3 Replies Latest reply on Apr 20, 2006 4:58 AM by Newsgroup_User

    PNG 8-bit Indexed With Alpha

    DavidManpearl
      Hello,

      I need to write PNG images in 8-bit indexed mode ( Color Type 3... ?) with an alpha channel. I believe that the only way to do this is by putting the Alpha (or Matte) information into a PNG tRNS Chunk. I have heard that Fireworks can do this, but have not yet been successful. Please tell me how.

      BTW, I can write PNG files in 32-bit ARGB mode, but this is unacceptible because the compression is lossless and the files become huge. XnView supports this as well. Photoshop will not allow me to write PNG with Alpha. Can Fireworks help me? How?

      - Thank you, David Manpearl <dmanpearl_at_imatte_dot_com>
        • 1. Re: PNG 8-bit Indexed With Alpha
          Level 7
          DavidManpearl wrote:


          It works the same way as a GIF file. Pick a single color to be transparent.



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          Linda Rathgeber ACE ::: PVII
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          • 2. Re: PNG 8-bit Indexed With Alpha
            DavidManpearl Level 1
            Hello Linda,

            Thank you very much for your suggestion of making one of the image colors represent transparent matte, as in a GIF format image.
            Unfortunately, this cannot work for me as I need color information for all of the pixels in the image, regardless of the setting of the matte, or alpha channel value. Perhaps this is impossible for PNG with indexed color? The answer to this question is what I hope to determine one way or the other through this forum.

            - Sincerely, David Manpearl <dmanpearl_at_imatte_dot_com>
            • 3. Re: PNG 8-bit Indexed With Alpha
              Level 7
              DavidManpearl wrote:
              > Hello Linda,
              >
              > Thank you very much for your suggestion of making one of the image colors
              > represent transparent matte, as in a GIF format image.
              > Unfortunately, this cannot work for me as I need color information for all of
              > the pixels in the image, regardless of the setting of the matte, or alpha
              > channel value. Perhaps this is impossible for PNG with indexed color? The
              > answer to this question is what I hope to determine one way or the other
              > through this forum.

              Why not just export in 8-bit PNG format, with no transparency, and see
              if it works?


              --
              Linda Rathgeber ACE ::: PVII
              http://www.projectseven.com
              Fireworks Newsgroup: news://forums.projectseven.com/fireworks/
              CSS Newsgroup: news://forums.projectseven.com/css/
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