moxcms/
lab.rs

1/*
2 * // Copyright (c) Radzivon Bartoshyk 2/2025. All rights reserved.
3 * //
4 * // Redistribution and use in source and binary forms, with or without modification,
5 * // are permitted provided that the following conditions are met:
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8 * // list of conditions and the following disclaimer.
9 * //
10 * // 2.  Redistributions in binary form must reproduce the above copyright notice,
11 * // this list of conditions and the following disclaimer in the documentation
12 * // and/or other materials provided with the distribution.
13 * //
14 * // 3.  Neither the name of the copyright holder nor the names of its
15 * // contributors may be used to endorse or promote products derived from
16 * // this software without specific prior written permission.
17 * //
18 * // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
19 * // AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
20 * // IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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27 * // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
28 */
29use crate::mlaf::{fmla, mlaf};
30use crate::{Chromaticity, LCh, Xyz};
31use pxfm::f_cbrtf;
32
33/// Holds CIE LAB values
34#[repr(C)]
35#[derive(Copy, Clone, Debug, Default, PartialOrd, PartialEq)]
36pub struct Lab {
37    /// `l`: lightness component (0 to 100)
38    pub l: f32,
39    /// `a`: green (negative) and red (positive) component.
40    pub a: f32,
41    /// `b`: blue (negative) and yellow (positive) component
42    pub b: f32,
43}
44
45impl Lab {
46    /// Create a new CIELAB color.
47    ///
48    /// # Arguments
49    ///
50    /// * `l`: lightness component (0 to 100).
51    /// * `a`: green (negative) and red (positive) component.
52    /// * `b`: blue (negative) and yellow (positive) component.
53    #[inline]
54    pub const fn new(l: f32, a: f32, b: f32) -> Self {
55        Self { l, a, b }
56    }
57}
58
59#[inline(always)]
60const fn f_1(t: f32) -> f32 {
61    if t <= 24.0 / 116.0 {
62        (108.0 / 841.0) * (t - 16.0 / 116.0)
63    } else {
64        t * t * t
65    }
66}
67
68#[inline(always)]
69fn f(t: f32) -> f32 {
70    if t <= 24. / 116. * (24. / 116.) * (24. / 116.) {
71        (841. / 108. * t) + 16. / 116.
72    } else {
73        f_cbrtf(t)
74    }
75}
76
77impl Lab {
78    /// Converts to CIE Lab from CIE XYZ for PCS encoding
79    #[inline]
80    pub fn from_pcs_xyz(xyz: Xyz) -> Self {
81        const WP: Xyz = Chromaticity::D50.to_xyz();
82        let device_x = (xyz.x as f64 * (1.0f64 + 32767.0f64 / 32768.0f64) / WP.x as f64) as f32;
83        let device_y = (xyz.y as f64 * (1.0f64 + 32767.0f64 / 32768.0f64) / WP.y as f64) as f32;
84        let device_z = (xyz.z as f64 * (1.0f64 + 32767.0f64 / 32768.0f64) / WP.z as f64) as f32;
85
86        let fx = f(device_x);
87        let fy = f(device_y);
88        let fz = f(device_z);
89
90        let lb = mlaf(-16.0, 116.0, fy);
91        let a = 500.0 * (fx - fy);
92        let b = 200.0 * (fy - fz);
93
94        let l = lb / 100.0;
95        let a = (a + 128.0) / 255.0;
96        let b = (b + 128.0) / 255.0;
97        Self::new(l, a, b)
98    }
99
100    /// Converts to CIE Lab from CIE XYZ
101    #[inline]
102    pub fn from_xyz(xyz: Xyz) -> Self {
103        const WP: Xyz = Chromaticity::D50.to_xyz();
104        let device_x = (xyz.x as f64 * (1.0f64 + 32767.0f64 / 32768.0f64) / WP.x as f64) as f32;
105        let device_y = (xyz.y as f64 * (1.0f64 + 32767.0f64 / 32768.0f64) / WP.y as f64) as f32;
106        let device_z = (xyz.z as f64 * (1.0f64 + 32767.0f64 / 32768.0f64) / WP.z as f64) as f32;
107
108        let fx = f(device_x);
109        let fy = f(device_y);
110        let fz = f(device_z);
111
112        let lb = mlaf(-16.0, 116.0, fy);
113        let a = 500.0 * (fx - fy);
114        let b = 200.0 * (fy - fz);
115
116        Self::new(lb, a, b)
117    }
118
119    /// Converts CIE [Lab] into CIE [Xyz] for PCS encoding
120    #[inline]
121    pub fn to_pcs_xyz(self) -> Xyz {
122        let device_l = self.l * 100.0;
123        let device_a = fmla(self.a, 255.0, -128.0);
124        let device_b = fmla(self.b, 255.0, -128.0);
125
126        let y = (device_l + 16.0) / 116.0;
127
128        const WP: Xyz = Chromaticity::D50.to_xyz();
129
130        let x = f_1(mlaf(y, 0.002, device_a)) * WP.x;
131        let y1 = f_1(y) * WP.y;
132        let z = f_1(mlaf(y, -0.005, device_b)) * WP.z;
133
134        let x = (x as f64 / (1.0f64 + 32767.0f64 / 32768.0f64)) as f32;
135        let y = (y1 as f64 / (1.0f64 + 32767.0f64 / 32768.0f64)) as f32;
136        let z = (z as f64 / (1.0f64 + 32767.0f64 / 32768.0f64)) as f32;
137        Xyz::new(x, y, z)
138    }
139
140    /// Converts CIE [Lab] into CIE [Xyz]
141    #[inline]
142    pub fn to_xyz(self) -> Xyz {
143        let device_l = self.l;
144        let device_a = self.a;
145        let device_b = self.b;
146
147        let y = (device_l + 16.0) / 116.0;
148
149        const WP: Xyz = Chromaticity::D50.to_xyz();
150
151        let x = f_1(mlaf(y, 0.002, device_a)) * WP.x;
152        let y1 = f_1(y) * WP.y;
153        let z = f_1(mlaf(y, -0.005, device_b)) * WP.z;
154
155        let x = (x as f64 / (1.0f64 + 32767.0f64 / 32768.0f64)) as f32;
156        let y = (y1 as f64 / (1.0f64 + 32767.0f64 / 32768.0f64)) as f32;
157        let z = (z as f64 / (1.0f64 + 32767.0f64 / 32768.0f64)) as f32;
158        Xyz::new(x, y, z)
159    }
160
161    /// Desaturates out of gamut PCS encoded LAB
162    pub fn desaturate_pcs(self) -> Lab {
163        if self.l < 0. {
164            return Lab::new(0., 0., 0.);
165        }
166
167        let mut new_lab = self;
168        if new_lab.l > 1. {
169            new_lab.l = 1.;
170        }
171
172        let amax = 1.0;
173        let amin = 0.0;
174        let bmin = 0.0;
175        let bmax = 1.0;
176        if self.a < amin || self.a > amax || self.b < bmin || self.b > bmax {
177            if self.a == 0.0 {
178                // Is hue exactly 90?
179
180                // atan will not work, so clamp here
181                new_lab.b = if new_lab.b < bmin { bmin } else { bmax };
182                return Lab::new(self.l, self.a, self.b);
183            }
184
185            let lch = LCh::from_lab(new_lab);
186
187            let slope = new_lab.b / new_lab.a;
188            let h = lch.h * (180.0 / std::f32::consts::PI);
189
190            // There are 4 zones
191            if (0. ..45.).contains(&h) || (315. ..=360.).contains(&h) {
192                // clip by amax
193                new_lab.a = amax;
194                new_lab.b = amax * slope;
195            } else if (45. ..135.).contains(&h) {
196                // clip by bmax
197                new_lab.b = bmax;
198                new_lab.a = bmax / slope;
199            } else if (135. ..225.).contains(&h) {
200                // clip by amin
201                new_lab.a = amin;
202                new_lab.b = amin * slope;
203            } else if (225. ..315.).contains(&h) {
204                // clip by bmin
205                new_lab.b = bmin;
206                new_lab.a = bmin / slope;
207            }
208        }
209        new_lab
210    }
211}
212
213#[cfg(test)]
214mod tests {
215    use super::*;
216
217    #[test]
218    fn round_trip() {
219        let xyz = Xyz::new(0.1, 0.2, 0.3);
220        let lab = Lab::from_xyz(xyz);
221        let rolled_back = lab.to_xyz();
222        let dx = (xyz.x - rolled_back.x).abs();
223        let dy = (xyz.y - rolled_back.y).abs();
224        let dz = (xyz.z - rolled_back.z).abs();
225        assert!(dx < 1e-5);
226        assert!(dy < 1e-5);
227        assert!(dz < 1e-5);
228    }
229
230    #[test]
231    fn round_pcs_trip() {
232        let xyz = Xyz::new(0.1, 0.2, 0.3);
233        let lab = Lab::from_pcs_xyz(xyz);
234        let rolled_back = lab.to_pcs_xyz();
235        let dx = (xyz.x - rolled_back.x).abs();
236        let dy = (xyz.y - rolled_back.y).abs();
237        let dz = (xyz.z - rolled_back.z).abs();
238        assert!(dx < 1e-5);
239        assert!(dy < 1e-5);
240        assert!(dz < 1e-5);
241    }
242}
moxcms/lab.rs

moxcms/
lab.rs
