"Ben Bowen" <> wrote in message
news: oups.com...
> Hi all. I recently purchased some non-OEM ink for my Canon MP730
> printer...and it sucked! It's a CMYK printer and I replaced the CM&K
> with the crappy ink. The output on color photos was terrible. It looked
> washed out and faded; just really really bad. So I replaced the C & M
> with regular Canon ink and things look a lot better. I did not,
> however, replace the black because I thought there's not much true
> black in color photos so probably wouldn't matter much. Is that a
> faulty assumption? I just printed a few images and there are some odd
> color artifacts it them. I don't know if it's dirty heads or the ink.
> The odd part is, the artifacts appear in places where I would think
> there would be no black at all. So, is there a decent amount of black
> ink used in color images, for shading, etc? Should I replace the
> non-OEM ink with trusty Canon stuff?
There can be a lot of black ink in a "color" image.
Let's say you've got a region of pixels with RGB
values near (15,5,5).
That basically means, "dark, dark gray --
almost black -- but slightly biased to red."
Most CMYK printers will take advantage
of that. Instead of using equal amounts of
CMY and K, they'll crank down the CMY
and crank up the K.
In other words: the amount of K (black) ink
will correspond to the overall "darkness"
of the image, while the relative proportions
of C/M/Y will determine the color.
In terms of Lab color space, the amount of
K ink will correspond to the L channel,
while the relative mix of C/M/Y will
correspond to the a and b axes.
"GCR" (gray color removal) and "UCR"
(undercolor removal) are two different
strategies for doing this.
rafe b
www.terrapinphoto.com