U of S | Mailing List Archive | alt-photo-process-l | Re: separations for gum printing

Re: separations for gum printing

On Nov 20, 2008, at 10:52 AM, Marek Matusz wrote:

Mostly everybody agrees that B channel (in the RGB color space) intended for yellow printing always requires a different curve then RG channels. The B channel is almost always much 'flatter" then oher channels and requires a more pronounced curvature.
Point of clarification: Actually, unless I've been misreading these discussions, this is opposite what other people are reporting, which is that the separation for yellow requires *less* curvature than the others, not more. For example Henry Rattle: "Yes, the Y curve is quite a lot closer to the 45 degree line - less sigmoid" On the other hand, I find no appreciable difference between the curves for the three colors. To me, the fact that some say yellow requires less curvature, some say it requires more curvature, and some (well, one anyway) says the curves for the three are essentially the same suggests that the crucial variable(s) influencing how the curve looks must be something other than the hue range of the color.

I took screen shots of my curves for PV19, thalo, and PY97 (a combination I've been using lately for tricolor test prints). The curve for yellow is slightly more curved than the other two, suggesting slight agreement with Marek that the yellow requires more curvature, but not enough to make a never mind, certainly not enough to say that the "yellow" curve is way different from the others. I didn't note which of the screen shots was which with the magenta and thalo, but they are so much alike it really doesn't matter.