Bug#787709: cups: wrong default "Color Model" setting for Canon Pixma MG2250
On Wed 01 Jul 2015 at 12:22:22 +0100, Brian Potkin wrote:
> > I'll join the list tomorrow and refer to the Debian bug in my post.
>
> Done.
>
> http://sourceforge.net/p/gimp-print/mailman/gimp-print-devel/thread/20150701101803.GB20876%40copernicus.demon.co.uk/#msg34257165
Meanwhile, I came across
http://sourceforge.net/p/gimp-print/bugs/632/
http://sourceforge.net/p/gimp-print/bugs/652/
http://sourceforge.net/p/gimp-print/mailman/gimp-print-devel/thread/467C7753.1010801%40tabi.org/#msg15590162
The third link has some quite detailed explanations. It is from eight
years ago; how accurate it is regarding CUPS' treatment of colour today
I do not know.
Some selected quotes in answer to suggestions and requests to the
Gutenprint maintainers that CMYK be the default Color Model:
Hi, thanks for the replort. However, I believe you are mistaken
about the requirement: as I understand it, the input color model
should be RGB by default. The output color model to the printer is
whatever the printer requires for the particular printmode, and is
set by the driver (for some simple modes it will be CMYK). If you
have a special requirement where the input to the printer driver is
CMYK, then you should set the input mode to that (and you can make
it the default) but for the vast majority of printing inputs, the
model to be used is RGB.
Gernot Hassenpflug
Regarding the color model, RGB is correct. The driver accepts RGB
input, as is standard also on Windows. The application therefore
sends RGB data to the driver. This has nothing to do with what ink
data the driver sends to the printer---that differs for each mode in
any case, and is mostly not settable by the user (a mode usually has
a fixed requirement for a particular inkset, they are not
independently settable).
Gernot Hassenpflug
The output will always be in the printer's space, whatever the input
may be. It's usually better for Gutenprint to do the RGB->CMYK
conversion than CUPS, because Gutenprint has more information.
Robert Krawitz
The choice of color model selects what's passed to Gutenprint, so
for any given document, it simply changes what color processing is
done in CUPS vs. what is done in Gutenprint. So when you select
CMYK, CUPS......
Robert Krawitz
If your document is RGB, and you select RGB as the Color Model, CUPS
won't do any conversion. Likewise if you print a CMYK document
using CMYK color model. If you print an RGB document but select
CMYK as the Color Model, CUPS *has* to do a color conversion.
Robert Krawitz
Apart from the printer model, #497936 is the same bug.
Regards,
Brian.
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