Split CFA with ISIS. What RAW file types?

[James Ley]

Can I use FITS files as the RAW files in ISIS to split CFA? Do they have to be CR2 or some other RAW file type?

I am trying to split a batch of FITS files into four groups of files, one for each channel of a CFA. ISIS doesn't seem to recognize my FITS files when I try to do this.

Thanks for any help.