On Monday 20 June 2005 04:34 pm, Bob Friesenhahn wrote: > On Mon, 20 Jun 2005, Hal V Engel wrote: > > Having ink specific IT8.7 charts would make the creation of printer > > profiles using a scanner significantly more accurate then when using > > generic IT8.7 charts since this would eliminate the metamerism problem. > > I would also > > You are saying that your scanner acts like a spectrophotometer? I > find it difficult to believe that using LEDs in the scanner causes it > to not suffer from metamerism. > > Bob
No I am saying that IF the amount and direction of the color shift caused by metamerism are the same for both the IT8.7 calibration chart and the printer target then metamerism in no longer a significant issue. LED scanners seem to reduce the amount of metamerism significantly and this results in better printer profiles because the magnitude of the difference of the color shift between the calibration target and the printer target is (much) smaller. But if the IT8.7 calibration chart and the printer target used the same inks then both will have almost exactly the same amount and direction of color shift due to metamerism. This would make metamerism (close to) a non-issue even for scanners with light sources that have high levels of metamerism with the inks being used in the printer. Again the real issue is not that there is metamerism in the scanned images but rather that the amount and direction of the color shift from metamerism is different for the calibration chart and the printer target and that the magnitude and direction of the shifts for each are not known. The above assumes that the profiling software is like ProfilePrism. With ProfilePrism you scan both the printer target and the IT8.7 target at the same time using the same settings. That image is pulled into the software and used to calibrate the scanned image as part of the process of creating the profile. When I tried to use ProfilePrism with a non-LED scanner I was never able to get good results when trying to profile with pigment inks. Others using the same software versions reported good results when using dye inks. Dye inks have low levels of metamerism. When I switched to a LED scanner my results improved dramatically with the same version of the software. One user on the ProfilePrism list has profiled the same printer using ProfilePrism with a LED scanner and some other software with a spectrophotometer and reported that the profiles were very close to the same with the spectrophotometer profile being a tiny bit better. So no I am not saying that my LED scanner is the same as a spectrophotometer or even that I can get results that are as good. But rather that if I get everything just right (this requires a significant amount of experience with the software) I can get results that are almost as good but at a lot lower cost. As I pointed out I am currently getting results that are somewhat better than the canned Epson profiles (the ones that need to be hand installed that are for specific printers, papers and resolutions). So I must be getting very close to the best results obtainable from my setup. Could I do better if I had a spectrophotometer? Yes I am sure that I could but I am also fairly sure that the difference would not be a large one. I would really like to have a spectrophotometer but I currently can not afford one so I have to make do with what I have. I suspect that there are many other users that would be more than a little reluctant to spend what it costs to buy a spectrophotometer but who would like to be able to get good results using less expensive equipment such as a scanner. ------------------------------------------------------- SF.Net email is sponsored by: Discover Easy Linux Migration Strategies from IBM. Find simple to follow Roadmaps, straightforward articles, informative Webcasts and more! Get everything you need to get up to speed, fast. http://ads.osdn.com/?ad_id=7477&alloc_id=16492&op=click _______________________________________________ Lcms-user mailing list Lcms-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/lcms-user
