On 09/23/2016 11:57 AM, Ross Martinek wrote:

> Thanks for jogging my memory. I think what I was thinking is that Adobe had 
> color palettes based on those catalogs, intended to produce printed colors 
> that matched the catalog. Like I said, it’s been a long time.

Those catalogs would be Pantone ones.  They are usually most relevant
when printing vector graphics, i.e. silk screen or offset printing.
Printer's inks have Pantone values printed on their labels, and very
precisely match the color chips on Pantone reference cards.  I have seen
"Pantone to HTML color" charts on the network, and they are better than
nothing but far from precise.  "HTML color" means hexadecimal RGB, which
is also the GIMP's native color model.

RGB stands for Red, Green and Blue.  It is an "additive" color model,
applicable to mixing colored light sources.  Example:  TV screens and
computer monitors.

LAB stands for Luminance, Red/Green, Blue/Yellow.  It is based on
studies of human color perception and is more or less universal, but no
monitor or printer can duplicate this color space directly - it has to
be exported to RGB (monitor) or CMYK (printer) for display.

CMYK stands for Cyan, Magenta, Yellow and Black.  It is a "subtractive"
color model, applicable to mixing ink or paint colors to control the
color of reflected light.

When people start talking about computer programs that can "natively
edit in CMYK", try not to groan:  The only way to edit images in CMYK is
with a paintbrush or comparable tool, because on a monitor you see the
image in RGB no matter what format the program is reading from and
writing to.

An RGB image can be exported to or imported from a file with CMYK data,
via a filter based on the intersection of RGB and CMYK values in LAB
color space.  But "what you see" on the monitor is not exactly "what you
get" on the printed page.  Upcoming versions of the GIMP with GEGL under
the hood will support /much/ higher resolution RGB color, improving the
potential color match between screen and paper versions of a given
image.  (GIMP layers can also include an Alpha channel for transparency;
hence "RGBA" values.)

In recent times I have had no problems with color management for print;
PNG files imported to Scribus and saved as PDF come out looking like I
want them to when printed.  A decade ago, this was not always the case.
I believe that LCD monitors and improvements in color conversion
algorithms probably account for this.

To get the best available color rendering, first check your monitor.  If
a color profile is available from the manufacturer, get it and install
it on your workstation machine, and make sure the GIMP knows about it:
Edit > Preferences > Color Management.  This will tweak your video
output for "best results."  An alternative to this is to glovally
disable color management and tweak your monitor by hand, see:


Color perception is also a factor:  The more neutral gray you see around
an image, the less your eye and brain will distort the colors in the
image.  Conversely, if you know that a bunch of images you are working
on will be displayed on a colored background - say a web page or
brochure - you can set the Canvas Padding color in the GIMP to that
color, and see your images in progress in their native color context:
Edit > Preferences > Image Windows > Appearance.

The GIMP includes a filter that converts the visible image to CMYK
layers, and the result can be exported as a CMYK TIFF file.  This may
facilitate color adjustment at the print shop, and any commercial
printers who still demand "Adobe Formats Only, or take your filthy money
elsewhere!" will usually accept CMYK TIFF files without complaint.

Color printing used to be a bit of a major nuisance, but lately not so
much - depending the use case, your mileage may vary.  The remaining
problem is color resolution:  If you have a big, subtle gradient you
have to get just exactly right, you are going to see banding on your
monitor and in the printed results.  The upcoming GEGL based GIMP color
model, with resolutions up to 64 bit floating point, should put a stop
to that nonsense.


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