Auke: This may be due to several reasons. I want to first check the accuracy of your profile to know where the problem actually is. So, the way to check the accuracy of your profile is to use absolute colorimetric. If this works, then rel. colorimetric is going to work too. But since rel. colorimetric implies a white point translation, there is no direct way to measure it.
So, I proposed to use a transform between Lab -> printer profile because Lab identity is operating on D50. It is not same as using AdobeRGB as input profile. At that point abs. colorimetric should work. If not, the profile is not proper and you cannot obtain any further improvement. >c. I don't *wan*t to use absolute colorimetry as it changes the RGB values >too much. For instance white (Lab 100,0,0) is trnaformed to 229,246,255. >If I print this, I don't get paper white anymore, yet my paper is becoming >even more blue :( But your unprinted paper is not of Lab=(100, 0, 0) right? Try to measure your unprinted paper and feed such value to the abs. colorimetric transform. It should give you a (255, 255, 255) or something really close to that. Regards, Marti. ----- Original Message ----- From: "Auke Nauta" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Cc: "Marti Maria" <[EMAIL PROTECTED]> Sent: Monday, December 13, 2004 1:43 PM Subject: Re: [Lcms-user] Get accurate Lab predictions from profile, how? Hi again Marti, Gerhard, others... I will try to be more clear in my wording and objectives: Objective: I want to get a fair estimation of the Lab colours from the ICC profile, when using relative colorimetric conversion. Current results / conclusions: a. After applying the output profile, the Lab values in Photoshop (or using lcms utilities) do not match the measured Lab values well. b. If I use absolute colorimetry during the transform, the whitepoint Lab display valus 'improve'. Some other colours are way off, however... c. I don't *wan*t to use absolute colorimetry as it changes the RGB values too much. For instance white (Lab 100,0,0) is trnaformed to 229,246,255. If I print this, I don't get paper white anymore, yet my paper is becoming even more blue :( Some thoughts: The ICC profile *knows* about the actual colour <> RGB relation (it is the major function of the profile). Therefore, I would think, it should be able to specify, approximately, using its 3D LUT, what the Lab values will be when I print using a particular RGB combination. However, the match is quite poor. Is this a bit more clear? Can you help? TIA and greetings, Auke > > Hi, > > Ok, this may be due to white point mismatch. AdobeRGB is operating under > D65, so > I wonder if this is the case. You could try that: > > - with icctrans, convert some Lab values using abs. colorimetric to the > printer profile. > > icctrans -t3 -i*Lab -o printer_profile.icc > > This will give you some RGB values. Create a image with such values. Print > the image TURNING ALL COLOR MANAGEMENT OFF! Measure the > patch. If the dE is not good, then the problem is in the output profile. > Besides, > this is a photosmart printer, a dE of 3-4 is actually not so bad if you > are > using a generic profile. > > Regards, > Marti Maria > The little cms project > http://www.littlecms.com > ------------------------------------------------------- SF email is sponsored by - The IT Product Guide Read honest & candid reviews on hundreds of IT Products from real users. Discover which products truly live up to the hype. Start reading now. http://productguide.itmanagersjournal.com/ _______________________________________________ Lcms-user mailing list [EMAIL PROTECTED] https://lists.sourceforge.net/lists/listinfo/lcms-user
