feat: add deltaE fn

src/color_calc/delta_e.rs

@@ -0,0 +1,128 @@
+use crate::{ Color, ColorSpace };
+
+/// Computes [color difference](https://en.wikipedia.org/wiki/Color_difference#CIEDE2000) as developed by the International Commission on Illumination (CIE) in 2000.
+///
+/// The implementation is based on the formula from [Bruce Lindbloom](http://www.brucelindbloom.com/index.html?Eqn_DeltaE_CIE2000.html).
+///
+/// Resulting values range from 0 (no difference) to 100 (maximum difference), and are a metric for how the human eye percieves color difference.
+///
+/// # Examples
+///
+/// ```
+/// use color_art::{delta_e, color};
+///
+/// let color1 = color!(#fefe0e);
+/// let color2 = color!(#fff);
+///
+/// let d = delta_e(&color1, &color2);
+/// assert_eq!(d, 30.165629067733235);
+/// ```
+pub fn delta_e(color1: &Color, color2: &Color) -> f64 {
+    let lab1 = color1.vec_of(ColorSpace::Lab);
+    let lab2 = color2.vec_of(ColorSpace::Lab);
+
+    let [l1, a1, b1] = [lab1[0], lab1[1], lab1[2]];
+    let [l2, a2, b2] = [lab2[0], lab2[1], lab2[2]];
+
+    let avg_l = (l1 + l2) / 2.0;
+
+    let c1 = (a1.powi(2) + b1.powi(2)).sqrt();
+    let c2 = (a2.powi(2) + b2.powi(2)).sqrt();
+
+    let avg_c = (c1 + c2) / 2.0;
+
+    let g = 0.5 * (1.0 - (avg_c.powi(7) / (avg_c.powi(7) + (25.0_f64).powi(7))).sqrt());
+
+    let a1p = (1.0 + g) * a1;
+    let a2p = (1.0 + g) * a2;
+
+    let c1p = (a1p.powi(2) + b1.powi(2)).sqrt();
+    let c2p = (a2p.powi(2) + b2.powi(2)).sqrt();
+
+    let avg_cp = (c1p + c2p) / 2.0;
+
+    let arctan1 = b1.atan2(a1p).to_degrees();
+    let arctan2 = b2.atan2(a2p).to_degrees();
+
+    let h1p = if arctan1 >= 0.0 { arctan1 } else { arctan1 + 360.0 };
+    let h2p = if arctan2 >= 0.0 { arctan2 } else { arctan2 + 360.0 };
+
+    let avg_hp = if (h1p - h2p).abs() > 180.0 {
+        (h1p + h2p + 360.0) / 2.0
+    } else {
+        (h1p + h2p) / 2.0
+    };
+
+    let t =
+        1.0 -
+        0.17 * (avg_hp - 30.0).to_radians().cos() +
+        0.24 * (2.0 * avg_hp).to_radians().cos() +
+        0.32 * (3.0 * avg_hp + 6.0).to_radians().cos() -
+        0.2 * (4.0 * avg_hp - 63.0).to_radians().cos();
+
+    let mut delta_hp = if (h2p - h1p).abs() <= 180.0 {
+        h2p - h1p
+    } else if h2p <= h1p {
+        h2p - h1p + 360.0
+    } else {
+        h2p - h1p - 360.0
+    };
+    delta_hp = 2.0 * (c1p * c2p).sqrt() * (delta_hp / 2.0).to_radians().sin();
+
+    let delta_l = l2 - l1;
+    let delta_cp = c2p - c1p;
+
+    let sl = 1.0 + (0.015 * (avg_l - 50.0).powi(2)) / (20.0 + (avg_l - 50.0).powi(2)).sqrt();
+    let sc = 1.0 + 0.045 * avg_cp;
+    let sh = 1.0 + 0.015 * avg_cp * t;
+
+    let delta_theta = 30.0 * (-((avg_hp - 275.0) / 25.0).powi(2)).exp();
+
+    let rc = 2.0 * (avg_cp.powi(7) / (avg_cp.powi(7) + (25.0_f64).powi(7))).sqrt();
+    let rt = -rc * (2.0 * delta_theta).to_radians().sin();
+
+    let kl = 1.0;
+    let kc = 1.0;
+    let kh = 1.0;
+
+    let result = (
+        (delta_l / (kl * sl)).powi(2) +
+        (delta_cp / (kc * sc)).powi(2) +
+        (delta_hp / (kh * sh)).powi(2) +
+        rt * (delta_cp / (kc * sc)) * (delta_hp / (kh * sh))
+    ).sqrt();
+
+    result.min(100.0).max(0.0)
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::*;
+
+    #[test]
+    fn test_distance() {
+        let color1 = color!(#fefe0e);
+        let color2 = color!(#fff);
+
+        let d = delta_e(&color1, &color2);
+        assert_eq!(d, 30.165629067733235);
+
+        let color1 = color!(#ededee);
+        let color2 = color!(#edeeed);
+
+        let d = delta_e(&color1, &color2);
+        assert_eq!(d, 1.2364506278716838);
+
+        let color1 = color!(#e0e0ee);
+        let color2 = color!(#e0eee0);
+
+        let d = delta_e(&color1, &color2);
+        assert_eq!(d, 14.618185117695797);
+
+        let color1 = color!(#fff);
+        let color2 = color!(#000);
+
+        let d = delta_e(&color1, &color2);
+        assert_eq!(d, 100.0);
+    }
+}

src/color_calc/mod.rs

@@ -1,4 +1,5 @@
 pub mod blend;
 pub mod distance;
+pub mod delta_e;
 
 pub use blend::BlendMode;

src/lib.rs

@@ -22,6 +22,7 @@ mod utils;
 pub use color::Color;
 pub use color_calc::blend::*;
 pub use color_calc::distance::*;
+pub use color_calc::delta_e::*;
 pub use color_space::ColorSpace;
 use data::alpha_hex_map::ALPHA_HEX_MAP;
 use data::chinese_color::CHINESE_COLOR_HASHMAP as CHINESE_COLOR;