Marti, Thank you again for replying, and please excuse my ignorance on this subject. I have spent many years coming to understand the math and constants used in the reflective end of this business, and I've spent the last year attempting to understand the same for the emissive end.
I have been looking closely at the changes you made to the spreadsheet. I have searched the ICC web page (color.org <http://color.org>) specifically and the web in general, but I have been unable to determine the source of the math, the constants, and the procedure that you used for correcting for veiling glare and scaling the luminance. The closest I've come is a reference to standard ISO 22028-1:2004, found here: http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=37161 <http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=37161> It was referenced here: http://www.color.org/rgbchardata.xalter At the suggestion of someone else, I've even grep'd the lcms and argyll source code for these constants, hoping to learn what they were, which equations they are used in, and what published standards I may find them in, but I came up empty. Except for the D50 XYZ white point, which is oddly very close but not exactly the same as that found in the ASTM E308 standard. Perusing the source code of lcms and argyll would, I am sure, be very educational, but I doubt I would recognize the needle I would be looking for in these two rather large haystacks of source code. I am not opposed to purchasing standards, but having done so in the past based on their description, I have wasted considerable money purchasing standards which did not contain the answers I was looking for. So, if I may ask for your help once more, in which published standard would I find the constants and the math that you used in that spreadsheet for removing veiling glare and scaling the luminance? Also, I will re-profile my monitor and create a LUT-based profile. Thank you for that advice. > > > Hi Mike, > > > > I've taken my time to check what you are reporting. After comparing > results with Photoshop, both gives same RGB values, so the problem, if > any, is not on lcms but in the profile. At that point, I wondered why > you got such big differences and here are some hints. > > > > * First and most important: you should not trust on RGB differences. > They are meaningless. Use Lab and DeltaE instead. > > * ICC states that some "pre cooking" should be applied to measured > data, specially on emissive devices: > > - You need to remove veiling glare (flare) > > - You need to scale the luminance (across 'lumi' tag). > > > > I've done those on the excel file you provided and the results, again > in RGB contone, are: > > http://www.littlecms.com/test%20chart%20simplified2.xls > <http://www.littlecms.com/test%20chart%20simplified2.xls> > > > > MIN > > > > -5 > > > > -1 > > > > 0 > > MAX > > > > 5 > > > > 13 > > > > 16 > > AVG > > > > 0.161616 > > > > 3.69697 > > > > 3.959596 > > > > If you compare those with your initial results, there is some difference: > > > > MIN > > > > -4 > > > > -1 > > > > 0 > > MAX > > > > 21 > > > > 22 > > > > 28 > > AVG > > > > 8.080808 > > > > 11.83838 > > > > 15.77778 > > > > > > But again, that is meaningless. Two contone values may differ 10 or > more units and be just on 0.1 dE colorimetrically. > > > > Finally, this is a Matrix-shaper profile, which may model a CRT quite > closely, but would probably fail on LCD. I think a LUT-based profile > would be more adequate, anyway that is up to the profile manufacturer. > > > > Hope this helps > > All the best > > Marti Maria > > The littleCMS project > > www.littlecms.com <http://www.littlecms.com> > > > ------------------------------------------------------------------------- SF.Net email is sponsored by: Check out the new SourceForge.net Marketplace. It's the best place to buy or sell services for just about anything Open Source. http://ad.doubleclick.net/clk;164216239;13503038;w?http://sf.net/marketplace _______________________________________________ Lcms-user mailing list Lcms-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/lcms-user
