Y'CBCR 8bv/w 4:2:2:
In Y'CBCR 8bv 4:2:2, the luma component has a nominal range of 220 unsigned integer values, and both chroma components have nominal ranges of 225 offset binary integer values. The chroma range of [16..240]->[-1/2..1/2] allows some play on both ends for out-of-range colors. Likewise, the luma component's [16..235]->[0..1] range leaves footroom at the bottom for subblack colors as well as headroom at the top for superwhite colors. This format is compliant with the International Telecommunication Union's Recommendation BT.601-4, and is used in standard uncompressed Y'CBCR 4:2:2 digital video tape (SMPTE D-1), standard uncompressed digital video links (SMPTE 259M), and professional video equipment.
The variant Y'CBCR 8bw 4:2:2 format has wide-range chroma components represented as two's-complement signed integers [-127..127]->[-1/2..1/2] and a full-range luma component [0..255]->[0..1]. While this format leaves no play for filter slop, it can represent significantly more displayable colors than the corresponding 601-compliant format, making it more useful for storage of video from higher-precision sources.
To convert the RGB footage to Y'CBCR 8bw 4:2:2 format, we encoded the RGB movie with Apple's Component Video codec. Rather than reduce or crop the frames down to SD resolution, we decided to test them at their original nonstandard video resolution to simplify comparison.
Curiously, although Apple has for years been urging people to use the international standard Y'CBCR 8bv 4:2:2 instead of Y'CBCR 8bw 4:2:2, QuickTime 6.0 itself still doesn't come with a Y'CBCR 8bv 4:2:2 encoder. So to convert the Y'CBCR 8bw 4:2:2 movie to Y'CBCR 8bv 4:2:2 format, we wrote our own codec to translate between yuv2 and 2vuy, using the simple standard equations given in Recommendation ITU-R BT.601-4:
Y' = floor(y' x 219 / 255 + 16.5)Note: Final Cut Pro 4 comes with a '2vuy' codec, listed as "Uncompressed 8-bit 4:2:2".
With only 2 byte-size components per pixel, the uncompressed size of each these Y'CBCR 8bv/w 4:2:2 frames is 2 x 768 x 512 = 786,432 bytes.
Within QuickTime, the preferred Y'CBCR 8bv 4:2:2 format is known as k422YpCbCr8CodecType, k2vuyPixelFormat, or '2vuy', with the components in the order CBY'0,CRY'1. A variant flavor, historically the most prevalent on both Mac and PC, known in QuickTime as kComponentVideoUnsigned, kYUVSPixelFormat, or 'yuvs', has its components in the order Y'0CBY'1CR.
The internal QuickTime designation for the Y'CBCR 8bv 4:2:2 format is kComponentVideoCodecType or 'yuv2', or, equivalently, kComponentVideoSigned, kYUVUPixelFormat, or 'yuvu'. output by codecs, is the QuickTime designation for a "full-range" format with unsigned luma samples in the range [0..255] and two's-complement chroma samples in the [-127..127], in the order (Y'0CBY'1CR). The yuv2 format is used by Apple's Component Video codec, and by many PC display and video digitizer cards.
Note that most video cards nowadays support all of these Y'CBCR 8bv/w 4:2:2 formats.
By throwing away half the chroma samples and losing further image information through round-off errors, the conversion from RGB 8p to Y'CBCR 8b 4:2:2 trashes the image quality. But we all put up with it because that's how television works. And television works that way because back when analog color TV was invented, they needed to compress the color signal to piggyback it onto the ubiquitous monochrome systems. Besides, in the analog world, perfect-fidelity compression isn't even imaginable anyway. That's why the American color-TV standard, NTSC, is affectionately known as "Never Twice the Same Color".