PATENT DOCUMENT

Publication Number: US-10283031-B2
Application Number: US-201514848769-A
Country: US
Kind Code: B2

Title: Electronic device with image processor to reduce color motion blur

Abstract:
An electronic device may generate content that is to be displayed on a display. The display may have an array of pixels each of which includes subpixels of different colors. The content that is to be displayed on the display may include an object such as a black object that is moved across a background. Due to differences in subpixel values in the background for subpixels of different colors, there is a potential for color motion blur to develop along a trailing edge portion of the object as the object is moved across the background. The electronic device may have a blur abatement image processor that processes the content to reduce color motion blur. The blur abatement image processor may identify which pixels are located in the trailing edge and may adjust subpixel values for pixels in the trailing edge.

Claims:
What is claimed is: 
     
       1. An electronic device, comprising:
 a display having an array of pixels each of which has subpixels of different colors; 
 control circuitry that generates content to be displayed on the display, wherein the content includes an object that is being moved across a background; and 
 a blur abatement image processor that processes the content to adjust subpixel values for the subpixels and thereby reduce color motion blur as the content is displayed on the display, wherein the blur abatement image processor adjusts a first subpixel value associated with a first color based on a second subpixel value associated with a second color by temporarily setting the first subpixel value to the second subpixel value, wherein the second subpixel value is lower than the first subpixel value before the first subpixel value is adjusted, wherein the first and second subpixel values are associated with a single given pixel of the array of pixels, and wherein the content processed by the blur abatement image processor comprises frames of color image data. 
 
     
     
       2. The electronic device defined in  claim 1  wherein the blur abatement image processor is configured to process the content to identify a trailing edge of the object. 
     
     
       3. The electronic device defined in  claim 2  wherein the blur abatement image processor is configured to slow the transition speed of subpixels of a given color in the trailing edge by temporarily using a subpixel value for the given color of subpixel that is lower than a final subpixel value for the given color that is associated with the background. 
     
     
       4. The electronic device defined in  claim 3  wherein the given color is red and wherein the blur abatement image processor is configured to slow the transition speed of red subpixels in the trailing edge by temporarily setting the red subpixels to a red subpixel value that is lower than a final red subpixel value associated with the background. 
     
     
       5. The electronic device defined in  claim 4  wherein the subpixels include the red subpixels, green subpixels, and blue subpixels and wherein the blur abatement image processor is configured to temporarily set the red subpixels to a red subpixel value that is equal to a subpixel values associated with the green subpixels in the background. 
     
     
       6. The electronic device defined in  claim 4  wherein the blur abatement image processor is configured to raise the red subpixel value to the final red subpixel value after temporarily setting the red subpixel value to the red subpixel value that is lower than the final red subpixel value. 
     
     
       7. Apparatus, comprising:
 a blur abatement image processor that compares a current color image frame to a previous color image frame to identify a trailing edge of an object being moved across a background and that, in response to detecting the trailing edge of the object being moved across the background, adjusts subpixel values for pixels in the trailing edge to reduce color motion blur by adjusting a first subpixel value associated with a first color based on a second subpixel value associated with a second color by temporarily setting the first subpixel value to the second subpixel value, wherein the first subpixel value is greater than the second subpixel value before it is temporarily set to the second subpixel value, wherein the first and second subpixels are associated with a single given pixel of the pixels; and 
 a display on which color images frames that have been processed by the blur abatement image processor are displayed. 
 
     
     
       8. The apparatus defined in  claim 7  wherein the display has an array of pixels, wherein the pixels each include a red subpixel, a green subpixel, and a blue subpixel, wherein the object is a black object, wherein the background has a background color with a red subpixel value, a green subpixel value, and a blue subpixel value, and wherein the blur abatement image processor is configured to transition the red subpixels in the trailing edge from a first value associated with the black object to the red subpixel value of the background color by temporarily setting the red subpixels in the trailing edge to an red subpixel value that is lower than the red subpixel value of the background color and subsequently setting the red subpixels in the trailing edge to the red subpixel value of the background color. 
     
     
       9. The apparatus defined in  claim 8  wherein red subpixel value that is lower than the red subpixel value of the background color is equal to the green subpixel value of the background color. 
     
     
       10. A method of displaying color content on a display having an array of pixels each having subpixels of different colors, comprising:
 reducing color motion blur in response to detecting that an object is moved across a background on the display by adjusting subpixel values associated with at least some of the subpixels, wherein adjusting the subpixel values comprises:
 adjusting a first value associated with a first subpixel of a first color based on a second value associated with a second subpixel of a second color by setting the first value to the second value, wherein the first value is greater than the second value before it is adjusted, wherein the first and second subpixels are associated with a single given pixel of the array of pixels. 
 
 
     
     
       11. The method defined in  claim 10  further comprising:
 processing the color content to identify a trailing edge of the object. 
 
     
     
       12. The method defined in  claim 11  wherein reducing the color motion blur comprises adjusting subpixel values for subpixels associated with pixels in the trailing edge. 
     
     
       13. The method defined in  claim 12  wherein subpixels of a given one of the different colors have a background subpixel value in the background and wherein adjusting the subpixel values comprises:
 setting subpixels of the given color that are associated with the pixels in the trailing edge to a subpixel value that is lower than the background subpixel value; and 
 after setting the subpixels of the given color that are associated with the pixels in the trailing edge to the subpixel value that is lower than the background subpixel value, setting the subpixels of the given color that are associated with the pixels in the trailing edge to the background subpixel value. 
 
     
     
       14. The method defined in  claim 13  wherein the given color is red and wherein setting the subpixels of the given color that are associated with the pixels in the trailing edge to the subpixel value that is lower than the background subpixel value comprises setting red subpixels that are associated with the pixels in the trailing edge to a red subpixel value that is lower than a red background subpixel value. 
     
     
       15. The method defined in  claim 14  wherein setting the red subpixels to the red subpixel value comprises adjusting the red subpixel value to be equal to a green subpixel value associated with green subpixels in the background. 
     
     
       16. The method defined in  claim 11  wherein reducing the color motion blur comprises slowing the transition speed of red subpixels by temporarily setting the red subpixels of pixels in the trailing edge to a red subpixel value that is less than a final red subpixel value associated with the background. 
     
     
       17. The method defined in  claim 16  further comprising:
 raising the red subpixel values from the red subpixel value that is less than the final red subpixel value to the final red subpixel value so that the trailing edge has a color matching the background. 
 
     
     
       18. The method defined in  claim 11  wherein processing the color content comprises comparing pixels in a current frame of the color content to pixels in a previous frame of the color content to identify the trailing edge. 
     
     
       19. The method defined in  claim 11  wherein the subpixels include red subpixels, green subpixels, and blue subpixels, wherein the object is a black object, wherein the background has a background color with a red subpixel value, a green subpixel value, and a blue subpixel value, and wherein reducing the color motion blur comprises:
 transitioning the red subpixels in the trailing edge from a first value associated with the black object to the red subpixel value of the background color by temporarily setting the red subpixels in the trailing edge to an red subpixel value that is lower than the red subpixel value of the background color and subsequently setting the red subpixel value to the red subpixel value of the background color. 
 
     
     
       20. The method defined in  claim 19  wherein red subpixel value that is lower than the red subpixel value of the background color is equal to the green subpixel value of the background color.

Description:
This application claims the benefit of provisional patent application No. 62/142,202 filed on Apr. 2, 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 and portable computers often include displays for presenting information to a user. 
     Liquid crystal displays contain a layer of liquid crystal material. 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. 
     The speed with which liquid crystal pixels switch can vary as a function of applied voltage. As a result, the amount of time required to switch a black pixel to a gray level will be longer than the amount of time required to switch a black pixel to a white level. In some situations, it may be desirable to move a black object on a screen with a colored background. In this type of scenario, subpixels of different colors may have different target pixel values and may therefore switch at different speeds. This may result in unpleasant color motion blur effects as the black object is moved. 
     It would therefore be desirable to be able to provide improved displays for electronic devices such as displays with reduced color motion blur. 
     SUMMARY 
     An electronic device may generate content that is to be displayed on a display. The display may have an array of pixels each of which includes subpixels of different colors. The content that is to be displayed on the display may include an object such as a black object that is moved across a background. Due to differences in subpixel values in the background for subpixels of different colors, there is a potential for color motion blur to develop along a trailing edge of the object as the object is moved across the background. The electronic device may have a blur abatement image processor that processes the content to reduce color motion blur. The blur abatement image processor may identify which pixels are located in the trailing edge and may adjust subpixel values in the trailing edge. 
     The subpixels may include red subpixels, green subpixels, and blue subpixels. The values of the subpixels of different colors may be different in the background. For example, the background may have a red subpixel value that is greater than green and blue subpixel values. To slow the red subpixel transition speed relative to the green and blue subpixel transmission speeds, the blur abatement image processor may momentarily adjust the red subpixel value for pixels in the trailing edge by setting the red subpixel value to a lower value such as that of the green subpixel in the background. The blur abatement image processor may then raise the temporarily lowered red subpixel value to its desired final target value in the background. 
    
    
     
       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 top view of a portion of an array of pixels in a display in accordance with an embodiment. 
         FIG. 7  is a diagram showing how motion of an object against a background has the potential to discolor pixels along the edges of the object and thereby create color motion blur effects. 
         FIG. 8  is a graph showing how red, green, and blue subpixels in a display may have different target pixel values during color transitions such as those associated with movement of the object of  FIG. 7  and therefore have the potential to switch at different speeds in accordance with an embodiment. 
         FIG. 9  is a diagram showing how the trailing edge of a moving object may be temporarily provided with modified subpixel values to reduce color motion blur effects in accordance with an embodiment. 
         FIG. 10  is a diagram showing how frames of image data may be compared to identify the pixels along the trailing edge of a moving object in accordance with an embodiment. 
         FIG. 11  is a diagram of illustrative circuitry of the type that may be used to modify subpixel values to reduce color motion blur effects in accordance with an embodiment. 
         FIG. 12  is a flow chart of illustrative steps involved in analyzing content with moving objects and in modifying certain pixels in the content to reduce color motion blur effects in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices may include displays. The displays may be used to display images to 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 computer display or other display or may be a computer that has been integrated into a computer display. With this type of arrangement, housing  12  for device  10  may be mounted on a support structure such as stand  27  or stand  27  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 computer monitor containing an embedded 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 display that does not contain an embedded computer, 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. 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  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 display 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 plate such as light guide plate  78 . Light guide plate  78  may be formed from a transparent material such as clear glass or plastic. 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 plate  78  due to the principal of total internal reflection. Light guide plate  78  may include light-scattering features such as pits or bumps. The light-scattering features may be located on an upper surface and/or on an opposing lower surface of light guide plate  78 . Light source  72  may be located at the left of light guide plate  78  as shown in  FIG. 5  or may be located along the right edge of plate  78  and/or other edges of plate  78 . 
     Light  74  that scatters upwards in direction Z from light guide plate  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 mirror thin-film coating. 
     To enhance backlight performance for backlight structures  42 , 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 brightness enhancement films (also sometimes referred to as turning films) for collimating backlight  44 . Optical films  70  may overlap the other structures in backlight unit  42  such as light guide plate  78  and reflector  80 . For example, if light guide plate  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). 
     As shown in  FIG. 6 , display  14  may include an array of pixels  90  such as pixel array  92 . Pixel array  92  may be controlled using control signals produced by display driver circuitry. Display driver circuitry may be implemented using one or more integrated circuits (ICs) and/or thin-film transistors or other circuitry. 
     During operation of device  10 , control circuitry in device  10  such as memory circuits, microprocessors, and other storage and processing circuitry may provide data to the display driver circuitry. The display driver circuitry may convert the data into signals for controlling pixels  90  of pixel array  92 . 
     Pixel array  92  may contain rows and columns of pixels  90 . The circuitry of pixel array  92  (i.e., the rows and columns of pixel circuits for pixels  90 ) may be controlled using signals such as data line signals on data lines D and gate line signals on gate lines G. Data lines D and gate lines G are orthogonal. For example, data lines D may extend vertically and gate lines G may extend horizontally (i.e., perpendicular to data lines D). 
     Pixels  90  in pixel array  92  may contain thin-film transistor circuitry (e.g., polysilicon transistor circuitry, amorphous silicon transistor circuitry, semiconducting-oxide transistor circuitry such as InGaZnO transistor circuitry, other silicon or semiconducting-oxide transistor circuitry, etc.) and associated structures for producing electric fields across liquid crystal layer  52  in display  14 . Each display pixel may have one or more thin-film transistors. For example, each display pixel may have a respective thin-film transistor such as thin-film transistor  94  to control the application of electric fields to a respective pixel-sized portion  52 ′ of liquid crystal layer  52 . 
     The thin-film transistor structures that are used in forming pixels  90  may be located on a thin-film transistor substrate such as a layer of glass. The thin-film transistor substrate and the structures of display pixels  90  that are formed on the surface of the thin-film transistor substrate collectively form thin-film transistor layer  58  ( FIG. 5 ). 
     Gate driver circuitry may be used to generate gate signals on gate lines G. The gate driver circuitry may be formed from thin-film transistors on the thin-film transistor layer or may be implemented in separate integrated circuits. The data line signals on data lines D in pixel array  92  carry analog image data (e.g., voltages with magnitudes representing pixel brightness levels). During the process of displaying images on display  14 , a display driver integrated circuit or other circuitry may receive digital data from control circuitry and may produce corresponding analog data signals. The analog data signals may be demultiplexed and provided to data lines D. 
     The data line signals on data lines D are distributed to the columns of display pixels  90  in pixel array  92 . Gate line signals on gate lines G are provided to the rows of pixels  90  in pixel array  92  by associated gate driver circuitry. 
     The circuitry of display  14  may be formed from conductive structures (e.g., metal lines and/or structures formed from transparent conductive materials such as indium tin oxide) and may include transistors such as transistor  94  of  FIG. 6  that are fabricated on the thin-film transistor substrate layer of display  14 . The thin-film transistors may be, for example, silicon thin-film transistors or semiconducting-oxide thin-film transistors. 
     As shown in  FIG. 6 , pixels such as pixel  90  may be located at the intersection of each gate line G and data line D in array  92 . A data signal on each data line D may be supplied to terminal  96  from one of data lines D. Thin-film transistor  94  (e.g., a thin-film polysilicon transistor, an amorphous silicon transistor, or an oxide transistor such as a transistor formed from a semiconducting oxide such as indium gallium zinc oxide) may have a gate terminal such as gate  98  that receives gate line control signals on gate line G. When a gate line control signal is asserted, transistor  94  will be turned on and the data signal at terminal  96  will be passed to node  100  as pixel voltage Vp. Data for display  14  may be displayed in frames. Following assertion of the gate line signal in each row to pass data signals to the pixels of that row, the gate line signal may be deasserted. In a subsequent display frame, the gate line signal for each row may again be asserted to turn on transistor  94  and capture new values of Vp. 
     Pixel  90  may have a signal storage element such as capacitor  102  or other charge storage elements. Storage capacitor  102  may be used to help store signal Vp in pixel  90  between frames (i.e., in the period of time between the assertion of successive gate signals). 
     Display  14  may have a common electrode coupled to node  104 . The common electrode (which is sometimes referred to as the common voltage electrode, Vcom electrode, or Vcom terminal) may be used to distribute a common electrode voltage such as common electrode voltage Vcom to nodes such as node  104  in each pixel  90  of array  92 . As shown by illustrative electrode pattern  104 ′ of  FIG. 6 , Vcom electrode  104  may be implemented using a blanket film of a transparent conductive material such as indium tin oxide, indium zinc oxide, other transparent conductive oxide material, and/or a layer of metal that is sufficiently thin to be transparent (e.g., electrode  104  may be formed from a layer of indium tin oxide or other transparent conductive layer that covers all of pixels  90  in array  92 ). 
     In each pixel  90 , capacitor  102  may be coupled between nodes  100  and  104 . A parallel capacitance arises across nodes  100  and  104  due to electrode structures in pixel  90  that are used in controlling the electric field through the liquid crystal material of the pixel (liquid crystal material  52 ′). As shown in  FIG. 6 , electrode structures  106  (e.g., a display pixel electrode with multiple fingers or other display pixel electrode for applying electric fields to liquid crystal material  52 ′) may be coupled to node  100  (or a multi-finger display pixel electrode may be formed at node  104 ). During operation, electrode structures  106  may be used to apply a controlled electric field (i.e., a field having a magnitude proportional to Vp-Vcom) across pixel-sized liquid crystal material  52 ′ in pixel  90 . Due to the presence of storage capacitor  102  and the parallel capacitances formed by the pixel structures of pixel  90 , the value of Vp (and therefore the associated electric field across liquid crystal material  52 ′) may be maintained across nodes  106  and  104  for the duration of the frame. 
     The electric field that is produced across liquid crystal material  52 ′ causes a change in the orientations of the liquid crystals in liquid crystal material  52 ′. This changes the polarization of light passing through liquid crystal material  52 ′. The change in polarization may, in conjunction with polarizers  60  and  54  of  FIG. 5 , be used in controlling the amount of light  44  that is transmitted through each pixel  90  in array  92  of display  14 . 
     In displays such as color displays, color filter layer  56  is used to impart different colors to different pixels. As an example, each pixel in display  14  may contain three (or more than three) different subpixels (pixels  90 ) each with a different respective color. With one suitable arrangement, which may sometimes be described herein as an example, each pixel has a red subpixel, a green subpixel, and a blue subpixel. Each subpixel is driven with an independently selected pixel voltage Vp. The amount of voltage that is supplied to the electrodes of each subpixel is associated with a respective digital pixel value (e.g., a value ranging from 0 to 255 or other suitable digital range). Desired pixel colors may be produced by adjusting the pixel values for each of the three subpixels in a pixel. For example, a black pixel may be associated with a 0 pixel value for the red subpixel, a 0 pixel value for the green subpixel, and a 0 pixel value for the blue subpixel. As another example, an orange pixel may be associated with pixel values of 245, 177, and 100 for the red, green, and blue subpixels. White may be represented by pixel values of 255, 255, and 255. 
     The response times of the pixels in display  14  may vary as a function of the magnitude of the liquid crystal switching voltage applied to electrodes  106 . When switching a black pixel, which has red, green, blue pixel values of (0, 0, 0), to a white pixel (255, 255, 255), each subpixel (red, green, and blue) is provided with the same target pixel value (i.e., 255) and starts from the same initial pixel value (i.e., 0), so the voltage applied across liquid crystal layer  52  during switching is the same for each subpixel. As a result, all subpixels will switch at the same time. This type of switching scenario may arise when moving black text, a black cursor, or other black item against a white background. 
     Other pixel switching scenarios may create color motion blur due to the unequal response times that arise when driving subpixels of different colors with different pixel values. As an example, consider the response of a pixel when switching from black (0, 0, 0) to orange (245, 177, 100). In this situation, a large voltage drop appears across the red subpixel (i.e., a voltage drop associated with a difference in before and after digital values of 245) and lower voltage drops appear across the green subpixel (a voltage associated with pixel value change of 177) and blue subpixel (a pixel value change of 100). Because the voltage on the red subpixel (and therefore the electric field applied by the red electrode  106  to the liquid crystal layer) is relatively large, the liquid crystal molecules of the red subpixel will rotate more quickly than the liquid crystal molecules of the green and blue subpixels. The red subpixel will therefore change color (from black to red) faster than the green and blue subpixels will switch from black to green and black to blue, respectively. The disparate switching speeds of the subpixels of different colors can lead to unpleasant visual artifacts. In the present example, in which a black item is being moved across an orange background, the relatively faster switching speed of the red subpixels has the potential to create undesirable red motion blur effects. 
     Color motion blur effects can arise both at the leading edge of a moving object and at the trailing edge of a moving object. For example, consider the movement of object  112  across background  110  of display  14  of  FIG. 7 . Object  112  may have a first color (e.g., black) and background  110  may have a second color (e.g., orange). Object  112  may be black text (as an example). Background  110  may have a color that is desirable when presenting electronic books to a user in a warm ambient lighting environment (e.g., indoor lighting). Object  112  may be moved across background  110  up and down during scrolling, right and left when panning, etc. In the example of  FIG. 7 , object  112  is moving to the right in direction  114 . 
     At trailing edge  118 , black pixels (0, 0, 0) are being switched to orange (245, 177, 100). Black-to-white switching speeds (rise times) may vary considerably depending on switching voltage levels. Because the red pixels are provided with a larger switching voltage than the green and blue pixels when switching from black to orange, the red pixels in region  116  may switch from black more quickly than the green and blue pixels, leading to blurred colors in region  118 . In particular, the pixels of display  14  in region  118  have the potential to develop a significant red color due to the enhanced switching speed of the red subpixels relative to the blue and green subpixels. 
     At leading edge  116  of object  112 , pixels are switching from background color  110  to the color of object  112 . For example, pixels in leading edge  116  may be switching from background color  110  (245, 177, 100) to black (0, 0, 0). The red pixels in this situation may exhibit slightly slower decay times than the green and blue pixels, leading to gray motion blur. 
     A graph showing how pixels with different colors have the potential to switch at different speeds during particular color transitions is shown in the graph of  FIG. 8  in which subpixel transmission T (proportional to subpixel output intensity) has been plotted as a function of time t. In the example of  FIG. 8 , the situation at trailing edge  118  of  FIG. 7  is being illustrated. Initially (at time t 1 ), the pixels are black (0, 0, 0). At time t 3 , object  112  has moved away from edge  118  and each of the subpixels have had sufficient time (in conventional displays) to acquire their desired target value (i.e., the red subpixel can acquire value 245, the green subpixel can acquire value 177, and the blue subpixel can acquire value 100). The switching progress of the red, green, and blue subpixels in a conventional display is illustrated by curves  120  (for red),  122  (for green), and  124  (for blue). These curves (which are not normalized in the graph of  FIG. 8 ) exhibit transitions at different speeds. The green and blue curves  122  and  124  transition relatively slowly. The red curve (curve  120 ) transitions rapidly, because the target value for the red subpixel is relatively high (245). Because red curve  120  rises steeply compared with green curve  122  and blue curve  124 , the color of the pixels in trailing edge  118  at times such as time t 2  before the green and blue subpixels have reached their target values will be overly red in color in conventional displays. 
     To restore the desired balance between the red, green, and blue subpixels in trailing edge  118  and therefore minimize red motion blur effects, red subpixel transitions may be momentarily slowed down in display  14  relative to the green and blue subpixel transitions in trailing edge  118 . This may be accomplished by creating an image frame for display  14  in which the target values for the red subpixels in trailing edge  118  are temporarily set to a reduced target value. The reduced target value may be, for example, the value of the next highest subpixel value (i.e., the green subpixel target value of 177 in the present example). Because the red subpixel has a lowered target pixel value, the red subpixel will not switch at an overly fast rate relative to the green and blue subpixels and red color motion blur will be suppressed. After processing the image frame with the temporarily reduced red subpixel target values, display  14  may be presented with a frame of image data in which the red subpixels are provided with their desired final target values (i.e., 245 in the present example). Because the green and blue subpixels have already at least partly transitioned to their final target values, the red subpixels can transition to their final red subpixel target values without risk of introducing red motion blur into trailing edge  118 . 
       FIG. 9  illustrates how pixels in trailing edge  118  may be provided with intermediate target values to suppress color motion blur. Initially, a pixel in image frame F 1  may have red, green, and blue subpixel values 128 of (0, 0, 0), corresponding to a portion of black item  112 . When item  112  is moved, the pixels in trailing edge  118  will need to transition to the color of background  110 . In this example, background  110  is orange, so the final target values 132 for the red, green, and blue subpixels of each pixel in trailing edge  118  are (245, 177, 100). This target pixel state will be reached when display  14  displays frame F 3 . To suppress color motion blur, an intermediate set of target values is temporarily imposed on the pixels in trailing edge  118 . The temporary target values for these pixel include a reduced red subpixel value. In the example of  FIG. 9 , intermediate frame F 2  has been provided with temporary target values 130 for the red, green, blue subpixels of (177, 177, 100)—i.e., the red subpixel value has been temporarily reduced to a value equal to the second highest subpixel value in the final target values, which is 177 in this example. Other intermediate subpixel values may be used to suppress motion blur, if desired. For example, the trailing edge pixels in frame F 2  may be provided with red subpixel values having values that lie between final target value 245 and the lowest final target subpixel value (100 in this example), that lie between 245 and 177 (the second highest final target subpixel value), that lie between 177 and 100, or that are otherwise reduced from the final target value 245. The example of  FIG. 9  is merely illustrative. 
     The impact of introducing an intermediate image frame with temporarily adjusted subpixel values in trailing edge  118  to suppress color motion blur is illustrated by curve  126  of  FIG. 8 . Initially, at time t 1 , initial frame F 1  has a pixel in object  112  that is black (0, 0, 0). When object  112  is moved, this pixel forms one of the pixels in trailing edge  118  and receives a final target value that is not black. The final target value of the pixel (in this example) is orange (245, 177, 100). 
     In the absence of intermediate frame F 2  at time t 3 , the red subpixel will transition rapidly relative to the green and blue subpixels as indicated by the rapid rise in curve  120  relative to curves  122  and  124 . As a result, trailing edge  118  will exhibit red motion blur at times such as time t 2 . When an intermediate frame such as frame F 2  of  FIG. 9  is used (e.g., at time T 3 ), the reduced subpixel target values in the intermediate frame, will cause the red subpixel to transition at a reduced rate, as indicated by curve  126 . For example, at time t 3 , the red subpixel may have a value of 177 (i.e., the same value as the green subpixel). Because the red subpixel transmission between time t 1  and time t 3  of curve  126  is slower than the conventional red subpixel transition between time t 1  and time t 3  of curve  120 , red motion blur will not be visible at time t 2 . After intermediate frame F 2  has been processed, the pixels in trailing edge  118  may be updated by displaying updated frame F 3  at time t 4 . During the transition period between time t 3  and t 4 , the red subpixel can transition from a value of 177 to its final target value of 245, as indicated by curve  126  between times t 3  and t 4 . The green and blue subpixels have already reached (or nearly reached) their final target values at time t 3 , so there will not be any excessive red present in trailing edge  118  between time t 3  and time t 4 . 
     Device  10  may process the image frames being displayed on display  14  to identify which pixel values are associated with trailing edge  118 . After the pixels of trailing edge  118  have been identified, the pixels of trailing edge  118  may be provided with intermediate values (i.e., values with reduced red subpixel values) during frame F 2  and then final values (i.e., values in which the red subpixels and the other subpixels have their desired final target levels) during frame F 3 , as described in connection with  FIG. 9 . 
     The diagram of  FIG. 10  shows how the pixels of successive frames may be compared to identify which pixels in display  14  make up trailing edge  118 . In the example of  FIG. 10 , object  112  has a first position P 1  at time t 1  and, by virtue of movement in direction  114 , has a second position P 2  at time t 2 . Object pixels  138  are black (in this example) and have subpixel values 128 of  FIG. 9 . Background pixels  136  are orange (in this example) and have subpixel values 132 (in this example). Trailing edge pixels  140  in trailing edge  118  can be identified by comparing the pixel values of a frame of data containing object  112  in position P 1  with the pixel values of a successive frame of data containing object  112  in position P 2  or can otherwise be identified by comparing the image data for object  112  in positions P 1  and P 2 . Scenarios in which image processing operations involve comparing frames of successive image pixels to identify which pixels form trailing edge  118  are sometimes described herein as an example. If desired, the leading edge of object  112  may likewise be identified and the pixels of object  112  along its leading edge may be modified to reduce motion blur. Scenarios in which the pixels of the trailing edge of object  112  are modified to reduce color motion blur are described as an illustrative example. 
     A diagram of illustrative resources that may be used in device  10  to reduce color motion blur effects is shown in  FIG. 11 . As shown in  FIG. 11 , device  10  may include control circuitry such as control circuitry  142 . Control circuitry  142  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  142  may be used to control the operation of device  10 . This processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, application specific integrated circuits, etc. 
     Control circuitry  142  may be used to run software on device  10 , such as operating system software, application software, firmware, etc. As shown in  FIG. 11 , the software running on control circuitry  142  may include code that generates content that is to be presented on display  14  (see, e.g., content generator  144 , which may be an operating system function, an e-book reader or other software application, or other code that is running on control circuitry  142 ). Content generator  144  may generate content that has not been corrected to reduce motion blur effects (uncorrected content) and this content may be supplied to graphics processing unit  150  via path  146 . 
     Graphics processing unit  150  may include an input frame buffer such as buffer  152  or other storage to maintain information on a current image frame  154  and one or more earlier frames such as previous image frame  156 . Graphics processing unit  150  may also include an output frame buffer such as output frame buffer  160  that stores content in which certain pixels (e.g., the pixel in trailing edge  118 ) have been modified to reduce motion blur. Blur abatement image processor (content processor)  158  may be used to process uncorrected content and produce corresponding content in which pixels have been modified to decrease motion blur. The content with decreased motion blur may be supplied to display driver circuitry  164  of display  14  over path  162 . Display driver circuitry  164  may include integrated circuit(s) and/or thin-film transistor circuitry on display  14  for displaying the content that is received over path  162  on pixels  90  in pixel array  92  of display  14 . 
     Illustrative operations involved in using resources of the type shown in  FIG. 11  in displaying content with reduced motion blur on display  14  are shown in  FIG. 12 . 
     Initially, content generator  144  may generate content to be displayed on display  14  and graphics processing unit  150  may receive the content over path  146 . The content may include frames of image data. Blur abatement image processor  158 , which may be implemented using software and/or hardware resources associated with graphics processing unit  150 , may acquire a frame of image data (sometimes referred to as an image frame or content frame) from content generator  144  at step  166 . 
     During the operations of step  168 , blur abatement image processor  158  may use frame buffer  152  to store frames of image data including current frame  154  and previous frame  156 . Blur abatement image processor  158  may compare the pixel values in current frame  154  and previous frame  156  to identify the location of object  112  and the direction of motion of object  112  relative to background  110  and to identify which pixels are in trailing edge  118 , as described in connection with  FIG. 10 . After each current frame is processed, processor  158  may store the data of the current frame as previous frame  156 . 
     After identifying the location of trailing edge  118  (i.e., after identifying the boundary of edge region  118  and the pixels that are located within this area of the image), blur abatement image processor  158  may adjust the pixel values of the pixels in the trailing edge to reduce motion blur (step  170 ). In particular, blur abatement image processor  158  may temporarily reduce the values of the red subpixels in trailing edge  118  as described in connection with the creation of temporary intermediate frame F 2  of  FIG. 9  (i.e., the value of these red subpixels is not increased immediately to the desired final target value of 245, but rather is raised first to an intermediate value). Frames of data that have been processed by blur abatement processor  158  may be stored in output frame buffer  160 . The modified frame (i.e., a frame such as frame F 2  of  FIG. 9  in this example) can be displayed at time t 3  of  FIG. 8  and the final desired frame (i.e., a frame such as frame F 3  of  FIG. 9  in this example) can be displayed following frame F 1  (i.e., at time t 4  of  FIG. 8 ). As indicated by line  144 , processing can then loop back to step  166  so that additional content from content generator  144  can be processed. 
     If desired, the image processing operations involved in implementing the color motion blur abatement process of processor  158  may be implemented in full or in part in control circuitry  142  (e.g., as part of an operating system or application or both an operating system and application), may be implemented in full or in part in display  14  (e.g., using resources in a timing controller integrated circuit or other circuitry in display drier circuitry  164 ), may be implemented in full or in part on graphics processing unit  150  as described in connection with  FIG. 12 , and/or may be implemented using other resources in device  10  or any combination of two or three or more of these sets of resources. The use of a scenario in which blur abatement image processor  158  is implemented on graphics processing unit  150  is merely illustrative. 
     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: 20150909
Publication Date: 20190507
Grant Date: 20190507
Priority Date: 20150402
Inventors: HERRANZ, ADRIA FORES
CHEN, CHENG
WU, JIAYING
ROLAND, NICHOLAS G.
Assignee: APPLE INC
CPC Classifications: [{"code": "G09G3/3648", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2340/16", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3607", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2320/0252", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/2003", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G5/003", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G3/2092", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G5/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2320/0242", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0261", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2340/16", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G5/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G5/003", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G3/3607", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G3/3648", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G3/2092", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2340/16", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3607", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G5/003", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G5/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G3/2092", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2320/0252", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0242", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0261", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3648", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2320/0252", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0261", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/2003", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G2320/0242", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 57015993