mirror of https://github.com/GNOME/gimp.git
f200594d1c
We already had import support through littleCMS. We now use fully
babl/GEGL which makes our code more straightforward and identical,
whichever the input format.
The export support is totally new. It comes with a checkbox to propose
selecting CMYK export and a label displaying the CMYK profile which will
be used.
Now this whole implementation has a few drawbacks so far, but it will be
a good first sample for future CMYK-related improvements to come:
* The export profile I am using is what we call the "simulation
profile" from the GimpColorConfig. This corresponds to the default
"Soft-proofing" profile as set in Preferences. In particular, this is
not the actual soft-proofing profile for this image which might have
been changed through the View menu because this information is
currently and unfortunately unavailable to plug-ins. It is not the
"Preferred CMYK Profile" either, as set in Preferences.
TODOS:
- We really need to straighten the soft-proof profile core concept by
storing it in the image and making it visible to plug-in.
- Another interesting improvement could be to create a
GimpColorProfile procedure argument which would be mapped to a color
profile chooser widget, allowing people to choose profiles in
plug-ins. For an export plug-in in particular, it could allow to
select a profile different from the soft-proof one at export time.
* When we export, if no profile is choosen, babl will use a naive
profile. It would be nice to store this naive profile into the JPEG if
the "Save color profile" option is checked (same as we store a generic
sRGB profile when no RGB profile is set).
* When we import, we just import the image as sRGB. Since CMYK gamuts
are not necessarily within sRGB (some part of the spectrum is usually
well within, but other well outside), other than the basic conversion
accuracy issue, we may lose colors. It would be much nicer to be able
to select an output RGB profile. Optionally if we could create a RGB
color space which is made to contain the whole input CMYK profile
color space, without explicit choice step, it would be nice too.
* I am using babl's "cmyk" format, not the expected "CMYK" format.
"cmyk" is meant to be an inverted CMYK where 0.0 is full ink coverage
and 1.0 none. Nevertheless when loading the resulting JPEG in other
software (editors or viewers alike), the normal CMYK would always
display inverted colors and the inverted cmyk would look fine.
Finally I found a docs from libjpeg-turbo library, explaining that
Photoshop was wrongly inverting CMYK color data while it should not.
This text dates back from 1994, looking at the commit date which
introduced this paragraph. In the 28 years since then, could this
color inversion have become the de-facto standard for JPEG because one
of the main editor would just output all its JPEG files this way?
See:
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| .. | ||
| common | ||
| file-bmp | ||
| file-dds | ||
| file-exr | ||
| file-faxg3 | ||
| file-fits | ||
| file-fli | ||
| file-ico | ||
| file-jpeg | ||
| file-psd | ||
| file-raw | ||
| file-sgi | ||
| file-tiff | ||
| file-webp | ||
| flame | ||
| fractal-explorer | ||
| gfig | ||
| gimpressionist | ||
| gradient-flare | ||
| help | ||
| help-browser | ||
| ifs-compose | ||
| imagemap | ||
| lighting | ||
| map-object | ||
| metadata | ||
| pagecurl | ||
| python | ||
| screenshot | ||
| script-fu | ||
| selection-to-path | ||
| twain | ||
| ui | ||
| .gitignore | ||
| Makefile.am | ||
| meson.build | ||