can`t get a Alpha-Channel from a CMYK-TIFF-File

Post any defects you find in the released or beta versions of the ImageMagick software here. Include the ImageMagick version, OS, and any command-line required to reproduce the problem. Got a patch for a bug? Post it here.
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magick
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Post by magick »

Recent versions of ImageMagick do not assume a 4th channel means its alpha. To specify an alpha channel you need to set the TIFF extra samples attribute and declare it pre or unmultiplied alpha. Post a URL to your image here and we will verify if that is the problem with your image.
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magick
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Post by magick »

As mentioned, the problem is that the extra samples are not specified as associated or unassociated alpha. See http://www.awaresystems.be/imaging/tiff ... mples.html. It states
If an extra sample is used to encode information that has little or nothing to do with alpha, ExtraSample=0 (EXTRASAMPLE_UNSPECIFIED) is recommended.
However, even the TIFF library has a workaround for folks that do not honor this field. We will get this patch into the latest ImageMagick development release.
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