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// Limited Use License – March 1, 2025
// This source code is provided for public use under the following conditions :
// It may be downloaded, compiled, and executed, including in publicly accessible environments.
// Modification is strictly prohibited without the express written permission of the author.
// © Michel Leonard 2025
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
public class Main {
// 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.
static double ciede_2000(final double l_1, final double a_1, final double b_1, final double l_2, final double a_2, final double b_2) {
// Working in Java 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...
final double k_l = 1.0, k_c = 1.0, k_h = 1.0;
double n = (Math.sqrt(a_1 * a_1 + b_1 * b_1) + Math.sqrt(a_2 * a_2 + b_2 * b_2)) * 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 - Math.sqrt(n / (n + 6103515625.0)));
// Application of the chroma correction factor.
final double c_1 = Math.sqrt(a_1 * a_1 * n * n + b_1 * b_1);
final double c_2 = Math.sqrt(a_2 * a_2 * n * n + b_2 * b_2);
// 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.
double h_1 = Math.atan2(b_1, a_1 * n), h_2 = Math.atan2(b_2, a_2 * n);
h_1 += 2.0 * Math.PI * Boolean.compare(h_1 < 0.0, false);
h_2 += 2.0 * Math.PI * Boolean.compare(h_2 < 0.0, false);
n = Math.abs(h_2 - h_1);
// Cross-implementation consistent rounding.
if (Math.PI - 1E-14 < n && n < Math.PI + 1E-14)
n = Math.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.
double h_m = (h_1 + h_2) * 0.5, h_d = (h_2 - h_1) * 0.5;
if (Math.PI < n) {
h_d += Math.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 += Math.PI;
// h_m += h_m < Math.PI ? Math.PI : -Math.PI;
}
final double p = 36.0 * h_m - 55.0 * Math.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.
final double r_t = -2.0 * Math.sqrt(n / (n + 6103515625.0))
* Math.sin(Math.PI / 3.0 * Math.exp(p * p / (-25.0 * Math.PI * Math.PI)));
n = (l_1 + l_2) * 0.5;
n = (n - 50.0) * (n - 50.0);
// Lightness.
final double l = (l_2 - l_1) / (k_l * (1.0 + 0.015 * n / Math.sqrt(20.0 + n)));
// These coefficients adjust the impact of different harmonic
// components on the hue difference calculation.
final double t = 1.0 + 0.24 * Math.sin(2.0 * h_m + Math.PI * 0.5)
+ 0.32 * Math.sin(3.0 * h_m + 8.0 * Math.PI / 15.0)
- 0.17 * Math.sin(h_m + Math.PI / 3.0)
- 0.20 * Math.sin(4.0 * h_m + 3.0 * Math.PI / 20.0);
n = c_1 + c_2;
// Hue.
final double h = 2.0 * Math.sqrt(c_1 * c_2) * Math.sin(h_d) / (k_h * (1.0 + 0.0075 * n * t));
// Chroma.
final double 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.
return Math.sqrt(l * l + h * h + c * c + c * h * r_t);
}
// GitHub Project : https://github.com/michel-leonard/ciede2000-color-matching
// Online Tests : https://michel-leonard.github.io/ciede2000-color-matching
// L1 = 49.7 a1 = 26.4 b1 = -3.8
// L2 = 47.1 a2 = 20.5 b2 = 3.6
// CIE ΔE00 = 6.2561715017 (Bruce Lindbloom, Netflix’s VMAF, ...)
// CIE ΔE00 = 6.2561556668 (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.
/////////////////////////////////////////////////
/////////////////////////////////////////////////
//////////// ////////////
//////////// CIEDE2000 Driver ////////////
//////////// ////////////
/////////////////////////////////////////////////
/////////////////////////////////////////////////
// Reads a CSV file specified as the first command-line argument. For each line, this program
// in Java displays the original line with the computed Delta E 2000 color difference appended.
// The C driver can offer CSV files to process and programmatically check the calculations performed there.
// Example of a CSV input line : 13,1,19.8,13.5,-5,26
// Corresponding output line : 13,1,19.8,13.5,-5,26,6.310811008250411986467320293303
public static void main(String[] args) {
if (args.length < 1) {
System.err.println("Filename argument missing.");
System.exit(1);
}
String filename = args[0];
try (BufferedReader reader = new BufferedReader(new FileReader(filename))) {
String line;
while ((line = reader.readLine()) != null) {
final String[] parts = line.split(",");
final double L1 = Double.parseDouble(parts[0]);
final double a1 = Double.parseDouble(parts[1]);
final double b1 = Double.parseDouble(parts[2]);
final double L2 = Double.parseDouble(parts[3]);
final double a2 = Double.parseDouble(parts[4]);
final double b2 = Double.parseDouble(parts[5]);
final double deltaE = ciede_2000(L1, a1, b1, L2, a2, b2);
System.out.printf("%s,%.17f%n", line, deltaE);
}
} catch (IOException e) {
e.printStackTrace();
}
}
}