PATENT DOCUMENT

Publication Number: US-9870739-B2
Application Number: US-201514918402-A
Country: US
Kind Code: B2

Title: Display with backlight and temperature color compensation

Abstract:
An electronic device may have a display such as a liquid crystal display. The display may have an array of pixels that display images to a user. Backlight structures may provide the array of pixels with backlight illumination at a backlight illumination level. The backlight structures may have a light source with an array of light-emitting diodes and photoluminescent material that is pumped by pump light from the light-emitting diodes. The backlight illumination may experience color variations as a function of the backlight illumination level. Circuitry in the electronic device may be used to implement a backlight level color compensator. The backlight level color compensator may apply color correction factors to the image data of the displayed images to compensate for variations in color of the image data due to variations in backlight illumination level and operating temperature.

Claims:
What is claimed is: 
     
       1. An electronic device, comprising:
 a display having an array of pixels; 
 backlight structures that supply backlight illumination for the array of pixels at a backlight illumination level; 
 control circuitry that generates image frames that are displayed on the array of pixels of the display; and 
 a color compensator that receives the backlight illumination level and operating temperature data for the backlight structures and that compensates the image frames for color deviations in the backlight illumination that depend on the backlight illumination level by applying respective correction factors to a plurality of color data values in the image data that are based on both the received backlight illumination level and the received operating temperature data. 
 
     
     
       2. The electronic device defined in  claim 1  wherein the display operates at an operating temperature, the electronic device further comprising:
 a temperature sensor that measures the operating temperature, wherein the color compensator uses the measured operating temperature from the temperature sensor to compensate the image frames for the color deviations. 
 
     
     
       3. The electronic device defined in  claim 2  wherein the backlight structures include a light source having light-emitting diodes that produce pump light and photoluminescent material that is pumped by the pump light. 
     
     
       4. The electronic device defined in  claim 3  wherein the light-emitting diodes produce blue light and wherein the photoluminescent material emits red and green light in response to pumping by the blue light. 
     
     
       5. The electronic device defined in  claim 4  wherein the photoluminescent material includes phosphorescent material. 
     
     
       6. The electronic device defined in  claim 5  wherein the phosphorescent material includes red phosphors that emit red light when pumped by the blue light and includes green phosphors that emit green light when pumped by the blue light and wherein the backlight illumination includes the red light, the green light, and a portion of the blue light produced by the light-emitting diodes. 
     
     
       7. The electronic device defined in  claim 6  wherein the color compensator applies the color correction factors to pixel data values in the images frames. 
     
     
       8. The electronic device defined in  claim 7  further comprising:
 look-up table circuitry that stores the color correction factors. 
 
     
     
       9. The electronic device defined in  claim 8  wherein the color correction factors includes red color correction factors for applying to red pixel data values in the pixel data values, green color correction factors for applying to green pixel data values in the pixel data values, and blue color correction factors for applying to blue pixel data values in the pixel data values and wherein the color compensator obtains the red, green, and blue color correction factors from the look-up table circuitry based on the backlight illumination level and the operating temperature. 
     
     
       10. The electronic device defined in  claim 9  wherein the array of pixels comprises liquid crystal display pixels. 
     
     
       11. The electronic device defined in  claim 10  wherein the backlight structures include a light guide layer and wherein the light source emits the red light, the green light, and the portion of the blue light produced by the light-emitting diodes into an edge of the light guide layer. 
     
     
       12. The electronic device defined in  claim 10  wherein the light-emitting diodes are arranged in a two-dimensional array that illuminates the array of pixels. 
     
     
       13. An electronic device that uses image data to display images for a user, comprising:
 an array of liquid crystal display pixels into which the image data is loaded to display the images; 
 a backlight that produces backlight illumination for the array of liquid crystal display pixels at a backlight illumination level, wherein the backlight illumination is characterized by color variations due to changes in the backlight illumination level; and 
 circuitry that receives operating temperature data associated with the electronic device, that receives the backlight illumination level, and that implements a backlight level color compensator that compensates the image data for the color variations by applying respective correction factors to a plurality of color data values in the image data, wherein the correction factors are based on both the operating temperature data associated with the electronic device and the backlight illumination level. 
 
     
     
       14. The electronic device defined in  claim 13  further comprising look-up table circuitry, wherein the backlight level color compensator obtains the color correction factors from the look-up table circuitry. 
     
     
       15. The electronic device defined in  claim 14  wherein the backlight level color compensator obtains the color correction factors from the look-up table circuitry based on the backlight illumination level. 
     
     
       16. The electronic device defined in  claim 15  further comprising a temperature sensor that measures a current operating temperature for the array of liquid crystal display pixels, wherein the backlight level color compensator obtains the color correction factors from the look-up table circuitry based on the current operating temperature. 
     
     
       17. An electronic device that displays image frames, comprising:
 an array of liquid crystal display pixels that displays the image frames; 
 backlight structures that produce backlight illumination for the array of liquid crystal display pixels at a backlight illumination level, wherein the backlight structures include a light source having an array of blue light-emitting diodes with red and green phosphors; and 
 circuitry that implements a backlight level color compensator that receives operating temperature data for the electronic device and that corrects the image frames for color variations due to changes in the backlight illumination level by adjusting a plurality of color data values in the image frames based on respective predetermined correction factors associated with both the operating temperature and the backlight illumination level. 
 
     
     
       18. The electronic device defined in  claim 17  further comprising a temperature sensor that provides the operating temperature data, wherein the backlight level color compensator corrects the image frames for color variations due to changes in the operating temperature data. 
     
     
       19. The electronic device defined in  claim 18  further comprising look-up table circuitry that stores the predetermined color correction factors that the backlight level color compensator applies to the plurality of color data values in the image frames to correct the image frames for the color variations due to the changes in the backlight illumination level and the changes in the operating temperature data.

Description:
This application claims the benefit of provisional patent application No. 62/160,763 filed on May 13, 2015, which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     This relates generally to electronic devices, and more particularly, to electronic devices with displays. 
     Electronic devices often include displays. For example, cellular telephones, tablet computers, and laptop computers often include displays for presenting information to a user. 
     Liquid crystal displays contain a layer of liquid crystal material sandwiched between upper and lower polarizers. Pixels in a liquid crystal display contain thin-film transistors and electrodes for applying electric fields to the liquid crystal material. The strength of the electric field in a pixel controls the polarization state of the liquid crystal material and thereby adjusts the brightness of the pixel. A liquid crystal display may have an array of color filter elements to provide the display with the ability to display color images. 
     The pixels in the liquid crystal display can be illuminated using a backlight unit. The backlight unit may include a light guide layer. The light guide layer may be formed from a transparent material such as a transparent polymer. An array of light-emitting diodes may emit light into the edge of the light guide layer. The light that is emitted into the edge of the light guide layer may be distributed throughout the light guide layer in accordance with the principle of total internal reflection. 
     It may be desirable to use light-emitting diode light sources with spectrally narrow bandwidths to enhance the color gamut of a display. One way in which to produce spectrally narrow backlight is to use backlight light sources that are based on blue light-emitting diodes pumping red and green phosphors. This type of approach produces narrow-bandwidth blue, green, and red light, but may introduce undesired color shifts as the level of the backlight is adjusted. Temperature variations may also affect display color accuracy. 
     It would therefore be desirable to be able to provide improved ways for ensuring that color images are accurately presented on a display in an electronic device. 
     SUMMARY 
     An electronic device may have a display such as a liquid crystal display. The display may have an array of pixels that display images to a user. Backlight structures may provide the array of pixels with backlight illumination at a backlight illumination level. 
     The backlight structures may have a light source with an array of light-emitting diodes and photoluminescent material that is pumped by pump light from the light-emitting diodes. The backlight illumination and therefore the display may experience color variations due to changes in the backlight illumination level. The display may also exhibit color variations due to changes in operating temperature. 
     Circuitry in the electronic device may be used to implement a backlight level color compensator. The backlight level color compensator may apply color correction factors to the image data of the displayed images to compensate for variations in color of the image data due to variations in backlight illumination level. The color compensator may also compensate for display color variations due to changes in operating temperature. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device such as a laptop computer with a display in accordance with an embodiment. 
         FIG. 2  is a perspective view of an illustrative electronic device such as a handheld electronic device with a display in accordance with an embodiment. 
         FIG. 3  is a perspective view of an illustrative electronic device such as a tablet computer with a display in accordance with an embodiment. 
         FIG. 4  is a perspective view of an illustrative electronic device such as a computer display with display structures in accordance with an embodiment. 
         FIG. 5  is a cross-sectional side view of an illustrative display in accordance with an embodiment. 
         FIG. 6  is a side view of an illustrative light-emitting diode with colored phosphors in accordance with an embodiment. 
         FIG. 7  is a diagram of an illustrative backlight unit that has a two-dimensional array of light-emitting diodes in accordance with an embodiment. 
         FIG. 8  is a graph showing how backlight of different wavelengths may exhibit spectra with intensities that vary differently as a function of total backlight intensity in accordance with an embodiment. 
         FIGS. 9 and 10  show illustrative variations in the color coordinates of backlight illumination that may be experienced by a backlight due to changes in backlight intensity in accordance with an embodiment. 
         FIG. 11  is a diagram showing look-up table entries of the type that may be used to calibrate a display with color variations of the type shown in  FIGS. 8 and 9  and temperature-based color variations in accordance with an embodiment. 
         FIG. 12  is a diagram of illustrative circuitry in an electronic device with color compensation capabilities in accordance with an embodiment. 
         FIG. 13  is a flow chart of illustrative steps involved in operating an electronic device having circuitry for compensating for color variations due to changes in backlight intensity and operating temperature in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices may include displays. The displays may be used to display images for a user. Illustrative electronic devices that may be provided with displays are shown in  FIGS. 1, 2, 3, and 4 . 
       FIG. 1  shows how electronic device  10  may have the shape of a laptop computer having upper housing  12 A and lower housing  12 B with components such as keyboard  16  and touchpad  18 . Device  10  may have hinge structures  20  that allow upper housing  12 A to rotate in directions  22  about rotational axis  24  relative to lower housing  12 B. Display  14  may be mounted in upper housing  12 A. Upper housing  12 A, which may sometimes referred to as a display housing or lid, may be placed in a closed position by rotating upper housing  12 A towards lower housing  12 B about rotational axis  24 . 
       FIG. 2  shows how electronic device  10  may be a handheld device such as a cellular telephone, music player, gaming device, navigation unit, or other compact device. In this type of configuration for device  10 , housing  12  may have opposing front and rear surfaces. Display  14  may be mounted on a front face of housing  12 . Display  14  may, if desired, have openings for components such as button  26 . Openings may also be formed in display  14  to accommodate a speaker port (see, e.g., speaker port  28  of  FIG. 2 ). 
       FIG. 3  shows how electronic device  10  may be a tablet computer. In electronic device  10  of  FIG. 3 , housing  12  may have opposing planar front and rear surfaces. Display  14  may be mounted on the front surface of housing  12 . As shown in  FIG. 3 , display  14  may have an opening to accommodate button  26  (as an example). 
       FIG. 4  shows how electronic device  10  may be a display such as a display with an embedded computer, a display without an embedded computer, or other suitable equipment for displaying images. With this type of arrangement, housing  12  for device  10  may be mounted on a support structure such as stand  30  or stand  30  may be omitted (e.g., to mount device  10  on a wall). Display  14  may be mounted on a front face of housing  12 . 
     The illustrative configurations for device  10  that are shown in  FIGS. 1, 2, 3, and 4  are merely illustrative. In general, electronic device  10  may be a laptop computer, a tablet computer, a cellular telephone, a media player, or other handheld or portable electronic device, a smaller device such as a wrist-watch device, a pendant device, a headphone or earpiece device, or other wearable or miniature device, a computer monitor or other display containing an embedded computer or other processor, a computer monitor or other display that does not contain an embedded computer or other processor, a gaming device, a navigation device, an embedded system such as a system in which electronic equipment with a display is mounted in a kiosk or automobile, equipment that implements the functionality of two or more of these devices, or other electronic equipment. 
     Housing  12  of device  10 , which is sometimes referred to as a case, may be formed of materials such as plastic, glass, ceramics, carbon-fiber composites and other fiber-based composites, metal (e.g., machined aluminum, stainless steel, or other metals), other materials, or a combination of these materials. Device  10  may be formed using a unibody construction in which most or all of housing  12  is formed from a single structural element (e.g., a piece of machined metal or a piece of molded plastic) or may be formed from multiple housing structures (e.g., outer housing structures that have been mounted to internal frame elements or other internal housing structures). 
     Display  14  may be a touch sensitive display that includes a touch sensor or may be insensitive to touch. Touch sensors for display  14  may be formed from an array of capacitive touch sensor electrodes, a resistive touch array, touch sensor structures based on acoustic touch, optical touch, or force-based touch technologies, or other suitable touch sensor components. 
     Display  14  for device  10  may include pixels formed from liquid crystal display (LCD) components or other suitable components (e.g., electrophoretic display pixels, electrowetting display pixels, etc.). A display cover layer may cover the surface of display  14  or a display layer such as a color filter layer or other portion of a display may be used as the outermost (or nearly outermost) layer in display  14 . The outermost display layer may be formed from a transparent glass sheet, a clear plastic layer, or other transparent member. 
     A cross-sectional side view of an illustrative configuration for display  14  of device  10  (e.g., for display  14  of the devices of  FIG. 1 ,  FIG. 2 ,  FIG. 3 ,  FIG. 4  or other suitable electronic devices) is shown in  FIG. 5 . As shown in  FIG. 5 , display  14  may include backlight structures such as backlight unit  42  for producing backlight  44 . During operation, backlight illumination  44  travels outwards (vertically upwards in dimension Z in the orientation of  FIG. 5 ) and passes through display pixel structures in display layers  46 . This illuminates any images that are being produced by the pixels for viewing by a user. For example, backlight  44  may illuminate images on display layers  46  that are being viewed by viewer  48  in direction  50 . 
     Display layers  46  may be mounted in chassis structures such as a plastic chassis structure and/or a metal chassis structure to form a display module for mounting in housing  12  or display layers  46  may be mounted directly in housing  12  (e.g., by stacking display layers  46  into a recessed portion in housing  12 ). Display layers  46  may form a liquid crystal display or may be used in forming displays of other types. 
     Display layers  46  may include a liquid crystal layer such a liquid crystal layer  52 . Liquid crystal layer  52  may be sandwiched between display layers such as display layers  58  and  56 . Layers  56  and  58  may be interposed between lower polarizer layer  60  and upper polarizer layer  54 . 
     Layers  58  and  56  may be formed from transparent substrate layers such as clear layers of glass or plastic. Layers  58  and  56  may be layers such as a thin-film transistor layer and/or a color filter layer. Conductive traces, color filter elements, transistors, and other circuits and structures may be formed on the substrates of layers  58  and  56  (e.g., to form a thin-film transistor layer and/or a color filter layer). Touch sensor electrodes may also be incorporated into layers such as layers  58  and  56  and/or touch sensor electrodes may be formed on other substrates. 
     With one illustrative configuration, layer  58  may be a thin-film transistor layer that includes an array of pixel circuits based on thin-film transistors and associated electrodes (pixel electrodes) for applying electric fields to liquid crystal layer  52  and thereby displaying images on display  14 . Layer  56  may be a color filter layer that includes an array of color filter elements for providing display  14  with the ability to display color images. If desired, layer  58  may be a color filter layer and layer  56  may be a thin-film transistor layer. Configurations in which color filter elements are combined with thin-film transistor structures on a common substrate layer in the upper or lower portion of display  14  may also be used. 
     During operation of display  14  in device  10 , control circuitry (e.g., one or more integrated circuits on a printed circuit) may be used to generate information to be displayed on display  14  (e.g., display data). The information to be displayed may be conveyed to a display driver integrated circuit such as circuit  62 A or  62 B using a signal path such as a signal path formed from conductive metal traces in a rigid or flexible printed circuit such as printed circuit  64  (as an example). 
     Backlight structures  42  may include a light guide layer such as light guide layer  78  (sometimes referred to as a light guide). Light guide layer  78  may be formed from a transparent material such as clear glass or plastic (e.g., molded plastic such as polymethyl methacrylate or other clear thermoplastic that forms a light guide plate, a thin flexible plastic film such as a sheet of polycarbonate or other thin polymer film, etc.). During operation of backlight structures  42 , a light source such as light source  72  may generate light  74 . Light source  72  may be, for example, an array of light-emitting diodes. 
     Light  74  from light source  72  may be coupled into edge surface  76  of light guide plate  78  and may be distributed in dimensions X and Y throughout light guide layer  78  due to the principal of total internal reflection. Light guide layer  78  may include light-scattering features such as pits or bumps or other light-scattering structures. The light-scattering features may be located on an upper surface and/or on an opposing lower surface of light guide layer  78 . Light source  72  may be located at the left of light guide layer  78  as shown in  FIG. 5  or may be located along the right edge of layer  78  and/or other edges of layer  78 . 
     Light  74  that scatters upwards in direction Z from light guide layer  78  may serve as backlight  44  for display  14 . Light  74  that scatters downwards may be reflected back in the upwards direction by reflector  80 . Reflector  80  may be formed from a reflective material such as a layer of plastic covered with a dielectric minor thin-film coating. Reflective tape (e.g., white plastic tape or tape formed from other reflective materials) may be incorporated into the backlight reflector for display  14 . For example, backlight structures  42  may include a strip of tape that runs along the edge of reflector  80  that is adjacent to light-emitting diodes  72 . 
     Backlight structures  42  may include optical films  70 . Optical films  70  may include diffuser layers for helping to homogenize backlight  44  and thereby reduce hotspots, compensation films for enhancing off-axis viewing, and light collimating films such as turning films (prism films, brightness enhancement films, etc.) for collimating backlight  44 . Optical films  70  may overlap the other structures in backlight unit  42  such as light guide layer  78  and reflector  80 . For example, if light guide layer  78  has a rectangular footprint in the X-Y plane of  FIG. 5 , optical films  70  and reflector  80  may have a matching rectangular footprint. If desired, films such as compensation films may be incorporated into other layers of display  14  (e.g., polarizer layers). 
     To enhance the color gamut of display  14 , it may be desirable to form light source  72  from light-emitting diode structures characterized by narrow spectral bandwidths. As an example, light source  72  may be based on light-emitting diodes of the type shown in  FIG. 6 . As shown in  FIG. 6 , light source (light-emitting diode)  72  may include light-emitting diode die  72 A and photoluminescent material  72 B. Die  72 A may emit pump light. Photoluminescent material  72 B may include photoluminescent elements (fluorescent material, phosphorescent material, quantum dots, etc.) that emit light of desired colors in response to illumination (pumping) from the pump light emitted by die  72 A. 
     The pump light from die  72 A may be, for example, blue light (i.e., die  72 A may be a blue light-emitting diode). Some of the blue pump light may be converted to red and green backlight illumination (or backlight of other colors) by photoluminescent material  72 B. Some of the blue pump light from die  72 A may remain as unconverted blue light. This unconverted portion of the blue light from die  72 A and the red and green emissions from photoluminescent material  72 B may form red, green, and blue components of light  74  for use as backlight illumination  44 . 
     If desired, photoluminescent material  72 B may be a phosphorescent coating containing phosphors such as red phosphors  100  (e.g., red phosphors such as K 2 SiF 6 ) and green phosphors  102  (e.g., β-SiAION). If desired, the pump light produced by die  72 A may have a color other than blue and/or the photoluminescent elements of material  72 B may emit light of different colors when pumped (e.g., colors other than red and green). The use of a blue light-emitting diode as pumping diode  72 A and red phosphors  100  and green phosphors  102  in photoluminescent coating  72 B of  FIG. 6  is merely illustrative. Other types of narrowband light source may be used to produce light  74  for use as backlight illumination  44  for display  14  if desired. 
     The light  74  that is produced by light source  72  may be emitted into edge  76  of light guide layer  78  as shown in  FIG. 5 . Alternatively, display  14  may be backlit using a two-dimensional array of light-emitting diodes  72 . The two-dimensional array of light-emitting diodes may be placed behind (under) display layers  46 , as shown in the illustrative side view of display  14  of  FIG. 7 . With this type of arrangement, the light output of each of the light-emitting diodes in the two-dimensional array may be individually controlled to implement a local dimming scheme for display  14 . 
     During operation of device  10 , it may be desirable to vary the total intensity of backlight  44 . For example, it may be desirable to decrease the intensity of backlight  44  when using device  10  in dim lighting conditions to conserve power and it may be desirable to increase the intensity of backlight  44  to help ensure that display  14  is visible when using device  10  in bright lighting conditions. Pulse width modulation and DC current adjustment schemes may be used in controlling the output of backlight structures  42 . 
     Ideally, the color of light  44  would not vary as a function of the output level of backlight structures  42 . In practice, color shifts in light  44  may arise when adjusting backlight output levels in backlights formed from light sources such as light source  72  of  FIG. 6 . 
     The risk of color shifts with changes in backlight level is illustrated in the graph of  FIG. 8 , in which the intensity I of light  74  has been plotted as a function of wavelength λ for illustrative high and low output settings. 
     When operated in its high setting (e.g., a maximum brightness setting in which the output from light source  72  and therefore backlight structures  42  has been maximized), backlight structures  42  may produce blue light B that is characterized by spectrum  108 , green light G that is characterized by spectrum  106 , and red light R that is characterized by spectrum  104 . 
     When operated in its low setting, the amount of light produced at each color may be reduced unevenly. As shown in  FIG. 8 , for example, the amount of blue light B and green light G that is produced may decrease significantly when the total output of backlight structures  42  is reduced, as illustrated by reduced spectrum  108 ′ (for blue light) and reduced spectrum  106 ′ (for green light). Red phosphors  100  may be particularly efficient at low light levels. As a result, backlight structures  42  may produce relatively more red light at low output settings than green and blue light (i.e., spectrum  104 ′ for red light R may be larger in magnitude than blue spectrum  108 ′ and green spectrum  106 ′ when operating at the low output setting). The amount of light produced at green and blue wavelengths may also vary unevenly with respect to each other. These changes in the behavior of backlight structures  42  can lead to undesired variations in the color of backlight illumination  44  as the magnitude of the total output intensity of backlight structures  42  (i.e., the backlight illumination level associated with light  44 ) is adjusted. 
     The graphs of  FIGS. 9 and 10  illustrate how the color coordinates for light  44  may vary as a function of changes in the backlight illumination level of backlight illumination  44  produced by backlight structures  42 . In particular, the graphs of  FIGS. 9 and 10  show how respective color coordinates u′ and v′ in the 1976 CEE Lu′v′ color space may increase with decreasing backlight brightness. This variation in the color of backlight illumination  44  represents a potential source of color error when displaying color images on display  14 . 
     During calibration operations, display  14  can be tested using color measurement equipment. The color measurement equipment may gather color measurements in red-green-blue (RGB) format or other suitable color measurement formats. Display  14  may, for example, be directed to display test images of various colors at various different backlight output levels while RGB data is gathered for one or more portions of the display. Operating temperature may influence the color of display  14  (e.g., due to temperature-induced changes in the birefringence of liquid crystal layer  52 ) so test may be performed at a variety of different operating temperatures. 
     By measuring deviations in the color of display  14  from a desired nominal white point under different operating conditions, calibration data such as red, green, and blue correction factors (weighting factors) or other suitable calibration data may be obtained. This information may then be stored in look-up table circuitry. During operation, the calibration data from the look-up table circuitry may be applied to the image data being provided to the pixel array of display layers  46 , thereby adjusting the color of the image data for display  14  sufficiently to compensate for any deviations in the desired color of backlight illumination  44  at different output levels, deviations in the desired color of images on display  14  due to changes in the operating temperature of display  14 , etc. 
     With one suitable arrangement, the color measurements made during testing may include color measurements at a maximum backlight illumination level and at minimum backlight illumination level and if desired, multiple measurements of this type may be made over a range of temperatures. Interpolation techniques may then be used to produce red, green, and blue correction factors over intermediate values of backlight intensity and, if desired, intermediate temperatures. With another suitable arrangement, color measurements are made over numerous different backlight output levels and temperatures, thereby eliminating or minimizing reliance on interpolation. Each individual display  14  may be calibrated in this way and provided with corresponding individual calibration data or batches of similar displays  14  may be calibrated using shared calibration data (e.g., calibration data gathered by making measurements on a single representative display for a batch of displays or on multiple representative displays for the batch). 
       FIG. 11  shows how the look-up table data for device  10  may include correction factors to apply to red data (see, e.g., red correction factors RCF 1  . . . RCF 100 ), green data (see, e.g., green correction factors GCF 1  . . . GCF 100 ), and blue data (see, e.g., blue correction factors BCF 1  . . . BCF 100 ). When operating at a backlight intensity of I 1 , display  14  can be calibrated to compensate for color variations by applying red correction factor RCF 1  to the data value of each red pixel in the pixel array of display  14 , by applying green correction factor GCF 1  to the data value of each green pixel in the pixel array of display  14 , and by applying blue correction factor BCF 1  to the data value of each blue pixel in the pixel array of display  14 . If the output intensity of backlight structures  42  is set to intensity level  13  (as another example), the circuitry of device  10  can correct the image data for display  14  by applying red correction factor RCF 3  to the data value of each red pixel, can apply the green correction factor GCF 3  to the data value of each green pixel, and can apply the blue correction factor BCF to the data value of each blue pixel. A look-up table of color correction factors may be generated for each of multiple operating temperatures (T 1 , T 2 , . . . TN). If desired, real time interpolation techniques may be used to produce correction factors for intermediate temperatures and/or backlight brightness settings. More brightness levels, fewer brightness levels, more operating temperatures, or fewer operating temperatures may be included. The color correction factors of  FIG. 11  are merely illustrative. 
     Illustrative circuitry of the type that may be used by device  10  to compensate display  14  for color deviations due to backlight brightness variations and temperature variations is shown in  FIG. 12 . As shown in  FIG. 12 , device  10  may have control circuitry  110 . Control circuitry  110  may include storage and processing circuitry for supporting the operation of device  10 . The storage and processing circuitry may include storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random-access-memory), etc. Processing circuitry in control circuitry  110  may be used to control the operation of device  10 . The processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio chips, application specific integrated circuits, etc. 
     Control circuitry  110  may include a graphics processing unit such as graphics processing unit  116 . Graphics processing unit  116  may receive image frames for frame buffer  120  (e.g., frame buffer  120 A) from content generator  114 . Content generator  114  may be an application running on control circuitry  110  such as a game, a media playback application, an application that presents text to a user, an operating system function, or other code running on control circuitry  110  that generates image data to be displayed on display  14 . While displaying content on display  14 , control circuitry  110  may adjust the output level of backlight unit  42 , thereby controlling the amount of backlight  44  that passes through display  14  and the associated brightness level of images being displayed on display  14 . 
     Control circuitry  110  may be coupled to input-output circuitry such as input-output devices  112 . Input-output devices  112  may be used to allow data to be supplied to device  10  and to allow data to be provided from device  10  to external devices. Input-output devices  112  may include buttons, joysticks, scrolling wheels, touch pads, key pads, keyboards, microphones, speakers, tone generators, vibrators, cameras, sensors, light-emitting diodes and other status indicators, data ports, etc. A user can control the operation of device  10  by supplying commands through input-output devices  112  and may receive status information and other output from device  10  using the output resources of input-output devices  112 . Input-output devices  112  may include a temperature sensor such as temperature sensor  140  to gather information on the current operating temperature of display  14 . 
     Control circuitry  110  may be used to run software on device  10  such as operating system code and applications. During operation of device  10 , the software running on control circuitry  110  (e.g., content generator  114 ) may display images on display  14  using pixels  90  of pixel array  92 . Display  14  may include display driver circuitry such as display driver circuitry  122  (see, e.g., circuitry  62 A and  62 B of  FIG. 5 ) that receives image data from graphics processing unit  116 . The display driver circuitry of display  14  may include one or more display driver integrated circuits (e.g., a timing controller integrated circuit or other display driver circuitry such as display driver circuitry  122  of  FIG. 9 ) and gate driver circuitry  124 . Gate driver circuitry  124  may be implemented using thin-film transistor circuitry on a display substrate and/or may be implemented using one or more integrated circuits. Array  92  may have display driver circuitry such as circuitry  124  that is located on the left and right edges of array  92 , on only the left edge or only the right edge of array  92 , or that is located elsewhere in display  14 . 
     Image frames to be displayed on array  92  by the display driver circuitry may be stored in frame buffer  120  (e.g., frame buffer  120 B). Look-up table circuitry  142  such as look-up table  142 A and/or look-up table  142 B may be used to store information for correcting the color of images displayed on display  14  such as the color correction factors of  FIG. 11 . 
     Backlight level color compensator  118  may be implemented using resources in graphics processing unit  116  (see, e.g., backlight level color compensator  118 A) and/or using resources in display driver circuitry of display  14  (see, e.g., backlight level color compensator  118 B). Color compensator  118  may use the temperature-based and backlight-intensity-level-based color correction factors of look-up table circuitry  142  to ensure that color image are accurately displayed on display  14 . 
     Illustrative steps involved in using color compensator  118  to ensure that display  14  displays color images accurately are shown in  FIG. 13 . 
     At step  150 , color compensator  118  may obtain information on the current operating temperature of device  10  and display  14  from temperature sensor  140 . 
     At step  152 , information on the current backlight illumination level of backlight unit  42  may be obtained by color compensator  118  from control circuitry  110  and/or other circuitry in device  10  (e.g., graphics processing unit  116 , display driver circuitry  122 , etc.). 
     At step  154 , color compensator  118  may obtain red, green, and blue color correction factors to use for the current operating temperature and backlight brightness setting of display  14  from look-up table circuitry  142 . 
     At step  156 , color compensator  118  may apply the red, green, and blue color correction factors to the data for a current frame of image data in frame buffer  120 . For example, the red pixel data may be corrected by multiplying the red pixel values by the red correction factor, the green pixel data may be corrected by multiplying the green pixel data by the green correction factor, and the blue pixel data may be corrected by multiplying the blue pixel values by the blue correction factor. If desired, the correction factors may be applied in other ways (e.g., by addition of correction offset values, by applying multiplicative and additive correction factors, etc.). The use of multiplicative color correction factors is merely illustrative. 
     After updating the data values of the array of pixels in the current image frame to compensate for variations in operating temperature and backlight brightness, the corrected image frame may be displayed on array  92  (step  158 ). Processing may then loop back to step  150  so that additional frames may be corrected and displayed, as indicated by line  160 . 
     The foregoing is merely illustrative and various modifications can be made by those skilled in the art without departing from the scope and spirit of the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20151020
Publication Date: 20180116
Grant Date: 20180116
Priority Date: 20150513
Inventors: HUANG YI
YOU CHENHUA
MARCU GABRIEL
QI JUN
ALBRECHT MARC
Assignee: APPLE INC
CPC Classifications: [{"code": "G09G2320/0233", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F2203/60", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3413", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G3/3607", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F2001/133601", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0242", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2360/16", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/041", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133621", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2320/0646", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133603", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F2202/36", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/0073", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G3/3611", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F2203/21", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F2001/133614", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0285", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F2203/21", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133614", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F2202/36", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2360/16", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0242", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133621", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2320/041", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/0073", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2320/041", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133603", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G3/3413", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133603", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G3/3611", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2320/0646", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/0055", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2320/0233", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0646", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3611", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F2202/36", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0285", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133601", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133601", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0285", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/0055", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F2203/60", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F2203/60", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F2203/21", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3413", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133614", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3607", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 57277709