Questions and postings pertaining to the usage of ImageMagick regardless of the interface. This includes the command-line utilities, as well as the C and C++ APIs. Usage questions are like "How do I use ImageMagick to create drop shadows?".
The proper way to convert RGBA to CMYK is with two color profiles (e.g. sRGB & SWOP). The alpha channel should automatically be carried forward during the conversion. If not, try upgrading your version of ImageMagick and see if that fixes the problem. The current version of ImageMagick is 6.2.7-0.
