| 摘要 |
A system for converting the color format of a digital video bitstream. The system accounts for the allowable formats of the pre- and post-conversion bitstreams, including quantizer (355) precision level, and whether luma and chroma data have separate quantization matrices (385, 390), or share a common quantization matrix. In a particular implementation, an MPEG-2 4:2:2P bitstream having a color format of 4:2:2 or 4:2:0 is converted to an MP bitstream having a color format of 4:2:0. Coding efficiencies are achieved by using the luma quantization matrix (390) to re-quantize the chroma data, and re-using luma motion vectors MV for performing motion compensation (320, 325, 510) of the chroma data. Further efficiencies can be achieved by representing a 4:2:2 reference picture in a 4:2:0 format for converting intercoded frames, and changing the position of a pixel downsizing filter (340) and clip function (335). Adjustment (130, 230, 382), of the quantization precision is provided as required. A transcoding function (800) can also be achieved.
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