Opening Generic PDFs Import PDF Color Mode

Question

Hi,
When opening generic PDFs in Photoshop I am asked to choose the color mode... my question is, how do I know which one to choose? i.e. is there a way of finding out if the PDF was created from a RGB image or CMYK one?
Thanks and kind regards,
Frank.

Answer 1

Photoshop creates one image. If the PDF page contains one or more tagged images,
they will be shown correctly, but they are converted into the chosen target color space.
The same image in different spaces and tagged correctly will look identical.
If the PDF was created by InDesign, then Grayscale images lose their profile.
The same image in different grayscale modes will look different in Photoshop, which
is wrong.
A test example (about 4MB):
http://docs-hoffmann.de/riptest05072013.pdf
Here we see the GretagMacbeth ColorChecker in RGB and CMYK spaces.
The appearance is correct and measured values (by Info) are almost identical, but
they differ a little, which is caused by rounding errors, going through many profiles.
As well we see Grayscale versions of the ColorChecker, and because of the
well known bug in InDesign (tested up to CS6) the appearance differs.
Besides test PDFs it's in my opinion a bad habit to assemble components with
different color spaces in one PDF. An exception may be the case of raster images
in one RGB and vector graphics in one CMYK, especially for large format printers.
Best regards  --Gernot Hoffmann