On 15 Mar 2010, at 15:32, Graeme Gill wrote:
Idea Digital Imaging wrote:Interesting. And the black in this profile is warm...Yes, this explains what you are seeing.So, working as designed, but feel free to convince me that this isn't the rightI can only convince you that a full black of C57 M67 Y72 K100 is a PITA to work with :(way to choose the black point for a CMYK device !My theory was that usually black ink has a very flat absorption spectrum,so that typically the K only hue is a good match to the plain paper. The fact that typically press control matches CMY to K only,and that a high K image has better neutrality under different illuminantssupported the notion that this was a good idea. [Doing tricks with crossing over from K only to rich black also work better when the black points are in the same direction.] If the K ink isn't very flat, then maybe it's not such a good basis to pick the black point ?
I don't see that the benefits of of setting the black point in this way outweigh the pain of having to deal with yellow-heavy blacks and the resulting crossover point where yellow exceeds cyan.
For a press, wouldn't it be better to work with a theoretical black point which is the black max + neutral CMY ratio = total ink limit ?That's generally the case, but there's no guarantee that the deepestblack is on the total ink limit boundary. (If yellow was quite reflectivefor instance, it might decrease density after some point).
Another good reason to avoid the risk of ending up with a dominant yellow :)
My assumption was that using -S would generate a perceptual table that behaves in the same way a device link with perceptual intent and gamut mapping from sRGB to PSO_LWC_Improved would.It should, yes. It's not quite as smooth or accurate, but the transformaims are the same.
Are they? I seem to get what I expect when I make a device link from sRGB to PSO_LWC_Improved_eci using -G -- a perceptual conversion with a full black of C71 M67 Y61 K98. That's how I want my perceptual table to work in the original profile.
-- Martin Orpen Idea Digital Imaging Ltd