2 Replies Latest reply on Jan 24, 2007 6:03 AM by Newsgroup_User

    Index and Alpha transparencies

    Level 7
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      I am saving images in Gif with a transparent background and it gives me =
      a choice of index or alpha transparancy choices.

      I searched on Google to try to find the difference, but cannot. Can =
      anyone explain the difference between the two?

      Thank you,

      Scott
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      <DIV><FONT face=3DArial size=3D2>I am saving images in Gif with a =
      transparent=20
      background and it gives me a choice of index or alpha transparancy=20
      choices.</FONT></DIV>
      <DIV><FONT face=3DArial size=3D2></FONT> </DIV>
      <DIV><FONT face=3DArial size=3D2>I searched on Google to try to find the =
      difference,=20
      but cannot. Can anyone explain the difference between the =
      two?</FONT></DIV>
      <DIV><FONT face=3DArial size=3D2></FONT> </DIV>
      <DIV><FONT face=3DArial size=3D2>Thank you,</FONT></DIV>
      <DIV><FONT face=3DArial size=3D2></FONT> </DIV>
      <DIV><FONT face=3DArial size=3D2>Scott</FONT></DIV></BODY></HTML>

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        • 1. Re: Index and Alpha transparencies
          Level 7
          Scott Powell wrote:

          > I am saving images in Gif with a transparent background and it gives me a choice of index or alpha transparancy choices.
          >
          > I searched on Google to try to find the difference, but cannot. Can anyone explain the difference between the two?

          Index transparency is used for GIF images. GIFs allow single-bit
          transparency, which means when you are creating your image, you can
          specify one color to be transparent.

          Alpha transparency is used for PNG files. Instead of the vestigial
          transparency option of the GIF format, where a pixel is either
          transparent or opaque, an alpha channel can specify the opacity of any
          pixel from 0–255, where 0 is fully transparent and 255 is fully opaque.
          This allows you to create a graphic that can be placed on top of any
          background color and will retain a translucent effect, with the
          background showing through the pixels that are not opaque. The drawback
          is that I.E. versions 5 & 6 do not display variable Alpha transparency
          without a workaround. I.E.7 gets it right, however.

          --
          Linda Rathgeber [PVII] *Adobe Community Expert-Fireworks*
          --------------------------------------------------------------
          http://www.projectseven.com
          Fireworks Newsgroup: news://forums.projectseven.com/fireworks/
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          • 2. Re: Index and Alpha transparencies
            Level 7
            On Wed, 24 Jan 2007 03:16:10 +0300, Scott Powell <sp2@glweb.biz> wrote:

            > I am saving images in Gif with a transparent background and it gives me
            > a choice of index or alpha transparancy choices.

            Transparency in GIF files themselves is always index one. However, you may
            try to use existing alpha channel in your PNG source to build the
            transparency for GIFs. Be warned, however, that since alpha transparency
            allows partial transparency, and index one does not, you may get ugly
            jaggies as a result, so choose "matte" color equal to that of your Web
            background.

            --
            Ilya Razmanov
            http://photoshop.msk.ru - Photoshop plug-in filters