Keying in this Crazy thing called Halo
Posted 10 November 2004 - 05:27 PM
Im really having a hard time pulling a good key in Halo. Is there a good way to do it, or is the keyer in Halo just not that powerful?
Posted 10 November 2004 - 09:15 PM
1. It uses HSV which we all know is 70s colour technology.
2. It's using colour for keying which we know will only work with specific types of images.
If you're simply doing blue/green screen keying of people (ie. lots of fleshtones in the foreground), I implemented a COP VOPnet a while back based on ultimatte equations from Jim Blinn and Alvy Ray Smith's paper, "Blue Screen Matting" (ftp://ftp.alvyray.com/Acrobat/BluSig96.pdf) which actually worked pretty well for the test images I tried.
Posted 12 November 2004 - 01:47 PM
Because, aside from the stock keyer, Halo seems to be a pretty powerful compositor.
Posted 14 November 2004 - 09:06 PM
Posted 15 November 2004 - 09:52 PM
If you look at the VOP network, the Parameter VOPs are named according to the paper. From a user's perspective, the process went something like this:
- Start off with the default parameters.
- Look at the A plane of the bluescreenkey cop
- Adjust each parameter in turn except for the first and last 3 until you get as good a looking matte as you can. Typically, adjust it so that you get the areas you want as white as you can and the areas you don't want as dark as you can.
- Once you're done that, adjust the Lower/Upper Alpha clamp parameters to isolate the range of the alpha you want to clamp at. Typically, you just need to raise the Lower Alpha clamp value high enough so that it completely remove the blue screen.
- Look at your result and then try tweaking the parameters again. Typically, I haven't found the Global Adjust parameter useful.
- The last parameter can be used to add back in some blue if the matte removed too much of it.
Oh and I just realized that I can't upload files here. Check in the main forum.
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