View Full Version : Color Keying

10-05-2005, 08:35 PM
Hello fellow Lightwavers;

The other night I was playing around compositing some HDV video shot infront of a green sceen with some animated stuff I did in LW. I did the following things:

1. captured HDV (from sony FX1) using Vegas 6.0.
2. I then used Vegas 6.0 to create an image sequence.
3. I imported this image sequence into LW Layout as a Foreground image sequence in the Compositing tab.
4. I then rendered the scened and got the brightest and darkest greens of the green screen from image viewer.
5. I went back to compositing window/tab and entered these values into the low color key and hight color key.
6. I then rendered 60 frames of the scene.

the resulting short movie looked like it should, except that there were some green lines that were not keyed out. Thus I have the following questions:

1. How are the darker and brighter key colors used to key out colors in the Foreground image/sequence? Does Lightware just key out any colors that have intensity (lumi) values between the two key colors, or is it more complicated?

2. If Lightwave used only the intensity (lumin) values, then I think that it would be better to use a black screen. One could then light the subject so that the darkest value on the subject is brighter than the black screen and then key out all colors brighter than the black screen.

Anyone have any thoughts on this?



10-05-2005, 09:21 PM
I don't think Lightwaves compositing feature is ment for green/blue screening compositing as you would almost always have spill, Lightwaves Compositing would be if you already have it keyed and rendering it onto a background or such. You would be better off in using Fusion, Shake or one of the other compositing applications to key out the green/blue screen.

for a free openSource Compositing app check out http://www.jahshaka.org/ if you don't have access to the others.

10-06-2005, 03:49 AM
It's more complicate ! Don't do it in LW !

I am doing a lot of compositing: ... and ...

There is no magic value ! Each shoots are differents ( sometime you will key in one click ("perfect blue screen" ... and sometime you have to do 5 or 6 pass + hand cleaning - rotoscoping ). You will have to go back and forth with different techniques (more complicate : Layer R , V , B substraction, addition,etc.. )

You need to use a real keyer ( After, combustion ,DF..)
there are some tool like "Spill" in after effect to remove all green edge around character...
You can use plugins too ( Keylight, Zbig, etc..)

In Lw you will never have a clean Matte. ( of course you can supress the green color in majority but no correction of the edge , or focus blur effect,etc.. )

some advice here for DV: