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Author Topic: ProPhoto vs sRGB, when ProPhoto clips and sRGB not  (Read 3467 times)

Hendrik

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ProPhoto vs sRGB, when ProPhoto clips and sRGB not
« on: June 10, 2006, 05:17:29 am »

I had the opportunity to try ColorThink for a moment when I visited a friend of mine. I played with some images and the traditional color spaces, like sRGB and ProPhoto RGB.

On the Internet you always see 2D and 3D graphs demonstrating how much bigger (and better) ProPhoto RGB is compared to sRGB and Adobe RGB. Well the bigger part is maybe true, but what I never have seen is that ProPhoto RGB clips some parts compared to sRGB.

Below are some pictures, demonstrating an image that fits easily in sRGB, but seem to exceed ProPhoto RGB borders. This would be an example were ProPhoto RGB seem to clip colors and sRGB is not.

Well, I’m not an expert and never used this program before so maybe I make some mistakes, but if this is true this would be another argument not to follow the ‘ProPhoto for all’ mantra.

See image attached
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Hermie

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ProPhoto vs sRGB, when ProPhoto clips and sRGB not
« Reply #1 on: June 10, 2006, 11:53:07 am »

Hendrik,

What you are seeing is what I described here:
http://luminous-landscape.com/forum/index....840&#entry67840

Quote from above thread:
"This is because of the way how graphing is implemented in ColorThink 2.1.2. ColorThink Pro 3 works a bit different.

This post on the ColorThink forum explains what is happening:
http://www.colorforums.com/viewtopic.php?t=286

Poster 'Kratzy974' writes in above thread:
"The White of the D65 Spaces are rotated to be viewed in a D50 . So the 100,0,0 value is moved to 100, x, y, where x and y are the difference values between the Colortemperature. Just open a sRGB, and you see what I mean. That is fully correct, and I don't want to argue against that. But :
The problem with the rel Colormetric calculation is, that if I view an Image (from sRGB) with Whitepoint away from 100,0,0. Then I use rel Colormetric to a D50 space : the grey line isn't rotated, so the bright values are mapped to the gamut of the D50 colorspace. This looks wrong (also with perceptual...). "
End of quote

Gamut comparisons should be done with the white points adapted in some manner. This will give a better indication of how two gamuts compare than when one of them has a shifted white point.

With adjusted white points the sRGB pRGB comparison looks like this (1st graph, 2nd one is with white points not adjusted):


You'll need ColorThink Pro 3.0 to do this.

Herman
« Last Edit: June 10, 2006, 12:14:07 pm by Hermie »
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Serge Cashman

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ProPhoto vs sRGB, when ProPhoto clips and sRGB not
« Reply #2 on: June 10, 2006, 01:03:15 pm »

This is an interesting point. So using most 3D gamut comparison tools (I've tried XP color applet, ICCView.de and DryCreek's viewer) you can't accurately compare files with different white points.
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Hendrik

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ProPhoto vs sRGB, when ProPhoto clips and sRGB not
« Reply #3 on: June 10, 2006, 03:23:10 pm »

Hermie, thank you for both posts.  
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