RE: U.S. Sheetfed vs. U.S. SWOP
RE: U.S. Sheetfed vs. U.S. SWOP
- Subject: RE: U.S. Sheetfed vs. U.S. SWOP
- From: Steve Upton <email@hidden>
- Date: Wed, 2 May 2007 16:10:31 -0700
At 8:21 AM -0400 5/2/07, Mike Eddington wrote:
> >>Thought I goofed so I looked at the profiles again and confirmed that
>I
>>>was looking at US Sheetfed Coated rather than the UnCoated. Yes, the
>>>profile appears smaller in gamut volume than US SWOP in the ColorSync
>>>utility using the Yuv view. Any suggestions on how to empirically
>evaluate
>>>the gamut of a profile when comparing to another profile?
>
>I was using ColorThink Pro, and also Monaco Gamut Works which both show
>the US sheetfed Coated profile as larger than the US SWOP profile...but
>yeah, I can confirm what you're saying. The Colorsync utility shows it
>as a smaller gamut. After viewing some other profiles of mine, I must
>say I'm clueless as to what's going on with how the colorsync utility
>displays gamut volume as there's some very strange plots compared to
>what ColorThink and GamutWorks come up with. In short, I don't trust
>it.
>
>Can anyone offer any insight the differences between the Colorsync
>Utility's gamut plots compared with say ColorThink Pro?
yup, I can :-)
The primary difference you are seeing between ColorThink Pro (CTPro) and the ColorSync Utility (CSU) is that CTPro plots using absolute colorimetry and the CSU plots using the 'perceptual' intent.
This is when you are looking at the list of profiles and select one profile to view. If you have opened a single profile into CSU and select any of the A2Bx intents, then they will be graphed with that intent...
What this really means:
There are 4 different ways of graphing the device->Lab transform of a profile:
1. Perceptual - CSU(A2B0 table or select profile in list), CTPro(option) - you are seeing the gamut of device-values as they are converted to Lab using the perceptual intent.
2. Relative Colorimetric - CSU(A2B1 table), CTPro(option) - you are seeing the gamut of device-values as they are converted to Lab using the rel con intent.
3. Saturation - CSU(A2B2 table), CTPro(option) - you are seeing the gamut of device-values as they are converted to Lab using the saturation intent.
4. Absolute Colorimetric - CSU( not available ), CTPro(default) - you are seeing the gamut of the device as described by the profile. The white point is lowered to actual paper white and the black point raised to ink black..
The graphs of 1-3 are of limited use (if any) to the average user as they describe the 'proofing' behavior of a specific part of the profile. They do NOT describe the gamut of the device OR the behavior of the profile when used to OUTPUT an image. It is interesting to see how rel col raises the black level vs perceptual and saturation though.
#4 describes the gamut of the device and is a far more useful graph - and is typically what people expect when graphing a profile.
A good way to confirm this device gamut is to also plot (in ColorThink) the measurement data that created the profile and you'll find that the profile conforms to the measurement data closely - at least on good profiles. This is a good sanity check for profiles.
The use of the perceptual intent for the default graph in the CSU is not a good idea - it probably grabs the default intent recorded in the profile's header, but I'm not sure. The gamut shown (without explanation) is again, NOT for the device and NOT the gamut produced when printing. Strictly speaking, it is the gamut that you'll receive from the profile when using it to convert a CMYK file to Lab (and on to another profile) using the perceptual intent; something that is rarely performed in a workflow. Even in CMYK to CMYK conversions, rel col with BPC is recommended...
Regards,
Steve
________________________________________________________________________
o Steve Upton CHROMiX www.chromix.com
o (hueman) 866.CHROMiX
o email@hidden 206.985.6837
o ColorGear ColorThink ColorValet ColorSmarts ProfileCentral
________________________________________________________________________
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