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.
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.
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.
