[PHP] Is it possible to see if a jpeg is RGB or CMYK via PHP GD2?

[SED]

I'm allowing user to upload images to a gallery. However, some user seem to
have both RGB and CMYK jpeg images. I get an error from ImageCreateFromJPEG
when the script is creating thumbnails from a CMYK jpeg. Can I somehow see
if the image is RGB or CMYK, so I know when to skip the automatic thumbnail
creation?
 
Regards,
SED