This completes the GimpRGB API removal
project for the color space invasion.
Note that the GIMP_RGB_LUMINANCE macro is
temporarily moved to gimpcolor. It does not
require GimpRGB but was included in gimprgb.h.
- gimp_rgb_list_names() ported as gimp_color_list_names() using NUL-terminated
GimpColorArray.
- GimpColorHexEntry uses the new function (and is therefore now GimpRGB free!).
- gimp_rgb_parse_name() deleted as it's unused since my previous commit.
With all this, gimprgb-parse.c is now deleted from the repository! \o/
… test-color-parser.c file.
The file libgimpcolor/test-color-parser.c was compiled but never actually called
by the build. Now that we have a nice infrastructure to test libgimp API, I am
moving it there with the new format. Doing this also allowed me to discover some
bugs in CSS parsing, as well as discover Python binding was failing here (cf.
the few previous commits).
Only one test is disabled so far, the one where 4 digits are used per channel in
hexadecimal notation: "#64649595eded". This format simply doesn't appear
anywhere in the spec, and also the result values in the samples listing don't
even fit. So far, I'm just unsure what to do with it, if we want to keep this
support (of some kind of higher precision hex notation, but not specified, so is
it even used by anyone?) or not.
All the other tests just work in both C and Python!
This is used for the gimp_color_is_perceptually_identical() function,
because the Euclidean distance in LCH is extremely limited, if not wrong
in many cases. Indeed LCH is not perfectly perceptually uniform, and for
this exact reason, the CIE defined the specific Delta E algorithms.
Later versions are also based on LCH values, so my intuition to use it
for distance was on a good start, yet these algorithms were refined a
few times to allow for corrections in perceptual uniformity
imperfections.
This was in particular needed to verify if a color is out of a CMYK
space gamut. The idea is to compare the distance of the RGB (or other)
and the CMYK version, since we cannot just check if the CMYK color is
out of the [0; 1] range (it never is). Instead if both colors are
perceptually identical, then we consider that the RGB color was inside
the CMYK space gamut.
The naive algorithm was giving any (or nearly) color as out-of-gamut.
Now using CIEDE2000, I get a much nicer results.
I still see some limitations in GimpGradient, and in particular, they are still
always stored as RGB in GGR files. It would be nice if we could store the actual
color format. This way, if someone chooses a gradient stop as Lab or CMYK color,
that's what the gradient file would keep track of. But also even storing the
space of a color (instead of storing/loading always in sRGB, even though this
may still work fine as we store unbounded double values). This might warrant for
a v2 of GGR file format.
This commit also fixes loading of SVG gradient which was apparently broken
regarding hexadecimal color parsing.
Finally I improve gegl_color_set_alpha() by adding an alpha channel when the
initial format had none.
… gimp_color_is_perceptually_identical().
gimp_color_is_perceptually_identical() is meant to replace gimp_rgb_distance()
which is anyway always used to decide whether 2 colors can be considered equal.
So rather than having a distance algorithm which we won't be able to change
later on (if people start relying on specific values), let's just give the
answer directly on what's a same color (perceptually) or not.
Also now the distance is computed through the intermediate color space LCh which
seems to be one of the most perceptually uniform space, therefore a good choice
for such an algorithm (comparing distances on a non-perceptual uniform space
doesn't make very much sense, since a same distance may be perceived differently
in different subspaces).
Alx Sa