Apple patent involves color correcting for digital video images
Posted by Dennis Sellers 
Dec 26, 2007 at 4:23pm
The U.S. Patent & Trademark Office has granted Apple a patent (number 7312800) for color correction of digital video images using a programmable graphics processing unit. In other words, it’s designed to make video viewing on Macs even better.
Here’s Apple’s background and summary of the invention: “The invention relates generally to computer display technology and, more particularly, to the application of visual effects using a programmable graphics processing unit during frame-buffer composition in a computer system.
“Presentation of video on digital devices is becoming more common with the increases in processing power, storage capability and telecommunications speed. Programs such as QuickTime by Apple Computer, Inc., allow the display of various video formats on a computer. In operation, QuickTime must decode each frame of the video from its encoded format and then provide the decoded image to a compositor in the operating system for display.
“Because of the limited power of the CPU, it has not been possible to provide real time color compensation for a single video stream, much less multiple video streams. As a result, when real time video is displayed using a computer, the colors are generally incorrect because no compensation can be performed. Instead, generic color spaces and conversions are used. Thus a displayed image’s appearance will change for each video source and video output. As this cannot be done for even one video stream, it becomes worse when multiple video streams are involved.
“Thus, it would be beneficial to provide a mechanism by which real time video can be color compensated, both for video source and for the ultimate display device. Further, it would be beneficial to do this for multiple, simultaneous video streams.
“A system according to the present invention utilizes the processing capabilities of the graphics processing unit (GPU) in the graphics controller. Each frame of each video stream or track is decoded into a buffer and a color profile indicating parameters of the color space of the video source is associated with the buffer. After all of the streams have been decoded, the compositor uses the color profile to convert each buffer to a defined working color space from the source color space. This conversion and rendering of the buffer is performed using the fragment processing capabilities of the GPU. After any other desired operations, the compositor instructs the GPU to convert the buffer to the final color space of the display device and the frame is rendered to the frame buffer for final display. Each of these operations is done in real time for each frame of the video. Because each stream or frame is properly color converted, the final displayed image will be the uniformly colored for each video source and each display.”
Apple says the patent is for a system that utilizes the processing capabilities of the graphics processing unit (GPU) in the graphics controller. Each frame of each video stream or track is decoded into a buffer and a color profile indicating parameters of the color space of the video source is associated with the buffer. The compositor uses the color profile to convert each buffer to a defined working color space from the source color space. This conversion and rendering of the buffer is performed using the fragment processing capabilities of the GPU. The compositor then instructs the GPU to convert the buffer to the final color space of the display device and the frame is rendered to the frame buffer for final display. Each of these operations is done in real time for each frame of the video.
The inventors are Sean Matthew Gies, James Batson and Tim Cherna. The graphic below illustrates a computer system with various video sources and displays.
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Contributor
Dennis Sellers
Dennis has been a newspaper editor/reporter (seven years) and teacher (seven years). He has over 4,000 magazine, newspaper and online articles to his credit. He has also covered the Mac and tech industries for over a decade for such online publications as MacCentral, MacMinute and now MacsimumNews.
