Gamut and tricolor gum

Hi All,

Several months ago, I think during the last iteration of the CMYK-RGB-
separations debate, someone brought up the question of gamut. The
argument was (if I'm recalling this right) that one reason to use CMYK
rather than RGB separations was that CMYK handles the issue of the
reduced gamut of printed color, and RGB doesn't. I argued that with
pigments, we don't have the same kind of issues about gamut as they have
in commercial printing, where the limitations of the process inks put
severe restrictions on gamut. (Gamut being the totality of colors that a
system can display or print). And I further argued that it didn't make
sense to me to make color separations that reduce the gamut in the image
to match the gamut of process inks, which is what you're doing when you
use the default CMYK.

Now, after spending some time looking at how different combinations of
pigments print tricolor, although I'm not close enough to the end of
that process to draw any definite conclusions yet, I think I can speak
to the issue of how gamut relates to tricolor gum with more
understanding than I was able to before. While I believe I was
essentially right before when I said that we don't have the same kind
of gamut issues with tricolor gum as they do with commercial printing,
still gamut is an issue with tricolor gum for anyone who wants an exact
reproduction of color in a color image. Every different combination of
pigments will probably yield a somewhat different gamut, because the
blended colors that can be produced using any combination of three
pigments are a function of the reflectance curves of the individual
pigments. Whether there is any one combination of pigments that could
accurately reflect every single color you might want to reproduce from
an RGB image is a question I don't have time or energy to determine
(I'm just looking at the most saturated secondary hues--orange, purple,
green-- you can print using some different combinations of three primary
pigments; it would be an enormous task to look at all the other possible
combinations of colors made from every single possible combination of
pigments) but I seriously doubt it. But for most of us, close enough is
probably good enough. After all, most of us are satisfied enough with
the colors that can be reproduced in color picture books, even though
process inks are much worse at accurately reproducing color, especially
bright and saturated colors, than the pigments that we use for tricolor.

More about this sometime later,
Katharine Thayer
Received on Thu Jun 23 15:53:25 2005