Abstract:
This invention provides a method and apparatus for displaying an unscaled image frame on an LCD panel. The method and apparatus uses the same line buffers available to the digital signal processor DSP formerly used for scaling the displayed image up or down in size. No extra frame buffers are required by this invention since the frame rates of the source image and the LCD panel are the same. The image frame buffer is written to the LCD panel on every other panel vertical synchronization pulse. The vertical synchronization timing is shifted to the left or right in the time domain to center the image on the LCD panel.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a method and apparatus for providing liquid crystal display LCD control. More particularly this invention relates to a method and apparatus for displaying unscaled images on LCD panels without a frame buffer. The method and apparatus uses the same buffers available to the digital signal processor DSP for displaying the image. 
   2. Description of Related Art 
   Today, conventional LCD controllers utilize a scaling up mapping.  FIG. 1  shows a mapping of a 640 by 480 pixel image  110  being displayed on a 1024 by 768 pixel LCD display  120 . The figure illustrates a scaling up of the image to fit the LCD display, which has a larger pixel format (1024 by 768) than the image (640 by 480). The mappings  130  &amp;  140  of the starting and finishing points of the image are shown in  FIG. 1 . The conventional circuit to perform the above scaling up operation requires a higher clock frequency to produce a display on the LCD panel. This higher frequency is required for the scaling up digital signal processor, DSP to keep the same frame rate as the smaller image. In addition, this convention implementation needs several line buffers for temporary data storage. 
     FIG. 2  shows the conventional implementation of the No-scaling LCD display. In this case, a frame buffer is required to capture the whole frame of image data so that the 640 by 768 image  210  can be displayed anywhere on the LCD panel&#39;s  1024  by 768 grid  220 . The mappings  230  &amp;  240  of the starting and finishing points of the image are shown in  FIG. 2 . A example to illustrate the conventional method&#39;s requirement for a frame buffer. If the source image is 640×480 and the LCD panel is 1024×768, the source frame time provided without a frame buffer would be defined by 480 Hsync pulses and the LCD image frame time is given by 768 Hsync pulses. The reason why the frame buffer must be used is because the frame time for the source image has to equal that of the entire larger LCD frame. However, the available frame time for the non-scaled display image is significantly less than that of the source image as illustrated above by the difference in the number of Hsync pulses. 
   U.S. Pat. No. 5,537,128 (Keene, et al.) “Shared Memory for Split-Panel, LCD Display Systems” describes a memory sharing method for a split panel LCD. The method enables efficient memory sharing and video processor usage between an LCD driver and a CRT driver in a common system. 
   U.S. Pat. No. 5,712,681 (Suh) “Apparatus for Inputting and Outputting an Optical Image with Means for Compressing or Expanding the Electrical Video Signals of the Optical Image” shows an apparatus capable of inputting and outputting an optical image. A means of compressing or expanding the electrical video data is provided. The circuit displays the captured image on an LCD panel. 
   U.S. Pat. No. 6,049,322 (Yoshikawa et al) “Memory Controller for Liquid Crystal Display Panel” provides a memory controller for an LCD panel. The apparatus allows the source driver for the LCD to operate at a lower frequency than the line buffer. 
   BRIEF SUMMARY OF THE INVENTION 
   It is the objective of this invention to provide a method and an apparatus to display a source image on a LCD panel without scaling. 
   It is further an object of this invention to provide this LCD display using lower clock frequencies than would normally be required using the scale up display methods of the present art. 
   In addition, it is further the object of this invention to display on a LCD panel without the use of a frame buffer. 
   The objects of this invention are achieved by a method to display a source image on a LCD panel without scaling. The method begins by transferring the even image line to line buffers. This is followed by the transferring the output of these line buffers to the input of the LCD panel drivers of the upper half portion within the LCD panel. Next, the method requires the skipping of the LCD Vsync at the end of a display within the even image lines. Then, there is the transferring the odd image lines to line buffers and the transferring the output of these line buffers to the input of the LCD panel drivers of the lower half portion within the LCD panel. Finally, the method requires the blanking of the data of the odd image of this lower portion of the LCD screen. 
   The objects of this invention are also achieved by an apparatus to display a source image on a LCD panel without scaling. This apparatus contains a means for transferring the even image line to line buffers and a means for transferring the output of these line buffers to the input of the LCD panel drivers of the upper half portion within the LCD panel. In addition, the apparatus contains a means for skipping the LCD Vsync-pl at the end of a display within the even image lines. There is also a means for transferring the odd image lines to line buffers and for transferring the output of these line buffers to the input of the LCD panel drivers of the lower half portion within the LCD panel. Finally, the apparatus contains a means for blanking the data of said odd image of said lower portion of the LCD screen. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a prior art scaling up mapping. 
       FIG. 2  shows a prior art no-scaling up mapping. 
       FIG. 3  shows the no-scaling up mapping algorithm of this invention Step  1 . 
       FIG. 4  shows the no-scaling up mapping algorithm of this invention Step  2 . 
       FIG. 5  shows the no-scaling up mapping algorithm of this invention (Step  3 ). 
       FIG. 6  shows the Vsync, Hsync Timing diagram. 
       FIG. 7  shows how movement of Vsync varies the position of the image display on the LCD. 
       FIG. 8  shows a circuit block diagram of the main embodiment of this invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 3  shows the first steps of the method of this invention. The even image lines  310  are mapped to the LCD panel. This figure shows the mapping of a no-scaling algorithm. The same number of line buffers are used for this mapping as is used in the traditional scaling algorithm. The digital signal processor, DSP, needs to implement and produce the non-scaling image on the LCD panel. The output of the DSP goes to the line drivers, which drive the cells of the LCD panel. The starting and finishing points of the even image lines are mapped  330 ,  340  to the LCD panel as shown in  FIG. 3 . The odd image lines are mapped  350  directly below the upper even lines. 
     FIG. 4  shows the next step of the method. The source  410  image and the LCD panel  440  are shown. The even image lines  420  are displayed and visible on the LCD panel. The odd image lines are blanked or not displayed  430 . This method requires that one frame of data, the odd frames, is skipped every other frame. Since the odd source lines are directly adjacent to the even source lines, eliminating the odd scan lines results in minimal loss of information. While the embodiment shows a non-scaled image that occupies about half of the display panel, in general, the invention will work with various fractional sizes of the display. For example, the non-scaled image might occupy ⅔ of the display. Any source resolution smaller than the display resolution will work. 
     FIG. 5  shows the final steps of the method. The source  510  image and the LCD panel  530  are shown. The mappings  540 ,  550  of the starting  560  and finishing  570  points of the image to the LCD panel are shown. The non-scaled display of the image on the LCD panel is shown  520 . Comparing  FIGS. 4 and 5 , the shift of the image display on the LCD panel is noticed. In  FIG. 4 , the displayable image  420  is shifted to the top of the LCD panel  440 . In  FIG. 5 , the displayable image  520  is centered on the LCD panel  530 . This shifting and centering of the image on the LCD panel is accomplished by shifting the vertical synchronization Vsync signal of the LCD panel. In this case, the Vsync signal is shifted to the left on the time domain timing diagrams. 
     FIG. 6  shows the time domain timing diagram. This diagram illustrated the source image buffer data — source  610 , Hsync — source  620 , and Vsync — source  630  signals. It also shows the LCD panel data panel  640 , Hsync panel  650 , and Vsync — panel  660  signals. The even image data  670  and the odd image data  680  are shown. However, on the LCD panel, the even data  690  is displayed while the odd data  691  is blanked out or not displayed. This is accomplished by skipping every other Vsync signal  615 ,  625  on the LCD panel. When a Vsync signal is skipped, the next odd frame of data is not begun at the normal starting point at the upper left of the displayable area on the LCD. Consequently, the present set of even image lines remains visable on the LCD panel. 
   In addition, moving the position of the even frame Vsync signals  635 ,  615 ,  655  controls the position of the image display on the LCD panel. The movement of the Vsync  635  to the left moves the image display downward. While movement of the Vsync  635  to the right moves the image display upward. 
     FIG. 7  further illustrates how the movement of the Vertical synchronization signal controls the position of the image display up or down on the LCD panel.  FIG. 7  shows the blanked out areas  701 ,  703  of the display data as well as the even frames of displayable data  702 ,  704 . There are three cases illustrated in  FIG. 7 . Case  1  shows the Vertical synchronization pulse lined up with the transition from blank data to Even frame displayable data  710 . The corresponding LCD image display showing the displayable image starting at the top of the LCD  720 . Case  2  shows the Vertical synchronization pulse occurring in the middle of the blank data  730 . The corresponding LCD image display showing the displayable image centered in the middle of the LCD  740 . Case  3  shows the Vertical synchronization pulse lined up with the transition from even displayable data to blank data  750 . The corresponding LCD image display showing the displayable image skewed toward the bottom of the LCD  760 . 
     FIG. 6  also illustrates that the frequency of the Vertical synchronization of the LCD panel is one half of the frequency of the Vertical synchronization of the source. Also, the frequency of the horizontal synchronization signal Hsync of the LCD panel  650  equals the Hsync of the source  620 . Therefore, the Vertical synchronization frequency requirements are equal to or less than those of the source. 
     FIG. 8  shows a block diagram of the circuitry of the main embodiment of this invention. The image frame buffer  810  used by the digital signal processing, DSP, circuitry is shown. No additional frame buffers are required. Similarly, the line buffers  830  used by the DSP circuitry is shown. No additional line buffers are required.  FIG. 8  also shows a direct connection  860  between the output of the image frame buffer  810  and the line buffer  830 . It also shows a direct connection  840  between the line buffer  830  and the LCD panel driver  850  which drives the LCD panel  820 .  FIG. 8  also shows a program retention device  870 , which is a networked  875 -computer device. The program instructions are stored in a program memory  880  shown. These program instructions  880  are used to eliminate the need for a frame buffer. The computer  870  moves the no scaling image and also simulates a model of an LCD panel without scaling.  FIG. 8  also shows a frequency divider  890 , which is used to divide the frequency of the Vertical synchronization of the source image buffer by two. This half frequency is used to drive the LCD panel.  FIG. 8  also shows logic circuitry  895 , which is used to blank the display during the odd frame time domain. This is known as skipping an LCD Vertical synchronization at the end of the display within the even image lines. This logic circuitry  895  utilizes a shift register to shift the position of the Vertical synchronization in the time domain for the LCD panel. 
   This invention has the advantage of lower cost since extra frame buffers are not required. In addition, the circuits and apparatus required to implement the method of this invention are relatively simple. They involve halving the frequency of the Vsync signal. In addition, the circuitry is required to move the position of the Vsync signal to establish the position of the displayed image on the LCD panel. 
   While this invention has been particularly shown and described with Reference to the preferred embodiments thereof, it will be understood by those Skilled in the art that various changes in form and details may be made without Departing from the spirit and scope of this invention.