mirror of https://github.com/GNOME/gimp.git
178 lines
3.8 KiB
C
178 lines
3.8 KiB
C
/* 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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* 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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* Library 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 <babl/babl.h>
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#include <glib-object.h>
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#include "libgimpmath/gimpmath.h"
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#include "gimpcolortypes.h"
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#include "gimpcolorspace.h"
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#include "gimprgb.h"
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/**
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* SECTION: gimpcolorspace
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* @title: GimpColorSpace
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* @short_description: Utility functions which convert colors between
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* different color models.
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*
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* When programming pixel data manipulation functions you will often
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* use algorithms operating on a color model different from the one
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* GIMP uses. This file provides utility functions to convert colors
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* between different color spaces.
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**/
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#define GIMP_HSL_UNDEFINED -1.0
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/* GimpRGB functions */
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/**
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* gimp_rgb_to_hsl:
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* @rgb: A color value in the RGB colorspace
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* @hsl: (out caller-allocates): The value converted to HSL
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*
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* Convert an RGB color value to a HSL (Hue, Saturation, Lightness)
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* color value.
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**/
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void
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gimp_rgb_to_hsl (const GimpRGB *rgb,
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GimpHSL *hsl)
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{
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gdouble max, min, delta;
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g_return_if_fail (rgb != NULL);
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g_return_if_fail (hsl != NULL);
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max = gimp_rgb_max (rgb);
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min = gimp_rgb_min (rgb);
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hsl->l = (max + min) / 2.0;
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if (max == min)
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{
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hsl->s = 0.0;
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hsl->h = GIMP_HSL_UNDEFINED;
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}
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else
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{
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if (hsl->l <= 0.5)
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hsl->s = (max - min) / (max + min);
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else
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hsl->s = (max - min) / (2.0 - max - min);
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delta = max - min;
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if (delta == 0.0)
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delta = 1.0;
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if (rgb->r == max)
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{
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hsl->h = (rgb->g - rgb->b) / delta;
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}
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else if (rgb->g == max)
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{
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hsl->h = 2.0 + (rgb->b - rgb->r) / delta;
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}
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else
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{
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hsl->h = 4.0 + (rgb->r - rgb->g) / delta;
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}
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hsl->h /= 6.0;
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if (hsl->h < 0.0)
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hsl->h += 1.0;
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}
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hsl->a = rgb->a;
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}
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static inline gdouble
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gimp_hsl_value (gdouble n1,
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gdouble n2,
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gdouble hue)
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{
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gdouble val;
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if (hue > 6.0)
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hue -= 6.0;
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else if (hue < 0.0)
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hue += 6.0;
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if (hue < 1.0)
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val = n1 + (n2 - n1) * hue;
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else if (hue < 3.0)
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val = n2;
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else if (hue < 4.0)
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val = n1 + (n2 - n1) * (4.0 - hue);
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else
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val = n1;
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return val;
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}
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/**
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* gimp_hsl_to_rgb:
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* @hsl: A color value in the HSL colorspace
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* @rgb: (out caller-allocates): The value converted to a value
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* in the RGB colorspace
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*
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* Convert a HSL color value to an RGB color value.
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**/
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void
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gimp_hsl_to_rgb (const GimpHSL *hsl,
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GimpRGB *rgb)
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{
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g_return_if_fail (hsl != NULL);
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g_return_if_fail (rgb != NULL);
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if (hsl->s == 0)
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{
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/* achromatic case */
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rgb->r = hsl->l;
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rgb->g = hsl->l;
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rgb->b = hsl->l;
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}
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else
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{
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gdouble m1, m2;
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if (hsl->l <= 0.5)
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m2 = hsl->l * (1.0 + hsl->s);
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else
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m2 = hsl->l + hsl->s - hsl->l * hsl->s;
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m1 = 2.0 * hsl->l - m2;
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rgb->r = gimp_hsl_value (m1, m2, hsl->h * 6.0 + 2.0);
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rgb->g = gimp_hsl_value (m1, m2, hsl->h * 6.0);
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rgb->b = gimp_hsl_value (m1, m2, hsl->h * 6.0 - 2.0);
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}
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rgb->a = hsl->a;
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}
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