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POConverting TIFF Alpha Channel from Unassociated to Associated
 

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  1. POConverting TIFF Alpha Channel from Unassociated to Associated
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    <p>For a dynamic imaging application I'm building, I have to take an image created by a rendering package and place it in an InDesign file. Because it needs to be CMYK with transparency, TIFF is the only possible format to use. The difficulty I'm having is that the renderer is generating an image with an unassociated alpha channel, which InDesign seems to have trouble understanding.</p> <p>I'm working with the renderer manufacturer to see if they can change their output format, but in the mean time I would like to find some automated workflow to convert a CMYK TIFF with unassociated alpha to have associated (premultiplied) alpha.</p> <p>I tried using GraphicsMagick's command-line tool (which would be easily scriptable), but the closest I could get simply forced the TIFF flag to get written as premultiplied--it didn't actually perform the premultiplication. The effect is a working alpha but with washed out color:</p> <pre><code>gm -convert &lt;infile&gt; -define tiff:alpha=associated &lt;outfile&gt; </code></pre> <p>Does anybody have other suggestions on how to achieve this conversion? My primary requirement is that it needs to be automatable in a Linux server environment, ideally via either scripting or a PHP library (since that's already being used elsewhere in the workflow), but I'm flexible on the PHP bit.</p> <hr> <p><strong>Edit:</strong></p> <p>For reference here are the two files (42MB each):</p> <ul> <li><a href="https://dl.dropbox.com/u/4829232/image.tif" rel="nofollow">Original TIFF with unassociated alpha</a></li> <li><a href="https://dl.dropbox.com/u/4829232/image-gm.tiff" rel="nofollow">Modified TIFF from GM with pseudo-associated alpha and washed out color</a></li> </ul>
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    1. PTQuestion
    1. USScott Buchanan
    1. USScott Buchanan
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    1. COCan you post a (link to a) sample TIFF file of yours with an unassociated alpha channel?
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      1. POConverting TIFF Alpha Channel from Unassociated to Associated
      1. USKurt Pfeifle
    2. COI added links to the question.
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      1. POConverting TIFF Alpha Channel from Unassociated to Associated
      1. USScott Buchanan
 

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