Katharine,
Perhaps I did not express myself clearly. My RG channels are almost always a straight line with some curvature to limit pigment at the high end, while yellow is deviating most from straight line. I apply mine in the nagative phase so will have to look how they relate to your snapshots.
Marek
PS> I am missing posts in this discussion. I have not even seen my original post as yet, and I see replies to notes that I have not seen as well. Anybody else having problems?
> Date: Thu, 20 Nov 2008 11:52:51 -0800
> From: kthayer@pacifier.com
> Subject: Re: separations for gum printing
> To: alt-photo-process-l@usask.ca
>
>
> 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.
>
> http://www.pacifier.com/~kthayer/html/tricolorcurves.html
> katharine
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