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// This function written in Java 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.
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;
class Verifier {
// 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 = 50.3 a1 = 12.0 b1 = 3.5
// L2 = 52.6 a2 = 17.9 b2 = -5.2
// CIE ΔE00 = 7.7217093369 (Bruce Lindbloom, Netflix’s VMAF, ...)
// CIE ΔE00 = 7.7216925478 (Gaurav Sharma, OpenJDK, ...)
// Deviation between implementations ≈ 1.7e-5
// See the source code comments for easy switching between these two widely used ΔE*00 implementation variants.
//////////////////////////////////////////////////////////////////////////
//////////////////////////////////////////////////////////////////////////
/////////////////////// ///////////////////////////
/////////////////////// TESTING ///////////////////////////
/////////////////////// ///////////////////////////
//////////////////////////////////////////////////////////////////////////
//////////////////////////////////////////////////////////////////////////
// The verification is performed here in Java.
// It reads the CSV data from STDIN and prints a completion message.
public static void main(String[] args) throws IOException {
final double tolerance = args.length > 0 && "--32-bit".equals(args[0]) ? 1E-2 : 1E-10;
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
String line;
long display = 10, success = 0, error = 0, start = System.nanoTime();
double l1, a1, b1, l2, a2, b2, delta_e, maxDiff = 0.0;
String lastLine = "N/A";
while ((line = reader.readLine()) != null) {
if (line.trim().isEmpty()) continue;
String[] parts = line.trim().split(",");
if (parts.length != 7)
continue;
try {
l1 = Double.parseDouble(parts[0]);
a1 = Double.parseDouble(parts[1]);
b1 = Double.parseDouble(parts[2]);
l2 = Double.parseDouble(parts[3]);
a2 = Double.parseDouble(parts[4]);
b2 = Double.parseDouble(parts[5]);
delta_e = Double.parseDouble(parts[6]);
} catch (NumberFormatException e) {
continue;
}
if (!Double.isFinite(l1) || !Double.isFinite(a1) || !Double.isFinite(b1) || !Double.isFinite(l2) || !Double.isFinite(a2) || !Double.isFinite(b2) || !Double.isFinite(delta_e))
continue;
final double expected_delta_e = ciede_2000(l1, a1, b1, l2, a2, b2);
lastLine = line;
double diff = Math.abs(expected_delta_e - delta_e);
if (diff > tolerance) {
if (--display > 0)
System.out.printf("Error: ciede_2000(%s, %s, %s, %s, %s, %s) !== %.17f ... got %s%n", parts[0], parts[1], parts[2], parts[3], parts[4], parts[5], expected_delta_e, parts[6]);
++error;
} else
++success;
if (diff > maxDiff)
maxDiff = diff;
}
final double durationSeconds = (System.nanoTime() - start) / 1e9;
System.out.println("CIEDE2000 Verification Summary :");
System.out.println("- Last Verified Line : " + lastLine);
System.out.printf("- Duration : %.2f s%n", durationSeconds);
System.out.println("- Successes : " + success);
System.out.println("- Errors : " + error);
System.out.println("- Maximum Difference : " + maxDiff);
}
}