Re: ProPhoto RGB or Adobe RGB 1998
Re: ProPhoto RGB or Adobe RGB 1998
- Subject: Re: ProPhoto RGB or Adobe RGB 1998
- From: Steve Upton <email@hidden>
- Date: Mon, 12 Jan 2004 17:26:04 -0800
I had a number of replies to this post (both on and off list) so to save time & space I'll respond to them piecemeal below
At 11:43 AM -0500 1/11/04, Roger Breton wrote:
>
> In other words when you move from camera/scanner profiles or large working
>
> space profiles to smaller working spaces, colorimetric intents are the only
>
> ones available - with the associated gamut clipping...
>
>
It never occurred to me that converting very saturated colors from AdobeRGB
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to sRGB or from a wider RGB working space to a smaller RGB working space
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*necessarily* involved gamut clipping and, for the moment, is only done
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through RelCol intents -- a matrix transform from one set of colorant matrix
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to another. Converting from scanner space to an RGB working space is done
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through the profiling package capabilities, either RelCol or Perceptual,
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depending on the profiling packag used to create the profile.
yes, but, While scanner/camera profiling packages could include a perceptual table in their RGB->Lab input profiles, the ICC spec did not require them to. So it is tough to say if Photoshop will even use the table when it is there (It has been a while since I tested this one - I;m pretty sure older versions of Photoshop will not use it)
>
What is the mechanism in the new ICC specs that will allow perceptual
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conversions from a larger RGB working space to a smaller RGB working space?
The mechanism is pretty much unchanged but the language in the spec a
>
>
Question: What is/are v4 profiles?
The ICC spec has been updated to version 4. So any profiles built to the new spec are now "v4" profiles. There have been some significant structural changes to the profile tags as well as a bunch (a whole bunch) of clarifications. As always, the spec is available from <
http://www.color.org>
>
Also, are you saying that what I am doing now, assigning and keeping the ProPhoto RGB working space, from camera RAW conversion on to printing on the 9600 is the right thing to do?
yes - to clarify what you said there RAW will do the conversion TO ProPhoto.
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From memory I seem to remember that matrix based spaces can't
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contain perceptual intents, so no perceptual on the Lab to RGB direction at
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least.
correct. Perceptual intents have to be built into a table unless CMM's get smarter.
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However what if you had a Lut based workingspace (J.Holmes ektaspace or
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whatever) Wouldn't it be possible then? Is there really such a beast?
yes it would be/is possible
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And wouldn't it be possible to use perceptual on the RGB to LAB part
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(camera) regardless of the output space?
yes if the app supports it. I think Photoshop finally does but am not sure. It's worth doing some testing on..
Regards,
Steve Upton
________________________________________________________________________
o Steve Upton CHROMiX www.chromix.com
o (hueman) 866.CHROMiX
o email@hidden 206.985.6837
o
o ColorGear ColorThink ColorValet ColorSmarts ProfileCentral
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