I have a problem. I print using a RIP (i.e. a separate image-to-pixel
converter), and have done a lot of software calibration using this RIP.
(It's TurboPrint, by the way). If I process my photographs using
Darktable, then export them to an image linked to the RIP's input
profile, then use PhotoPrint without any correction to send it to the
RIP, I get very good results. However, I cannot find out how to do this
printing using just Darktable.

Things are not helped by the manual, which is very uninformative about
the various places in Darktable where you can assign a profile (as the
profile for software proofing, as the output profile in the output
profile filter, as the profile in the printer part of the print
dialogue, or as the profile in print-settings of the print dialogue.
Only the "profile for software proofing" setting is unambiguous, and if
I select the profile I have made for TurboPrint for this then I get a
wonderful looking screen proof (which looks pretty much like the print I
get using the above export-then-use-photoprint workflow). But I have
been unable to get anything which I print, using Darktable printing to
Turboprint, to look anything like that: it always looks much darker.

And I have done some reading of the Darktable source code, which is much
more illuminating than the manual, and that seems to indicate that
Darktable expects to do all the colour management itself.

At which I can only think "why?". Because Darktable is really good in
other respects, and this is clearly a bad design decision, because it is
terribly unmodular. Unix/Linux expects software to be modular, to do one
job, and to communicate using well defined interfaces to other software
in order to do other jobs. And the ICC colour profile specifications
basically specify a pipeline, at each stage of which you know the
correspondence between the internal representation of colour and some
standardised representation of colours (Lab in practice). So that all a
program should do is to be able to export a file in such a way that the
next stage in the chain knows what colours the file represents, and that
ought to be equally true of writing to a file or sending data to a
printer (in fact, Linux treats the two exactly the same).

So what on earth is going on here?

Graham
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