Merge "Add API to ColorSpace to compute chromaticity coordinates from CCT"

graphics/java/android/graphics/ColorSpace.java

@@ -1778,6 +1778,36 @@ public abstract class ColorSpace {
         return mul3x3(inverse3x3(matrix), mul3x3Diag(LMS, matrix));
     }
 
+    /**
+     * <p>Computes the chromaticity coordinates of a CIE series D illuminant
+     * from the specified correlated color temperature (CCT). The specified CCT
+     * must be greater than 0. A meaningful CCT range is [4000, 25000].</p>
+     *
+     * <p>The transform is computed using the methods referred to in Kang et
+     * al., <i>Design of Advanced Color - Temperature Control System for HDTV
+     * Applications</i>, Journal of Korean Physical Society 41, 865-871
+     * (2002).</p>
+     *
+     * @param cct The correlated color temperature, in Kelvin
+     * @return Corresponding XYZ values
+     * @throws IllegalArgumentException If cct is invalid
+     */
+    @NonNull
+    @Size(3)
+    public static float[] cctToIlluminantdXyz(@IntRange(from = 1) int cct) {
+        if (cct < 1) {
+            throw new IllegalArgumentException("Temperature must be greater than 0");
+        }
+
+        final float icct = 1.0f / cct;
+        final float icct2 = icct * icct;
+        final float x = cct <= 7000.0f ?
+            0.244063f + 0.09911e3f * icct + 2.9678e6f * icct2 - 4.6070e9f * icct2 * icct :
+            0.237040f + 0.24748e3f * icct + 1.9018e6f * icct2 - 2.0064e9f * icct2 * icct;
+        final float y = -3.0f * x * x + 2.87f * x - 0.275f;
+        return xyYToXyz(new float[] {x, y});
+    }
+
     /**
      * <p>Computes the chromatic adaptation transform from the specified
      * source white point to the specified destination white point.</p>