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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
package main
import (
"bufio"
"fmt"
"math"
"os"
"strconv"
"strings"
)
// 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.
func ciede_2000(l_1 float64, a_1 float64, b_1 float64, l_2 float64, a_2 float64, b_2 float64) float64 {
// Working in Go with the CIEDE2000 color-difference formula.
const (
// k_l, k_c, k_h are parametric factors to be adjusted according to
// different viewing parameters such as textures, backgrounds...
k_l = 1.0
k_c = 1.0
k_h = 1.0
)
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.
c_1 := math.Sqrt(a_1 * a_1 * n * n + b_1 * b_1)
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.
h_1 := math.Atan2(b_1, a_1 * n)
h_2 := math.Atan2(b_2, a_2 * n)
if h_1 < 0.0 { h_1 += 2.0 * math.Pi }
if h_2 < 0.0 { h_2 += 2.0 * math.Pi }
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.
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
// if h_m < math.Pi { h_m += math.Pi } else { h_m -= math.Pi }
}
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.
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.
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.
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.
h := 2.0 * math.Sqrt(c_1 * c_2) * math.Sin(h_d) / (k_h * (1.0 + 0.0075 * n * t))
// Chroma.
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 = 24.5 a1 = 13.2 b1 = 3.3
// L2 = 26.5 a2 = 18.4 b2 = -4.0
// CIE ΔE00 = 6.3972611989 (Bruce Lindbloom, Netflix’s VMAF, ...)
// CIE ΔE00 = 6.3972478430 (Gaurav Sharma, OpenJDK, ...)
// Deviation between implementations ≈ 1.3e-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 Go 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 : 13.5,-16.4,127,18,2,97
// Corresponding output line : 13.5,-16.4,127,18,2,97,9.926292672470492681983541384971
func main() {
if len(os.Args) < 2 {
fmt.Fprintln(os.Stderr, "Usage: go run ciede-2000-driver.go <file>")
os.Exit(1)
}
filename := os.Args[1]
file, err := os.Open(filename)
if err != nil {
fmt.Fprintln(os.Stderr, "Failed to open file:", err)
os.Exit(1)
}
defer file.Close()
scanner := bufio.NewScanner(file)
for scanner.Scan() {
line := scanner.Text()
fields := strings.Split(line, ",")
if len(fields) != 6 {
continue
}
l_1, _ := strconv.ParseFloat(fields[0], 64)
a_1, _ := strconv.ParseFloat(fields[1], 64)
b_1, _ := strconv.ParseFloat(fields[2], 64)
l_2, _ := strconv.ParseFloat(fields[3], 64)
a_2, _ := strconv.ParseFloat(fields[4], 64)
b_2, _ := strconv.ParseFloat(fields[5], 64)
delta := ciede_2000(l_1, a_1, b_1, l_2, a_2, b_2)
fmt.Printf("%s,%.17f\n", line, delta)
}
if err := scanner.Err(); err != nil {
fmt.Fprintln(os.Stderr, "Error reading file:", err)
}
}