PDA

View Full Version : Creating Mattes



hoopsking
01-15-2007, 12:31 PM
Hi,

I have a subject I shot behind a green screen. I want to create a matte so that only video will play inside of their cut out body. I've somewhat accomplished this accept I have a white border showing up in FCP. I just want the video in the outline of their body to show up. I've tried all the composite modes in FCP so I guess I'm doing something wrong in Photoshop. Please help.

Gord.T
01-20-2007, 08:50 PM
Your question is confusing:
I have a subject I shot behind a green screen ~=
I have a subject I shot 'in front of' a green screen

I want to create a matte so that only video will play inside of their cut out body
OR
I just want the video in the outline of their body to show up
________________________________________________
I assume you want video within the body shape cast over another video.
This is not photo shop specific, but,
1/ Chroma key the green screen image onto a black background.
so that the person image animates over a black background. (rgb(0,0,0)
2/ Make a positive mask of that. That is, anything not ==rgb(0,0,0) = White.
This is your alpha channel.
3/ In a compositor, set your video background image as background.
Set your insert/filler video as foreground with an alpha channel.
Use the mask as the alpha channel. That is, anything white on the mask gets transferred, else it is blocked. You will likely need to pre-blur the mask or you'll
get jagged-edges. A grayscale mask allows you to blend in the edges.

You are more than likely going to need two or more softwares to do this.
One for chroma keying onto black.
One fore making masks (photoshop or other)
One for putting all together. (3dsMax is good for that)

If you can't find a masking program, let me know and I'll make you a little utility. (free)

Gord.T
01-20-2007, 08:55 PM
Edit: After-thought: Your white outline may be an artifact of the jagged edge syndrome. If your using a mask, pre-blur it and the edges should dissapear.

Matt Grunau
01-24-2007, 04:11 PM
Use FCP with it's keying capabilities to create a good clean pull from you pic. then, instead of setting it normally to show the removed background, set it to show the mask/alpha you have created. render that. then simply invert that alpha. Then use the inverted alpha to put your video in.