TheAlgorithms · SethFalco · Nov 5, 2020
diff --git a/src/main/java/com/others/ColorContrastRatio.java b/src/main/java/com/others/ColorContrastRatio.java
@@ -0,0 +1,71 @@
+package com.others;
+
+import java.awt.Color;
+
+/**
+ * A Java implementation of the official W3 documented procedure
+ * to calculate contrast ratio between colors on the web.
+ *
+ * This is used to calculate the readability of a foreground color
+ * on top of a background color.
+ *
+ * @since 2020-10-15
+ * @see <a href="https://www.w3.org/TR/WCAG20-TECHS/G17.html#G17-procedure">Color Contrast Ratio Procedure</a>
+ */
+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 value The 8-bit representation 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 representation of a color component value.
+     * @return A percentile value of the color component.
+     */
+    private double getColorSRgb(double color8Bit) {
+        return color8Bit / 255.0;
+    }
+}
diff --git a/src/test/java/com/others/ColorContrastRatioTest.java b/src/test/java/com/others/ColorContrastRatioTest.java
@@ -0,0 +1,56 @@
+package com.others;
+
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+import java.awt.Color;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+/**
+ * You can check the examples against another open-source implementation available on GitHub.
+ *
+ * @see <a href="https://contrast-ratio.com/#rgb%28226%2C%20229%2C%20248-on-rgb%2823%2C%20103%2C%20154%29">Online Contrast Ratio</a>
+ * @see <a href="https://github.com/LeaVerou/contrast-ratio">GitHub Repository for Online Contrast Ratio</a>
+ */
+public class ColorContrastRatioTest {
+
+    private static ColorContrastRatio ccr;
+
+    @BeforeAll
+    public static void before() {
+        ccr = new ColorContrastRatio();
+    }
+
+    @Test
+    public void testRelativeLuminance() {
+        final double expected = 0.12215748057375966;
+        final double actual = ccr.getRelativeLuminance(new Color(23, 103, 154));
+
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    public void testRelativeLuminance2() {
+        final double expected = 0.7898468477881603;
+        final double actual = ccr.getRelativeLuminance(new Color(226, 229, 248));
+
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    public void testColorContrastRatio() {
+        final double expected = 4.878363954846178;
+        final double actual = ccr.getContrastRatio(new Color(23, 103, 154), new Color(226, 229, 248));
+
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    public void testColorContrastRatioInverse() {
+        final double expected = 4.878363954846178;
+        final double actual = ccr.getContrastRatio(new Color(226, 229, 248), new Color(23, 103, 154));
+
+        assertEquals(expected, actual);
+    }
+}