I was looking up technical information suitable for implementing some of the SSTV modes (Robot 36, given the recent satellite activity). Here’s a paper by JL Barber, N7CXI that gives you what you need to know. Robot36 is particularly fussy: uses an odd color space, Y, R-Y, and B-Y, with the difference channels sent only at half the rate of the Y (intensity) information. I have something in mind for this, and I’ll probably dummy up a Robot36 encoder soon.