RE: the look of tricolor vs CMYK

[Keith Gerling <Keith@GumPhoto.com>]

Hi Michael,

Bent, huh?  Cool.  Of course, I don't use all of those techniques on every work.  Regarding that calculations step: All I've done is perform the very same channel-tweaking that any Photoshopper might employ, but rather than "assemble" the picture with layers in Photoshop, I've made "hard-copy" layers in the form of negatives and assemble the layers on the final gum print.  The one I mentioned, I blended 80% of the inverse of the Magenta with soft light into the Blue channel of a copy of the original image.  Now, if you take the result and create a new layer, fill it with black and blend it on top of the original with soft light you'll have something similar to the gum print.  But doing it "outside" of Photoshop allows for more control.  Most of these things are done on whim and aren't all planned out.   

The turquoise selection technique was used recently for a picture of a dancer.  Her costume had a very distinctive color that I was afraid would not combine perfectly using tri-color RGB separations.  I prepared a spot channel mask that I prepared by selecting the color range and used that negative to hammer home that distinctive turquoise. Of course, if one really wanted the results to be Perfect, one would subtract the colors out of the original RGB negatives.  But this is gum, so why worry?

Hope this makes sense.

Keith


-----Original Message-----
From: Michael Koch-Schulte [mailto:mkochsch@shaw.ca]
Sent: Wednesday, January 31, 2007 9:21 PM
To: alt-photo-process-l@usask.ca
Subject: Re: the look of tricolor vs CMYK


That's seriously bent Keith ;^). With the technique(s) like the one you've
outlined below, do you do a mock up in photoshop first to give you an idea
of what the final "look" will be? Or is it more like pottery where you don't
know until it comes out of the oven? (or you keep sending it back to the
kitchen until it looks right?) Do you have a name for this cross colour
mapping technique? What does the label on the Photoshop Layer read on that
Blue-Inverted-Magenta (80% difference) channel?

>" My negatives come from a combination of CMYK and RGB and might include
something as specialized as a negative that is produced from the 80%
difference between the blue channel and the inverse of the magenta channel
as defined in the Calculations function of Photoshop"

I'm guessing to get a turquoise layer requires a special selection
technique?

>"or a "spot" channel that included only the turquoise in the original
non-separated image.  So I might start out with 7 negatives, but the end
result might use three or four or all seven negatives to apply the same gray
pigment.  So what do you call that?  I call it a "gum print".  And I call it
that even if it happens to also use a cyano or vandyke layer in the mix.  "

This kind of info is invaluable. It sort of blows the door open for trying
new things. It's a very three dimensional approach. One of the things that
really interests me is the "decision" making process with gum. Thank you for
sharing it.

~m