Re: [Lcms-user] Re: New page for 1.10 betas available on site

[<ma...@li...>]

Hi,

> One (stupid) question right now:  Was there any substantial change in
> softproof/preview between 1.10 beta and release candidate?  I noticed
> that doing softproof+out-of-gamut check with some profiles in 1.10
> beta showed the entire image as green (out of gamut) but with the same
> profiles using 1.10 release candidate, small parts of the image are in
> gamut.

This is not in any way a stupid question. I've been talking about the
gamut checking problem with Tony Johnson, Professor of
London College of Printing, active member of  ISO TC130,
CIE TC8-03 and TC8-05 and one of the really  knowleageable
people on color science world.

He told me that true gamut checking using only a profile, simply
cannot be done.

So... lcms is doing only a *very coarse* approximation. It may
work on some profiles, and will totally fail on others. How far this
matches Photoshop is a open question, but clearly the gamut checking
done by Photoshop is one of the many "secret sauces" owned by
Adobe.

The conclusion is: don't trust too much in gamut checking facility, at
least right now. Version 4.2 ICC profiles will have means to do an
accurate gamut checking. But not with current profiles.


Regards,
Martí Maria
The little cms project
http://www.littlecms.com
ma...@li...

P.S. Please, don't misunderstand my words as I'm not saying in
any way Photoshop doesn't work. I simply am saying the gamut
checking done by Photoshop is propietary, and Im not willing to
reverse engineering it in any way :-)



----- Original Message -----
From: "Mark Rubin" <mar...@ya...>
To: <lcm...@li...>
Sent: Wednesday, February 19, 2003 7:14 PM
Subject: [Lcms-user] Re: New page for 1.10 betas available on site


> "Martí_Maria" <ma...@li...> writes:
>
> > This includes fixes for all bugs uncovered up to date. As usual, any
> > feedback would be greatly appreciated.
>
> As always, Marti -- thanks.
>
> I compiled and lightly tested the release candidate code.  No problems
> so far.  I hope to get back to actively developing code using LCMS, so
> will probably have more (stupid) questions soon.  :-)
>
> One (stupid) question right now:  Was there any substantial change in
> softproof/preview between 1.10 beta and release candidate?  I noticed
> that doing softproof+out-of-gamut check with some profiles in 1.10
> beta showed the entire image as green (out of gamut) but with the same
> profiles using 1.10 release candidate, small parts of the image are in
> gamut.
>
> This is not an important question because I'm unsure of the quality of
> the profiles I'm using, and also unsure that the GIMP plugin is
> working correctly (as I wrote previously, I hacked it only enough to
> compile, read profiles, and verify there was a change to the image).
> The profiles, when used normally without softproof, don't seem that
> radical, so I'm surprised by the amount of out-of-gamut areas that are
> shown.  Again, I intend to get back to fixing the GIMP plugin (or re-
> writing it from scratch since I've spent the last week successfully
> deciphering the GIMP plugin API) and to generating my own printer
> profile rather than using the manufacturer-supplied one (which I know
> is wrong).
>
> Thanks again, and I'm looking forward to the 1.10 final release.
>
>
> =====
> --
> MARK
> mar...@ya...
>
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