This forum Topic was archived from the Adobe Photoshop Mac Forum in an effort to save this enlightening post by Photoshop color–management expert Andrew Rodney digitaldog.imagingrevue.com. All words copyrighted by their respective owner(s).

g ballard (wrote) - Jun 28, 2004

• "You cannot turn Photoshop's Color Management Off (since version 5)"
• I recall Andrew Rodney wrote those immortal words here in this forum.
• My question is: Do we really need the "since version 5"?
• I mean, if we feed v4 Adobe RGB (1998), it hosed, right?

Andrew Rodney (wrote) - Jun 29, 04 (#6 of 12)

Photoshop 4 (and earlier) operated quite differently than (today's) Photoshop in that (PS 4 and earlier sent) the numbers in the document straight to the display.

If you sent an Adobe RGB 1998 file to Photoshop 4, it would look pretty ugly (like how it appears in a dumb web browser) plus every user would see the same numbers differently.

In Photoshop 4 (and older), conversions from RGB to CMYK were assumed to be based upon your display (if you happen to even have an accurate Monitor preference file based on your display). Most users just had a preference that wasn't based on anything other than what got installed. What this means is even if you did calibrate say using the good old Radius Pressview (which had the option to save out a custom monitor preference file), any user who produced a CMYK conversion could not be insured that the same RGB doc would produce the same CMYK numbers even if they used the same separation setup (since the source plays a role in the destination and in this case, the source is based on your individual display). So CMYK conversions from PS4 and earlier could be rather chaotic in a mixed user environment.

Anyway, since PS5, the architecture has been such that Photoshop always makes some assumption about the numbers for previewing and conversions using ICC profiles. You can try and turn it off but it's always looking for a display profile for previews along with an embedded profile in a document. Even if you strip out the profile, Photoshop is still going to make an (assumption) about the numbers, again based on some ICC profile.

Prior to PS5, ICC profiles didn't enter the picture. You could have Photoshop ignore just about anything to do with color (it did of course have to make some assumption about RGB to make CMYK but this was based on the old Monitor preference). Other than that, Photoshop 4 would happily send the raw RGB numbers to a display that might or might not have been calibrated on a system that might or might not have an ICC profile for that display. That's no longer the case after PS5.

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Please see my BASIC PHOTOSHOP COLOR MANAGEMENT THEORY for how Photoshop deals with profiles and color spaces through CS5 Ps12.