Re: The color of gray
Re: The color of gray
- Subject: Re: The color of gray
- From: Peter Miles <email@hidden>
- Date: Tue, 02 Sep 2014 04:10:08 -0700
Previously I wrote...
So Judging by both the CMYK numbers (0,1,2,0 CMYK) I'm getting (when printing) "AdobeRGB White", and how the resulting print hues looks _very_ similar to my 5000K monitor when the print is viewed in a GTI viewing booth, it would appear....
That with the printer colorspace profiled as a CMYK space and Adobe doing the Absolute transform from AdobeRGB to the printer colorspace, what I effectively get is a relative colorimetric transform from AdobeRGB's D65 white into D50 white, followed by an Absolute Colorimetric transform from this D50 space into the CMYK printer color space.
<end snip>
..and this also makes sense of other issues I have encountered. Recently an artists work required very accurate solid-color print matches to real-wold samples, for a installation called "∆E2000 1.1" (see http://shaunwaughphotography.blogspot.co.nz/search/label/2014). We used SpectraShop4 to take readings of the bright orange of Agfa boxes and calculate the RGB values needed to match the colors of each box.
The orange color we measured was outside both sRGB and AdobeRGB and so we ended up using ProPhotoRGB as our source colorspace. Using Spectrshop4 to compare the original spectral sample from the box to a reading from the print we made to match it (printed absolute colorimetric from photoshop), I was surprised to see that there was only Delta E2000 1.1 between them. Thats the best match to a real-world sample our facility has been able to make using calculations alone. (i'm sure the 'Pro's' out there can get much closer than this)
On reflection, I reasonably sure tit's a combination of the way we have set up our printer, and having used a source colorspace (ProPhotoRGB) having a D50 white point. With the way we have set up our printer, the first half of the Adobe's "Absoulte Colorimetric" print pipeline leaves the D50 of ProPhotoRGB untouched. And then Adobe does a 'Real' absolute transform from that into our printers CMYK colorspace, which is why I think we came so close to hitting the color 'out of the box', so to speak.
Previously, with other artists work that might have benefited from hitting specific colors measured from real-world objects, I'd used smaller RGB spaces (AdobeRGB) and not being happy with the results, not realizing the consequences of those spaces being D65 for our printer set-up.
So recently I'd begun exploring SpectraShop4 a bit more and noticed how the calculated RGB values from spectral readings of the neutral samples in a Color Checker Chart became approximately R=G=B only when the illuminant for the observer viewing condition matched the white point of the colorspace I was calculating the RGB values for. Which now makes sense. And that got me to thinking about the color of gray and if equal RGB values really are neutral.
Anyway next time I need to hit specific colors from measurements made from real-world objects i'll use D50 editing spaces. (as long I'm printing from photoshop, absolute colorimetric, and into a CMYK printer colorspace). I'd like to learn to use Argyll, but need to get to grips with using command line interface.
Thanks again for all the help
Best Regards
Peter
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