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libgimpcolor: new functions gimp_color_set_alpha() and…
… 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).
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Jehan
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/* LIBGIMP - The GIMP Library
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* Copyright (C) 1995-1997 Peter Mattis and Spencer Kimball
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*
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* gimpcolor.c
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* Copyright (C) 2023 Jehan <jehan@gimp.org>
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*
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* This library is free software: you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 3 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library. If not, see
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* <https://www.gnu.org/licenses/>.
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*/
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#include "config.h"
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#include <cairo.h>
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#include <gdk-pixbuf/gdk-pixbuf.h>
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#include <babl/babl.h>
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#include <gegl.h>
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#include "gimpcolor.h"
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/**
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* SECTION: gimpcolor
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* @title: GimpColor
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* @short_description: API to manipulate [class@Gegl.Color] objects.
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*
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* #GimpColor contains a few helper functions to manipulate [class@Gegl.Color]
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* objects more easily.
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**/
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/**
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* gimp_color_set_alpha:
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* @color: a [class@Gegl.Color]
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* @alpha: new value for the alpha channel.
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*
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* Update the @alpha channel, and any other component if necessary (e.g. in case
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* of premultiplied channels), without changing the format of @color.
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*
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* If @color has no alpha component, this function is a no-op.
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*
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* Since: 3.0
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**/
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void
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gimp_color_set_alpha (GeglColor *color,
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gdouble alpha)
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{
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const Babl *format;
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gdouble red;
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gdouble green;
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gdouble blue;
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guint8 pixel[40];
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format = gegl_color_get_format (color);
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gegl_color_get_rgba (color, &red, &green, &blue, NULL);
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gegl_color_set_rgba (color, red, green, blue, alpha);
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/* I could stop at this point, but we want to keep the initial format as much
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* as possible. Since we made a round-trip through linear RGBA float, we need
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* to reset the right format.
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*
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* Also why we do this round trip is because we know we can just change the
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* alpha channel and babl fishes will do the appropriate conversion. I first
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* thought of updating the alpha channel directly by editing the raw data
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* depending on the format, but doing so would break e.g. with premultiplied
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* channels. Babl already has all the internal knowledge so let it do its
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* thing. The only risk is the possible precision loss during conversion.
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* Let's assume that since we use an unbounded 32-bit intermediate value
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* (float), the loss would be acceptable.
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*/
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gegl_color_get_pixel (color, format, pixel);
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gegl_color_set_pixel (color, format, pixel);
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}
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/**
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* gimp_color_is_perceptually_identical:
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* @color1: a [class@Gegl.Color]
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* @color2: a [class@Gegl.Color]
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*
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* Determine whether @color1 and @color2 can be considered identical to the
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* human eyes, by computing the distance in a color space as perceptually
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* uniform as possible.
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*
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* Returns: whether the 2 colors can be considered the same for the human eyes.
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*
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* Since: 3.0
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**/
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gboolean
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gimp_color_is_perceptually_identical (GeglColor *color1,
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GeglColor *color2)
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{
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gfloat pixel1[3];
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gfloat pixel2[3];
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g_return_val_if_fail (GEGL_IS_COLOR (color1), FALSE);
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g_return_val_if_fail (GEGL_IS_COLOR (color2), FALSE);
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/* CIE LCh space is considered quite perceptually uniform, a bit better than
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* Lab on this aspect, AFAIU.
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*/
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gegl_color_get_pixel (color1, babl_format ("CIE LCH(ab) float"), pixel1);
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gegl_color_get_pixel (color2, babl_format ("CIE LCH(ab) float"), pixel2);
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/* This is not a proper distance computation, but is acceptable for our use
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* case while being simpler. While we used to use 1e-6 as threshold with float
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* RGB, LCh is not in [0, 1] range, and some channels can reach over 300 with
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* wide gamut spaces. This is why use the threshold is 1e-4 right now.
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*/
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#define SQR(x) ((x) * (x))
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return (SQR (pixel1[0] - pixel2[0]) +
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SQR (pixel1[1] - pixel2[1]) +
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SQR (pixel1[2] - pixel2[2]) <= 1e-4);
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#undef SQR
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}
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@ -19,6 +19,7 @@ EXPORTS
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gimp_cmyka_get_uchar
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gimp_cmyka_set
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gimp_cmyka_set_uchar
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gimp_color_is_perceptually_identical
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gimp_color_managed_get_color_profile
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gimp_color_managed_get_icc_profile
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gimp_color_managed_get_simulation_bpc
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@ -58,6 +59,7 @@ EXPORTS
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gimp_color_profile_new_rgb_srgb_linear
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gimp_color_profile_new_srgb_trc_from_color_profile
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gimp_color_profile_save_to_file
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gimp_color_set_alpha
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gimp_color_transform_can_gegl_copy
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gimp_color_transform_get_type
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gimp_color_transform_new
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@ -38,4 +38,22 @@
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#undef __GIMP_COLOR_H_INSIDE__
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G_BEGIN_DECLS
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/*
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* GEGL_TYPE_COLOR
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*/
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#define GIMP_VALUE_HOLDS_COLOR(value) (G_TYPE_CHECK_VALUE_TYPE ((value), GEGL_TYPE_COLOR))
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void gimp_color_set_alpha (GeglColor *color,
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gdouble alpha);
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gboolean gimp_color_is_perceptually_identical (GeglColor *color1,
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GeglColor *color2);
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G_END_DECLS
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#endif /* __GIMP_COLOR_H__ */
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@ -28,12 +28,6 @@ G_BEGIN_DECLS
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/* For information look into the C source or the html documentation */
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/*
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* GIMP_TYPE_COLOR
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*/
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#define GIMP_VALUE_HOLDS_COLOR(value) (G_TYPE_CHECK_VALUE_TYPE ((value), GEGL_TYPE_COLOR))
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/*
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* GIMP_TYPE_RGB
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*/
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@ -4,6 +4,7 @@ libgimpcolor_sources = files(
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'gimpbilinear.c',
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'gimpcairo.c',
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'gimpcmyk.c',
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'gimpcolor.c',
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'gimpcolormanaged.c',
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'gimpcolorprofile.c',
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'gimpcolorspace.c',
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