I expect many different problems manifest as GMIC simply not appearing at the bottom of the Filters menu, but it's worth making sure you're running the latest Gimp for Mac (2.6.11 from
http://gimp.lisanet.de/). I was running 2.6.7, which silently failed.
A good test for any problematic GMIC installation is to try running gmic_gimp directly from Terminal (doesn't have to be run from the correct installation directory, but putting it there is a start):
$ ~/Library/Application\ Support/Gimp/plug-ins/gmic_gimp
If you get something like this:
dyld: Library not loaded: /tmp/skl/Gimp.app/Contents/Resources/lib/libgimpui-2.0.0.dylib
Referenced from: ~/Library/Application Support/Gimp/plug-ins/gmic_gimp
Reason: no suitable image found. Did find:
/tmp/skl/Gimp.app/Contents/Resources/lib/libgimpui-2.0.0.dylib: no matching architecture in universal wrapper
Trace/BPT trap
then your problem could be the same I had. GIMP 2.6.7 has libraries for PPC and i386:
$ file /tmp/skl/Gimp.app/Contents/Resources/lib/libgimpui-2.0.0.dylib
/tmp/skl/Gimp.app/Contents/Resources/lib/libgimpui-2.0.0.dylib: Mach-O universal binary with 2 architectures
/tmp/skl/Gimp.app/Contents/Resources/lib/libgimpui-2.0.0.dylib (for architecture i386): Mach-O dynamically linked shared library i386
/tmp/skl/Gimp.app/Contents/Resources/lib/libgimpui-2.0.0.dylib (for architecture ppc7400): Mach-O dynamically linked shared library ppc
but the latest gmic_gimp wants libraries for i386 and x86_64:
$ file ~/Library/Application\ Support/Gimp/plug-ins/gmic_gimp
~/Library/Application Support/Gimp/plug-ins/gmic_gimp: Mach-O universal binary with 2 architectures
~/Library/Application Support/Gimp/plug-ins/gmic_gimp (for architecture i386): Mach-O executable i386
~/Library/Application Support/Gimp/plug-ins/gmic_gimp (for architecture x86_64): Mach-O 64-bit executable x86_64
GIMP 2.6.11 has the architectures you want (same command as above, but after upgrading GIMP):
$ file /tmp/skl/Gimp.app/Contents/Resources/lib/libgimpui-2.0.0.dylib
/tmp/skl/Gimp.app/Contents/Resources/lib/libgimpui-2.0.0.dylib: Mach-O universal binary with 2 architectures
/tmp/skl/Gimp.app/Contents/Resources/lib/libgimpui-2.0.0.dylib (for architecture i386): Mach-O dynamically linked shared library i386
/tmp/skl/Gimp.app/Contents/Resources/lib/libgimpui-2.0.0.dylib (for architecture x86_64): Mach-O 64-bit dynamically linked shared library x86_64
Hope that helps someone.
zw