François Zaïdi wrote: I searched for Jello 123, but to no avail. Can you point me in the right direction ?
Sorry, that isn't a literal reference, I was referring to a gelatin dessert that used to be popular, but its spokesperson has fallen into disrepute, among other things. I was really just trying to be picturesque -- maybe like a cafe latte with the coffee on the bottom, a layer of steamed milk and then foam. Hard to separate them after the drink has been made, and as Andrew correctly points out, some math has been done on them - my reference to the "matrix" processing.
Many VFX applications have channel splitters and "swap channels" behaviour or nodes. Your challenge is to try to get the system to "get some eggs out of an omelette." In the ideal situation, it would work like ProRes 4:4:4, which at least conceptually carries either Red or Luminance in Channel 1, Green or B-Y in Channel 2, and Blue or R-Y in the third channel.(if the order was Y', U, V). At the very least, though if you were capturing in a 4:2:2 format, the original material probably has been bandwidth limited (low-pass filter in chrominance), re-ranged and gamma-indexed. All bad for RGB recovery or re-coding.
jPo