Hi, > My question (if you have time to consider this further) is still > whether there is something conceptually wrong in my workflow, or if > it's just a mistake in coding/usage details. Unfortunately, I've > checked the latter -- comparing my code's results with those of > icctrans, which matched -- and can't see any problem there.
I tell you the icc2it8 stuff because it could be a great debug tool. Just compare the RGB of values obtained by icc2it8 and those in your synthetic image. If they don't match, then the error is there. Your workflow seems correct, but you have to take into account that not all Lab values will give ingamut RGB. As said, target gamut is bigger. Some thoughts... Lab is enough, your don't need XYZ anymore. In fact it would mess all, since XYZ -> Lab is done using D50 and this is not the case of sRGB, which has D65 as whitepoint. Perhaps you are choosing the RGB values of your image arbitrarily? Don't do that... Lab values of targets are carefully chosen and fine tuned. And finally, you should use absolute intent, since this is how real world works... perceptual and relative colorimetric does have a white point adaptation that only happens in our brain. Anyway, you could take a look on icc2it8 source (which I'm emailing you). The code is almost same as your, so search for the error elsewhere. Regards, Mart� Maria The little cms project http://www.littlecms.com [EMAIL PROTECTED] ----- Original Message ----- From: "Mark Rubin" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Wednesday, January 22, 2003 8:38 PM Subject: Re: [Lcms-user] Unexpected results with "zero error" IT8.7 test > "Mart�_Maria" <[EMAIL PROTECTED]> writes: > > > What you are trying to do, is easely done by a utility called > > "icc2it8". > > Thanks, Marti, for the instantaneous response (and, again, for all of > your LCMS work). > > I did the experiment with icc2it8 you suggest, and it worked as you > said. However (unless I missing something), what it seems to do is > convert an *existing* profile to an IT8 data sheet, in this case with > sRGB, XYZ, and L*a*b* data. > > What I'm trying to do is to start from an IT8 image, generate sRGB, > XYZ, and L*a*b* data, and create a *new* profile from that. > > More exactly, what I'm trying to do is understand LCMS with the goal > of generating profiles for several physical devices, and possibly > writing some code (GIMP plug-ins?). The experiment I originally > described is, in itself, meaningless: Generate an "identity" profile > which will lossly convert sRGB to sRGB. I thought this would be a > good test of my understanding, and it failed miserably. :-) > > My question (if you have time to consider this further) is still > whether there is something conceptually wrong in my workflow, or if > it's just a mistake in coding/usage details. Unfortunately, I've > checked the latter -- comparing my code's results with those of > icctrans, which matched -- and can't see any problem there. > > > ===== > -- > MARK > [EMAIL PROTECTED] > > __________________________________________________ > Do you Yahoo!? > Yahoo! Mail Plus - Powerful. Affordable. Sign up now. > http://mailplus.yahoo.com > > ------------------------------------------------------- This SF.net email is sponsored by: Scholarships for Techies! Can't afford IT training? All 2003 ictp students receive scholarships. Get hands-on training in Microsoft, Cisco, Sun, Linux/UNIX, and more. www.ictp.com/training/sourceforge.asp _______________________________________________ Lcms-user mailing list [EMAIL PROTECTED] https://lists.sourceforge.net/lists/listinfo/lcms-user
