Abstract:
The system and method of forming a display from a sequence of blocks of pixel data includes intermediate storage of selected blocks of pixel data in sequence for subsequent selective access in the stored sequence. One or more accesses to a given block of pixel data from intermediate storage provides zoom expansion or compression of displayable images represented by the blocks of pixel data.

Description:
RELATED APPLICATIONS 
     The subject matter of this application relates to the subject matter set forth in pending U.S. patent applications Ser. No. 07/547,060, entitled &#34;Graphic Animation System and Method,&#34; filed on Jun. 29, 1990 by Pierre-Alain Cotte, et al.; Ser. No. 07/546,916, entitled &#34;Methods and Means for Manipulating Pixel Data,&#34; filed on Jun. 29, 1990 by Pierre-Alain Cotte, et al.; Ser. No. 07/546,712, entitled &#34;Memory Structure and Method for Managing Pixel Data,&#34; filed on Jun. 29, 1990 by Pierre-Alain Cotte et al.; Ser. No. 07/546,915, entitled &#34;Method and Apparatus for Binary Value Modification by a Percentage,&#34; filed on Jun. 29, 1990 by Thierry Mantopoulos; Ser. No. 07/547,023 entitled &#34;Phase Locked Loop,&#34; filed on Jun. 29, 1990 by Thierry Mantopoulos and Fabrice Quinard; Ser. No. 07/547,026, entitled &#34;Video Synchronization Generator and Method,&#34; filed on Jun. 29, 1990 by Fabrice Quinard; and Ser. No. 07/547,024, entitled &#34;Bus Structure and Method for Compiling Pixel Data with Priorities,&#34; filed on Jun. 29, 1990 by Thierry Mantopoulos and Fabrice Quinard, incorporated herein by reference. 
     BACKGROUND AND FIELD OF THE INVENTION 
     This invention relates to video displays and more particularly to a video buffer system and method for selectively altering the pixels in memory that are displayed. 
     Traditionally, pixel data stored in a memory such as a Video Random Access Memory (VRAM) is scanned out of memory on a line-by-line basis for display on a raster-type display screen on a corresponding line-by-line basis. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, each line of pixel data that is accessed from a VRAM is selectively stored in a First-In, First-Out (FIFO) buffer memory under selective write controls. In addition, the pixel data stored in the FIFO Buffer may be selectively read out for display under selective control in order to alter the display of the stored data. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a system block diagram of the preferred embodiment of the present invention. 
     FIG. 2 is a timing diagram illustrating video data compression through the FIFO, in accordance with the present invention. 
     FIG. 3 is a timing diagram illustrating video data expansion through the FIFO, in accordance with the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG. 1, there is shown a block schematic diagram of one embodiment of the present invention in which a standard VRAM 9 is coupled to a standard FIFO buffer 11 for accessing lines of pixel data from the VRAM 9 to store in the FIFO buffer 11. Devices of this type are commercially available as devices which operate in response to clock input signals (not shown). In addition, the FIFO buffer 11 also responds to read and write signals 10, 12 applied thereto from Random Access Memory (RAM) 13 that also receives an input signal 15 indicative of the pixel number being accessed either from the VRAM 9 for selective writing into the FIFO buffer, or from the FIFO buffer 11 for selective reading to the output converter circuit 17. The FIFO buffer 11 may be as wide as a line of bytes of displayable pixel data (typically, 640 to 768 bytes), and one line deep. Thus, as successive lines of pixel data (each pixel containing, for example, 8 bits of color information) are accessed from successive addressed locations in the VRAM 9, a write signal 12 may be applied to the FIFO buffer 11 under control from RAM 13 to enable (or not enable) the particular pixel data to be written into the FIFO 11. As illustrated in the graph of FIG. 2, the alternate numbered blocks of pixel data 19 may be selected for storage in FIFO 11 in response to write signals 21, 23, 25, thereby resulting in horizontal compression of the image to be displayed. Of course, other ones of successive blocks of pixel data accessed from the VRAM 9 may also be selected, including aperiodic block selections, each third block, a burst of successive blocks, and the like. The intermediate storage operation of FIFO buffer 11 delays the display of the selected pixel data until the time interval of the next display line, as illustrated in FIG. 2. In the graph, a read signal is illustrated as occurring at each interval corresponding to a block of pixel data in the FIFO buffer 11. In this operating mode, each block of pixel data from the VRAM 9 that was selected to be written into the FIFO buffer 11 is thus read out 27 of the buffer 11 into the output converter 17 which may, for example, include a Digital-to-Analog (D/A) converter for producing the display-driving signal 20 in conventional manner. 
     With reference to the graph of FIG. 3, there is shown an alternate operating mode in which each successive block of pixel data that is accessed from the VRAM 9 is written 29 into the FIFO buffer 11. In addition, and independently of the write mode, the read mode may be operated at a slower rate to duplicate selected blocks of pixel date and thereby create an expanded image on the display. As shown, each block of pixel data may be read out twice 31 from the FIFO buffer to create a `zoom` effect on the displayed image by a factor of two. Similarly, each block of pixel data may be read out three or four or M times to produce corresponding zoom effects by factors of three, four, and M, respectively. Of course, an active line of pixel data stored in the VRAM may also be accessed repeatedly a corresponding number of times to create uniform `zoom` effect both horizontally (by repeated pixels) and vertically (by repeated lines). The read and write control signals 10, 12 for selecting which blocks of accessed pixel data are stored in the FIFO buffer 11, and the number of times each stored block is read out from the FIFO buffer 11 is controlled by data stored in RAM 13 which may be updated by a microprocessor 33 and controlled by an address generator 34 that also supplies addresses 35 to the VRAM 9 to control which lines of pixel data are accessed. 
     Therefore, the system and method of the present invention selectively alters pixel data per line of raster-type display, and selectively modifies the displayable data to create zoom effects under control of intermediate buffer memory.