Luma Mattes as used in Grant Swanson Sin City Tutorial
by bill Carboni
on
Jun 23, 2008 at 5:36:39 pm
Hi, I tried posting in Grants tutorial page but it would'nt work.
Grant made a great tutorial on the sin city effect. It is two parts. The second part uses a luma matte to add color to the b+w image, I believe I followed all the steps correctly. I have two layers of the same video. The top layer is affected using color correction/curves which create all these bright colors. Then tint is applied to that layer to turn it black and white and put above the curves effect. The bottom layer is set to luma matte. Soloing the luma matte layer and toggling transparency you can see the luma mattes color transparency as in the tutorial.
When I toggle the top layer on I can't see any color from the luma matte. I've looked at the Meyers AE books, the adobe CS3 AE book,
and this forum to try to figure out what I was doing wrong to no avail. I have never used luma mattes before and I am sure there is something very basic I'm missing. Also I'm having a hard time understanding how lums mattes work. They are below the layer that it affects, yet somehow it would have to put itself on top of the layer above it to be seen. But I could be wrong. That'll learn ya.
Re: Luma Mattes as used in Grant Swanson Sin City Tutorial by Grant Swanson on Jun 23, 2008 at 10:33:09 pm
Hi Bill,
Luma mattes in After Effects work like this: you start out with a black and white matte which will be used to generate the alpha channel. Brigther areas will be opaque and darker areas will be transparent. You place this black and white matte ON TOP of the layer you want to matte out, and then set the layer ON BOTTOM to use the layer directly above it (the black and white matte) as the luma matte.
After this, the layer on bottom will only be visible in the brighter areas of the matte, and the rest will be transparent.
Hope that helps!
Grant Swanson
Visual Effects Supervisor
Video Apex
videoapex.blogspot.com
