Added algorithm for color contrast ratio.

SethFalco · Seth Falco · commit 5a78f44f2e1c · 2021-02-27T07:03:58.000+01:00
diff --git a/Misc/ColorContrastRatio.java b/Misc/ColorContrastRatio.java
@@ -0,0 +1,67 @@
+package Misc;
+
+/**
+ * A Java implementation of the offcial W3 documented procedure
+ * to calculate contrast ratio between colors on the web.
+ *
+ * @since 2020-10-15
+ * @see <a href="https://www.w3.org/TR/WCAG20-TECHS/G17.html#G17-procedure">Color Contrast Ratio Procedure</a>
+ * @author Seth Falco (https://elypia.org/)
+ */
+public class ColorContrastRatio {
+
+    /**
+     * Calculates the contrast ratio between two given colors.
+     *
+     * @param a Any color, used to get the red, green, and blue values.
+     * @param b Another color, which will be compared against the first color.
+     * @return The contrast ratio between the two colors.
+     */
+    public double getContrastRatio(Color a, Color b) {
+        final double aColorLuminance = getRelativeLuminance(a);
+        final double bColorLuminance = getRelativeLuminance(b);
+
+        if (aColorLuminance > bColorLuminance)
+            return (aColorLuminance + 0.05) / (bColorLuminance + 0.05);
+        else
+            return (bColorLuminance + 0.05) / (aColorLuminance + 0.05);
+    }
+
+    /**
+     * Calculates the relative luminance of a given color.
+     *
+     * @param color Any color, used to get the red, green, and blue values.
+     * @return The relative luminance of the color.
+     * @see <a href="https://www.w3.org/TR/2008/REC-WCAG20-20081211/#relativeluminancedef">More info on relative luminance.</a>
+     */
+    public double getRelativeLuminance(Color color) {
+        final double red = getColor(color.getRed());
+        final double green = getColor(color.getGreen());
+        final double blue = getColor(color.getBlue());
+
+        return 0.2126 * red + 0.7152 * green + 0.0722 * blue;
+    }
+
+    /**
+     * Calculates the final value for a color to be used in the
+     * relative luminance formula as described in step 1.
+     *
+     * @param color8Bit The 8-bit repretation of a color component value.
+     * @return Value for the provided color component to be used in the relative luminance formula.
+     */
+    public double getColor(int value) {
+        final double sRgb = getColorSRgb(value);
+        return (sRgb <= 0.03928) ? sRgb / 12.92 : Math.pow((sRgb + 0.055) / 1.055, 2.4);
+    }
+
+    /**
+     * Calculates the Color sRGB value as denoted in step 1
+     * of the procedure document.
+     *
+     * @param color8Bit The 8-bit repretation of a color component value.
+     * @return A percentile value of the color component.
+     */
+    private double getColorSRgb(double color8Bit) {
+        return color8Bit / 255.0;
+    }
+}
