RES: Colorsync-users Digest, Vol 5, Issue 248
RES: Colorsync-users Digest, Vol 5, Issue 248
- Subject: RES: Colorsync-users Digest, Vol 5, Issue 248
- From: "Pedro Gargalaca" <email@hidden>
- Date: Fri, 25 Jul 2008 16:35:04 -0300
1. Re: Color values for paint matching? (Calabria, Anthony)
Reply
Anthony, the Paint stores normally will work with an spectrophotometer and a
database to make custom colors. The database will formulate based on
spectral values generated by the spectro.
Pedro Gargalaca
Coralis | Authorized Distributor X-Rite®
LÃder em soluções para gerenciamento de cores
* Para conhecer nossos produtos, seviços e cursos, acesse nosso site.
http://www.coralis.com.br | +55 11 2915-0544
Blog - gerenciamento de cores e colorimetria
http://pedrogargalaca.blogspot.com/
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Enviada em: sexta-feira, 25 de julho de 2008 16:03
Para: email@hidden
Assunto: Colorsync-users Digest, Vol 5, Issue 248
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Today's Topics:
1. Re: Color values for paint matching? (Calabria, Anthony)
2. Re: Rendering intents in source profiles? (Uli Zappe)
3. Re: Rendering intents in source profiles? (Karl Koch)
4. Re: Rendering intents in source profiles? (Uli Zappe)
5. Re: Rendering intents in source profiles? (Marc Levine)
6. Re: Rendering intents in source profiles? (Roger Breton)
7. Re: Rendering intents in source profiles? (Roger Breton)
8. Re: Rendering intents in source profiles? (Roger Breton)
9. Colorsync utility and unfixable profiles (J Richter)
10. Re: Colorsync utility and unfixable profiles (Klaus Karcher)
11. Re: Rendering intents in source profiles? (Klaus Karcher)
12. Re: Rendering intents in source profiles? (Klaus Karcher)
----------------------------------------------------------------------
Message: 1
Date: Thu, 24 Jul 2008 15:21:57 -0400
From: "Calabria, Anthony" <email@hidden>
Subject: Re: Color values for paint matching?
To: <email@hidden>
Cc: email@hidden
Message-ID:
<email@hiddenminmoore1
.com>
Content-Type: text/plain; charset="us-ascii"
Eric,
Most commercial paint software matches spectral reflectance with some
form of a Kubelka-Munk or Multiflux system.
Anthony
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Wed, 23 Jul 2008 16:03:40 -0400
> From: Eric Bullock <email@hidden>
> Subject: Color values for paint matching?
> To: <email@hidden>
> Message-ID: <C4AD06DC.19E8ëemail@hidden>
> Content-Type: text/plain; charset="ISO-8859-1"
>
> Does anyone know what kinds of color values are used in matching paint
> samples? For instance if I take my sample to a paint store and they
put it
> in their "matching doodad", what kind of colorimetry is it recording?
Lab?
> Lch?
>
> Cheers,
>
> : : : : : :
> Eric Bullock
> Manager of Information Technology
> Center for Digital Imaging Arts at Boston University
>
> www.cdiabu.com
>
>
>
*****************************
------------------------------
Message: 2
Date: Fri, 25 Jul 2008 08:43:52 +0200
From: Uli Zappe <email@hidden>
Subject: Re: Rendering intents in source profiles?
To: email@hidden
Cc: ColorSync <email@hidden>
Message-ID: <email@hidden>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed; delsp=yes
Am 24.07.2008 um 05:05 schrieb Graeme Gill:
> Welcome to the path of enlightenment :-)
I already felt more enlightened at times ... ;-)
>> For instance, take the classic example of a conversion from working
>> space to printer space. Since the printer space is smaller, gamut
>> compression or clipping obviously has to be performed. *But* this
>> should take place in the B2An tag of the printer profile (= target
>> profile), which "knows" about the limitations of the printer and
>> can adjust the gamut accordingly.
>
> Oh, how can that work, since the output profile does not "know" what
> input profile it is going to be linked to ?
I see your point in that it would be practically unreasonable to
provide for a gamut compression so intense that each and every Lab
color from the PCS could be matched to the target space, even those
that will probably never come from any kind of source profile.
However, impossible as it may be to fulfill it, the task is clear at
least: take care that all colors from the PCS are either clipped (no
problem) or compressed (above problem) so that they fit into the
target space. I can't even formulate the related task for the A2B
direction: map every color to the PCS - yep, this will always work by
definition, so what?
*Maybe* (just maybe) this is a vendor specific strategy: build target
profiles that assume that only a specific subset of Lab colors has to
be matched *AND* take care in your source profiles that only these
colors will be delivered to the PCS (thus already an A2B match)? This
would mean that profiles of such a vendor would be "more compatible"
to themselves than to profiles from other vendors. But this is pure
speculation on my part ...
> [ Note that my ArgyllCMS profiler solves this problem by allowing a
> source profile or gamut to be specified at output profile creation
> time.]
A very compelling idea. :-)
> My guess has always been that the the allowance for intent in the
> A2B tables is part of a (flawed or at least limited) scheme to make
> gamut mapping work in the ICC profile world, by allowing the input
> profile to map the input device gamut to a "standard" PCS gamut, and
> then have the output profile map from the PCS gamut to the output
> device gamut. It's limitation is that it only really works for (what
> I would call) saturation intent, since the gamut surfaces will be
> mapped to gamut surface (expansion of gamut as well as compression).
OK, so I don't feel alone with my thoughts ... :-)
> Up until an addendum to ICCV4 however (PRMG),
Oh, thanks for this hint - I hadn't heard about the PRMG, and this is
extremely interesting in that it basically confirms the above thoughts.
> there has been no standard PCS gamut to make this scheme inter-
> operable between profiles from different profile creation software.
Exactly ...
Again, thanks a lot, this cleared this up quite a bit, and I'm kind of
relieved that it wasn't only stupidity on my part ;-))
Bye
Uli
________________________________________________________
Uli Zappe, Solmsstra_e 5, D-65189 Wiesbaden, Germany
http://www.ritual.org
Fon: +49-700-ULIZAPPE
Fax: +49-700-ZAPPEFAX
________________________________________________________
------------------------------
Message: 3
Date: Fri, 25 Jul 2008 09:43:22 +0200
From: Karl Koch <email@hidden>
Subject: Re: Rendering intents in source profiles?
To: ColorSync <email@hidden>
Cc: Uli Zappe <email@hidden>, email@hidden
Message-ID: <email@hidden>
Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed
Hi all,
>
>> [ Note that my ArgyllCMS profiler solves this problem by allowing
>> a source profile or gamut to be specified at output profile
>> creation time.]
>
> A very compelling idea. :-)
you can add basICColor print to the list of products that allow a
source profile to be specified for output profile creation. In
addition to that you can define the gamut compression ratio in the
perceptual rendering intent on a scale from 0 to 100.
Best regards,
Karl Koch
------------------------------
Message: 4
Date: Fri, 25 Jul 2008 09:48:05 +0200
From: Uli Zappe <email@hidden>
Subject: Re: Rendering intents in source profiles?
To: Karl Koch <email@hidden>
Cc: ColorSync user <email@hidden>
Message-ID: <email@hidden>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed; delsp=yes
Am 25.07.2008 um 09:43 schrieb Karl Koch:
> you can add basICColor print to the list of products that allow a
> source profile to be specified for output profile creation. In
> addition to that you can define the gamut compression ratio in the
> perceptual rendering intent on a scale from 0 to 100.
With "100" meaning all colors will be compressed (if necessary), and
"0" meaning all will be clipped (if necessary)? So that perceptual set
to "0" basically is relative colorimetric?
Bye
Uli
________________________________________________________
Uli Zappe, Solmsstra_e 5, D-65189 Wiesbaden, Germany
http://www.ritual.org
Fon: +49-700-ULIZAPPE
Fax: +49-700-ZAPPEFAX
________________________________________________________
------------------------------
Message: 5
Date: Fri, 25 Jul 2008 10:35:03 -0400
From: Marc Levine <email@hidden>
Subject: Re: Rendering intents in source profiles?
To: email@hidden
Message-ID: <email@hidden>
Content-Type: text/plain; charset=US-ASCII; format=flowed;
delsp=yes
Uli,
The ICC spec allows for different A2B tables to permit users to take
an image in and out of that colorspace without changing the original
color content. In other words, A2B tables are supposed to be the
inverse of the B2A tables. If the B2As are different, then the A2Bs
will be different. For example, the gamut compression in a perceptual
B2A0 tag is uncompressed in the A2B0 tag. If you transform an RGB
image using a CMYK profile and then go back to RGB......
RGB image1->B2A0->CMYK image->A2B0->RGB image2
You would end up with two RGB images that looked very similar to each
other.
For an input profile, the A2B0 tag can be used to create a more
pleasing image. For example, a digital camera profile cam pump up the
saturation and contrast in the A2B0 tag, but have colorimetric data in
the A2B1 tag.
Hope this helps.
Marc
--
Marc Levine
Color Management Group Guy
email@hidden
PS: James, thanks for the guidance.
>> So why are there rendering intents for A2Bn tags, and what do they
>> actually do? The ICC spec does define separate perceptual,
>> colorimetric and saturation intents for A2Bn tags (A2B0, A2B1 and
>> A2B2), and if you test real world profiles as built by e.g.
>> ProfileMaker, you will find that they do produce different PCS Lab
>> values for the three intents. But according to which logic??
>>
>> Thanks a lot in advance for any insight!
>>
>> Bye
>> Ul
------------------------------
Message: 6
Date: Fri, 25 Jul 2008 10:58:11 -0400
From: Roger Breton <email@hidden>
Subject: Re: Rendering intents in source profiles?
To: Graeme Gill <email@hidden>, ColorSync
<email@hidden>
Message-ID: <C4AF6243.26C99%email@hidden>
Content-Type: text/plain; charset=US-ASCII
Graeme,
Are you implying that, for optimal gamut mapping, today, we'd benefit by
taking the time to develop collections of devicelink profils for use with
our favorite Source color spaces going out to our favorites Destination
spaces?
If, for instance, I have a collection of RGB images, say in PhotodiscRGBI
space, which was popular with Photodisc images at one point, you're saying
that, in order to get optimal gamut mapping between PhotodiscRGBI and, say,
my lowly HP or Canon printer profile, I'd benefit from creating an ArgyllCMS
devicelink profile that would convert from PhotodiscRGBI to HP or Canon?
As oppose to using a "blind", fixed, uninformed conversion taking place in
PCS? As in any regular ICC conversion?
> Oh, how can that work, since the output profile does not "know" what
> input profile it is going to be linked to ?
>
> [ Note that my ArgyllCMS profiler solves this problem by allowing
> a source profile or gamut to be specified at output profile creation
time.]
>
> Graeme Gill.
Roger Breton
------------------------------
Message: 7
Date: Fri, 25 Jul 2008 11:02:14 -0400
From: Roger Breton <email@hidden>
Subject: Re: Rendering intents in source profiles?
To: Karl Koch <email@hidden>, ColorSync
<email@hidden>
Message-ID: <C4AF6336.26C9B%email@hidden>
Content-Type: text/plain; charset=US-ASCII
Karl,
The more you describe basICColor on this list, the more I have the
impression that it's very advanced. Is there like, possibly, some
time-limited, fully functional version one could try? Available on your web
site, by any chance? And how is your documentation?
MfG,
> you can add basICColor print to the list of products that allow a
> source profile to be specified for output profile creation. In
> addition to that you can define the gamut compression ratio in the
> perceptual rendering intent on a scale from 0 to 100.
>
> Best regards,
>
> Karl Koch
Roger Breton
------------------------------
Message: 8
Date: Fri, 25 Jul 2008 11:06:53 -0400
From: Roger Breton <email@hidden>
Subject: Re: Rendering intents in source profiles?
To: Uli Zappe <email@hidden>, Karl Koch <email@hidden>
Cc: ColorSync <email@hidden>
Message-ID: <C4AF644D.26C9D%email@hidden>
Content-Type: text/plain; charset=US-ASCII
Hallo Karl und Uli,
I suspect, to really do a good job of gamut mapping, you would not want to
have a "global" approach but a "selective", "local" approach? If 100 means
all farben kompressed, surely all colors could not be compressed the *same*?
Or uniformly? Across all hue angles?
I am refering to the typical RGB gamut shape where the blue has a large
chroma and, in my mind, would require a differential compression than, say,
the reds or greens? Because those have typical less chroma? So therefore,
the rate of compression would have to be adjusted according to the hue
angle?
>> you can add basICColor print to the list of products that allow a
>> source profile to be specified for output profile creation. In
>> addition to that you can define the gamut compression ratio in the
>> perceptual rendering intent on a scale from 0 to 100.
>
> With "100" meaning all colors will be compressed (if necessary), and
> "0" meaning all will be clipped (if necessary)? So that perceptual set
> to "0" basically is relative colorimetric?
>
> Bye
> Uli
Roger Breton
------------------------------
Message: 9
Date: Fri, 25 Jul 2008 12:45:44 -0400
From: J Richter <email@hidden>
Subject: Colorsync utility and unfixable profiles
To: Colorsync-users on Apple Lists <email@hidden>
Message-ID: <email@hidden>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
I am in the process of moving my color setup from my Apple G4 under
Tiger to a G5 under Leopard (X.5.2). I've moved/copied/collected all my
profiles into the ~/library/colorsync/profiles folder and ran verify and
repair on the complete list. Problem is now that the Repair utility is
unable to fix many of the previously working profiles. Is there some
manual way to repair them? This is the most frequent error:
Library/ColorSync/Profiles/SC3000_GP_720.icc
Tag 'dmnd': Tag size is not correct. Could not be fixed.
Library/ColorSync/Profiles/SC3000_PQP_1440.icc
Tag 'dmnd': Tag size is not correct. Could not be fixed.
A bunch of these are Epson factory provided profiles for my trusty 3000
and 1270 printers and I would hate to lose them.
Any ideas? Thank you...
------------------------------
Message: 10
Date: Fri, 25 Jul 2008 19:20:15 +0200
From: Klaus Karcher <email@hidden>
Subject: Re: Colorsync utility and unfixable profiles
To: colorsync-users <email@hidden>
Message-ID: <email@hidden>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
J Richter wrote:
> I am in the process of moving my color setup from my Apple G4 under
> Tiger to a G5 under Leopard (X.5.2). I've moved/copied/collected all my
> profiles into the ~/library/colorsync/profiles folder and ran verify and
> repair on the complete list. Problem is now that the Repair utility is
> unable to fix many of the previously working profiles. Is there some
> manual way to repair them? This is the most frequent error:
>
> Library/ColorSync/Profiles/SC3000_GP_720.icc
> Tag 'dmnd': Tag size is not correct. Could not be fixed.
> Library/ColorSync/Profiles/SC3000_PQP_1440.icc
> Tag 'dmnd': Tag size is not correct. Could not be fixed.
The 'dmnd' tag contains the device manufacturer -- it's not required for
color conversions, so the profiles will still work in almost every case.
> A bunch of these are Epson factory provided profiles for my trusty 3000
> and 1270 printers and I would hate to lose them.
>
> Any ideas? Thank you...
You can try to re-install the profiles (I guess they are part of the
driver or utility installation), but it's quite possible that the dmnd
tag is also invalid in the original profile. I have seen many flawed or
not standard-compliant profiles from different vendors. That's not not
pretty, but as long as they basically work, there is no mandatory reason
to trow them away.
You can also try to fix the profiles by editing the dmnd in colorsync
utility: duplicate one of the profiles, edit the dmnd, save in and check
if profile repair still complains.
Klaus
------------------------------
Message: 11
Date: Fri, 25 Jul 2008 19:31:31 +0200
From: Klaus Karcher <email@hidden>
Subject: Re: Rendering intents in source profiles?
To: colorsync-users <email@hidden>
Message-ID: <email@hidden>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Marc Levine wrote:
> [...] In other words, A2B tables are supposed to be the inverse of
> the B2A tables.
That's what the ICC whitpaper provideds. Unfortunately this symmetry
conflicts with the aim of the perceptual intent as Graeme pointed out.
Klaus
------------------------------
Message: 12
Date: Fri, 25 Jul 2008 20:41:11 +0200
From: Klaus Karcher <email@hidden>
Subject: Re: Rendering intents in source profiles?
To: colorsync-users <email@hidden>
Message-ID: <email@hidden>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Karl Koch wrote:
> you can add basICColor print to the list of products that allow a source
> profile to be specified for output profile creation.
congratulations :-)
The "list" you mentioned is pretty manageable. AFAIK it has only two
members: ArgyllCMS and basICColor.
And with basICColor DeviL and demon you have already take the second
step on the "path of enlightenment" ;-): the optimal gamut mapping can
not be computed until both the input and output gamuts are known.
But Graeme is sill at least one step ahead: optimal gamut mapping does
not depend on the "gamut" of the input /device/ (what is the gamut of an
input device? [1]) -- optimal gamut mapping depends on the /subjects/
you want to reproduce. Therefore Argyll provides tools to identify the
gamut of /images/ and Argyll's profiling tools can use these gamut files
to adapt the gamut mapping.
... and for a short time there is a Tool form Alastair M. Robinson that
aggregates the steps of gamut identification, DL profile creation and
image conversion in a nice an simple to use GUI app [2].
Klaus
[1] <http://www.freelists.org/archives/argyllcms/01-2008/msg00092.html>
[2]
<http://www.freelists.org/cgi-bin/archive-search.fcgi?query=imgtarget&list=a
rgyllcms>
------------------------------
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End of Colorsync-users Digest, Vol 5, Issue 248
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