PATENT DOCUMENT

Publication Number: US-10262605-B2
Application Number: US-201715699366-A
Country: US
Kind Code: B2

Title: Electronic display color accuracy compensation

Abstract:
Systems, methods, and non-transitory media are presented that provide for improving color accuracy. An electronic display includes a display region having multiple pixels each having multiple subpixels. The electronic device also includes a display pipeline coupled to the electronic display. The display pipeline is configured to receive image data and perform white point compensation on the image data to compensate for a current drop in the display to cause the display to display a target white point when displaying white. The display pipeline also is configured to correct white point overcompensation on the image data to reduce possible oversaturation of non-white pixels using the white point compensation. Finally, the display pipeline is configured to output the compensated and corrected image data to the electronic display to facilitate displaying the compensated and corrected image data on the display region.

Claims:
What is claimed is: 
     
       1. An electronic device, comprising:
 an electronic display comprising a display region comprising a plurality of pixels each comprising a plurality of subpixels; and 
 a display pipeline coupled to the electronic display, wherein the display pipeline is configured to: 
 receive image data; 
 perform white point compensation on the image data to compensate for a current drop in the display to cause the display to display a target white point when displaying white; 
 correct oversaturation of non-white pixels due to the white point compensation; and 
 output the compensated and corrected image data to the electronic display to facilitate displaying the compensated and corrected image data on the display region. 
 
     
     
       2. The electronic device of  claim 1 , wherein the display pipeline comprises a multi-dimensional lookup table, and wherein correcting the oversaturation comprises looking up values in the multi-dimensional lookup table based at least in part on a color overcompensation correction value determined for the electronic display. 
     
     
       3. The electronic device of  claim 2 , wherein the multi-dimensional lookup table comprises a number of dimensions equal to a number of the subpixels corresponding to each pixel of the plurality of pixels. 
     
     
       4. The electronic device of  claim 2 , wherein the multi-dimensional lookup table is populated based on cross-talk compensation to compensate for cross-talk between the plurality of subpixels. 
     
     
       5. The electronic device of  claim 4 , wherein the cross-talk compensation for a first subpixel of the plurality of subpixels is based at least in part on driving levels for other subpixels of the plurality of subpixels. 
     
     
       6. The electronic device of  claim 1 , wherein the current drop comprises a reduced current through a subpixel based on resistances between a power supply and the display region. 
     
     
       7. The electronic device of  claim 1 , wherein correcting the overcompensation comprises pre-correcting for the white point compensation before performing white point compensation. 
     
     
       8. A method comprising:
 receiving, in a display pipeline, a frame of video data to drive a plurality of emissive elements in an electronic display; 
 receiving compensation information for the frame of video data; 
 looking up, in a three-dimensional lookup table, converted driving values for an emissive element corresponding to the frame of video data, wherein the converted driving values are looked up based at least in part on values in the frame for other emissive elements of the plurality of emissive elements; and 
 driving, via the display pipeline, the emissive element to the converted driving values. 
 
     
     
       9. The method of  claim 8  comprising populating the three-dimensional lookup table to compensate for cross-talk between the plurality of emissive elements. 
     
     
       10. The method of  claim 9 , wherein populating the three-dimensional lookup table comprises:
 measuring values for the three-dimensional lookup table for multiple brightness levels for the electronic display; 
 computing mapping to a given target from a measured color for the electronic display; 
 setting linear mapping for gray levels for the electronic display; and 
 checking integrity of the three-dimensional lookup table for the electronic display. 
 
     
     
       11. The method of  claim 10 , wherein populating the three-dimensional lookup table comprises averaging three-dimensional lookup tables from a plurality of electronic displays. 
     
     
       12. The method of  claim 10 , wherein the gray levels comprise red pixel value equal to a green pixel value equal to a blue pixel value. 
     
     
       13. The method of  claim 8 , wherein the compensation information comprises white point compensation correction that corrects for oversaturation of nonwhite image values in the frame of video data. 
     
     
       14. The method of  claim 8 , wherein the compensation information comprises tone compensation that compensates for a display tone of the frame of video data based on ambient light. 
     
     
       15. The method of  claim 14 , wherein the tone compensation comprises compensation to adjust the display tone of the frame of video data based at least in part on a tone of the ambient light. 
     
     
       16. The method of  claim 14 , wherein the tone compensation comprises compensation to reduce blue light in the display tone of the frame of video data. 
     
     
       17. An electronic device comprising:
 a display pipeline comprising: 
 a color manager configured to receive incoming image data, wherein the color manager comprises a multi-dimensional color lookup table configured to convert the incoming image data to converted image data; and 
 white point compensation circuitry configured to produce a target white point for white values by compensating for a current drop in an electronic device in the converted image data, wherein the display pipeline is configured to correct for overcompensation of nonwhite pixels by the white point compensation circuitry. 
 
     
     
       18. The electronic device of  claim 17 , wherein correction for overcompensation of nonwhite pixels is performed in the multi-dimensional color lookup table, wherein the multi-dimensional color lookup table includes populated values based at least in part on tone compensation settings and linear accessibility filters, and wherein changing the tone compensation settings or the linear accessibility filters causes recomputation of the populated values. 
     
     
       19. The electronic device of  claim 17 , wherein correction for overcompensation of nonwhite pixels is performed in the multi-dimensional color lookup table, and tone compensation is performed in the white point compensation circuitry after the correction for overcompensation of nonwhite pixels is performed. 
     
     
       20. The electronic device of  claim 17 , wherein correction for overcompensation of nonwhite pixels is performed in the multi-dimensional color lookup table when a tone compensation mode is not set to compensate for tone related to ambient light in the white point compensation circuitry.

Description:
BACKGROUND 
     The present disclosure relates generally to electronic displays and, more particularly, to gain applied to display an image or image frame on an electronic display. 
     This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present techniques, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. 
     Electronic devices often use electronic displays to provide visual representations of information by displaying one or more images. Such electronic devices may include computers, mobile phones, portable media devices, tablets, televisions, virtual-reality headsets, and vehicle dashboards, among many others. To display an image, an electronic display may control light emission from display pixels based at least in part on image data, which indicates target characteristics of the image. The electronic displays may be calibrated to compensate for a current drop due to resistance on a path from a power supply, such as a power management integrated circuit (PMIC), to the electronic display. The compensation may be determined and/or tuned based on a white point for the electronic display. However, this compensation may result in overcompensation for non-white colors resulting in oversaturation of at least some colors. 
     SUMMARY 
     A summary of certain embodiments disclosed herein is set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of these certain embodiments and that these aspects are not intended to limit the scope of this disclosure. Indeed, this disclosure may encompass a variety of aspects that may not be set forth below. 
     The present disclosure generally relates to improving perceived image quality on an electronic display. To display an image, the electronic display may control light emission from its display pixels based at least in part on image data that indicates target characteristics (e.g., luminance) at image pixels in the image. In some instances, the image data may be generated by an image data source. 
     An electronic display may experience display variations based on resistance of connections between a power supply and emissive elements of the display (e.g., current drop). To correct for these display variations, the electronic device (e.g., including the display) may be set to drive levels to produce a target white point for white pixels. However, nonwhite pixels may be oversaturated. Furthermore, color accuracy of the display may be decreased by cross-talk on an emissive element from data signals for other emissive elements in the display. 
     To address white color overcompensation and/or other cross-talk, a multi-dimensional color lookup table (CLUT) to convert incoming image data into compensated and/or corrected image data. For example, the CLUT may be populated to map incoming data values to correct for upcoming white point overcompensation. In other words, the mapping may be used to invert the overcompensation. The usage of the CLUT enables correction of non-linear white point overcompensation by choosing values that undue overcompensation that are mapped using empirical data and/or calculations. Furthermore, the mapping in the CLUT may account for data values adjacent channels that may cause cross-talk between the emissive element data paths to compensate for the cross-talk by reducing or eliminating cross-talk-based color inaccuracies. In other words, empirical data reflecting cross-talk variations may be input into the CLUT to adjust a subpixel based on other subpixels, such as pixel values (e.g., including multiple subpixel values) of a pixel and/or adjacent pixels. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various aspects of this disclosure may be better understood upon reading the following detailed description and upon reference to the drawings in which: 
         FIG. 1  is a block diagram of an electronic device including an electronic display to display images, in accordance with an embodiment; 
         FIG. 2  is an example of the electronic device of  FIG. 1 , in accordance with an embodiment; 
         FIG. 3  is another example of the electronic device of  FIG. 1 , in accordance with an embodiment; 
         FIG. 4  is another example of the electronic device of  FIG. 1 , in accordance with an embodiment; 
         FIG. 5  is another example of the electronic device of  FIG. 1 , in accordance with an embodiment; 
         FIG. 6  is a block diagram of a display pipeline implemented in the electronic device of  FIG. 1 , in accordance with an embodiment; 
         FIG. 7  is a flow diagram of a process for operating the display pipeline of  FIG. 6 , in accordance with an embodiment; 
         FIG. 8  is a schematic diagram of a portion of the electronic display of  FIG. 1 , in accordance with an embodiment; 
         FIG. 9  is a block diagram of the display pipeline of  FIG. 6  with white color compensation circuitry, in accordance with an embodiment; 
         FIG. 10  is a graph illustrating color accuracy in the display pipeline of  FIG. 9 , in accordance with an embodiment; 
         FIG. 11  is a flow diagram of a process that may be used to increase color accuracy in the display pipeline of  FIG. 9 , in accordance with an embodiment; 
         FIG. 12  a block diagram representing an embodiment of the display pipeline of  FIG. 6  with increased color accuracy using a color lookup table (CLUT) to correct oversaturation and perform tone compensation, in accordance with an embodiment; 
         FIG. 13  a block diagram representing an embodiment of the display pipeline of  FIG. 6  with increased color accuracy using a color lookup table (CLUT) to correct oversaturation and using white point compensation circuitry to perform tone compensation, in accordance with an embodiment; and 
         FIG. 14  a block diagram representing an embodiment of the display pipeline of  FIG. 6  with increased color accuracy using a color lookup table (CLUT) to correct oversaturation mutually exclusive to tone compensation performed in white point compensation circuitry, in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     One or more specific embodiments of the present disclosure will be described below. These described embodiments are only examples of the presently disclosed techniques. Additionally, in an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but may nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
     When introducing elements of various embodiments of the present disclosure, the articles “a,” “an,” and “the” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Additionally, it should be understood that references to “one embodiment” or “an embodiment” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. 
     The present disclosure generally relates to electronic displays, which may be used to present visual representations of information, for example, as images in one or more image frames. To display an image, an electronic display may control light emission from its display pixels based at least in part on image data that indicates target characteristics of the image. For example, the image data may indicate target luminance (e.g., brightness) of specific color components in a portion (e.g., image pixel) of the image, which when blended (e.g., averaged) together may result in perception of a range of different colors. 
     An electronic display may experience display variations based on resistance of connections between a power supply and emissive elements of the display (e.g., current drop). To correct for these display variations, the electronic device (e.g., including the display) may be set to drive levels to produce a target white point for white pixels. However, nonwhite pixels may be oversaturated. Furthermore, color accuracy of the display may be decreased by cross-talk on an emissive element from data signals for other emissive elements in the display. 
     To address white color overcompensation and/or other cross-talk, a multi-dimensional color lookup table (CLUT) to convert incoming image data into compensated and/or corrected image data. For example, the CLUT may be populated to map incoming data values to correct for upcoming white point overcompensation. In other words, the mapping may be used to invert the overcompensation. The usage of the CLUT enables correction of non-linear white point overcompensation by choosing values that undue overcompensation that are mapped using empirical data and/or calculations. Furthermore, the mapping in the CLUT may account for data values adjacent channels that may cause cross-talk between the emissive element data paths to compensate for the cross-talk by reducing or eliminating cross-talk-based color inaccuracies. In other words, empirical data reflecting cross-talk variations may be input into the CLUT to adjust a subpixel based on other subpixels, such as pixel values (e.g., including multiple subpixel values) of a pixel and/or adjacent pixels. 
     In some embodiments, tone compensation, brightness compensation, device-specific calibrations, and linear accessibility filters may also be used to select values to populate the CLUT to map incoming data to corrected and/or compensated data. Additionally or alternatively, device-specific calibrations, brightness compensations, linear accessibility filters, and/or tone compensation may be performed in other parts of a display pipeline including the CLUT. 
     Furthermore, the CLUT may be any suitable size. For example, the size of the CLUT may be based on a number available colors for the electronic display and/or other parameters. Moreover, the number of dimensions of the CLUT may be set according to a number of indexes used to lookup data. For example, if a subpixel value is to be compensated and/or corrected from a pixel having three subpixels, the CLUT may have at least three dimensions. 
     With the foregoing in mind, one embodiment of an electronic device  10  that utilizes an electronic display  12  is shown in  FIG. 1 . As will be described in more detail below, the electronic device  10  may be any suitable electronic device, such as a handheld electronic device, a tablet electronic device, a notebook computer, and the like. Thus, it should be noted that  FIG. 1  is merely one example of a particular implementation and is intended to illustrate the types of components that may be present in the electronic device  10 . 
     In the depicted embodiment, the electronic device  10  includes the electronic display  12 , input devices  14 , input/output (I/O) ports  16 , a processor core complex  18  having one or more processor(s) or processor cores, local memory  20 , a main memory storage device  22 , a network interface  24 , a power source  26 , and image processing circuitry  27 . The various components described in  FIG. 1  may include hardware elements (e.g., circuitry), software elements (e.g., a tangible, non-transitory computer-readable medium storing instructions), or a combination of both hardware and software elements. It should be noted that the various depicted components may be combined into fewer components or separated into additional components. For example, the local memory  20  and the main memory storage device  22  may be included in a single component. Additionally, the image processing circuitry  27  (e.g., a graphics processing unit) may be included in the processor core complex  18 . 
     As depicted, the processor core complex  18  is operably coupled with local memory  20  and the main memory storage device  22 . In some embodiments, the local memory  20  and/or the main memory storage device  22  may be tangible, non-transitory, computer-readable media that store instructions executable by the processor core complex  18  and/or data to be processed by the processor core complex  18 . For example, the local memory  20  may include random access memory (RAM) and the main memory storage device  22  may include read only memory (ROM), rewritable non-volatile memory such as flash memory, hard drives, optical discs, and the like. 
     In some embodiments, the processor core complex  18  may execute instruction stored in local memory  20  and/or the main memory storage device  22  to perform operations, such as generating source image data. As such, the processor core complex  18  may include one or more general purpose microprocessors, one or more application specific processors (ASICs), one or more field programmable logic arrays (FPGAs), or any combination thereof. 
     As depicted, the processor core complex  18  is also operably coupled with the network interface  24 . Using the network interface  24 , the electronic device  10  may be communicatively coupled to a network and/or other electronic devices. For example, the network interface  24  may connect the electronic device  10  to a personal area network (PAN), such as a Bluetooth network, a local area network (LAN), such as an 802.11x Wi-Fi network, and/or a wide area network (WAN), such as a 4G or LTE cellular network. In this manner, the network interface  24  may enable the electronic device  10  to transmit image data to a network and/or receive image data from the network. 
     Additionally, as depicted, the processor core complex  18  is operably coupled to the power source  26 . In some embodiments, the power source  26  may provide electrical power to operate the processor core complex  18  and/or other components in the electronic device  10 . Thus, the power source  26  may include any suitable source of energy, such as a rechargeable lithium polymer (Li-poly) battery and/or an alternating current (AC) power converter. 
     Furthermore, as depicted, the processor core complex  18  is operably coupled with I/O ports  16  and the input devices  14 . In some embodiments, the I/O ports  16  may enable the electronic device  10  to interface with various other electronic devices. Additionally, in some embodiments, the input devices  14  may enable a user to interact with the electronic device  10 . For example, the input devices  14  may include buttons, keyboards, mice, trackpads, and the like. Additionally or alternatively, the electronic display  12  may include touch sensing components that enable user inputs to the electronic device  10  by detecting occurrence and/or position of an object touching its screen (e.g., surface of the electronic display  12 ). 
     In addition to enabling user inputs, the electronic display  12  may facilitate providing visual representations of information by displaying images (e.g., in one or more image frames). For example, the electronic display  12  may display a graphical user interface (GUI) of an operating system, an application interface, text, a still image, or video content. To facilitate displaying images, the electronic display  12  may include a display panel with one or more display pixels. Additionally, each display pixel may include one or more subpixels, which each control luminance of one color component (e.g., red, blue, or green). 
     As described above, the electronic display  12  may display an image by controlling luminance of the subpixels based at least in part on corresponding image data (e.g., image pixel image data and/or display pixel image data). In some embodiments, the image data may be received from another electronic device, for example, via the network interface  24  and/or the I/O ports  16 . Additionally or alternatively, the image data may be generated by the processor core complex  18  and/or the image processing circuitry  27 . 
     As described above, the electronic device  10  may be any suitable electronic device. To help illustrate, one example of a suitable electronic device  10 , specifically a handheld device  10 A, is shown in  FIG. 2 . In some embodiments, the handheld device  10 A may be a portable phone, a media player, a personal data organizer, a handheld game platform, and/or the like. For example, the handheld device  10 A may be a smart phone, such as any IPHONE® model available from APPLE INC. 
     As depicted, the handheld device  10 A includes an enclosure  28  (e.g., housing). In some embodiments, the enclosure  28  may protect interior components from physical damage and/or shield them from electromagnetic interference. Additionally, as depicted, the enclosure  28  surrounds the electronic display  12 . In the depicted embodiment, the electronic display  12  is displaying a graphical user interface (GUI)  30  having an array of icons  32 . By way of example, when an icon  32  is selected either by an input device  14  or a touch-sensing component of the electronic display  12 , an application program may launch. 
     Furthermore, as depicted, input devices  14  open through the enclosure  28 . As described above, the input devices  14  may enable a user to interact with the handheld device  10 A. For example, the input devices  14  may enable the user to activate or deactivate the handheld device  10 A, navigate a user interface to a home screen, navigate a user interface to a user-configurable application screen, activate a voice-recognition feature, provide volume control, and/or toggle between vibrate and ring modes. As depicted, the I/O ports  16  may also open through the enclosure  28 . In some embodiments, the I/O ports  16  may include, for example, an audio jack to connect to external devices. 
     To further illustrate, another example of a suitable electronic device  10 , specifically a tablet device  10 B, is shown in  FIG. 3 . For illustrative purposes, the tablet device  10 B may be any IPAD® model available from APPLE INC. A further example of a suitable electronic device  10 , specifically a computer  10 C, is shown in  FIG. 4 . For illustrative purposes, the computer  10 C may be any MACBOOK® or IMAC® model available from APPLE INC. Another example of a suitable electronic device  10 , specifically a watch  10 D, is shown in  FIG. 5 . For illustrative purposes, the watch  10 D may be any APPLE WATCH® model available from APPLE INC. As depicted, the tablet device  10 B, the computer  10 C, and the watch  10 D each also includes an electronic display  12 , input devices  14 , I/O ports  16 , and an enclosure  28 . 
     As described above, the electronic display  12  may display images based at least in part on image data received, for example, from the processor core complex  18  and/or the image processing circuitry  27 . Additionally, as described above, the image data may be processed before being used to display an image on the electronic display  12 . In some embodiments, a display pipeline may process the image data, for example, based on gain values associated with corresponding pixel position to facilitate improving perceived image quality of the electronic display  12 . 
     To help illustrate, a portion  34  of the electronic device  10  including a display pipeline  36  is shown in  FIG. 6 . In some embodiments, the display pipeline  36  may be implemented by circuitry in the electronic device  10 , circuitry in the electronic display  12 , software running in the processor core complex  18 , or a combination thereof. For example, the display pipeline  36  may be included in the processor core complex  18 , the image processing circuitry  27 , a timing controller (TCON) in the electronic display  12 , or any combination thereof. 
     As depicted, the portion  34  of the electronic device  10  also includes an image data source  38 , a display driver  40 , a controller  42 , and external memory  44 . In some embodiments, the controller  42  may control operation of the display pipeline  36 , the image data source  38 , and/or the display driver  40 . To facilitate controlling operation, the controller  42  may include a controller processor  50  and controller memory  52 . In some embodiments, the controller processor  50  may execute instructions stored in the controller memory  52 . Thus, in some embodiments, the controller processor  50  may be included in the processor core complex  18 , the image processing circuitry  27 , a timing controller in the electronic display  12 , a separate processing module, or any combination thereof. Additionally, in some embodiments, the controller memory  52  may be included in the local memory  20 , the main memory storage device  22 , the external memory  44 , internal memory  46  of the display pipeline  36 , a separate tangible, non-transitory, computer readable medium, or any combination thereof. 
     In the depicted embodiment, the display pipeline  36  is communicatively coupled to the image data source  38 . In this manner, the display pipeline  36  may receive image data corresponding with an image to be displayed on the electronic display  12  from the image data source  38 , for example, in a source (e.g., RGB) format. In some embodiments, the image data source  38  may be included in the processor core complex  18 , the image processing circuitry  27 , or a combination thereof. 
     As described above, the display pipeline  36  may process the image data received from the image data source  38 . To process the image data, the display pipeline  36  may include one or more image data processing blocks  54 . For example, in the depicted embodiment, the image data processing blocks  54  include a color manager  56 . Additionally or alternatively, the image data processing blocks  54  may include an ambient adaptive pixel (AAP) block, a dynamic pixel backlight (DPB) block, a white point correction (WPC) block, a subpixel layout compensation (SPLC) block, a burn-in compensation (BIC) block, a panel response correction (PRC) block, a dithering block, a subpixel uniformity compensation (SPUC) block, a content frame dependent duration (CDFD) block, an ambient light sensing (ALS) block, or any combination thereof. The color manager  56  controls and/or compensates color in the displayed image presented on the electronic display  12 . 
     After processing, the display pipeline  36  may output processed image data, such as display pixel image data, to the display driver  40 . Based at least in part on the processed image data, the display driver  40  may apply analog electrical signals to the display pixels of the electronic display  12  to display images in one or more image frames. In this manner, the display pipeline  36  may operate to facilitate providing visual representations of information on the electronic display  12 . 
     To help illustrate, one embodiment of a process  60  for operating the display pipeline  36  is described in  FIG. 7 . Generally, the process  60  includes receiving image pixel image data (block  62 ), processing the image pixel image data to determine display pixel image data (block  64 ), and outputting the display pixel image data (block  66 ). In some embodiments, the process  60  may be implemented based on circuit connections formed in the display pipeline  36 . Additionally or alternatively, in some embodiments, the process  60  may be implemented by executing instructions stored in a tangible non-transitory computer-readable medium, such as the controller memory  52 , using processing circuitry, such as the controller processor  50 . 
     As described above, the display pipeline  36  may receive image pixel image data, which indicates target luminance of color components at points (e.g., image pixels) in an image, from the image data source  38  (block  62 ). In some embodiments, may include other display parameters, such as pixel greyscale levels, compensation settings, accessibility settings, brightness settings, and/or other factors that may change appearance of display. In some embodiments, the image pixel image data may be in a source format. For example, when the source format is an RGB format, image pixel image data may indicate target luminance of a red component, target luminance of a blue component, and target luminance of a green component at a corresponding pixel position. 
     Additionally, the controller  42  may instruct the display pipeline  36  to process the image pixel image data to determine display pixel image data to correct white point overcompensation (block  64 ) and output the display pixel image data to the display driver  40  (block  66 ). To determine the display pixel image data, the display pipeline  36  may convert image data from a source format to a display format based on the various display parameters. In some embodiments, the display pipeline  36  may determine the display format may be based at least in part on layout of subpixels in the electronic display  12 . For example, the display pipeline  36  may use white-point compensation to compensate for current drop in the panel and also utilizing white-point correction to correct potential compensation of the white-point. 
     To help illustrate white-point compensation and overcompensation correction, a portion  70  of the display  12  is presented in  FIG. 8 . The portion  70  includes a portion  72  of an active area of the display  12 . The portion  72  includes a pixel that includes three subpixels  74 ,  76 , and  78 . In the illustrated embodiment, the subpixel  74  corresponds to a red subpixel, the subpixel  76  corresponds to a green subpixel, and the subpixel  78  corresponds to a blue subpixel. In other embodiments, subpixels may be arranged in different orientation and/or may correspond different colors than those represented in the portion  72 . In some embodiments, a pixel (e.g., the portion  72 ) may include a different number of subpixels other than three. 
     This of pixels in that light using an emissive element  79 . The emissive element  79  may include organic light-emitting diode (OLED) and/or any other emissive elements. An amount of light emitted from the emissive elements  79  is based on a respective current  80 ,  82 , or  84 . For example, the current  80  controls how much red light is emitted from a corresponding emissive element  79 , the current  82  controls how much green light is emitted from a corresponding emissive element  79 , and the current the four controls how much blue light is emitted from a corresponding emissive elements  79 . 
     Amount of electricity going through the currents  80 ,  82 , and  84  is controlled by voltage difference between ELVDD  86  and ELVSS  88 . However, due to resistances  90  in the connections between a power supply (e.g., PMIC), the voltage across the portion  72  may be different than the difference between ELVDD  86  and ELVSS  88 . In other words, ΔFLVDD  92  and ΔFLVSS  94  may cause a driving current (e.g., the current  80 ) through the corresponding emissive element  79  to be reduced. This reduction may be referred to as the current drop on the panel of the display  12 . 
     To address current drop, the display pipeline  100  (e.g., display pipeline  36 ) attempts to compensate by tuning currents through the emissive elements  79  to produce a white point corresponding to a greyscale value of 255 of combining a maximum driving of the subpixels. This white point compensation performed in display pipeline  100 , specifically, in a white point compensation transform block  102 . This white point compensation transform block  102  may receive various parameters that control this compensation. For example, the white point compensation transform block  102  may utilize a tone compensation  104 , brightness compensation  106 , and primary calibration  108  to determine the white point for the display  12 . The tone compensation  104  may compensate for ambient light (e.g., color and/or brightness). For example, the tone compensation  104  may be used to compensate for colors and brightness of ambient light to ensure that parents of the display image is the same between different ambient light conditions. Additionally or alternatively, the tone compensation  104  may be used to set certain tones for display images based on settings. For example, night mode may be used to reduce blue light emission by adjusting the white point determined from the white point compensation transform block  102 . The brightness compensation  106  is based on a brightness setting that is used display  12 . The primary calibration  108  may include panel specific calibration factors to correct for panel variability. 
     The color manager  56  may include a three-dimensional color lookup table (CLUT)  110  that is may be used to convert the image data from one format to another. The color manager  56  may also be used to convert image data into a suitable panel gamut (e.g., display range of colors) for the display  12  using panel gamut conversion parameters  112  in a pre-CLUT transformation block  113 . The panel gamut conversion parameters  112  may include a palette of physical colors available for display using the display  12 . The color manager  56 , using the three-dimensional lookup table  110 , may also be used for image data based on linear accessibility filters  114  and non-linear accessibility features  116 . The linear accessibility filters  114  may include various linear filters the change in appearance of display data on the display  12 . For example, these linear accessibility filters  114  may include color filters that adjusts the incoming data to compensate for color vision efficiency. For instance, the color filters may include a grayscale filter, a red/green filter for Protanopia, a green/red filter for Deuteranopia, a blue/yellow filter for Tritanopia, and/or other custom filters. Since these linear accessibility filters  114  are linear, these filters may be applied in the pre-CLUT transformation block  113  in the pipeline  100  before the CLUT  110 . The color manager  56  may also include a pre-CLUT range map block  115  that maps colors from the image data to the CLUT  110 . 
     The non-linear accessibility features  116  may include other accessibility features that are non-linear and change in appearance display data on the display  12 . For example, the non-linear accessibility features  116  may include an inversion mode that inverts colors in the image data to aid in readability for those with certain vision deficiencies. These non-linear accessibility features may be applied in a post-CLUT range map  118  and/or a post-CLUT transform block  120 . 
     The display pipeline  100  may include other processing blocks. For example, the illustrated embodiment of the display pipeline  100  and includes an ambient adaptive pixel (AAP) block  122  and a dynamic pixel backlight (DPB) block  124 . The AAP block  122  may adjust pixel values in the image content in response to ambient conditions. The DPB block  124  may adjust backlight setting up backlight for the display  12  according to the image content. For example, in some embodiments, the DPB clock  124  may perform histogram equalization on image data and decrease the backlight output to reduce power consumption without changing appearance of the image data on the display  12 . 
     Note that color accuracy of the display  12  is at least partially driven by white point compensation in the white point compensation transform block  102  (e.g., in a frame-by-frame basis). As previously noted, white point compensation using a white point (e.g., grayscale value 255 for multiple pixels) may address some issues with current drop. However, performing white point compensation based on the white point may cause oversaturation of nonwhite colors due to overcompensation since the compensation is based on the white point rather than the nonwhite color (e.g., R=0, G=100, and B=0). Moreover, color accuracy issues may be derived from cross-talk that changes (e.g., increases) an emission level away from a target value for the display as the emission target value increases. For example,  FIG. 10  identifies a graph  130  that illustrates a color accuracy of a target color point  132 . A first set of emission level points  134  may be relatively close to the target color point  132 . A second set of luminance level points  136  may be a little bit further from the target color point  132 . This larger variance results from a higher luminance level for the second set of luminance level points  136 . And even higher level of luminance for a third set of luminance level points  138  causes the third set of luminance level points  138  to various greater distance from the target color point  132 . 
     To address these issues, the display pipeline  36 ,  100  may utilize the three-dimensional CLUT  110  to modulate luminance of subpixels based on total current level in the display  12  and/or compensations for the data. In other words, modulation of a luminance level of a subpixel is a function of current through other channels. To aid in explanation,  FIG. 11  illustrates a process  150  that may be used to increase color accuracy in the display  12  using the CLUT  110 . The process  150  includes receiving image values to drive multiple emissive elements of the display  12  (block  152 ). These plurality of image values may be included in image data (e.g., a frame of video data) passed into the display pipeline  36 ,  100  and may correspond to current levels and/or voltage levels used to drive the emissive elements  79  to produce a corresponding greyscale level. In some embodiments, the display pipeline  36 ,  100  also receives compensation information (block  154 ). The compensation information may include accessibility settings, brightness compensations, panel-specific calibrations, tone compensation, and/or color oversaturation corrections. The brightness of a pixel may be used to determine a cross-talk compensation in the CLUT  110 . This brightness (e.g., including the brightness compensation) may be used in a per-panel compensation. In other words, each panel may be characterized by 1) measuring the CLUT  110  for one or more brightness levels, 2) computing RGB values to map a given target to a measured color, 3) set linear mapping for gray levels (e.g., R=G=B) to preserve display driver integrated circuit calibration, and 4) checking integrity of the CLUT  110 . In some embodiments, the CLUT  110  values may be averaged for multiple panels to address cross-talk. 
     The display pipeline  36 ,  100  then utilizes the CLUT  110  to lookup a driving level for an emissive element of the multiple emissive elements based at least in part on the driving values for the multiple emissive elements (block  156 ). By looking up a driving level for the emissive element (e.g., green subpixel) based on other emissive elements (e.g., red and blue subpixels), the effect on cross-talk on the display  12  may be reduced and/or eliminated. Additionally or alternatively to using multiple channel information to calculate driving levels of a single subpixel, in some embodiments, the lookup table may include the compensation information to correct for oversaturation and/or other compensation issues. The electronic device  10  then drives the emissive element to the driving level (block  158 ). 
       FIG. 12  illustrates an embodiment of a display pipeline  170  that utilizes a color oversaturation correction  172  to undo overcompensation that may be induced by the white point compensation transform block  102 . In other words, the CLUT  110  may be populated with driving values indexed by incoming image values that take into account color oversaturation that would occur in the white point compensation transform block  102  to pre-compensate for such overcompensation. In the illustrated embodiment, the CLUT  110  is also populated according to the linear accessibility filters  114 , the tone compensation  104 , the brightness compensation  106 , primary calibration  108 , and/or other compensations/calibrations. By applying all of these compensations in the CLUT  110 , panel-to-panel variation may be reduced. In some embodiments, the data in the CLUT  110  may be populated to compensate for cross-talk by taking into account of driving energy (e.g., currents and/or voltages) on other channels and/or the brightness compensation  106 . In the illustrated embodiment, if any of the factors (e.g., tone compensation  104 ) changes, the CLUT  110  is recomputed. For example, in some embodiments, the CLUT  110  may include a 17×17×17 LUT that is entirely recalculated when the tone compensation  104  and/or the linear accessibility filters  114  are changed. 
       FIG. 13  illustrates an embodiment of a display pipeline  174  that is similar to the display pipeline  170  except that the display pipeline  174  utilizes the white point compensation transform block  102  to perform tone compensation and utilizes the post-CLUT transform block  120  to process linear accessibility filters  114 . By applying tone compensation  104  and linear accessibility filters  114  after utilizing the CLUT  110 , calculation for different sets of LUT entries may be performed at boot with no recalculation needed when the linear accessibility filters  114 , non-linear accessibility features  116 , and/or the tone compensation  104  are changed. However, tone compensation  104  and/or linear accessibility filters  114  applied after primary calibration  108  may induce differences from panel-to-panel. 
       FIG. 14  illustrates an embodiment of a display pipeline  176  that applies color oversaturation correction  172  mutually exclusive to tone compensation  104 . In other words, the primary calibration  108  for the display  12  may be applied in a first portion  178  (e.g., in the CLUT  110 ) of the display pipeline  176  when tone compensation  104  and/or linear accessibility filters  114  are not applied to the image data. Alternatively, the primary calibration  108  may be applied in a second portion  180  of the display pipeline when tone compensation  104  and/or linear accessibility filters  114  are applied to the image data after the CLUT  110 . This display pipeline  176  does not utilize repopulation of the CLUT  110  after changing the tone compensation  104  and/or the linear accessibility filters  114 . Furthermore, since the CLUT  110  takes into account panel-to-panel variation via the primary calibration  108 , variability from panel to panel may be reduced or eliminated. However, when tone compensation  104  and/or the linear accessibility filters  114  are applied, the resulting displayed image may suffer from saturated colors do to the color oversaturation correction  172  not being applied to these features. 
     Although the foregoing embodiments include using a three-dimensional CLUT, some embodiments may utilize a multi-dimensional CLUT that includes a different number of dimensions than three. For example, when a pixel includes a different number of subpixels (e.g., 4 subpixels RGBW), the CLUT may have a number of dimensions that match the number of subpixels in a pixel. 
     Furthermore, each of the display pipelines  100 ,  170 ,  174 , and  176  include a CLUT  110  in a static location. However, in some embodiments, the CLUT  110  may be located at a different location in a display pipeline. For example, instead of using software compensation of cross-talk as previously discussed, the CLUT  110  may be moved closer to an end of the display pipeline to reduce cross-talk without convoluting the LUT data to deal with cross-talk. 
     The specific embodiments described above have been shown by way of example, and it should be understood that these embodiments may be susceptible to various modifications and alternative forms. It should be further understood that the claims are not intended to be limited to the particular forms disclosed, but rather to cover all modifications, equivalents, and alternatives falling within the spirit and scope of this disclosure. 
     The techniques presented and claimed herein are referenced and applied to material objects and concrete examples of a practical nature that demonstrably improve the present technical field and, as such, are not abstract, intangible or purely theoretical. Further, if any claims appended to the end of this specification contain one or more elements designated as “means for [perform]ing [a function] . . . ” or “step for [perform]ing [a function] . . . ”, it is intended that such elements are to be interpreted under 35 U.S.C. 112(f). However, for any claims containing elements designated in any other manner, it is intended that such elements are not to be interpreted under 35 U.S.C. 112(f).

Metadata:
Filing Date: 20170908
Publication Date: 20190416
Grant Date: 20190416
Priority Date: 20170908
Inventors: HERRANZ, ADRIA FORES
CÔTÉ, Guy
SPENCE, ARTHUR L.
CHAPPALLI, MAHESH B.
HOLLAND, PETER F.
THOMPSON, ROSS
Assignee: APPLE INC
CPC Classifications: [{"code": "G09G2320/0242", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G5/06", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0666", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/029", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0242", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0233", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3607", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G3/2003", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2320/0693", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0242", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0666", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0233", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/029", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/2003", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G3/3607", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G5/06", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G5/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2320/0693", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0242", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G5/06", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G5/02", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G3/2003", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 62846261