Re: [darktable-user] Colour profiles

[Graham White]

Thanks for this. I still have questions, though.
On 13/08/16 19:28, Matthieu Moy wrote:
> Graham White  writes:
> 
>> I have a problem understanding the various options for selecting a
>> colour profile for printing. There seem to be three places where you can
>> set this, namely:
> 
> And there are indeed 3 things you may want to do with profiles:
> 
> 1) Make sure images are displayed properly on your screen. This is the
>"display profile" and is typically obtained by calibrating your
>screen. It's independant from your printer, obviously.
I wasn't concerned about this: I tell Darktable to use the system
display profile, and it does. Though this may have led to confusion in
my email, because when I said "three different places where you can
select a profile", I didn't mean this (sorry about the ambiguity).
> 
> 2) Make sure colors are rendered properly when printing. If I understand
>correctly, this is done in two steps: first export the picture to a
>large colorspace (as much as possible larger than your printer's),
>and then correct the colors while sending the image to the printer.
>You would distinguish both steps if you were sending the file to
>someone else: you'd do the export and the other end would do the
>printer-specific stuff.
> 
>These are the two profiles listed in the print dialog:
>https://www.darktable.org/usermanual/ch07s02.html.php
>https://www.darktable.org/usermanual/ch07s02s03.html.php
> 
The manual says (7.2.1): "This profile is the last color space
transformation done to the picture whose goal is to create a high
quality print."
OK: so is this transformation done by Darktable, or by the printer? I am
asking because I'm using Turboprint to drive my printer, and Turboprint
applies a user-specified profile to the image it receives from the
application. So, presumably when it says "the last color space
transformation", it actually means "the last color space transformation
performed by Darktable"? Or does it mean that it wants to know if any
other transformations are going to be applied to the image after it gets
to the printer?

and in 7.2.3: "This allows you to select the export profile to use. This
profile is the entry point used for the next transformation using the
printer's ICC profile above."
So, presumably, the export profile will be the same as the profile that
you can set using the Export Profile filter in the Darkroom view? And
what happens if the two selections conflict? Presumably (one would
think) the profile selected in the print dialogue overrides the profile
selected in the Export Profile filter?

> 3) Softproof: get the best possible approximation on screen of what the
>final printout will look like. In other words, replace colors that
>your screen can render but that your printer can't with a color that
>your printer will be able to print. You can customize this with the
>softproof button (right-click for details) in the darkroom view. This
>is not strictly needed to get a good print, but you probably want
>this if you have you printer's profile.
That's fairly clear, and it seems to work (except that the softproof is
really quite different from what comes out of the printer, presumably
because I haven't got the print profile selection done right.
> 
> (disclaimer: I don't do printing myself, so my explanations may have to
> be taken with a grain of salt)
> 
Thanks for this: it's very helpful, and a good guide to further
experiments.

Graham

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Re: [darktable-user] Colour profiles

[Matthieu Moy]

Graham White  writes:

> I have a problem understanding the various options for selecting a
> colour profile for printing. There seem to be three places where you can
> set this, namely:

And there are indeed 3 things you may want to do with profiles:

1) Make sure images are displayed properly on your screen. This is the
   "display profile" and is typically obtained by calibrating your
   screen. It's independant from your printer, obviously.

2) Make sure colors are rendered properly when printing. If I understand
   correctly, this is done in two steps: first export the picture to a
   large colorspace (as much as possible larger than your printer's),
   and then correct the colors while sending the image to the printer.
   You would distinguish both steps if you were sending the file to
   someone else: you'd do the export and the other end would do the
   printer-specific stuff.

   These are the two profiles listed in the print dialog:
   https://www.darktable.org/usermanual/ch07s02.html.php
   https://www.darktable.org/usermanual/ch07s02s03.html.php

3) Softproof: get the best possible approximation on screen of what the
   final printout will look like. In other words, replace colors that
   your screen can render but that your printer can't with a color that
   your printer will be able to print. You can customize this with the
   softproof button (right-click for details) in the darkroom view. This
   is not strictly needed to get a good print, but you probably want
   this if you have you printer's profile.

(disclaimer: I don't do printing myself, so my explanations may have to
be taken with a grain of salt)

-- 
Matthieu Moy
http://www-verimag.imag.fr/~moy/

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[darktable-user] Colour profiles

[Graham White]

I have a problem understanding the various options for selecting a
colour profile for printing. There seem to be three places where you can
set this, namely:

1. In the Output Profile filter in Darkroom: you can select from various
possible profiles in .config/darktable/color/out or in /usr/share/whatever

2. In Print: you can select a profile in printer (at the top of the
print settings dialogue) and in print settings (at the bottom).

So, firstly, what do these different choices mean? (I am asking for a
reply in the style of the admirably clear explanation, in 3.2.10 of the
manual,  of the role of colorspaces in the internals of Darktable.

Secondly, do they override one another? Can you get correction applied
twice if you are overenthusiastic about specifying profiles? And so on.

By the way, I'm using Ubuntu 16.04, printing via CUPS to Turboprint, and
generating my own profiles with Argyll. And I can print OK with
PhotoPrint, but printing in Darktable seems hard to understand and hard
to get right.

I'm very impressed by Darktable, though, and would consequently like to
be able to print from it.

Graham

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