Decompressing and compositing graphical image data

Details Decompressing and compositing graphical image data Decompressing and compositing graphical image data

1998-09-16

2002-07-23

Zimmerman, Mark (Department: 2671)

Computer graphics processing and selective visual display system

Computer graphics processing

C382S232000

Reexamination Certificate

active

06424342

ABSTRACT:

BACKGROUND OF THE INVENTION
1. The Field of the Invention
The present invention relates to systems and methods for processing graphical image data in preparation for displaying a graphical image on a display screen. In particular, the present invention relates to systems and methods for sequentially mapping graphical image data to pixel positions on the display screen, decompressing the graphical image data, and compositing the graphical image data one scanline at a time as the graphical image is refreshed.
2. The Prior State of the Art
As computer use has become increasingly common, many techniques for displaying information on computer display screens have been developed. One of the reasons that computer use is widespread is the ability to display large amounts of information on display screens. For example, much of the recent dramatic growth of the Internet, particularly the World Wide Web (“Web”), has been caused by the ability to rapidly transmit and display graphical images and information.
Many conventional methods for displaying graphical image data involve one or more of the following techniques: decompressing compressed data, mapping image data to pixel locations, and compositing multiple images. These techniques are discussed in reference to
FIG. 1
, which illustrates a conventional system
10
capable of decompressing, mapping, and compositing graphical image data in preparation for generating an image on a display screen. System
10
may be embodied, for example, in a general purpose or special purpose computer.
System
10
receives compressed image data
12
from a source such as a remote server or a local computer-readable medium. Data compression decreases the amount of computer memory required to store graphical image data, and reduces the bandwidth and the transmission time needed to send the graphical image data between computers. However, there is a tradeoff for the efficiency gains provided by data compression. In particular, decompression of compressed data consumes computing resources and many data compression techniques result in some loss of image quality.
The compressed image data
12
is processed by a decompression module
14
according to any known decompression algorithm. The resulting decompressed image data
16
is then processed by a mapping module
18
, whereby the image data is associated with specific pixels on display screen
22
. Mapping image data to pixel locations involves selecting the position, orientation, etc., of the image data on the display screen. The processing capabilities of computers allow graphical image data to be manipulated, moved, scaled, warped, and otherwise processed in order to display information to the user in interesting and useful ways. For example, many Web pages, computer games, and other computer applications generate images that incorporate moving images or other image manipulation. In its most simple manifestation, mapping of image data to pixel locations simply involves directly associating data points in a two-dimensional graphical image data array to the corresponding pixel locations on the display screen.
In the example of
FIG. 1
, decompressed image data
16
may include pixel display parameters that define the luminance, chrominance, translucence, or other characteristics of pixels that will be selected on the display screen. Thus, mapping module
18
specifies the pixels on the display screen that are to be lighted according to the pixel display parameters encoded in decompressed image data
16
.
Once decompressed image data
16
is mapped to pixel locations on display screen
22
, the data is written to a frame buffer
20
, which contains the information needed to refresh the entire frame on display screen
22
. Once the image data is assembled at frame buffer
20
, it is transmitted to display screen
22
to refresh the previous image displayed thereon.
The process of writing the data to frame buffer
20
may include compositing the data with other image data that has previously been written to frame buffer
20
. Compositing multiple images is a technique whereby several graphical images are assembled to form a larger image, such as a full frame image on a display screen. For example, the display generated by a Web page may consist of several component images that are arranged on the display screen. Some of the images might appear to be in the foreground, with others in the background. Foreground images may cover portions of background images to produce the perception of depth. In addition, each image can be assigned a translucence value, such that background images can be partially seen through the foreground images.
While the system of
FIG. 1
can be used to display graphical images on display screens, it is subject to several limitations. First, decompression module
14
decompresses the entire volume of compressed image data
12
and stores the resulting decompressed image data
16
in a random access memory device. The entire volume of decompressed image data
16
requires significant memory resources, which must have access times fast enough to keep pace with the refresh rate of display screen
22
. Depending on the mapping procedures executed by mapping module
18
, some of the decompressed image data
16
may never appear on display screen
22
, but is nonetheless decompressed and stored in the random access memory device. Second, frame buffer
20
receives and temporarily stores the entire volume of image data needed to refresh a full frame at display screen
22
. The storage of this data also requires significant memory resources, which also must have access times fast enough to keep pace with the refresh rate of display screen
22
. If the expense of the memory and bandwidth resources needed to support decompression, mapping, and compositing of graphical image data could be reduced, the availability and complexity of graphical imaging could be increased.
In view of the foregoing, there is a need in the art for systems and methods that do not require decompression and storage of the full volume of compressed image data prior to the steps of mapping and compositing the data in preparation for refreshing an image on a display screen. It would also be advantageous to provide systems and methods for compositing the image data that have reduced memory requirements compared to the conventional frame buffer systems that store enough data to refresh an entire frame of a display screen. It would be advantageous if such systems and methods could be compatible with compression and decompression techniques that allow image data to be accessed while requiring relatively small data transmission bandwidth or memory resources.
SUMMARY AND OBJECTS OF THE INVENTION
The present invention relates to systems and methods for mapping, decompressing, and compositing graphical image data using less random access memory and bandwidth resources than have been possible according to conventional techniques. Unlike prior techniques, the invention does not require the entire volume of compressed graphical image data received by the graphics engine to be decompressed and stored in a random access memory device before being mapped to pixels on the display screen. Furthermore, the systems of the invention include scanline buffers for storing composited data used to refresh a single scanline on the display screen, in contrast to full frame buffers of conventional systems, which store enough composited image data to refresh an entire frame on the display screen.
As compressed graphical image data is provided to the graphics engine of the invention, the compressed data is first mapped to pixel locations of the display screen and then decompressed. Conducting the step of mapping the graphical image data before conducting the decompression step provides the advantage of eliminating the need to store decompressed image data in a random access memory device before the data is mapped to pixel locations. In addition, conducting the mapping step first can allow some of the compressed graphical image data to remain compressed. F

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