I’ll give you the basic, if you want more detail, search for it on the forums or look at this page http://www.digitaltelevision.com/publish/dtvbook/ch2.shtml
but here is the run down, to allow a small camera to playback good quality video, yet not cost a fortune or be as big as a full size camera, they had to compress the video. same as they do on a DVD, digital cable, or your DirectTV satellite.
besides a lower resolution, they remove color values that the average person won’t notice on a normal TV. this is your color sampling. 4:4:4 is all there, all the original color and everything is saved, 4:2:2 certain values are cut in half and 4:1:1 the values are cut by a quarter.
4:4:4 is used on high end HD cameras ($100,000 plus)
4:2:2 is used on high end Digital Beta cams and analog beta cams ($10-30,000)
4:1:1 is used on DV, HDV, MPEG2 (DVD, Digital Cable, DirecTV) ($200-10,000)
I believe, for example, that the same price camera in a digital format will be a much better image, because when you dump it to the computer, it’s all numbers, nothing is lost, where as when you dump your analog footage, you just made a copy. but an analog camera and setup, such as a Betacam 4:2:2 will have more color value for something like greenscreening. also most analog cameras are older, where as newer gererations of digital stuff is constantly inproved upon
but nowadays, almost eveything is in some digital format, unless you go find some old Betacam stuff, you will most likely be limited by your budget.