4 Replies Latest reply on Oct 1, 2007 1:09 PM by Newsgroup_User

    PNG8+alpha colour banding.

    numbertwosuperguy Level 1
      I have a slice of an image that is of a solid dark grey colour, with a gradient at one edge. Its not a colour gradient, but a transparency gradient.
      It should work fine without any noticeable banding if I use an 8 bit palette.
      However, I get awful banding over the transparency-gradient.

      Yep, normal for 256 colours you may think... but despite asking for 256 colours, its using only 62!!!

      So I tried changing the colour selection method from Adaptive to Exact. The banding lessens, but all transparency is lost!!! (and uses only 57 colours) (...also, it forgets I selected Exact and still says Adaptive.)


      Whats going on????
        • 1. Re: PNG8+alpha colour banding.
          Level 7
          numbertwosuperguy wrote:
          > I have a slice of an image that is of a solid dark grey colour, with a gradient
          > at one edge. Its not a colour gradient, but a transparency gradient.
          > It should work fine without any noticeable banding if I use an 8 bit palette.

          8 bit color does not produce smooth gradients. It is also not capable of
          producing full, variable transparency. You need to use the 32 bit PNG
          format for that.

          --
          Linda Rathgeber [PVII] *Adobe Community Expert-Fireworks*
          --------------------------------------------------------------
          http://www.projectseven.com
          Fireworks Newsgroup: news://forums.projectseven.com/fireworks/
          CSS Newsgroup: news://forums.projectseven.com/css/
          http://www.adobe.com/communities/experts/
          --------------------------------------------------------------
          • 2. Re: PNG8+alpha colour banding.
            numbertwosuperguy Level 1
            Thanks Linda, but for anyone else trying to help out this is not a newbie question...

            Please read carefully the point I'm making about how Fireworks is only selecting 62 colours.
            If it were using the full 256 colours and I saw banding, then I would put my hands in the air and say fair enough.

            Why is Fireworks only electing to use 62 colours in my 256 colour png? Its giving me loads of banding!!!

            (I would attach screenshots if I could...)
            • 3. Re: PNG8+alpha colour banding.
              Level 7
              numbertwosuperguy wrote:

              > Why is Fireworks only electing to use 62 colours in my 256 colour
              > png? Its giving me loads of banding!!!

              >
              > (I would attach screenshots if I could...)

              If you want an answer to technical question about why the software works
              the way it does, then call Adobe support and see if you can't get an
              answer from one of the software Engineers. Otherwise, use 32 bit PNG or
              JPEG format.


              --
              Linda Rathgeber [PVII] *Adobe Community Expert-Fireworks*
              --------------------------------------------------------------
              http://www.projectseven.com
              Fireworks Newsgroup: news://forums.projectseven.com/fireworks/
              CSS Newsgroup: news://forums.projectseven.com/css/
              http://www.adobe.com/communities/experts/
              --------------------------------------------------------------
              • 4. Re: PNG8+alpha colour banding.
                Level 7

                > If it were using the full 256 colours and I saw banding, then I would put
                > my
                > hands in the air and say fair enough.

                Unless your gradient is going from pure black to pure transparent over a
                span of 256 pixels, then there simply ISN'T 256 colors to use in your image.

                Typically, to get rid of banding, in general, you want to add noise. You
                don't actually want a perfectly smooth gradient.

                > (I would attach screenshots if I could...)

                You can upload it to a server and link to it.

                -Darrel