RgbHsvConversion.java

package Conversions;

import java.util.Arrays;

/**
 * The RGB color model is an additive color model in which red, green, and blue light are added
 * together in various ways to reproduce a broad array of colors. The name of the model comes from
 * the initials of the three additive primary colors, red, green, and blue. Meanwhile, the HSV
 * representation models how colors appear under light. In it, colors are represented using three
 * components: hue, saturation and (brightness-)value. This class provides methods for converting
 * colors from one representation to the other. (description adapted from
 * https://en.wikipedia.org/wiki/RGB_color_model and https://en.wikipedia.org/wiki/HSL_and_HSV).
 */
public class RgbHsvConversion {

  public static void main(String[] args) {
    // Expected RGB-values taken from https://www.rapidtables.com/convert/color/hsv-to-rgb.html

    // Test hsvToRgb-method
    assert Arrays.equals(hsvToRgb(0, 0, 0), new int[] {0, 0, 0});
    assert Arrays.equals(hsvToRgb(0, 0, 1), new int[] {255, 255, 255});
    assert Arrays.equals(hsvToRgb(0, 1, 1), new int[] {255, 0, 0});
    assert Arrays.equals(hsvToRgb(60, 1, 1), new int[] {255, 255, 0});
    assert Arrays.equals(hsvToRgb(120, 1, 1), new int[] {0, 255, 0});
    assert Arrays.equals(hsvToRgb(240, 1, 1), new int[] {0, 0, 255});
    assert Arrays.equals(hsvToRgb(300, 1, 1), new int[] {255, 0, 255});
    assert Arrays.equals(hsvToRgb(180, 0.5, 0.5), new int[] {64, 128, 128});
    assert Arrays.equals(hsvToRgb(234, 0.14, 0.88), new int[] {193, 196, 224});
    assert Arrays.equals(hsvToRgb(330, 0.75, 0.5), new int[] {128, 32, 80});

    // Test rgbToHsv-method
    // approximate-assertions needed because of small deviations due to converting between
    // int-values and double-values.
    assert approximatelyEqualHsv(rgbToHsv(0, 0, 0), new double[] {0, 0, 0});
    assert approximatelyEqualHsv(rgbToHsv(255, 255, 255), new double[] {0, 0, 1});
    assert approximatelyEqualHsv(rgbToHsv(255, 0, 0), new double[] {0, 1, 1});
    assert approximatelyEqualHsv(rgbToHsv(255, 255, 0), new double[] {60, 1, 1});
    assert approximatelyEqualHsv(rgbToHsv(0, 255, 0), new double[] {120, 1, 1});
    assert approximatelyEqualHsv(rgbToHsv(0, 0, 255), new double[] {240, 1, 1});
    assert approximatelyEqualHsv(rgbToHsv(255, 0, 255), new double[] {300, 1, 1});
    assert approximatelyEqualHsv(rgbToHsv(64, 128, 128), new double[] {180, 0.5, 0.5});
    assert approximatelyEqualHsv(rgbToHsv(193, 196, 224), new double[] {234, 0.14, 0.88});
    assert approximatelyEqualHsv(rgbToHsv(128, 32, 80), new double[] {330, 0.75, 0.5});
  }

  /**
   * Conversion from the HSV-representation to the RGB-representation.
   *
   * @param hue Hue of the color.
   * @param saturation Saturation of the color.
   * @param value Brightness-value of the color.
   * @return The tuple of RGB-components.
   */
  public static int[] hsvToRgb(double hue, double saturation, double value) {
    if (hue < 0 || hue > 360) {
      throw new IllegalArgumentException("hue should be between 0 and 360");
    }

    if (saturation < 0 || saturation > 1) {
      throw new IllegalArgumentException("saturation should be between 0 and 1");
    }

    if (value < 0 || value > 1) {
      throw new IllegalArgumentException("value should be between 0 and 1");
    }

    double chroma = value * saturation;
    double hueSection = hue / 60;
    double secondLargestComponent = chroma * (1 - Math.abs(hueSection % 2 - 1));
    double matchValue = value - chroma;

    return getRgbBySection(hueSection, chroma, matchValue, secondLargestComponent);
  }

  /**
   * Conversion from the RGB-representation to the HSV-representation.
   *
   * @param red Red-component of the color.
   * @param green Green-component of the color.
   * @param blue Blue-component of the color.
   * @return The tuple of HSV-components.
   */
  public static double[] rgbToHsv(int red, int green, int blue) {
    if (red < 0 || red > 255) {
      throw new IllegalArgumentException("red should be between 0 and 255");
    }

    if (green < 0 || green > 255) {
      throw new IllegalArgumentException("green should be between 0 and 255");
    }

    if (blue < 0 || blue > 255) {
      throw new IllegalArgumentException("blue should be between 0 and 255");
    }

    double dRed = (double) red / 255;
    double dGreen = (double) green / 255;
    double dBlue = (double) blue / 255;
    double value = Math.max(Math.max(dRed, dGreen), dBlue);
    double chroma = value - Math.min(Math.min(dRed, dGreen), dBlue);
    double saturation = value == 0 ? 0 : chroma / value;
    double hue;

    if (chroma == 0) {
      hue = 0;
    } else if (value == dRed) {
      hue = 60 * (0 + (dGreen - dBlue) / chroma);
    } else if (value == dGreen) {
      hue = 60 * (2 + (dBlue - dRed) / chroma);
    } else {
      hue = 60 * (4 + (dRed - dGreen) / chroma);
    }

    hue = (hue + 360) % 360;

    return new double[] {hue, saturation, value};
  }

  private static boolean approximatelyEqualHsv(double[] hsv1, double[] hsv2) {
    boolean bHue = Math.abs(hsv1[0] - hsv2[0]) < 0.2;
    boolean bSaturation = Math.abs(hsv1[1] - hsv2[1]) < 0.002;
    boolean bValue = Math.abs(hsv1[2] - hsv2[2]) < 0.002;

    return bHue && bSaturation && bValue;
  }

  private static int[] getRgbBySection(
      double hueSection, double chroma, double matchValue, double secondLargestComponent) {
    int red;
    int green;
    int blue;

    if (hueSection >= 0 && hueSection <= 1) {
      red = convertToInt(chroma + matchValue);
      green = convertToInt(secondLargestComponent + matchValue);
      blue = convertToInt(matchValue);
    } else if (hueSection > 1 && hueSection <= 2) {
      red = convertToInt(secondLargestComponent + matchValue);
      green = convertToInt(chroma + matchValue);
      blue = convertToInt(matchValue);
    } else if (hueSection > 2 && hueSection <= 3) {
      red = convertToInt(matchValue);
      green = convertToInt(chroma + matchValue);
      blue = convertToInt(secondLargestComponent + matchValue);
    } else if (hueSection > 3 && hueSection <= 4) {
      red = convertToInt(matchValue);
      green = convertToInt(secondLargestComponent + matchValue);
      blue = convertToInt(chroma + matchValue);
    } else if (hueSection > 4 && hueSection <= 5) {
      red = convertToInt(secondLargestComponent + matchValue);
      green = convertToInt(matchValue);
      blue = convertToInt(chroma + matchValue);
    } else {
      red = convertToInt(chroma + matchValue);
      green = convertToInt(matchValue);
      blue = convertToInt(secondLargestComponent + matchValue);
    }

    return new int[] {red, green, blue};
  }

  private static int convertToInt(double input) {
    return (int) Math.round(255 * input);
  }
}