Abstract:
Visual quality of a liquid crystal display (LCD) panel is enhanced by combining black pixel insertion with response time correction (RTC) to mitigate motion blur. The black pixel insertion is performed during a portion of a current frame to establish a baseline for RTC in a next frame and therefore does not result in an increase in the frame rate of the LCD panel.

Description:
FIELD 
       [0001]    This disclosure relates to Liquid Crystal Displays (LCDs) and in particular to motion blur mitigation for LCD panels. 
       BACKGROUND 
       [0002]    A mobile computer typically includes a display device in the form of a low power Liquid Crystal Display (LCD) panel. A voltage is applied across liquid crystals in a liquid crystal layer in the LCD panel in order to illuminate pixels (picture elements), that is, discrete elements that together constitute an image. By controlling the voltage applied to each pixel, the amount of light allowed to pass through each pixel can be varied in order to display an image on the LCD panel. 
         [0003]    The LCD panel may be used to display a static image or to view motion pictures (videos, movies). A motion picture is a sequence of static images (frames) that are projected on a screen in rapid succession. The location of the objects in successive frames is modified so as to produce the optical effect of a continuous picture in which the objects move. 
         [0004]    However, one limitation to displaying motion pictures on a conventional LCD panel is motion blur that is visible on the display when displaying fast moving objects. Motion blur occurs due to slow response time of the liquid crystals, and hold-type characteristics of the LCD pixels. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    Features of embodiments of the claimed subject matter will become apparent as the following detailed description proceeds, and upon reference to the drawings, in which like numerals depict like parts, and in which: 
           [0006]      FIG. 1  is a block diagram of a system that includes an embodiment of a motion blur mitigator according to the principles of the present invention; 
           [0007]      FIG. 2  is a block diagram of the system shown in  FIG. 1  that includes an embodiment of a motion blur mitigator in a controller for mitigating motion blur in an LCD panel according to the principles of the present invention; 
           [0008]      FIG. 3  is a graph illustrating drive level output from the motion blur mitigator shown in  FIG. 2  and the corresponding luminance response; and 
           [0009]      FIG. 4  is a block diagram of the LCD display shown in  FIG. 2  that includes an embodiment of a motion blur mitigator according to the principles of the present invention. 
       
    
    
       [0010]    Although the following Detailed Description will proceed with reference being made to illustrative embodiments of the claimed subject matter, many alternatives, modifications, and variations thereof will be apparent to those skilled in the art. Accordingly, it is intended that the claimed subject matter be viewed broadly, and be defined only as set forth in the accompanying claims. 
       DETAILED DESCRIPTION 
       [0011]    Due to the slow response time of the liquid crystals, the final intensity corresponding to the value of a pixel in the LCD panel may not be reached within the time period for displaying a frame (a frame time). Response time is the time a pixel takes to reach its final luminance within some tolerance after it is driven with a new pixel value. The response time varies widely in LCD panels, depending on the previous pixel value and the new value and is typically measured in milliseconds. 
         [0012]    Response Time Compensation (RTC) is a technique used to decrease the response time in a sequence of frames that comprise a motion picture. RTC overdrives or underdrives a pixel value based on a pixel value for the current frame and the pixel value for the previous frame. RTC may be implemented in a Liquid Crystal Display (LCD) panel or a graphics controller that controls the display of frames for the LCD panel. If implemented in the LCD panel, the LCD panel includes a frame buffer to store pixel values for the previous frame and a two dimensional look-up table (LUT) to determine the required overdrive or underdrive for the pixel value. This additional frame buffer results in increasing the cost of the LCD panel. 
         [0013]    If implemented in the graphics controller, the need for an additional frame buffer is avoided because the frame buffer in the graphics controller may be used. Also, the LUT is implemented within the graphics controller and may include overdrive or underdrive values in order to provide support for different types of LCD panels. 
         [0014]    Thus, the LUT may be customized for each different type of LCD panel that is supported. However, the disadvantage of this scheme is that an additional frame buffer fetch is required per pixel in order to retrieve the pixel value for the previous frame in the sequence of frames. The additional frame buffer fetch results in increased power consumption. 
         [0015]    Another characteristic of an LCD panel that contributes to motion blur is that a LCD panel is a hold-type display device, that is, a pixel value is displayed for the entire frame duration. In contrast, in an impulse-type display device such as a Cathode Ray Tube (CRT), a pixel value is displayed for a fraction of the frame duration. Thus, even if the response time of the LCD is reduced through RTC via overdriving or underdriving, motion blur may still occur due to the hold-type characteristic. 
         [0016]    In order to minimize the motion blur resulting from the hold-type characteristic, some high-end LCD televisions blank the screen for a portion of the frame time by employing a double refresh rate, that is, a refresh rate of 120 Hertz (Hz) instead of at 60 Hz and inserting a black frame, known as Black Frame Insertion (BFI) or through the use of backlight shuttering. For BFI, the data is driven to the LCD pixels at twice the normal rate and a frame buffer is required on the display in order to convert the data from a 60 Hz rate to a 120 Hz rate. In backlight shuttering, the backlight is “blinked” for a portion of the frame. However, improving the motion blur due to hold-type characteristics remains limited to high-end (expensive) LCD televisions only, due to the extra costs in the LCD driving circuits (due to increased data rate) and frame buffer for BFI and in the LCD backlight control for backlight shuttering. 
         [0017]    In an embodiment of the present invention, in contrast to backlight shuttering where a backlight is blanked for a portion of a frame, and BFI, where a black frame is inserted between frames, a pixel is driven to its associated pixel value for a portion of the frame and the pixel value is then driven to a value of zero (logical 0) for the remainder of the frame without the addition of a frame buffer. In order to further mitigate motion blur, response time correction (RTC) is also applied to provide an RTC adjusted pixel value to apply overdrive to the pixel value. 
         [0018]    Driving the pixel value to logical 0 corresponds to displaying a “black” pixel. A black pixel is displayed for the remainder of the frame time prior to writing the next RTC adjusted pixel value for the next frame in the sequence of frames. Thus, the pixel value for each pixel is always logical 0 at the end of the current frame period prior to the start of a new frame period. This simplifies a LUT for applying overdrive or underdrive by reducing it from a two-dimensional LUT (previous and current frame) to a one dimensional LUT (current frame). 
         [0019]    In one embodiment, the pixel value is driven to 0 during the frame period by a source driver in the LCD panel. In this embodiment with RTC implemented in the LCD panel, the need for a frame buffer for storing pixel values for the prior frame is eliminated. Furthermore, in this embodiment, by driving each pixel value to logical 0 for a remainder of the current frame prior to the start of the next frame, there is no increase in the refresh rate of the LCD panel as in BFI. 
         [0020]    In another embodiment, the pixel value is driven to 0 by the graphics controller before applying a new pixel value. In this embodiment in which RTC is implemented in the graphics controller, the need for an additional frame buffer fetch is avoided. However, the refresh rate is increased. 
         [0021]      FIG. 1  is a block diagram of a system  114  that includes an embodiment of a motion blur mitigator  150  according to the principles of the present invention. The system  114  includes a processor  100  and a chipset that includes an Input/Output (I/O) Controller Hub (ICH)  106  and a Graphics Memory Controller Hub (GMCH)  102 . 
         [0022]    The GMCH  102  manages a memory  104  that is coupled to the GMCH  102 . The system  114  may also include memory such as Dynamic Random Access Memory (DRAM), Static Random Access Memory (SRAM), Synchronized Dynamic Random Access Memory (SDRAM), Double Data Rate 2 (DDR2) RAM or Rambus Dynamic Random Access Memory (RDRAM) or any other type of memory. 
         [0023]    The processor  100  is coupled to the GMCH  102  by a host interface  132 . The GMCH  102  is coupled to the ICH  106  by a high-speed direct media interface  124 . The ICH  106  may be coupled to the GMCH  102  using a high speed chip-to-chip interconnect  124  such as Direct Media Interface (DMI). DMI supports 2 Gigabit/second concurrent transfer rates via two unidirectional lanes. 
         [0024]    The ICH  106  manages I/O devices including storage devices  108  coupled to a storage controller  134 . In other embodiments the storage devices controlled by the ICH  104  may include a Digital Video Disk (DVD) drive, compact disk (CD) drive, Redundant Array of Independent Disks (RAID), or tape drive. The storage controller  134  may communicate with the storage devices using storage protocols such as Serial Advanced Technology Attachment (SATA), Fibre Channel, and Small Computer System Interface (SCSI). 
         [0025]    The ICH  104  may also include a system bus controller  144  for controlling communication with other devices, for example, Network Interface Controllers. In one embodiment the system bus may be the Peripheral Component Interconnect (PCI) or the Peripheral Component Interconnect Express (PCI-e) bus. 
         [0026]    The GMCH  102  may include a graphics controller for controlling a display device such as a Liquid Crystal Display (LCD) panel  130  coupled to the GMCH  102 . In the embodiment show, a motion blur mitigator  150  is included in the graphics controller in the GMCH  102  to mitigate motion blur in the display. In another embodiment, a motion blur mitigator may be included in the LCD panel  130 . 
         [0027]      FIG. 2  is a block diagram of the system shown in  FIG. 1  that includes an embodiment of a motion blur mitigator  150  in a controller  202  for mitigating motion blur in an LCD panel according to the principles of the present invention. 
         [0028]    In the embodiment shown, the controller (“graphics controller”)  202  is included in the GMCH  102  shown in  FIG. 1 . Graphics controller  202  generates image data for display by LCD display  206 . The image data may be for a video (sequence of images) with high motion content. The graphics controller  202  is coupled to an LCD display  206  for transmitting image data (frames) for display on the LCD display. Frames to be transmitted by the controller  202  are stored in a frame buffer memory bitmap  204  which may be a portion of memory  104  ( FIG. 1 ) coupled to the GMCH  102  ( FIG. 1 ). A motion blur mitigator  150  in the controller  202  mitigates motion blur by driving a pixel value to logical 0 to display a pixel having minimum brightness (“black pixel”) during a portion of a current frame period prior to applying a new overdrive value to the pixel for a subsequent frame period. 
         [0029]    The motion blur mitigator  150  may also include a Response Time Compensation (RTC) module to apply Response Time Compensation (RTC) to image data. The RTC module determines the final drive level to the panel, that is, the overdrive or underdrive or whether to allow the pixel to pass with neither over or under drive applied. For example, no compensation may be applied if a black (zero luminance) pixel can not be inserted because the LCD display  206  does not support a high refresh rate. 
         [0030]    In one embodiment, the controller  202  operates at a 2× frame rate and the black pixel is generated by not fetching any data from frame buffer memory bitmap  204  for the “black” frame. Instead of fetching data from the frame buffer bitmap  204 , the black pixel values are generated by the motion blur mitigator  150 . 
         [0031]    In other embodiments, the black pixel value may be generated in the display FIFO  212 , pixel formatting  214  or even in frame buffer memory bitmap  204 . However, in these embodiments there may be a resulting increase in power consumption. In yet another embodiment, the motion blur mitigator  150  may drive a value of logical 0 on the output. 
         [0032]    In some embodiments, controller  202  may include a frame buffer memory bitmap  204  for storing image data (frames) and a display fetch engine  202  for generating a frame buffer memory address and control signals to obtain a next frame to be displayed on the LCD panel  204 . The image data from frame buffer memory bitmap  204  is processed through display First In First Out (FIFO)  212 , pixel formatting  214 , motion blur mitigator  150  and pixel coding serializer  216  to provide frames of pixels over interface  112  for display panel  206 . Motion blur mitigator  150  may perform response time compensation to provide compensated pixel values that may compensate for a slower response time of the elements of LCD panel  206 . Controller  202  may also include display timing generation  210  to generate and/or provide clock signals and/or other timing signals for use within controller  202 . In the embodiment shown, display timing generating  210  generates Address line Offset Horizontal signal  218  and starting address vertical signal  220  used by the display fetch engine  202  to select frames stored in the frame buffer memory bitmap  204  and by the pixel coding serializer  216  to transmit frames to the LCD display  206 . 
         [0033]    In the embodiment shown, LCD display  206  includes row drivers  232  and column drivers  230 , for providing signals to drive and/or control the individual elements (pixels) of display  134 . The LCD display includes an LCD panel  207  and a Thin Film Transistor (TFT) LCD Timing Controller (TCON)  236 . The TCON  236  controls timing for row drivers (RD)  232  and column drivers (CD)  230  based on pixel data and LCD timing control signals received from the controller  202  to control the display of each frame on display panel  207 . Each pixel in the LCD panel  207  may have an associated column and row address allowing it to be refreshed independently. 
         [0034]    In an embodiment the controller  202  is coupled to the LCD display  206  through a Low Voltage Differential Signaling (LVDS) Display Interface (LDI). LDI includes signals to enable panel power and to control the brightness of the panel backlight. LVDS is an electrical standard that defines driver output characteristics and receiver input characteristics. Data may be transmitted serially over the interface to the LCD display  206 , seven bits at a time per data signal. 
         [0035]      FIG. 3  is a graph illustrating drive level output from the motion blur mitigator shown in  FIG. 2  and the corresponding luminance response. 
         [0036]    As shown, in  FIG. 3 , at frame N+1, RTC applies compensation to the pixel to overdrive the pixel value, that is, to drive pixel to desired level. In one embodiment, the motion blur mitigator  150  in the controller  202  may break up each frame as shown into two fields or subframes. During one of the fields the frame data is displayed and during the other field the data is logical 0. Thus, each pixel has a valid data value in one field and a logical 0 value in the other field. In an embodiment in which each field is half of a frame period, as shown in the embodiment in  FIG. 3 , a pixel is logical 0 (“black”) for about 50% of the frame and has valid data for about 50% of the frame period. Thus, the pixel is overdriven based on the pixel value for about 50% of the frame and a pixel value of logical 0 is transmitted to the LCD panel  206  for about the other 50% of the frame. 
         [0037]    Referring to  FIG. 3 , during frame period  300 , valid pixel data with luminance value of a is overdriven to drive level A for portion  304  of the frame period  300  and driven to logical 0 for portion  306  of the frame period  300 . During frame period  302 , valid pixel data with luminance response b is overdriven to drive level B for portion  308  of frame period  302  and is driven to logical 0 for portion  310  of frame period  302 . 
         [0038]    Thus, motion blur is mitigated because the intended level (a, b) of the pixel value is reached within the time frame and the luminance response mimics the impulse-type behavior of a Cathode Ray Tube (CRT) by driving the pixel value to logical 0 for a portion of the frame period. Furthermore, the LUT is also greatly simplified because the pixel value for the current frame before the pixel value for the next frame, is always logical 0. This reduces the need for a two-dimensional LUT needed for RTC to a 1-dimensional LUT because only the pixel value for the current frame is required as the prior frame is always logical 0. The RTC LUT may also be eliminated in certain embodiments by combining it with the existing gamma table in the LCD panel, with values stored in the gamma table used to code luminance values in frames, thereby significantly reducing the complexity. 
         [0039]    The combination of RTC and insertion of a black pixel for a portion of the current frame period prior to the start of a next frame period is effective at mitigating motion blur caused by both slow response time and hold-type characteristics of the LCD panels. The combination also makes the pixel luminance response much more like the pixel luminance response of a pixel in a Cathode Ray Tube (CRT). 
         [0040]    In an embodiment in which the insertion of a black pixel value for a portion of a current frame period is implemented in the panel, the double refresh rate is not required. Thus, this embodiment may be more easily implemented in LCD panels that are used in mobile computers such as notebook computers. 
         [0041]      FIG. 4  is a block diagram of the LCD display shown in  FIG. 2  that includes an embodiment of a motion blur mitigator  400  according to the principles of the present invention. 
         [0042]    In the embodiment shown, the motion blur mitigator  400  is included in the LCD Timing Controller (TCON)  236 . The LCD panel  206  writes a line at a time by first shifting the pixel values for a line into the column drivers  230  and then activating the row driver  232  for the line to be written. The lines are written sequentially by increasing line number, with the top line written first and the bottom line written last. 
         [0043]    The motion blur mitigator  400  applies RTC and determines which lines in the LCD panel  206  to drive to black. In the embodiment shown, a line is driven to black by the row drivers  232  dependent on the state of a black line control signal controlled by the motion blur mitigator  400 . However, in other embodiments a line may be driven black using a method that does not use the row drivers  232 . 
         [0044]    The TCON  236  drives line N+M to black while line N is driven with the active pixel data. Line N is the last active line of data, before the first black data line. Line N+1 is the first black line of data and line N+M is the last black line of data. M is the number of lines that are black at any given time. The remaining lines are active lines with valid data. In one embodiment, M may be configurable by the motion blur mitigator  400 . If N+M is greater than the number of lines in the display, then the lines at the top of the screen are driven to black, modulo the number of lines in the display. For instance if there are 800 lines in the display and N+M is equal to 801, then line 1 is driven to black. Similarly, if N+M equals 819, then line 19 is driven to black. 
         [0045]    It will be apparent to those of ordinary skill in the art that methods involved in embodiments of the present invention may be embodied in a computer program product that includes a computer usable medium. For example, such a computer usable medium may consist of a read only memory device, such as a Compact Disk Read Only Memory (CD ROM) disk or conventional ROM devices, or a computer diskette, having a computer readable program code stored thereon. 
         [0046]    While embodiments of the invention have been particularly shown and described with references to embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of embodiments of the invention encompassed by the appended claims.