Thank you for looking into this. Here is what I understand,
unfortunately my knowledge is quite limited, so thanks for your patience!
We need the display profile to display the image on the monitor that DT
is using, but the ultimate destination of the image is something
different: it could be the Web (sRGB) or a printer. In my case I export
images with ProPhoto and then the Turboprint driver applies the correct
profile for the printer and paper combination.
In other words the display profile and the output profile (meaning: the
profile that will be used for export) are different and should be
treated distinctly in DT. As M. Moy said in an earlier post (same thread):
"A more rigorous approach would run the image through the pipeline up to
the output color profile, and then export to monitor space to display
the image and to another monitor-independant space for the picker and
histogram."
I think this is also what S. Klinger what referring to in yet another
post from same thread:
"Hmmm, does that mean that the histogram is calculated from the
on-screen representation instead of from the image that would be
created just before export? I was hoping for the latter, and expected
that to be also used to implement gamut checking?"
I would prefer that, past the stage where camera (input) RGB is used,
processing be done within the largest possible color space to minimize
artifacts, etc (this is why DT used 32bit floating, I assume). Since
some modules work/display data in RGB and some in Lab, the RGB space
should be as large as possible to minimize data loss during to and fro
conversions. Adjustments for a narrower space on output should be done
on export or using soft proofing.
This is what RawTherapee and Adobe products do, I think: PS uses
ProPhoto as a working space, but offers Lab modules as well (while DT
takes the reverse approach). (See earlier post:
https://www.mail-archive.com/darktable-user@lists.darktable.org/msg06968.html).
In this perspective the display profile is not satisfactory since it
could be rather narrow. Besides, using the display profile for modules
that work in RGB means such processing done on the image will be
impossible to reproduce exactly on a different monitor (unless keeping a
copy of the profile of the monitor with which the image was processed).
Normand Fortier
Le 19-02-05 à 22 h 23, Edgardo Hoszowski a écrit :
In dt some modules work on camera rgb, others on lab or prophotoRGB or
whatever the output color profile returns. The final histogram and color
picker collect the data after the last module (gamma) has been processed
and display it in the display profile (and lab).
The color picker is returning inaccurate results and is being fixed in
PR 2066 [1] (you are welcome to test it)
Other than that, I'm not sure what your request is. We are talking about
the final histogram, so this is the right place to collect the data. Do
you want the data to be displayed in other format than the display profile?
[1] https://github.com/darktable-org/darktable/pull/2066
El mié., 23 ene. 2019 a las 15:22, Normand Fortier
(<normand.fort...@cgocable.ca <mailto:normand.fort...@cgocable.ca>>)
escribió:
I am creating test images in order to get a better grasp on soft
proofing for printing. These images simply contain patches of different
shades of gray. I created them using Inkscape and then exported to png
(see appended image).
If I inspect the image using Geeqie or Gimp with the same monitor color
profile I am using in Darktable, the rgb values all match the intended
value: each hexagonal patch has an rgb value which corresponds to its
displayed number (e.g. "24" -> rgb 24,24,24). However in DT, the values
provided by the global color picker (set to point and rgb) are
different.
For example, in the upper left group:
24 -> (29,29,28)
25 -> (29,30,29)
26 -> (30,30,29)
27 -> (31,31,30)
28 -> (31,32,31)
29 -> (32,33,32)
30 -> (33,34,33)
I set the monitor profile explicitly in Geeqie and Gimp, as well as in
DT using the monitor icon in lighttable mode and the soft proofing and
gamut icons in darkroom mode.
It seems DT is not displaying the image properly, or the picker is
reporting faulty values. Could anyone offer an explanation?
Thanks!
Normand
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