1 Reply Latest reply on Jan 25, 2010 1:05 PM by Chris Cox

    Alpha Blending

    iFezec Level 3

      Is there a formula to take a final flattened rgb color and if you know the matte color, to extract the original topLayer color and its alpha?

       

      Suppose i have ffff0000  and the matte is ffffffff  and i apply 50% blend,  the flattened layer would be a rose.

       

      can i take that rose hex if i knew there was 50 alpha to it and bring it back to ffff0000?

        • 1. Re: Alpha Blending
          Level 7

          result = (alpha * top) + ((1-alpha) * bottom)

           

          That would, of course, be normalized and rounded for whatever bit precision you are using.

           

          There are 4 values involved.  If you know 3 of them, you can recover the fourth.

          In some cases (composite against black or white), you can estimate the alpha value and thus get a decent result with only 2 known values (result and matte color).