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

Re: separations for gum printing


Interesting.  The curves you referenced below are quite similar.  Though my guess is that the curves may be so similar because in general the exposure is overwhelmed by either too dense of a negative or over exposure.  I say this because of the rapid drop on the right side, where the curve drops 75% of the vertical axis while only moving to the left about 25% of the horizontal axis—thus 75% if the image data is compressed into 25% of the available tones.

On Nov 20, 2008, at 1:52:51 PM, "Katharine Thayer" <kthayer@pacifier.com> wrote:
From:"Katharine Thayer" <kthayer@pacifier.com>
Subject:Re: separations for gum printing
Date:November 20, 2008 1:52:51 PM CST
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.