Re: preview/photoshop
Re: preview/photoshop
- Subject: Re: preview/photoshop
- From: Chris Murphy <email@hidden>
- Date: Thu, 13 Jan 2005 06:16:28 -0700
On Jan 12, 2005, at 3:39 PM, Ross Peterson wrote:
Yes. Or at least pretty darn close. I still see a very slight difference when things are working properly. If you are experiencing what I had going in the past you can expect better than that. I have not seen, but would like to see a good explanation from Apple why they are not exactly the same however.
There are a couple of explanations. If the source and destination (display) profile are the small, simple, matrix-based profiles the CMM plays a huge role in gamut mapping and probably accounts for most of the difference. Photoshop always uses ACE as the CMM when performing display compensation. Photoshop also uses Relative Colorimetric rendering to the display. Preview *converts* tagged images upon being opened, and always uses the Apple CMM. I'm not sure what intent it defaults to but it could be the profile default which is often Perceptual.
If the source profile is an input or output profile (scanner profile or printer profile for example), Photoshop is using Relative Colorimetric plus black point compensation to the display. Whatever intent Preview is using, it's not using black point compensation.
So in both of these cases you can be virtually assured of some differences between how the same image is displayed in Photoshop and Preview (or any other application that's unable to use ACE).
Chris Murphy
Color Remedies (TM)
www.colorremedies.com/realworldcolor
-------------------------------------------------------------
Co-author "Real World Color Management, 2nd Edition"
Published by PeachPit Press (ISBN 0-321-26722-2)
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