Fix CMYK PTIFF generation

[mikeapp]

This PR fixes two issues:

• CMYK color profiles are not converted to sRGB successfully
• After conversion of the primary image, the compression applied in the generation of the PTIFF via tiffcp causes a failure, even if the constituent TIFFs all have an sRGB profile.

This needs further testing and we need to understand how many CMYK images we are likely to encounter, since the resulting files will be larger w/o compression.