Codec Pixel Format Resource - 'cpix'

Both the Image Decompressor ('imdc') and Image Compressor ('imco') will need to supply a 'cpix' component public resource used to inform Final Cut Pro (and other applications) that the Image Codec supports 'r4fl' rendering (this is no different that what would need to be done when supporting the 'r408' pixel format).

A codec advertising support for '2vuy', 'r408' and 'r4fl' would for example, include a 'cpix' resource as part of its public resource list ('thnr') which looks like Listing 1.

Listing 1  Codec Pixel Format and Component Public Resource Map

resource 'cpix' (kMyCPIXResID) {
    {
        '2vuy','r408','r4fl'
    }
};

resource 'thnr' (kMyTHNRResID) {
    {
        'cdci', 1, 0,
        'cdci', kMyCDCIResID, 0,

        'cpix', 1, 0,
        'cpix', kMyCPIXResID, 0,
    }
};

Decompressors Generating 'rf4l'

Image Decompressors are expected to convert subsampled (eg. 4:2:2) material into the appropriate 4:4:4:4 format. It is the implementor's decision as to what approach is used to synthesize the missing chroma value.

If the on-disk format does not include alpha, the Image Decompressor should fill the entire alpha channel with 1.0 (opaque).

Compressors Receiving 'r4fl'

Image Compressors are expected to convert the fully sampled 4:4:4:4 material into the appropriate subsampled format (eg. 4:2:2) as needed. It is the implementor's decision what filtering (if any) is used during the conversion.

The values supplied in the pixel buffer may include illegal undershoot/overshoot. It is the compressor's responsibility to clamp these values into the minimum/maximum legal SDI signal (but continue to allow values outside of CCIR recommendations).

For example, when converting an fp Y-value to 10-bit, the math would normally look like a multiplication.

However, Yint is constrained by the illegal CCIR values shown in Figure 1.

In other words, for n = 10-bits, the values 0, 1, 2, 3 and 1020, 1021, 1022, 1023 are illegal (reserved) synchronization values. Values of “>=4” and “<= 1019” may include values outside of CCIR recommendations, but should be preserved in the data, to allow preservation of superblack/superwhite material and so on.

It is the implementor's (hardware or compressor) responsibility to prevent these illegal values from being sent out in a digital stream. It is probably simplest for the Image Compressor to clamp these values.

Color Information

It is expected that Image Codecs outputting 'r4fl' will operate natively at CCIR video gamma.

Final Cut Pro assumes the following for 'r4fl' pixel buffers:

• Primaries - SMPTE C primaries for Standard Definition Video (kQTPrimaries_SMPTE_C) and ITU-R BT.709-2 primaries for High Definition Video (kQTPrimaries_ITU_R709_2).

• Transfer Function - ITU-R BT.709-2 (kQTTransferFunction_ITU_R709_2).

• Matrix - ITU-R BT.601-4 for Standard Definition Video (kQTMatrix_ITU_R_601_4) and ITU-R BT.709-2 for High Definition Video (kQTMatrix_ITU_R_709_2).