Katharine Thayer (kthayer@pacifier.com)
Fri, 22 Jan 1999 16:58:59 +0000
FotoDave@aol.com wrote:
>
> In a message dated 1/21/99 11:24:45 PM Pacific Standard Time,
> akimball@finebrand.com writes:
>
> > I've been wondering why I here so much about CMYK gum and so little about
> RGB. I don't need a lot of information, just a little?
>
> Adam, I am not sure if I understand your question correctly. Were you asking
> why people use CMYK (or CMY) pigment in printing their gum, but not using red,
> green, and blue pigment for gum printing?
>
> RGB are additive primaries. They work for light...[cut textbook definitions from color photography 101..]
Dave, I'm not sure if I understand Adam's question correctly either, but
I am assuming that since Adam is starting to work digitally, his
question had to do with what digital color space he should be working in
to create negatives for color gum printing: RGB or CMYK.
So if we're going to lecture on color models, I'll continue from Dave's
basic beginning and add more overly simplistic explanations of color
theory to his, as follows: The traditional photographic color printing
model goes this way: Color film has three layers of emulsion: one each
sensitive to Red, Blue and Green light. When exposed color film is
developed, a colored dye is combined with each negative image formed
from the the three emulsion layers. The dyes are cyan, magenta, and
yellow, which are the complements of red, green and blue. After the
silver is bleached away, three dye images remain, which are CMY
negatives of the original RGB image. Then light (RGB) is again passed
through the film and to the emulsion of color print paper, forming
positive CMY dye layers and a color print.
It makes perfect sense to me to take the basic steps of this model to
the digital world, staying in RGB space and forming CMY negatives by
inverting the RGB layers (Remember, RGB inverted=CMY) and then using
those negatives to gum print using CMY pigments. It does not make sense
to me to move into CMYK color space, which is not like RGB inverted but
is a different animal altogether, and as I have tried to explain here
more times than I wish to think of, has much more to do with the
commercial printing industry than with photography.
The only place in the universe I've ever heard it suggested that it
makes sense to use CMYK for photographic work is this list, and no one
here has yet explained to me what the logic is for the list's acceptance
of this idea. I suspect maybe it's due to a naive adherence to the rule
that Dave invoked: "RGB is for light, CMY is for printing." By
extension, since CMYK has the letters CMY in it, CMYK must be the right
space to work in, because RGB is just for monitors. Maybe I'm not
understanding, but the way I read this argument, it shows a certain lack
of understanding of how color printing works in traditional photography.
Adam, I hope I've answered the question you asked, not a different one,
and that the information will be useful to you.
Katharine Thayer
This archive was generated by hypermail 2.0b3 on Sat Nov 06 1999 - 10:06:44