4 Replies Latest reply on Jun 5, 2008 2:07 AM by Jonas Hummelstrand

    Why is a layer blending mode result altered by adding and effect?

      I've done a search online and haven't come up with an answer but does anyone
      know why a layers blending mode result is altered by adding an effect?

      I am using CS3 on a PC (Windows XP SP2) and have two layers; one a Tiff and
      a second a text layer with an ambient light and a spot shining on them. Both
      layers have 3D turned on and accept lights and are in the same position in
      space.

      To make the text, which is coloured black, sit better I changed the layers
      blend mode to soft light which works well.

      I wanted to soften the edge of the text a little so I added a Fast Blur
      effect and suddenly the result of the blend was completely different. If I
      turn off the effect it goes back to what it was before but even if the Fast
      Blur is set to zero, ie no blur on the layer, the blend result is altered.

      Does anyone know what's going on?
        • 1. Re: Why is a layer blending mode result altered by adding and effect?
          Mylenium Most Valuable Participant
          Presumably a bug that uses the blur's convolution kernel when it shoulddn't. Please report at http://www.adobe.com/go/wish. Still, sometimes changing the blend behavior is inevitable. Even if the layers visually look the same, the actual pixel values may change and thus create a different result in the blend formulas. That should not be the case here, though. Replace the Fast Blur with Box Blur set to 8 or 9 iterations and the result should look the same, but without the blending problem, I guess.

          Mylenium
          • 2. Re: Why is a layer blending mode result altered by adding and effect?
            Level 1
            Many thanks for that. I tried the Box Blur but it too shifted the result of <br />the blend. In the end, to get this job out of the door, I changed the colour <br />of the text to orange, lowered the opacity and used Multiply as the layer <br />blend mode. Adding the Fast Blur effect to this didn't shift the result of <br />the blend mode. It's not as sexy a look as using Soft Light but it works.<br /><br />I wonder if it's something going on with the maths or this a real bug?<br /><br /><br /><Mylenium@adobeforums.com> wrote in message <br />news:59b56faf.0@webcrossing.la2eafNXanI...<br />> Presumably a bug that uses the blur's convolution kernel when it <br />> shoulddn't. Please report at <a href=http://www.adobe.com/go/wish>. Still, <br />> sometimes changing the blend behavior is inevitable. Even if the layers <br />> visually look the same, the actual pixel values may change and thus create <br />> a different result in the blend formulas. That should not be the case <br />> here, though. Replace the Fast Blur with Box Blur set to 8 or 9 iterations <br />> and the result should look the same, but without the blending problem, I <br />> guess.<br />><br />> Mylenium
            • 3. Re: Why is a layer blending mode result altered by adding and effect?
              Mylenium Most Valuable Participant
              Well, if it occurs with different effects, it certainly is "as designed", you are just not seeing the subtleties of how the effect shifts the colors. Blendmodes such as Soft Light that use non-linear formulas are more prone o exposing these changes, especially in combination with 3D lighting.

              Mylenium
              • 4. Re: Why is a layer blending mode result altered by adding and effect?
                Jonas Hummelstrand Level 2
                You could have precomposed the text and moved the blur effect into the precomp and added a Levels effect so that you could tweak the values so that the layer in your main comp could have used the desired blend mode.

                - Jonas Hummelstrand
                http://generalspecialist.com/