Separate Alpha Matte W/ Jpg

[soupman99]

I'm rendering out jpgs and need an alpha matte. Is there a way to batch render just the alpha channel? I'm only rendering jpgs because it seems to be speeding up the process of rendering...is this accurate or is it a figment of my imagination that jpgs take less time to render rather than tiff or something that has an alpha channel?

[soupman99]

NM, I just discovered there was a preset in the render layers.

[gmask]

saving out iff's should be the fastest .. all other formats are converted from this to tif or jpg etc after the frame is completed
I suppose it's possible that if your file server was slow larger uncompressed files would take longer to write

you can render out just alpha from the render settings..

I will mention that the jpg settings maya uses are horrible and it would be better quality wise to make jpgs from another program if you have to do that.. if you are doing just because of file space it seems kind of ridiculous considering how cheap drives are these days

[adam-clear]

Soupman - gmask is very right about the JPGs that come out of Maya (including FCheck). I've found that the IFFs work wonderfully in After Effects.

If you want your alphas to be completely separate you can use Render Layers. When I need extra control of my alphas (as in, I want to highlight one object in the scene later in AE) I'll make a separate render layer and use two Surface Shaders - one for the pure black and one for pure white.