Add ColorUtil.xyToDuv

bundles/org.openhab.core/src/main/java/org/openhab/core/util/ColorUtil.java

@@ -34,6 +34,7 @@
  * @author Holger Friedrich - Transfer RGB color conversion from HSBType, improve RGB conversion, restructuring
  * @author Chris Jackson - Added fromRGB (moved from HSBType)
  * @author Andrew Fiddian-Green - Extensive revamp to fix bugs and improve accuracy
+ * @author Cody Cutrer - Added xyToDuv
  */
 @NonNullByDefault
 public class ColorUtil {
@@ -45,11 +46,12 @@ public class ColorUtil {
  private static final BigDecimal BIG_DECIMAL_120 = BigDecimal.valueOf(120);
  private static final BigDecimal BIG_DECIMAL_100 = BigDecimal.valueOf(100);
  private static final BigDecimal BIG_DECIMAL_60 = BigDecimal.valueOf(60);
- private static final BigDecimal BIG_DECIMAL_50 = BigDecimal.valueOf(50);
  private static final BigDecimal BIG_DECIMAL_5 = BigDecimal.valueOf(5);
  private static final BigDecimal BIG_DECIMAL_3 = BigDecimal.valueOf(3);
  private static final BigDecimal BIG_DECIMAL_2 = BigDecimal.valueOf(2);
  private static final BigDecimal BIG_DECIMAL_2_POINT_55 = new BigDecimal("2.55");
+ private static final double[] CORM_COEFFICIENTS = { -0.00616793, 0.0893944, -0.5179722, 1.5317403, -2.4243787,
+ 1.925865, -0.471106 };
 
  public static final Gamut DEFAULT_GAMUT = new Gamut(new double[] { 0.9961, 0.0001 }, new double[] { 0, 0.9961 },
  new double[] { 0, 0.0001 });
@@ -523,6 +525,39 @@ public static HSBType xyToHsb(double[] xyY, Gamut gamut) throws IllegalArgumentE
  return hsb;
  }
 
+ /**
+ * Calculate the Duv (Delta u,v) metric from a
+ * <a href="https://en.wikipedia.org/wiki/CIE_1931_color_space">CIE 1931</a> {@code xy} format color.
+ *
+ * Duv describes the distance of a color point from the black body curve. It's useful for calculating
+ * if a color is near to "white", at any color temperature.
+ * 
+ * @param xy array of double with CIE 1931 x,y in the range 0.0000 to 1.0000
+ * @return the calculated Duv metric
+ * @throws IllegalArgumentException when input array has wrong size or exceeds allowed value range.
+ */
+ public static double xyToDuv(double[] xy) throws IllegalArgumentException {
+ if (xy.length != 2) {
+ throw new IllegalArgumentException("xyToDuv() requires 2 arguments");
+ }
+
+ for (int i = 0; i < xy.length; i++) {
+ if (xy[i] < 0 || xy[i] > 1) {
+ throw new IllegalArgumentException(
+ String.format("xyToDuv() argument %d value '%f' out of range [0..1.0]", i, xy[i]));
+ }
+ }
+
+ double x = xy[0];
+ double y = xy[1];
+ double u = 4.0 * x / (-2.0 * x + 12 * y + 3.0);
+ double v = 6.0 * y / (-2.0 * x + 12 * y + 3.0);
+ double Lfp = Math.sqrt(Math.pow(u - 0.292, 2) + Math.pow(v - 0.24, 2));
+ double a = Math.acos((u - 0.292) / Lfp);
+ double Lbb = polynomialFit(a, CORM_COEFFICIENTS);
+ return Lfp - Lbb;
+ }
+
  /**
  * Get an array of int from an array of PercentType.
  */
@@ -1176,4 +1211,25 @@ public static double xyToKelvin(double[] xy) {
  double n = (xy[0] - 0.3320) / (0.1858 - xy[1]);
  return (437 * Math.pow(n, 3)) + (3601 * Math.pow(n, 2)) + (6861 * n) + 5517;
  }
+
+ /**
+ * Calculates a polynomial regression.
+ *
+ * This calculates the equation K[4]*x^0 + K[3]*x^1 + K[2]*x^2 + K[1]*x^3 + K[0]*x^4
+ *
+ * @param x The independent variable distributed through each term of the polynomial
+ * @param coefficients The coefficients of the polynomial. Note that the terms are in
+ * order from largest exponent to smallest exponent, which is the reverse order
+ * of the usual way of writing it in academic papers
+ * @return the result of substituting x into the regression polynomial
+ */
+ private static double polynomialFit(double x, double[] coefficients) {
+ double result = 0.0;
+ double xAccumulator = 1.0;
+ for (int i = coefficients.length - 1; i >= 0; i--) {
+ result += coefficients[i] * xAccumulator;
+ xAccumulator *= x;
+ }
+ return result;
+ }
 }

bundles/org.openhab.core/src/test/java/org/openhab/core/util/ColorUtilTest.java

@@ -274,6 +274,20 @@ public void testConversionRgbToHsb(int[] hsb, int[] rgb) {
  assertTrue(hsbType.closeTo(new HSBType(expected), 0.01));
  }
 
+ @Test
+ public void testXyToDuv() {
+ // Black
+ assertEquals(-0.0017d, ColorUtil.xyToDuv(new double[] { 0.3227d, 0.3290d }), 0.0001);
+ // 2700K
+ assertEquals(0.0000d, ColorUtil.xyToDuv(new double[] { 0.4599d, 0.4106d }), 0.0001);
+ // 3000K
+ assertEquals(0.0000d, ColorUtil.xyToDuv(new double[] { 0.4369d, 0.4041d }), 0.0001);
+ // Red
+ assertEquals(0.2727d, ColorUtil.xyToDuv(new double[] { 0.6987d, 0.2974d }), 0.0001);
+ // Yellow
+ assertEquals(0.0387d, ColorUtil.xyToDuv(new double[] { 0.4442d, 0.5166d }), 0.0001);
+ }
+
  private void xyToXY(double[] xy, Gamut gamut) {
  assertTrue(xy.length > 1);
  HSBType hsb = ColorUtil.xyToHsb(xy, gamut);