On Monday 20 June 2005 06:05 pm, Bob Friesenhahn wrote: > On Mon, 20 Jun 2005, Hal V Engel wrote: > >> 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. > > > > 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 > > Ahhh, but metamerism still exists! Metamerism due to different ink > will be elminated but there may still be metamerism which causes the > scanner to think that two colors are very similar when they are > actually not. > > Bob
Yes when the calibration chart and the printer target have different inks or colorants then the only question is the magnitude of the difference. If it is very small (like with an LED scanner) then the profile can be very good. But if it is large than the profile is very bad. If both the calibration chart and the printer target use the same inks then both will have almost exactly the same metamerism characteristics since in the scanner both will be lighted by the same light source and imaged using the same sensor and if scanned in the same pass, like they are in ProfilePrism, scanned with the same scanning parameters. Under those conditions if two colors on the two charts appear to the scanner to be the same color then they are extremely close to the same color. That was the whole point behind having both use the same inks. It almost totally eliminates one vary large variable. Of course it can not totally eliminate it since the calibration chart and the printer target will very likely be on different papers. But the light source, sensor and ink are no longer variables and have instead been transformed into constants. The only remaining variable that can influence metamerism is, in your words, "the properties of what is being scanned" which in this case is the media that the calibration chart and printer target are printed on. If the media are different (highly likely) then there will still be a very slight difference in the metamerism characteristics of the calibration chart and the printer target. But my experience is that the same ink printed on different media will have almost exactly the same metamerism characteristics - the ink formulation accounts for at least 90% of the metamerism characteristic. In addition my experience is that the difference between the same inks on different media is less if the media are similar. That is the metamerism characteristics of a given ink will be almost identical if both media are glossy or both are mat. The ideal setup would be to have the calibration chart printed on the exact same media as will be used in the printer and if possible on the same type of printer. This would result in the calibration chart having exactly the same metamerism characteristics as the printer target. Again the real issue is how to minimize the affects of metamerism on a scanner based printer profiling process. If the calbration chart and the printer target have nearly the same metamerism characteristics, no matter how much metamerism actually takes place, metamerism's impact on the profiling process has been minimized. I should add that although I think that ink specific calibration charts would be helpful to those using scanners to profile printers I do not think that there is anything other than an extremely low probability that these will ever become available. So how useful these may be is likely a mote point. Hal ------------------------------------------------------- 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_idt77&alloc_id492&op=click _______________________________________________ Lcms-user mailing list Lcms-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/lcms-user
