Chromatic Vibration Packet

NOTE: This post is from my long-dead previous blog, reposted in celebration of the newly completed GCC website and forum, which will host this and other VFX schwag.

I’ve discovered whenever I pull a green screen with Primatte I tend to get lazy and avoid rotoscoping a garbage or holdout matte. In its stead I came up with a little recipe to pull a rough green screen and dilate or erode for use as a garbage or holdout matte.

Technically, you create an alpha channel for green screen footage by subtracting the maximum of red or blue from green. The formula is g-(max(r,b)) in Shake’s ColorX node.

After adjusting the levels so the alpha channel is pure white and black, the alpha channel is dilated or eroded by 10 or so pixels, and input into Primatte’s garbage or holdout matte input.

The only funky thing with it, is that you have to start pulling your green screen with primatte and THEN do the trick. So I set the center color, swipe a foreground color and then plug in the magic.

While I was in the lab today I wrote 2 macros to bundle it up and make it easy.

Introducting: LazyHoldOut and LazyGarbage.

Update: LazyHoldOut and LazyGarbage are available at the new GCC website.