3 Replies Latest reply on Feb 11, 2016 11:55 PM by Warren Heaton

    Assigning alpha channel for output

    Navarro Parker Level 3

      Nuke has a nice trick where I can create 4 different mattes in one render (RGB +A), where the alpha isn't the image transparency, it's just another channel for a grayscale image (which is perfect for storing mattes).


      Is there a way to do this in AE?

        • 1. Re: Assigning alpha channel for output
          Dave LaRonde Level 6

          Sure is!  Add your comp to the AE Render Queue.  For the Output Module, pick a good codec like Photo JPEG or RroRes 422.  Under the Channel dropdown, Pick Alpha.  Then render.  The result: a B&W movie where black is transparent, white is opaque, and gray is semi-opaque.

          • 2. Re: Assigning alpha channel for output
            Navarro Parker Level 3

            Yes, but outputting alpha only requires a separate file output. So instead of one image sequence per 4 mattes, I have to deal with two.


            My original question was getting four mattes in one image sequence (RGBA).

            • 3. Re: Assigning alpha channel for output
              Warren Heaton Adobe Community Professional

              Hmm... you mean four channels in one image, right?  Red channel, green channel, blue channel and alpha channel.


              "Four mattes" implies that you'd have RBG+A+B+C+D which exists in some graphics formats (and while it could exist in a video format, I've never seen it).


              Try setting your Output Module to the "Lossless with Alpha" template and report back if this is what you're looking for.


              The trick to getting RGB+A is to pick a CODEC that supports the "+A".  So, Animation, Apple ProRes 4444, etc.