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

Re: separations for gum printing

That's exactly what I thought you meant; I was simply saying that the way I'm reading these threads, others are reporting the opposite: yellow being the most like a straight diagonal line, and RG most deviating from a straight line. While I, on the other hand, don't see that much difference in the curves for the three colors, as long as the pigment mixes are similarly color-saturated; a deep saturation yields a deep curve and a lighter mix yields a more straight line curve, with all three of these pigments. It could be interesting to see how our curves compare, though because of all the variables intervening, it would be impossible to draw any meaningful conclusions from the comparison. If you want to compare my curves to yours, just click one of the arrows in the gradient below the curve and that will reverse the direction of the curve.

I'm having the same problem, not getting posts I send, and missing posts in the discussion.

On Nov 20, 2008, at 4:07 PM, Marek Matusz wrote:

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.

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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