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Author Topic: Curious why i1Profiler's CCSG test-chart has negative and >255 RGB values?  (Read 5303 times)

l_d_allan

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I was looking at the i1Profiler's 1.4.2 (demo) CCSG RGB values for scanners, and noticed what seem to be strange RGB values ... negatives and numbers > 255.

NUMBER_OF_SETS   140
BEGIN_DATA
15   B5     -45.00     121.00     193.00   
16   B6     -29.00     155.00     184.00   
17   B7      -5.00      51.00      50.00   
18   B8     -25.00     157.00     157.00   
......
126   M6     297.00     173.00       0.00   
127   M7     271.00     189.00      -6.00   

"Inquiring minds want to know"   .... what's going on? A bug? Typo? Or some kind of code to the scanner about out-of-gamut? Special handling?

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pherold

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How did you find this file in i1Profiler?  Give us the steps to duplicate what you found and we can take a look at it.  This does look odd for RGB values.
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l_d_allan

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My error ... the test-chart came from ProfileMakerPro 5.0.10 ...
"D ColorChecker SG Format.txt"
in the installed directory:
[Install-Dir]\Reference Files\Others
(also attached)
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pherold

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I don't have a very good answer, but I see the same thing in the scanner reference files as well as the camera references.  And negative RGB values show up in the references for the regular ColorChecker too.  All I can guess is that originally the references were made using something that applied RGB values to a certain gamut, and so the negative numbers and the >255 numbers represent what is outside of that gamut?  Or something?   ???  Check this out on Bruce Lindbloom's site:

http://www.brucelindbloom.com/index.html?ColorCheckerRGB.html
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