Luminance.java

Below is the syntax highlighted version of Luminance.java from §3.1 Using Data Types.

/******************************************************************************
 *  Compilation:  javac Luminance.java
 *  Execution:    java Luminance r1 g1 b1 r2 g2 b2
 *
 *  Library for dealing with monochrome luminance.
 *  Uses the NTSC formula Y = 0.299*r + 0.587*g + 0.114*b.
 *
 *  % java Luminance 0 0 0 0 0 255
 *
 ******************************************************************************/

import java.awt.Color;

/**
 *  The class {@code Luminance} is a library of static methods related to
 *  the monochrome luminance of a color. It supports computing the monochrome
 *  luminance of a color (r, g, b) using the NTSC formula
 *  Y = 0.299*r + 0.587*g + 0.114*b; converting the color to a grayscale color,
 *  and checking whether two colors are compatible.
 *  <p>
 *  For additional documentation, see <a href="https://introcs.cs.princeton.edu/31datatype">Section 3.1</a>
 *  of <i>Computer Science: An Interdisciplinary Approach</i>
 *  by Robert Sedgewick and Kevin Wayne.
 *
 *  @author Robert Sedgewick
 *  @author Kevin Wayne
 *
 */
public class Luminance {

    /**
     * Returns the monochrome luminance of the given color as an intensity
     * between 0.0 and 255.0 using the NTSC formula Y = 0.299*r + 0.587*g + 0.114*b.
     *
     * @param color the color to convert
     * @return the monochrome luminance (between 0.0 and 255.0)
     * @deprecated Replaced by {@link #intensity(Color)}.
     */
    @Deprecated
    public static double lum(Color color) {
        return intensity(color);
    }

    /**
     * Returns the monochrome luminance of the given color as an intensity
     * between 0.0 and 255.0 using the NTSC formula
     * Y = 0.299*r + 0.587*g + 0.114*b. If the given color is a shade of gray
     * (r = g = b), this method is guaranteed to return the exact grayscale
     * value (an integer with no floating-point roundoff error).
     *
     * @param color the color to convert
     * @return the monochrome luminance (between 0.0 and 255.0)
     */
    public static double intensity(Color color) {
        int r = color.getRed();
        int g = color.getGreen();
        int b = color.getBlue();
        // return 0.299*r + 0.587*g + 0.114*b;
        return (299*r + 587*g + 114*b) / 1000.0;  // to avoid floating-point issues
    }

    /**
     * Returns a grayscale version of the given color as a {@code Color} object.
     *
     * @param color the {@code Color} object to convert to grayscale
     * @return a grayscale version of {@code color}
     */
    public static Color toGray(Color color) {
        int y = (int) (Math.round(intensity(color)));   // round to nearest int
        Color gray = new Color(y, y, y);
        return gray;
    }

    /**
     * Are the two given colors compatible? Two colors are compatible if
     * the difference in their monochrome luminances is at least 128.0).
     *
     * @param a one color
     * @param b the other color
     * @return {@code true} if colors {@code a} and {@code b} are compatible;
     *    {@code false} otherwise
     */
    public static boolean areCompatible(Color a, Color b) {
        return Math.abs(intensity(a) - intensity(b)) >= 128.0;
    }

   /**
     * Takes six command-line arguments r1, g1, b1, r2, g2, and b2, prints to
     * standard output the monochrome luminances of (r1, g1, b1) and (r2, g2, b2)
     * and whether they are compatible.
     *
     * @param args the six command-line arguments
     */
    public static void main(String[] args) {
        int[] a = new int[6];
        for (int i = 0; i < 6; i++) {
            a[i] = Integer.parseInt(args[i]);
        }
        Color c1 = new Color(a[0], a[1], a[2]);
        Color c2 = new Color(a[3], a[4], a[5]);
        Color c3 = Luminance.toGray(c1);
        StdOut.println("c1 = " + c1);
        StdOut.println("c2 = " + c2);
        StdOut.println("c3 = " + c3);
        StdOut.println("intensity(c1) =  " + intensity(c1));
        StdOut.println("intensity(c2) =  " + intensity(c2));
        StdOut.println("intensity(c3) =  " + intensity(c3));
        StdOut.println(areCompatible(c1, c2));
    }
}