[cups] Color issues when printing via lp

[Henry Betts]

Hi,

I'm having some issues printing from the command line, and I wondered if
anyone had any thoughts, or could point me in the right direction.

My system is ubuntu 18.04 and the printer driver is provided by gutenprint.
If I print an image (I am currently testing with a png) from ubuntu /
gnome's image viewer, the print comes out fine. However, if I print the
same file from the command line (i.e. *lp print.png*) then the print comes
out with the colors not looking quite right.

I can't see any mention of a color profile / icc in the printer's ppd file,
however I can see, looking at colord, that a profile has been generated and
set as the printer's default. My guess is that this is not being applied
when printing via lp.

Looking at the cups logfile, I see that the image viewer submits the job as
type application/pdf (it must convert the png to pdf beforehand) and uses
the filters:
*pdftopdf*
*gstoraster*
*rastertogutenprint*

Printing from lp uses the filters:
*imagetoraster*
*rastertogutenprint*

I had a quick look through the source code for gstoraster and
imagetoraster, and it looks like imagetoraster doesn't perform a colord
lookup, whereas gstoraster does - is this correct?
I then tried converting the png to pdf myself (*convert print.png print.pdf*)
and then printed the pdf (*lp print.pdf*). This now uses the gstoraster
filter, and I can also see in the logs that it is finding the correct
profile from colord. However, it still prints with the same color issues as
before, so I am not sure what the problem could be.

I would appreciate any suggestions.

Many thanks,

Henry

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