Replaced the algorithm for determining whether two colors are distinguishable. Merged some duplicated code into its own methods.

app/src/main/java/com/kabouzeid/gramophone/util/ColorUtil.java

@@ -138,16 +138,91 @@ public class ColorUtil {
         return backgroundColor;
     }
 
+    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;
+    }
+
     /**
-     * Calculates the distance of two colors in 3D Space.
+     * 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}
      *
-     * Taken from http://stackoverflow.com/a/1725535/984061
+     * @return > 23 corresponds to a JND (just noticeable difference)
      */
-    public static boolean calculateColorDistance(int color1, int color2) {
-        double red = Math.pow(Math.abs(Color.red(color2) - Color.red(color1)), 2);
-        double green = Math.pow(Math.abs(Color.green(color2) - Color.green(color1)), 2);
-        double blue = Math.pow(Math.abs(Color.blue(color2) - Color.blue(color1)), 2);
-        double distance = red + green + blue;
-        return distance < 55000;
+    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));
     }
 }