Device and method for compositing video planes

摘要

A device and method of forming a video frame from a video stream made up of a multiplexed plurality of sub-streams is disclosed. The method includes forming a foreground plane, forming a mask that represents opaque pixels in the foreground plane, and forming an underlying plane from at least one of the sub-streams and extracting a transparency value associated with each pixel in the foreground and underlying planes. Only those pixels in the underlying and foreground planes not covered by the mask, are blended in accordance with their associated transparency value in a buffer. The buffer is populated with opaque pixels from the foreground plane, at pixel locations corresponding to the mask.

主权项

1. A method of forming a video frame from a video stream comprising a multiplexed plurality of sub-streams, said method comprising:
forming a foreground plane comprising a plurality of foreground pixels, said pixels having color values and alpha values associated therewith; forming one or more underlying planes from at least one of said sub-streams; forming a mask data structure comprising a bit corresponding to each pixel location in said foreground plane, said data structure for storing a mask to identify pixel locations at which pixels of said foreground plane are opaque; determining an alpha value associated with each of said foreground pixels, wherein at least some foreground pixels have alpha values indicative of full opacity and occlude corresponding pixels of said underlying plane at the same pixel locations; populating said mask data structure by setting the bit for each pixel location corresponding to a foreground pixel with an associated alpha value indicative of full opacity to a first binary value indicating that the corresponding pixel locations of the underlying planes are occluded, and setting the bit for each pixel location corresponding to a foreground pixel with an associated alpha value indicative of non-full opacity to a second binary value indicating that the corresponding pixel locations of said underlying planes are not occluded; and blending only those pixels in said one or more underlying planes and said foreground plane at pixel locations not identified as occluded by said mask, in accordance with their associated alpha value, in a buffer; and populating said buffer at pixel locations identified by said mask as occluded, with opaque pixels from said foreground plane.