PDA

View Full Version : chrominance vs color difference keying


mister3d
02-11-2010, 03:18 AM
Hi guys. What is the difference between chrominance and color difference keying? They are both based on color, that's what I got. Color difference, as I understood is more tied to the pure values of RGB, but in which way?

Aneks
02-20-2010, 07:30 PM
the internal mathematics of a most chroma keyer uses both luminance and chrominance to determine what is being isolated. There are a lot of resources which explain the colour expressions used in commercial keyers. You can pretty much make one with a colour expression node in any composting application. However if you are after something more visual I wrote this tutorial a long time ago showing the process of building a keyer without using expressions(creative crash where kind enough to host it after I took it off my site):

http://www.creativecrash.com/shake/tutorials/keying/c/build-a-keyer

mister3d
02-20-2010, 09:03 PM
Thank you, I will look at that when I get some rest. :bowdown:
I think I got that color difference keys out whatever color is less than blue in a particular pixel. For example, it makes the bluescreen as transparent (as the blue B channel dominantes here), but the areas where RG are dominant in value, it makes it solid.

RogerWickes
02-28-2010, 02:18 AM
I talk about the differences and uses in two of my video tutorials in my sfx tutorial album (http://www.vimeo.com/album/16278). YCbCr etc are used mostly to matte a constant color, whereas difference can be used to matte an actor in a normal scene where you have a background plate of many colors.

CGTalk Moderation
02-28-2010, 02:18 AM
This thread has been automatically closed as it remained inactive for 12 months. If you wish to continue the discussion, please create a new thread in the appropriate forum.