7 Replies Latest reply on Mar 9, 2011 1:39 PM by reallyconfused

    Problems with Alpha Channel

    reallyconfused

      Hey,
      This has been an issue I have been confused on for some time. When I export a project out of After effects CS5 into VT5 in SD (720x486i, 29.97fps in both programs) the alpha channel is fine and I can use the animated .avi. It is when I try to use an HD time line (1920x1080i, 29.97fps in both programs) that the alpha won't allow me to see through. As a matter of fact when I scrub the time line in VT5 (and the overlay option is activated on the rendered .avi) I can see through the alpha and the overlay project beneath it. It is when I play the time line or even render it the supposed to be alpha channel just shows up blank. I have played with the settings in After effects and cant seem to tweak them in the right way to make them produce a workable .avi. Any Ideas would be appreciated.

       

      sincerely,
      Confused

        • 1. Re: Problems with Alpha Channel
          Rick Gerard Adobe Community Professional & MVP

          You're not using the right codec. Even though the Output Module may show RGB+Alpha, the codec may not support it. In this screenshot the output is set to JPEG Sequence but JPGS don't support alphas.

           

          I'd suggest that you read up on Windows Codecs that support Alpha Channels.

           

          FakeAlpha.png

          • 2. Re: Problems with Alpha Channel
            reallyconfused Level 1

            Rick,

            Thank you for the responce.  As for jpeg,  that is true that alpha is not supported, but (and correct me if I am wrong) I use the "video for windows" format in for after effects cs5 below are the output settings I used.  I have heard that sometimes pre-render can effect alpha when rendered out of adobe after effects, has anyone else heard of this?  If so what settings are the best when rendering out a project?  Please point out if I am still doing something wrong, any input would be appreciated.

            Screen-01.jpg

            P.S.

            I have tried both Straight and Premultiplied in the color option.  I know that for my purposes premultiplied is the best setting, but I am getting desperate.

            • 3. Re: Problems with Alpha Channel
              Dave LaRonde Level 6

              Got Quicktime?  Use either the Animation or PNG codecs for rendering.  They both support alpha channels, both straight and premultiplied.

              • 4. Re: Problems with Alpha Channel
                reallyconfused Level 1

                Yes I have used the quicktime as an output with alpha to my timeline and that will give me the effect I need to produce.  The problem is that my editor (NewTek's, VT5) is a native AVI timeline and when I render out large projects with quicktime's on an HD Timeline it crashes the system.  That is another issue, I need to figure out how to create a working alpha channel on an HD 1920x1080 29.97 timeline.  I am just not having luck.  Any other suggestions would be appreciated.  I appreciate the ones I have received so far.

                 

                Sincerely,

                Confused

                • 5. Re: Problems with Alpha Channel
                  Dave LaRonde Level 6

                  I don't EVER use AVI's, even on my Windows machine at home.  Even so, I'm pretty sure an uncompressed AVI supports alpha channels.  Try rendering one out and see what happens.  There may be other codecs for AVI's that support alpha channels, but I have no knowledge of them.

                  • 6. Re: Problems with Alpha Channel
                    bogiesan-gyyClL Level 3

                    reallyconfused wrote:

                    The problem is that my editor (NewTek's, VT5) is a native AVI timeline and when I render out large projects with quicktime's on an HD Timeline it crashes the system. 

                     

                    It's not really your problem, it's the editor's. NewTek is nothing special, there's a user support forum, probably, and he's got a powerful PC that is capable of importing and converting whatever you hand to him. Find the specs for the application and figure out what your common alpha-supported codec will be. You've got realize AVI was orphaned more than 15 years ago, it's a dead system. That NewTek is hanging onto it is weird and might one of the reasons NewTek is a footnote in this business.

                     

                    Failure to render huge timelines is often a RAM issue but it can also be related to bad drive connections. But debugging big renders is out of my experience.

                     

                    bogiesan

                    • 7. Re: Problems with Alpha Channel
                      reallyconfused Level 1

                      Thanks Bogiesan, I will have to look into those ideas.