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Re: v4 profiles and PRMG
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Re: v4 profiles and PRMG


  • Subject: Re: v4 profiles and PRMG
  • From: Graeme Gill <email@hidden>
  • Date: Wed, 06 Jun 2007 10:54:37 +1000

Andrew Rodney wrote:

On 6/5/07 8:36 AM, "Graeme Gill" wrote:

It's not a PCS, it's a gamut. It's designed around typical printing colors.
The idea of the V4 sRGB profile is that it will gamut map between sRGB and
the PRMG.

Just sRGB? I was under the impression it could be used for all color transforms (to print etc).

It can only have an influence over color transforms performed using profiles that make use of the PRMG as the target gamut, ie. using profiles that are build using the PRMG. So to do a transform from sRGB to PrinterA, both the sRGB and PrinterA profiles need to have been built using the PRMG as the target gamut.

Good deal. I just heard from X-Rite that so far, their product do not
support this. So the question is, what's the advantage and can one 'see' it
on output? My understanding is the use of this tag 'reduces ambiguity' for
end users since now there is a rendering-rerendering color space for
conversions that is well defined. I was also told that the difference in its
use versus a non defined (well non defined to the user) space might be quite
small. So while I can see the benefits in reducing ambiguity here, is this
helpful to the end user?

According to the proponents, it noticeably improves results for the casual color user. It may benefit the professional user as well, but there is limited flexibility, since the fundamental nature of making use of a standardized PCS gamut such as the PRMG is that you get a "Saturation" type intent, where the source gamut is both compressed and expanded to conform to the destination gamut.

If you do gamut mapping from the original source colorspace
directly to the destination colorspace (which is the workflow Argyll
supports) then you get a great deal more flexibility in choosing the
rendering intent, at the cost of the profiles being more specifically
tuned for a particular source to destination gamut, rather than
maintaining a neutral "mix and match" profile.

Ideally I'd like to test the differences and see what effects they produce.
Can this be done today? It sounds like Argyll can.

To a degree you can simulate the same result since you can plug in the PRMG as a source gamut during profile or link construction, but the results would not be expected to be exactly the same as other profiles from different tools, since Argyll (currently) is tuned for a single step gamut mapping rather than a two step via the PRMG, and each profile tool will have different gamut mapping algorithms (as per usual!).

Graeme Gill.

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