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// This function written in Rust is not affiliated with the CIE (International Commission on Illumination),
// and is released into the public domain. It is provided "as is" without any warranty, express or implied.
use rand::Rng;
// The classic CIE ΔE2000 implementation, which operates on two L*a*b* colors, and returns their difference.
// "l" ranges from 0 to 100, while "a" and "b" are unbounded and commonly clamped to the range of -128 to 127.
fn ciede_2000(l_1: f64, a_1: f64, b_1: f64, l_2: f64, a_2: f64, b_2: f64) -> f64 {
// Working in Rust with the CIEDE2000 color-difference formula.
// K_L, K_C, K_H are parametric factors to be adjusted according to
// different viewing parameters such as textures, backgrounds...
const K_L: f64 = 1.0;
const K_C: f64 = 1.0;
const K_H: f64 = 1.0;
const M_PI: f64 = std::f64::consts::PI;
let mut n = ((a_1 * a_1 + b_1 * b_1).sqrt() + (a_2 * a_2 + b_2 * b_2).sqrt()) * 0.5;
n = n * n * n * n * n * n * n;
// A factor involving chroma raised to the power of 7 designed to make
// the influence of chroma on the total color difference more accurate.
n = 1.0 + 0.5 * (1.0 - (n / (n + 6103515625.0)).sqrt());
// Application of the chroma correction factor.
let c_1: f64 = (a_1 * a_1 * n * n + b_1 * b_1).sqrt();
let c_2: f64 = (a_2 * a_2 * n * n + b_2 * b_2).sqrt();
// atan2 is preferred over atan because it accurately computes the angle of
// a point (x, y) in all quadrants, handling the signs of both coordinates.
let mut h_1 = b_1.atan2(a_1 * n);
let mut h_2 = b_2.atan2(a_2 * n);
if h_1 < 0.0 { h_1 += 2.0 * M_PI; }
if h_2 < 0.0 { h_2 += 2.0 * M_PI; }
n = (h_2 - h_1).abs();
// Cross-implementation consistent rounding.
if (M_PI - 1e-14..=M_PI + 1e-14).contains(&n) { n = M_PI; }
// When the hue angles lie in different quadrants, the straightforward
// average can produce a mean that incorrectly suggests a hue angle in
// the wrong quadrant, the next lines handle this issue.
let mut h_m = (h_1 + h_2) * 0.5;
let mut h_d = (h_2 - h_1) * 0.5;
if M_PI < n {
h_d += M_PI;
// 📜 Sharma’s formulation doesn’t use the next line, but the one after it,
// and these two variants differ by ±0.0003 on the final color differences.
h_m += M_PI;
// if h_m < M_PI { h_m += M_PI; } else { h_m -= M_PI; }
}
let p = 36.0 * h_m - 55.0 * M_PI;
n = (c_1 + c_2) * 0.5;
n = n * n * n * n * n * n * n;
// The hue rotation correction term is designed to account for the
// non-linear behavior of hue differences in the blue region.
let r_t = -2.0 * (n / (n + 6103515625.0)).sqrt() * (M_PI / 3.0 * (p * p / (-25.0 * M_PI * M_PI)).exp()).sin();
n = (l_1 + l_2) * 0.5;
n = (n - 50.0) * (n - 50.0);
// Lightness.
let l = (l_2 - l_1) / (K_L * (1.0 + 0.015 * n / (20.0 + n).sqrt()));
// These coefficients adjust the impact of different harmonic
// components on the hue difference calculation.
let t = 1.0 + 0.24 * (2.0 * h_m + M_PI * 0.5).sin()
+ 0.32 * (3.0 * h_m + 8.0 * M_PI / 15.0).sin()
- 0.17 * (h_m + M_PI / 3.0).sin()
- 0.20 * (4.0 * h_m + 3.0 * M_PI / 20.0).sin();
n = c_1 + c_2;
// Hue.
let h = 2.0 * (c_1 * c_2).sqrt() * (h_d).sin() / (K_H * (1.0 + 0.0075 * n * t));
// Chroma.
let c = (c_2 - c_1) / (K_C * (1.0 + 0.0225 * n));
// Returning the square root ensures that dE00 accurately reflects the
// geometric distance in color space, which can range from 0 to around 185.
(l * l + h * h + c * c + c * h * r_t).sqrt()
}
// GitHub Project : https://github.com/michel-leonard/ciede2000-color-matching
// Online Tests : https://michel-leonard.github.io/ciede2000-color-matching
// L1 = 92.6 a1 = 34.7 b1 = 3.8
// L2 = 94.0 a2 = 29.5 b2 = -2.8
// CIE ΔE00 = 4.5842493835 (Bruce Lindbloom, Netflix’s VMAF, ...)
// CIE ΔE00 = 4.5842651916 (Gaurav Sharma, OpenJDK, ...)
// Deviation between implementations ≈ 1.6e-5
// See the source code comments for easy switching between these two widely used ΔE*00 implementation variants.
///////////////////////////////////////////////
///////////////////////////////////////////////
/////// ///////
/////// CIEDE 2000 ///////
/////// Testing Random Colors ///////
/////// ///////
///////////////////////////////////////////////
///////////////////////////////////////////////
// This Rust program outputs a CSV file to standard output, with its length determined by the first CLI argument.
// Each line contains seven columns :
// - Three columns for the random standard L*a*b* color
// - Three columns for the random sample L*a*b* color
// - And the seventh column for the precise Delta E 2000 color difference between the standard and sample
// The output will be correct, this can be verified :
// - With the C driver, which provides a dedicated verification feature
// - By using the JavaScript validator at https://michel-leonard.github.io/ciede2000-color-matching
fn main() {
let args: Vec<String> = std::env::args().collect();
let mut n_iterations = 10000;
if args.len() > 1 {
if let Ok(val) = args[1].parse::<i32>() {
if val >= 1 {
n_iterations = val;
}
}
}
unsafe {
libc::signal(libc::SIGPIPE, libc::SIG_DFL);
}
let mut rng = rand::rng();
for _ in 0..n_iterations {
let l1 = (rng.random_range(0.0..=10000.0) as f64).round() / 100.0;
let a1 = (rng.random_range(-12800.0..=12800.0) as f64).round() / 100.0;
let b1 = (rng.random_range(-12800.0..=12800.0) as f64).round() / 100.0;
let l2 = (rng.random_range(0.0..=10000.0) as f64).round() / 100.0;
let a2 = (rng.random_range(-12800.0..=12800.0) as f64).round() / 100.0;
let b2 = (rng.random_range(-12800.0..=12800.0) as f64).round() / 100.0;
let delta_e = ciede_2000(l1, a1, b1, l2, a2, b2);
println!("{},{},{},{},{},{},{}", l1, a1, b1, l2, a2, b2, delta_e);
}
}