Computes the difference between two RGB colors - Android Graphics

Android examples for Graphics:Color RGB Value

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Description

Computes the difference between two RGB colors

Demo Code

/**//from w  w  w  .  j  a v a 2s  .c o  m
 * Created by Jaime on 4/12/2015.
 * Based on the work of: Daniel Strebel,University of Zurich
 * Explained by Ivo Stoyanov in http://stackoverflow.com/questions/9018016/how-to-compare-two-colors
 */
//package com.java2s;
import android.graphics.Color;

public class Main {
    /**
     * Computes the difference between two RGB colors by converting them to the L*a*b scale and
     * comparing them using the CIE76 algorithm { http://en.wikipedia.org/wiki/Color_difference#CIE76}
     */
    public static double getColorDifference(int a, int b) {
        int r1, g1, b1, r2, g2, b2;
        r1 = Color.red(a);
        g1 = Color.green(a);
        b1 = Color.blue(a);
        r2 = Color.red(b);
        g2 = Color.green(b);
        b2 = Color.blue(b);
        int[] lab1 = rgb2lab(r1, g1, b1);
        int[] lab2 = rgb2lab(r2, g2, b2);
        return Math.sqrt(Math.pow(lab2[0] - lab1[0], 2)
                + Math.pow(lab2[1] - lab1[1], 2)
                + Math.pow(lab2[2] - lab1[2], 2));
    }

    public static int[] rgb2lab(int R, int G, int B) {
        //http://www.brucelindbloom.com

        float r, g, b, X, Y, Z, fx, fy, fz, xr, yr, zr;
        float Ls, as, bs;
        float eps = 216.f / 24389.f;
        float k = 24389.f / 27.f;

        float Xr = 0.964221f; // reference white D50
        float Yr = 1.0f;
        float Zr = 0.825211f;

        // RGB to XYZ
        r = R / 255.f; //R 0..1
        g = G / 255.f; //G 0..1
        b = B / 255.f; //B 0..1

        // assuming sRGB (D65)
        if (r <= 0.04045)
            r = r / 12;
        else
            r = (float) Math.pow((r + 0.055) / 1.055, 2.4);

        if (g <= 0.04045)
            g = g / 12;
        else
            g = (float) Math.pow((g + 0.055) / 1.055, 2.4);

        if (b <= 0.04045)
            b = b / 12;
        else
            b = (float) Math.pow((b + 0.055) / 1.055, 2.4);

        X = 0.436052025f * r + 0.385081593f * g + 0.143087414f * b;
        Y = 0.222491598f * r + 0.71688606f * g + 0.060621486f * b;
        Z = 0.013929122f * r + 0.097097002f * g + 0.71418547f * b;

        // XYZ to Lab
        xr = X / Xr;
        yr = Y / Yr;
        zr = Z / Zr;

        if (xr > eps)
            fx = (float) Math.pow(xr, 1 / 3.);
        else
            fx = (float) ((k * xr + 16.) / 116.);

        if (yr > eps)
            fy = (float) Math.pow(yr, 1 / 3.);
        else
            fy = (float) ((k * yr + 16.) / 116.);

        if (zr > eps)
            fz = (float) Math.pow(zr, 1 / 3.);
        else
            fz = (float) ((k * zr + 16.) / 116);

        Ls = (116 * fy) - 16;
        as = 500 * (fx - fy);
        bs = 200 * (fy - fz);

        int[] lab = new int[3];
        lab[0] = (int) (2.55 * Ls + .5);
        lab[1] = (int) (as + .5);
        lab[2] = (int) (bs + .5);
        return lab;
    }
}

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