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Posted: 2006-02-13T10:19:11-07:00
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.
Posted: 2006-02-13T14:55:33-07:00
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.