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+/* GrayScaleConverter.java -- Linear grayscale conversion class
+ Copyright (C) 2004 Free Software Foundation
+
+This file is part of GNU Classpath.
+
+GNU Classpath is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2, or (at your option)
+any later version.
+
+GNU Classpath is distributed in the hope that it will be useful, but
+WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with GNU Classpath; see the file COPYING. If not, write to the
+Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+02110-1301 USA.
+
+Linking this library statically or dynamically with other modules is
+making a combined work based on this library. Thus, the terms and
+conditions of the GNU General Public License cover the whole
+combination.
+
+As a special exception, the copyright holders of this library give you
+permission to link this library with independent modules to produce an
+executable, regardless of the license terms of these independent
+modules, and to copy and distribute the resulting executable under
+terms of your choice, provided that you also meet, for each linked
+independent module, the terms and conditions of the license of that
+module. An independent module is a module which is not derived from
+or based on this library. If you modify this library, you may extend
+this exception to your version of the library, but you are not
+obligated to do so. If you do not wish to do so, delete this
+exception statement from your version. */
+
+package gnu.java.awt.color;
+
+
+/**
+ * Linear Grayscale converter
+ *
+ * @author Sven de Marothy
+ */
+public class GrayScaleConverter implements ColorSpaceConverter
+{
+ // intensity factors (ITU Rec. BT.709)
+ double[] coeff = { 0.2125f, 0.7154f, 0.0721f };
+
+ /**
+ * CIE 1931 D50 white point (in Lab coordinates)
+ */
+ private static float[] D50 = { 0.96422f, 1.00f, 0.82521f };
+
+ public float[] toCIEXYZ(float[] in)
+ {
+ float g = in[0];
+ if (g < 0)
+ g = 1 + g;
+ float[] out = { g * D50[0], g * D50[1], g * D50[2] }; // White spot
+ return out;
+ }
+
+ public float[] toRGB(float[] in)
+ {
+ float[] out = new float[3];
+ if (in[0] <= 0.00304f)
+ out[0] = in[0] * 12.92f;
+ else
+ out[0] = 1.055f * ((float) Math.exp((1 / 2.4) * Math.log(in[0])))
+ - 0.055f;
+ out[1] = out[2] = out[0];
+ return out;
+ }
+
+ public float[] fromCIEXYZ(float[] in)
+ {
+ float[] temp = new float[3];
+ temp[0] = 3.1338f * in[0] - 1.6171f * in[1] - 0.4907f * in[2];
+ temp[1] = -0.9785f * in[0] + 1.9160f * in[1] + 0.0334f * in[2];
+ temp[2] = 0.0720f * in[0] - 0.2290f * in[1] + 1.4056f * in[2];
+ float[] out = new float[1];
+ for (int i = 0; i < 3; i++)
+ out[0] = (float) (temp[i] * coeff[i]);
+ return out;
+ }
+
+ public float[] fromRGB(float[] in)
+ {
+ float[] out = new float[1];
+
+ // Convert non-linear RGB coordinates to linear ones,
+ // numbers from the w3 spec.
+ out[0] = 0;
+ for (int i = 0; i < 3; i++)
+ {
+ float n = in[i];
+ if (n < 0)
+ n = 0f;
+ if (n > 1)
+ n = 1f;
+ if (n <= 0.03928f)
+ out[0] += (float) (coeff[i] * n / 12.92);
+ else
+ out[0] += (float) (coeff[i] * Math.exp(2.4 * Math.log((n + 0.055) / 1.055)));
+ }
+ return out;
+ }
+}