3 Replies Latest reply on Oct 17, 2010 5:10 PM by Kevin Goldsmith

    Box Blur darkens blurred alpha edges in After Effects

    Christian Lett Level 3



      As part of a more complex filter I've created a simple box blur graph in Pixel Bender that simply blurs pixels by an integer amount. It's split into horizontal and then vertical processing for speed (basically it's pretty much the same as the box blur part of the example given in the Pixel Bender Developers Guide).


      I'm using it to blur an image with an alpha channel.


      In the Toolkit it works absolutely fine, however when I use it in After Effects CS5 the blurred edges look dark, as if the filter is assuming the background of the blurred alpha is black. In the Toolkit, if I set the Preferences->Image Window->Background color to white it works as expected, but that's because the Toolkit knows the colour is white and unpremults accordingly. I've tried premultiplying the pixels by the alpha to see if that works, but it just makes it worse!


      Any suggestions on how to fix this would be appreciated!


      Thanks, Christian