package com.thealgorithms.misc;
import java.awt.Color;
/**
* @brief 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</a>
* @author [Seth Falco](https://github.com/SethFalco)
*/
public class ColorContrastRatio {
/**
* @brief 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);
}
return (bColorLuminance + 0.05) / (aColorLuminance + 0.05);
}
/**
* @brief 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;
}
/**
* @brief Calculates the final value for a color to be used in the relative luminance formula as described in step 1.
* @param color8Bit 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 color8Bit) {
final double sRgb = getColorSRgb(color8Bit);
return (sRgb <= 0.03928) ? sRgb / 12.92 : Math.pow((sRgb + 0.055) / 1.055, 2.4);
}
/**
* @brief Calculates the Color sRGB value as denoted in step 1 of the procedure document.
* @param color8Bit 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;
}
}