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YUV pixel formats are typically generated by video input hardware from video cameras, videocassette recorders, and so on; they are not normally generated by software. Although there are various YUV formats possible, determined by the ratio and size of luminance samples (Y) and chroma (U and V) values, PCI-based Power Macintosh computers support only the 4-2-2 format. This format includes two 8-bit Y samples for each pair of 8-bit U and V samples. While 2 pixels (even-odd pairs) are packed into a 32-bit word, each pixel can be thought of as being composed of a luminance component (Y) and a chroma component (U or V) packed into 16-bit values.
The transformations of YUV pixels across a PCI bridge from BIG to GIB format are similar to those of 16-bit pixels. Figure B-4 shows the YUV 4-2-2 pixel formats. As is the case with 16-bit pixels, the pixels in YUV GIB format are in the correct positions but the bytes within each pixel have been swapped.
