Re: CMM "interfering" with PS color picker?
Re: CMM "interfering" with PS color picker?
- Subject: Re: CMM "interfering" with PS color picker?
- From: Chris Murphy <email@hidden>
- Date: Fri, 2 Feb 2001 11:51:29 -0700
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There are a lot of things happening when converting RGB to CMYK:
That is the problem. If the specification expects white point mapping to
only occur with the absolute colorimetric rendering intent, then in order
to PREVENT it from happening with the other rendering intents, it doesn't
make sense to do all of these white point calculations when 255,255,255
RGB is encountered.
It makes more sense for the CMM to go "oh, 255,255,255 RGB is inherently
255,255,255 RGB *OR* 0,0,0,0CMYK (or 0% of any other channel in
multi-channel profiles)" There is no need to be doing calculations on
white. To do calculations on 255,255,255 means there is a great
possibilty for various errors to make themselves known, and to randomly
get something other than 0,0,0,0CMYK on press. That's potentially
disastrous.
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Interesting answer: take a look at the Euroscale Coated profile
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that ships with Photoshop 6. If you input L=100, a=0, b=0 for example
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in the ColorSync Profile inspector, the CMYK output is 14, 14, 14, 0.
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(ranging from 0-255, 14 is about 5,49%).
I'm not understanding how you are getting this. I have a ColorSync
Profile Inspector (no version information) but it doesn't allow me to
enter in any information. When I enter these Lab values into any other
application and generate CMYK values for it, I get 0,0,0,0 CMYK.
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3. rounding error in the information palette: 5,49% yields in 5% in
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the palette.
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Even more interesting: The Adobe CMM returns values of 0, 0, 0, 0.
Agfa CMM 1,1,1,0
Apple CMM 0,0,0,0
ColorGear CMM Lite 0,1,1,0
Heidelberg CMM 1,0,0,0
Kodak CMM 0,1,1,0
X-Rite CMM 1,1,1,0
I wish I had my Imation CMM working, but no one at Imation is returning
my emails (I did beta testing, had a final copy, but then it broke, and
they now have a different serial number system so downloading a new copy
doesn't make any difference without that.)
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The only conclusion I have what Adobe is doing is that they really control
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if the given input values should be white and override the values with the
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whitepoint values, as Chris Murphy already suggested.
Not always because at least in Terry's case (the original poster of this
thread), a ProfileMaker Pro 3.1.3 profile with the Adobe (ACE) engine
generated values other than 0,0,0,0CMYK for 255,255,255 RGB.
So it does a better job, but not a perfect job.
Chris Murphy