model (which is adjusted according to the environment data120; seeFIG. 1) affects the control signals124for the back modulator202bin response to the input video data122. Given the back modulator202bbeing so controlled, the control signals124then control the scaling of the front modulator204bin response to the input video data122.

The back modulator202bgenerates back modulator output signals210bin response to the control signals124from the control circuit100b. The back modulator output signals210bgenerally correspond to low resolution images. The back modulator202bmay be implemented by light emitting diodes (LEDs). Each LED element may be implemented as one or more LED devices; for example, each LED element may include a red LED, a green LED and a blue LED that are controlled together to generate a particular color of light. The LEDs may be organic LEDs (OLEDs). According to an embodiment, the back modulator202bmay be implemented by a field emission display (FED). According to an embodiment, the back modulator202bmay be implemented by a surface-conduction electron-emitter display (SED).

The front modulator204bfurther modifies the back modulator output signals210baccording to the control signals124to produce front modulator output signals212. The front modulator output signals212generally correspond to high resolution images. As a more specific example, the front modulator204bselectively blocks the back modulator output signals (low resolution image)210bto produce the front modulator output signals (high resolution image)212. The front modulator204bmay be implemented by liquid crystal elements of a liquid crystal display (LCD).

The sensor206senses the display environment220and generates the environment data120. As discussed above, the environment data120may include information such as the color and brightness of the light in the display environment220. Additional details of the environment data120are provided in subsequent paragraphs.

Comparing the embodiment ofFIG. 2Bto that ofFIG. 2A, the control circuit100buses the environment data120and the input video data122to generate the control signals124for dual modulation control of the back modulator202band the front modulator204b.

FIG. 3is a flowchart of a method300of adjusting a display device according to the display environment. At least part of the method300may be performed by the control circuit100(seeFIG. 1), the display device200a(seeFIG. 2A), or the display device200b(seeFIG. 2B). According to an embodiment, the method300may be implemented by a computer program that controls the operation of the control circuit100, the display device200a, or the display device200b.

At302, the display environment is sensed. The display environment corresponds to the color, brightness, etc. of the light in the environment that the display device is located. The sensor206(seeFIG. 2Aor2B) may perform block302.

At304, environment data that corresponds to the display environment is generated. For example, the analog information sensed from the display environment (see302) may be transformed into digital data for further processing by digital circuit components. The environment data includes color data. The sensor206(seeFIG. 2Aor2B) may perform block304. According to an embodiment, the sensor206includes an analog to digital converter circuit.

At306, a color appearance model is adjusted according to the color data. More information regarding the specific adjustments performed is provided in subsequent paragraphs. According to an embodiment, the CAM may be implemented by lookup tables that store a set of initial values based on particular default assumptions regarding the source environment or the display environment. These initial values may be replaced according to changes in the source environment or the display environment. Changes to the source environment may be detected via the input video data, either directly or by metadata. Changes to the target environment may be detected by the sensor (see302). The processor circuit106(seeFIG. 1) may perform block306on a CAM stored in the memory104(seeFIG. 1).

At308, the CAM information is provided to the backlight of the display device. The CAM information may include a target white point. Since the CAM has been adjusted according to the display environment (see306), the target white point likewise depends upon the detected display environment (see302). More specifically, the color of the target white point depends upon the color of the display environment. The video interface108(seeFIG. 1) may provide the CAM information as the control signals124.

At310, the backlight uses the CAM information (see308) to generate its light. The color of the light generated by the backlight thus depends upon the detected display environment (see302). The backlight202a(seeFIG. 2A) may perform block310to generate the backlight output signals210a.

At312, the display device controls its front panel to generate an image corresponding to the input video data122(seeFIG. 2A). According to an embodiment, the front panel includes LCD elements that selectively modify the light generated by the backlight (see310) to produce the image. Since the backlight was adjusted according to the CAM information (see308), and since the CAM was adjusted according to the display environment (see306), the image generated by the display device hence is adjusted according to the display environment. Thus, a viewer's perception of the image is unaffected by the color of the ambient light in the display environment. The display device200a(seeFIG. 2A) may perform block312.

In summary, the method300is used to affect the viewer's perception of the input video data. By manipulation of the color of the light emitted by the backlight, the perception of the image is altered to match the environment. For example, if the environment has an orange color, the backlight light will be adjusted toward orange, making the image take into account the orange environment with respect to the senses of the viewer. This is to account for the fact that the viewer will adapt to the environment (e.g., an image of a white wall may be measured as orange because of the reflection of the orange light, however it will still appear white when the viewer is adapted to this environment). For on-screen colors to appear as intended by the content creator, the backlight is adjusted to match the environment.

According to another embodiment, the method300may be modified as follows for use with a dual modulation display device (e.g., the display device200bofFIG. 2B). The block308may be modified such that the control signals124also correspond to the video input data122. The block310may be modified such that the back modulator202buses the control signals124to generate a low resolution image (e.g.,210b). The block312may be modified to selectively block the low resolution image to generate a high resolution image (e.g.,212).

FIG. 4is a block diagram of a display device400, according to an embodiment. The display device400is similar to the display device200a, with additional details. The display device400includes a control signal generator402, a user color preference graphical user interface (GUI)404, a local sensor406, a threshold memory408, a backlight threshold evaluator circuit410, a front modulator scaling circuit412, a backlight unit (BLU)414, and a front modulator416.

The control signal generator402generally corresponds to the control circuit100(seeFIG. 1). The control signal generator402includes a memory420, a preference adjustment circuit426, a color appearance model428, a chromatic adaptation lookup table (LUT)430, and an adjustment circuit432. The memory420stores default values for use by the color appearance model428, such as reference environment information422and reference white point information424. The memory420may receive metadata from the content440, such as via an Exif header442, that may be used instead of the default values.

The preference adjustment circuit426receives the reference white point information424(or the metadata that contains replacement white point information) and interfaces with the user color preference GUI404to adjust the reference white point (or the replacement white point) according to user preference. For example, if the user prefers a different white point than the reference white point, the user may select it using the user color preference GUI404; the preference adjustment circuit426then provides the different white point (instead of the reference white point) to the color appearance model428. As another example, if the user prefers a different white point than the metadata white point (via, e.g., the Exif header442), the user may select it using the user color preference GUI404; the preference adjustment circuit426then provides the different white point (instead of the metadata white point) to the color appearance model428.

The color appearance model428receives the reference environment information422and the white point information (which may be modified by the content metadata or user preference). The color appearance model428also implements a selected CAM for the display device400, for example, the CIECAM02 color appearance model. The color appearance model428interfaces with the local sensor406in a manner similar to that described above with reference toFIG. 2(note the sensor206interfacing to the control circuit100). The color appearance model428generates a target white point450.

The chromatic adaptation LUT430stores chromatic adaptation information. Chromatic adaptation is useful because chromatic adaptation by the human visual system is not instantaneous; it takes some time to adapt to a change in environment lighting color. This change takes the form of a curve over time. For example, when a large change in lighting occurs, the human visual system quickly starts to adapt to the new color, however the rate of adaption slows does as a state of full adaption takes place. Based on the target white point450, the adjustment circuit432selects the appropriate chromatic adaptation information (from the chromatic adaptation LUT430) to generate the backlight control signals452.

The BLU414receives the backlight control signals452and generate a backlight output. Generally the backlight output corresponds to the target white point450, which is based on the color of the environment (note the CAM428). According to another embodiment (see, e.g.,FIG. 2B), the backlight output also corresponds to a low resolution image (or series of images).

The threshold memory408stores minimum backlight threshold information. The backlight threshold evaluator circuit410compares the backlight control signals452and the minimum backlight threshold information. If the backlight control signals452are below the minimum backlight threshold, the threshold evaluator circuit410provides the minimum backlight threshold to the front modulator scaling circuit412; otherwise the threshold evaluator circuit410provides the backlight control signals452to the front modulator scaling circuit412.

The front modulator scaling circuit412receives the content440and the backlight information from the threshold evaluator circuit410, and generates control signals for the front modulator416that scale the display of the content correctly given the backlight information.

FIG. 5is a block diagram of a display device500, according to an embodiment. In general, the display device500is similar to the display device400(seeFIG. 4) or the display device200a(seeFIG. 2A), with the addition of a second sensor and related control circuitry. The display device500includes a control signal generator502, a first adjustment circuit504, a second adjustment circuit506, an interpolation circuit510, and an averaging circuit512. The BLU414is a locally modulated BLU, as further detailed below. The display device500also includes a number of components similar to the display device400(seeFIG. 4), such as front modulator416, etc. for which a discussion is not repeated.

The display device500includes two sensors406aand406b. The sensors406aand406bmay be mounted on opposing sides of the display device500. The sensor406aprovides its environment information to the adjustment circuit504, and the sensor406bprovides its environment information to the adjustment circuit506. The adjustment circuit504generates dampened target backlight information according to the environment detected by the sensor406a, and the adjustment circuit506generates dampened target backlight information according to the environment detected by the sensor406b. The adjustment circuits504and506may be further configured by the user color preference GUI404in a manner similar to that described above inFIG. 4.

The interpolation circuit510receives the dampened target backlight information from the adjustment circuits504and506, interpolates the appropriate backlight settings across the backlight according to the dampened target backlight information, and generates the appropriate backlight control signals for the BLU414. For example, for regions of the BLU414closer to the sensor406a, the dampened target backlight information from the adjustment circuit504may be weighted more heavily than the dampened target backlight information from the adjustment circuit506. As another example, for regions of the BLU414closer to the sensor406b, the dampened target backlight information from the adjustment circuit506may be weighted more heavily than the dampened target backlight information from the adjustment circuit504. The weighting can be a linear weighting based on the distance from the region to the respective sensors. For example, if a region is 10 inches from the sensor406aand 40 inches from the sensor406b, the dampened target backlight information corresponding to the sensor406ais weighted at 0.8 (⅘) and that corresponding to the sensor406bis weighted at 0.2 (⅕). The weighting can be a geometric weighting based on the square of the distance from the region to the respective sensors. For example, if a region is 10 inches from the sensor406aand 40 inches from the sensor406b, the dampened target backlight information corresponding to the sensor406ais weighted at 0.96 ( 24/25) and that corresponding to the sensor406bis weighted at 0.04 ( 1/25).

The averaging circuit512receives the dampened target backlight information from the adjustment circuits504and506, averages the dampened target backlight information, and provides the average to the backlight threshold evaluator circuit410. The front modulator scaling circuit412then generates the control signals for the front modulator416based on the information provided by the backlight threshold evaluator circuit410in a manner similar to that described above inFIG. 4.

Environment Data Details

According to an embodiment, the environment data sensed corresponds to the whitepoint of the environment in absolute terms. The sensor (e.g., the sensor206ofFIG. 2A) measures the colors of the environment, generates an average from the measurement, and provides the average (as a single color, e.g. in RGB or XYZ color space) as the environment data. The CAM then uses this environment data as input parameters corresponding to the adapting luminance parameter (La) and the adapting whitepoint.

CAM Details

According to an embodiment, the color appearance model implemented as the CAM428(seeFIG. 4) corresponds to a modified CIECAM02 color appearance model.FIGS. 6-8show further details regarding this CAM.FIG. 6is a diagram illustrating the relationships between the parameters of the CAM that may be pre-calculated based on environment conditions,FIG. 7is a table listing the parameters in the CAM, andFIG. 8shows the equations that relate the parameters of the CAM.

The parameters shown inFIG. 6may be pre-calculated from either the source or target viewing condition. The source viewing condition relates to the environment where the content was created (and artistically signed-off on). The target viewing condition relates to the environment where a viewer is viewing the environment.

In general, the source viewing conditions are very similar for the majority of content (e.g., color timing suites are for the most part very similar to each other); however, the source viewing environment information may be included with the content for more accurate rendition at the target viewing site. Target viewing conditions may be measured by a sensor as described above (see, e.g.,FIG. 2A). For the elements shown inFIG. 6, the sensor may be used to determine the target adapting white point (Xw, Yw, and Zw) and the target adapting luminance level (La) (also referred to as the target adapting field luminance level).

According to an embodiment, the relative luminance (Yb, also referred to as the relative background luminance) and surround luminance (S) parameters have notably less impact than the other parameters on the CAM implemented (e.g., the modified CIECAM02 described above). In such an embodiment, the Yb and S parameters are not determined by the sensor. Instead, preset values are used, and the Yb and S parameters are kept static. According to another embodiment, the Yb and S parameters have more of an influence on the CAM implemented; in such case, the sensor may also be used to measure the Yb and S of the display environment in order to determine the Yb and S parameters.

The process flow for performing the calculations for the CAM is as follows (with reference toFIG. 6). Note that some processing depends upon other processing, so the process flow inFIG. 6is not just one way left-to-right. In box602, the sensor makes measurements corresponding to the input parameters (e.g., Xw, Yw, Zw, La, etc.). At box604, the display device (e.g., the processor106) processes the S parameter into the surround conditions c, Nc and F (see above regarding TABLE 1). At box606, the environment information, including the surround condition information, is stored in the display device (e.g., in the memory104).

At608, the display device (e.g., the processor106) processes the environment information into the various CAM parameters. This processing may implement the equations shown inFIG. 8(e.g., to compute n, D, etc.) as well as converting the XYZ color space information to Hunt-Pointer-Estevez (HPE) color space information. Rectangular boxes (e.g., for XYZ_To_HPE) in608denote processing according to standard color space equations or to the equations ofFIG. 8. Hexagonal boxes (e.g., for c*z) denote straightforward equations. The specifics of the equations implemented by the processing of608are shown inFIG. 7andFIG. 8.

At610, the display device (e.g., the memory104) stores the CAM parameters corresponding to the environment information (e.g., as the CAM428). Note that some of these parameters (e.g, z, Fl, etc.) depend upon further processing in612.

At612, the display device (e.g., the processor106) performs processing on some of the CAM parameters in610to generate additional CAM parameters. For example, the whitepoint in HPE space is converted to the whitepoint sigma. As discussed above regarding608, some of the parameters in612depend upon other parameters (e.g., SigmaRp depends upon SigmaR, etc.). The specifics of the equations implemented by the processing of612are shown inFIG. 7andFIG. 8.

According to an embodiment, instead of using the environment information sensed by the sensor as inputs to equations, the environment information is used as an index to access pre-calculated parameters stored in memory (e.g., the memory104). For example, sixteen sets of CAM parameters may be stored in memory, corresponding to sixteen different color measurements. For example, the sixteen sets can correspond to a red environment, a red-orange environment, an orange environment, etc. The display device (e.g., the processor106) then uses the environment information to select the most appropriate set of CAM parameters.

For example, the sets of CAM parameters may be indexed according to a range of colors in RGB (or XYZ, etc.) color space. The sensor senses the color in the display environment and generates the environment information as a single RGB color (e.g., as an average of all the information sensed) corresponding to the display environment. The display device (e.g., the processor106) then selects the set of CAM parameters whose index range includes that single color.

As another example, the sets of CAM parameters may be indexed according to a single index color. The display device (e.g., the processor106) then selects the set of CAM parameters whose index color is closest to the sensed color. The closeness may be based on the linear distance between the sensed color and the index colors. In the case where each index color includes a number of components (e.g., an index color in the RGB color space includes R, G and B components), the closeness may be based on the cumulative distance between each component of the sensed color and the index colors.

FIG. 9is a block diagram of a display system900, according to an embodiment. The display system900includes a sensor206, a memory902that stores default source environment data, a CAM processor904that generates CAM lookup tables, a memory906that stores dynamic CAM lookup tables, a memory908that stores static CAM lookup tables, a memory910that stores original color information, a color appearance model912, and a memory914that stores adapted color information. Note that many of the components of the display system900are similar to, or may be implemented by, components previously described with reference to other figures. For example, the control circuit100(seeFIG. 1) may implement the memories902,906,908,910and914via the memory104; the processor106may implement the CAM processor904; the processor106and the memory104may implement the CAM912.

As discussed above regarding other embodiments, the sensor206senses the light in the environment220where the display device900is located and provides the environment data to the CAM processor904. The CAM processor904also receives the default source environment data from the memory902. The CAM processor904may also receive source environment data from the video content440, for example as metadata in the content. (The display device900may use the default source environment data when the content does not provide the source environment data.) The CAM processor904builds the dynamic CAM lookup tables based on the environment data and the source environment data, as discussed above.

The memory906stores the dynamic CAM lookup tables generated by the CAM processor904, and the memory908stores the static CAM lookup tables. The dynamic CAM lookup tables depend upon the environment data, and the static CAM lookup tables do not. Thus, the content of the lookup tables may vary depending upon the environmental parameters that are sensed. For example, as discussed above with reference toFIG. 6, the sensor is used to sense Xw, Yw, Zw and La, and the sensor does not sense Yb and S. Thus, the dynamic CAM lookup tables depend upon Xw, Yw, Zw and La, and the static CAM lookup tables depend upon Yb and S. According to another embodiment in which the sensor also detects Yb, the parameters related to Yb would be in the dynamic CAM lookup tables instead of the static CAM lookup tables. Similarly, according to another embodiment in which the sensor also detects S, the parameters related to S would be in the dynamic CAM lookup tables instead of the static CAM lookup tables.

The memory910stores the original color information, which the display device900determines according to the video content440. The original color information may be in the form of a whitepoint that corresponds to the video content440.

The CAM912uses the lookup tables in the memories906and908, and the original color information in the memory910, to generate the CAM used by the display device900. The process the CAM912performs may be as described above regardingFIG. 6. The output of the CAM912may be the target white point450as discussed above regardingFIG. 4, which may be stored in the memory914as the adapted backlight information for controlling the backlight of the display device900.

Implementation Details

An embodiment of the invention may be implemented in hardware, executable modules stored on a computer readable medium, or a combination of both (e.g., programmable logic arrays). Unless otherwise specified, the steps included as part of the invention need not inherently be related to any particular computer or other apparatus, although they may be in certain embodiments. In particular, various general-purpose machines may be used with programs written in accordance with the teachings herein, or it may be more convenient to construct more specialized apparatus (e.g., integrated circuits) to perform the required method steps. Thus, the invention may be implemented in one or more computer programs executing on one or more programmable computer systems each comprising at least one processor, at least one data storage system (including volatile and non-volatile memory and/or storage elements), at least one input device or port, and at least one output device or port. Program code is applied to input data to perform the functions described herein and generate output information. The output information is applied to one or more output devices, in known fashion.

Each such computer program is preferably stored on or downloaded to a storage media or device (e.g., solid state memory or media, or magnetic or optical media) readable by a general or special purpose programmable computer, for configuring and operating the computer when the storage media or device is read by the computer system to perform the procedures described herein. The inventive system may also be considered to be implemented as a computer-readable storage medium, configured with a computer program, where the storage medium so configured causes a computer system to operate in a specific and predefined manner to perform the functions described herein. (Software per se and intangible signals are excluded to the extent that they are unpatentable subject matter.)