[argyllcms] Re: ArgyllCMS: shadow details and blue color issues. What I'm doing incorrectly?

  • From: Nikolay Pokhilchenko <nikolay_po@xxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Fri, 19 Oct 2012 18:47:43 +0400

Hello, Xavi.
Absolute cororimetric compiance between display and the paper is only 
achievable in controlled condition when the paper brightness has the same level 
as the display brightness because very vell controlled illumination. Is this 
Your case?
If the brightness of media white is differ from the display white, You can't 
achieve equal perception from the display and from the print even if measured 
Lab values of the print (which are normalized to the print illuminant) are qual 
to the values in PhotoShop. In such case it would be better to apply some kind 
of color mapping (for example -ila) which actually can improove the image 
appearance but can't gain colorimetric compliance.
If You want really same colors between display and Your lightbox, You can 
perform the measurements of printed target with "chartread -e" while 
calibrating white on Your display nor Your lightbox. I.e. You should start the 
measurements, calibrate the instrument, calibrate the white (the light source) 
right on Your display and continue to measure patches on lightbox. With this 
workflow You'll obtain the same Lab on the print as on the display. With the 
same basis. And after profiling You should be able achieve equal Lab and equal 
perception of the colors in gamut. This is what I think about Your problem.

Fri, 19 Oct 2012 13:41:06 +0200 "Xavi" wrote:

>Hello Nikolay.
>To print my photos I wish to use the intent that gives me similar results to 
>what I see on my calibrated screen or beeing more objetive, to the Lab values 
>that PS informs me that a color has.
>I thought that the more simmilar results were offered by the relative 
>colorimetric intent. The other usually used intent, when speaking of printing 
>photographs, the perceptual intent,Âthought that was more visual adaptative, 
>than "real".
>After receive your reply, I have printed, withÂabsolute colorimetric intent 
>without BPC (is not posible to print with BPC option enabled), Âthe same 7 
>patches that I use to do my tests , and reading them with an spectro, the 
>deltaE values are between the results obtained with the relative colorimetric 
>and the obtained when printed with perceptual intent. But very very near from 
>the relative colorimetric. Exactly only a difference on deltaE2000 of 0,20 and 
>0,32 of deltaE76.
>When I try to show my profile results, specially of the blue color using 
>perceptual intent, Graeme Gill, commented me that he don't see the results on 
>my prints and that he don't know how the application that I use do the soft 
>Then I have decided to not to use soft proof to compare results.
>Then, the only way that I think that I can compare results is printing patches 
>that I know their Lab value(photoshop gives me the Lab value of a color when 
>the cursor is over it), read these patches with an spectro and calculate the 
>difference between the Lab value of the patch and the Lab value of the same 
>patch printed on paper. I use the deltaE76 and the deltaE2000. I think that a 
>correct profile must have deltaE values near zero when speaking of inside 
>gamut colors.Â
>This method is correct? If yes, I must to print the patches using relative 
>colorimetric without BPC or absolute colorimetric intent?
>If you have other ideas of how to verify if the workflow of creatingÂa printer 
>profile, than use it and measure the results, please tell me it that I will 
>try it to check the results.
>Any idea will be wellcome.
>Thank you very much.
>Best Regards,

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