Retrieving raw YCoCg value?

[saschanaz]

I'd like to get raw YCoCg without RGB conversion for a file format converter, can I do it?

[jonsneyers]

You could implement somethingl like that, but why? It's a lossless conversion, so not like YCbCr. And the way it is implemented in FLIF, you need 9 bit Co/Cg if the input RGB is 8 bit, so that's not very practical...