Well you should be able to do it on small ARM processor, but you've always got to take transmission time into account - those pesky satellites do tend to move about quite a bit :)
There's also the format used by the NOAA weather satellites - simple and works...
Simon Brown, HB9DRV http://sdr-radio.com
-----Original Message----- From: Graham Shirville [mailto:g.shirville@btinternet.com]
Good question - "medium" was a deliberately vague term as it will also depend on the camera and available data rates etc.
I was hoping we might be able to move on from analogue SSTV now.. we should be able to achieve much better quality images,,,as you suggest the challenge would be to do the digital encoding on board the spacecraft without using lots of power but, as mentioned, - if they can do it on a tiny payload hanging beneath a small helium balloon then it should be possible to do something similar on a spacecraft even a 1U cubesat!