[vox] Software for Flyers

[Marianne Waage]

On Tue, Sep 05, 2006 at 09:48:10AM -0700, Bill Kendrick wrote:
> On Tue, Sep 05, 2006 at 08:11:32AM -0700, Marianne Waage wrote:
> > Hrm. According to the online manual, GIMP *still* doesn't support CMYK.
> > But hey, if you enjoy having your color horribly mangled once you print,
> > go ahead. ;)
> 
> I'm still kind of confused by this.  What is it about having the ability
> to convert RGB pixels in a bitmap into CMYK that makes it print better?
> Is it because you get the opportunity to tweak some configuration in
> between?  (i.e., how the RG and B become CMY and K?)

Actually, I generally work in CMYK mode. Although this often means I take
a digital camera photo, convert to CMYK, and continue from there.

Since printers print using CMYK, you rely less on what color the print
driver thinks "R" or even "black" should be. For instance, should the
printer driver say black is just "K"? Or should it be just "CMY"? For
"rich" blacks, sometimes it ends up being "K" with a liberal amount of
"CMY" added in.

"Rich" blacks can be rather a pain if you're printing a grey gradient, as
if you look closely you can see color speckles in the gradient. However,
if you're making the gradient with CMYK rather than relying on a print
driver's interpretation of RGB, you can force your gradient to be just
K, or, if you wanted, you could even make it K with a bit of C, for a 
blue-grey.

> In any case, why does one's front-end application (like The GIMP) need to
> do this?  Can't this be part of a system-wide printer config, or at least
> system-wide printer dialog (e.g., so that other applications can share it)?

Printers prefer to receive files in CMYK format, so they have less color
concerns. If you convert the file to CMYK, print your CMYK file on your 
printer, and send them that file, their final result will more closely 
match your copy than if you had sent them an RGB file.

I can show you an example with Cafepress products, when you're in Davis. 
They don't allow CMYK files and it drives me crazy.

> I realize a lot of printing services prefer CMYK format (like, what, is
> there a ".cmyk" file that you convert an image into?), but I've always heard
> that it's best to send them your original bitmap, and let THEM do the
> color separation, since they know what they're doing, and are familiar
> with their printers and ink.

TIFF can be either RGB or CMYK. I'm 90% certain JPG can as well. I don't
usually save CMYK files in anything other than TIFF or the native file
format, but I imagine there are other popular formats that allow for
it.

Certainly, if you create the file in RGB, then it might be best to send 
it in that format. CMYK format does not have the insanely bright colors 
that RGB has, since it was designed for the color gamut of printers, not 
the brightly saturated colors you can get from a lit screen.

Here's a page that shows the brightness difference:
   http://en.wikipedia.org/wiki/Color_space

This page has a graph which shows the visible spectrum, with a large
dashed blob for RGB, and a small dotted blob for CMYK. Note the
ridiculous amount of greens we can visualize but not print :)
   http://dx.sheridan.com/advisor/cmyk_color.html

> CMYK has always kind of been the 'silver bullet' for The GIMP, but obviously
> I still don't understand why. :^)

CMYK, and spot colors would be handy. Likely if they could do one, the
other would be easy.

I suspect one reason they don't try it is that filters are often
color-space specific. And every tool that applies color probably is also.
It would likely be a major overhaul for a very minor audience. I mean,
how many print-designing Linux users could there be? :)

-Marianne