4 Replies Latest reply on Jul 10, 2016 5:27 PM by Roei Tzoref

    black edges problem with a Pre-comp

    Roei Tzoref Adobe Community Professional

      hey everybody. got a situation here would like to ask for help figuring it out.

       

      got black edges around my precomp.

      this is a setup I have used in a few composition and it works in all of them but two

      the give me black edges.

       

      this is my Master Comp:

      notice the dark edges around the white dress over the shoulder and the hair to the right

       

      in my Master Comp there is a background - a PSD file with many layers and color correction folder, imported as Footage to AE.

      and on top of it there is a precomp - this is my Precomp:

      it's with elements inside and color correction precomp on top (imported separately from the same PSD file)

       

      in theory it should be composited on top of the background in the Master Comp and fit in perfectly.

      it's supposed to look like this

      (notice the edges are clean)

       

       

      for some reason the edges around the alpha are dark as if Ae is giving me premultiplied result of the precomp on top of background of the master comp.

      mind you, this is not rendered alpha from another application. it's all AE on top of a full frame footage

       

      what I eventually ended up doing was move the Color Correction precomp to the Master Comp

      on top of both the composited elements precomp, and changed the PSD background layer with no CC folder visibilty inside  and saved it again.

      this is instead applying the color correction separately

       

      still would like to know what went wrong?

        • 1. Re: black edges problem with a Pre-comp
          Rick Gerard Adobe Community Professional & MVP

          Try changing the blend mode to Alpha Add.

          • 2. Re: black edges problem with a Pre-comp
            Roei Tzoref Adobe Community Professional

            thanks for answering Rick.

            nope. it did not do the job. here is a project recreating the problem:

             

            Master Comp Contents

             

            Precomp - background sliced with masks with a Color Correction Adjustment Layer

            Color Correction Adjustment Layer

            Background layer - (same as inside the precomp)

            notice the fringe around the edges

             

            I noticed that only when the Adjustment layer is in a blend mode, this situation occurs.

            • 3. Re: black edges problem with a Pre-comp
              Rick Gerard Adobe Community Professional & MVP

              I looked at your sample comp. I hate to tell you this but what you are seeing is normal and expected when you anti alias an edge by drawing a curve and then apply a blend mode to an adjustment layer. You have a very odd workflow going here and you have very extreme adjustments that leave very little room for calculations.

              Screen Shot 2016-07-10 at 7.23.51 AM.png

              If you just look at the edge of one of the layers in your pre-comp with the adjustment layer turned off and the magnification factor set to max you can see the aliasing and the difference in the color values of the individual pixels:

              Screen Shot 2016-07-10 at 7.31.17 AM.png

              Blend modes work on color values so when you add the adjustment layer with the Luminosity blend mode you get this:

              Screen Shot 2016-07-10 at 7.32.19 AM.png

              This is normal and expected and also happens if you are in Photoshop or any other compositing app where you try and use this workflow. The problem is even more obvious when you try a blend mode like difference:

              Screen Shot 2016-07-10 at 7.34.25 AM.png

              There are many work arounds but the easiest thing to do to have the luminosity blend mode work is to copy the curves effect to the masked layer, turn off the adjustment layer, set the mask layer's blend mode to luminosity and then collapse transformations in the main comp.

               

              With your original example, the girl, I would either work without blend modes draw the masks on the adjustment layer instead instead of pre-composing. You just have a very odd workflow going here and you are failing to consider that blend modes work on pixel values and anti aliased edges change the pixel values.

               

              I hope this helps. Your problem isn't a bug, it's a workflow issue.

              • 4. Re: black edges problem with a Pre-comp
                Roei Tzoref Adobe Community Professional

                thank you Rick. eventually as I mentioned I changed my workflow and it did solve it. I guess I tried to hold the rope at both ends and at some point the pixels said enough. your example illustrates why. note that these extreme adjustment were only for illustrating purposes. you can do very mild adjustments and even then this will happen but as you explained - it's because the anti-aliasing caused by the adjustment in the precomp - so the solution should be make it happen in the same comp.

                this is me trying to explain in a very simple way.

                 

                thank you for the technical breakdown. you put time and effort in your posts and I appreciate it.