Source for gnu.java.awt.color.GrayScaleConverter

   1: /* GrayScaleConverter.java -- Linear grayscale conversion class
   2:    Copyright (C) 2004 Free Software Foundation
   3: 
   4: This file is part of GNU Classpath.
   5: 
   6: GNU Classpath is free software; you can redistribute it and/or modify
   7: it under the terms of the GNU General Public License as published by
   8: the Free Software Foundation; either version 2, or (at your option)
   9: any later version.
  10: 
  11: GNU Classpath is distributed in the hope that it will be useful, but
  12: WITHOUT ANY WARRANTY; without even the implied warranty of
  13: MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14: General Public License for more details.
  15: 
  16: You should have received a copy of the GNU General Public License
  17: along with GNU Classpath; see the file COPYING.  If not, write to the
  18: Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  19: 02110-1301 USA.
  20: 
  21: Linking this library statically or dynamically with other modules is
  22: making a combined work based on this library.  Thus, the terms and
  23: conditions of the GNU General Public License cover the whole
  24: combination.
  25: 
  26: As a special exception, the copyright holders of this library give you
  27: permission to link this library with independent modules to produce an
  28: executable, regardless of the license terms of these independent
  29: modules, and to copy and distribute the resulting executable under
  30: terms of your choice, provided that you also meet, for each linked
  31: independent module, the terms and conditions of the license of that
  32: module.  An independent module is a module which is not derived from
  33: or based on this library.  If you modify this library, you may extend
  34: this exception to your version of the library, but you are not
  35: obligated to do so.  If you do not wish to do so, delete this
  36: exception statement from your version. */
  37: 
  38: package gnu.java.awt.color;
  39: 
  40: 
  41: /**
  42:  * Linear Grayscale converter
  43:  *
  44:  * @author Sven de Marothy
  45:  */
  46: public class GrayScaleConverter implements ColorSpaceConverter
  47: {
  48:   // intensity factors (ITU Rec. BT.709)
  49:   double[] coeff = { 0.2125f, 0.7154f, 0.0721f };
  50: 
  51:   /**
  52:    * CIE 1931 D50 white point (in Lab coordinates)
  53:    */
  54:   private static float[] D50 = { 0.96422f, 1.00f, 0.82521f };
  55: 
  56:   public float[] toCIEXYZ(float[] in)
  57:   {
  58:     float g = in[0];
  59:     if (g < 0)
  60:       g = 1 + g;
  61:     float[] out = { g * D50[0], g * D50[1], g * D50[2] }; // White spot
  62:     return out;
  63:   }
  64: 
  65:   public float[] toRGB(float[] in)
  66:   {
  67:     float[] out = new float[3];
  68:     if (in[0] <= 0.00304f)
  69:       out[0] = in[0] * 12.92f;
  70:     else
  71:       out[0] = 1.055f * ((float) Math.exp((1 / 2.4) * Math.log(in[0])))
  72:                - 0.055f;
  73:     out[1] = out[2] = out[0];
  74:     return out;
  75:   }
  76: 
  77:   public float[] fromCIEXYZ(float[] in)
  78:   {
  79:     float[] temp = new float[3];
  80:     temp[0] = 3.1338f * in[0] - 1.6171f * in[1] - 0.4907f * in[2];
  81:     temp[1] = -0.9785f * in[0] + 1.9160f * in[1] + 0.0334f * in[2];
  82:     temp[2] = 0.0720f * in[0] - 0.2290f * in[1] + 1.4056f * in[2];
  83:     float[] out = new float[1];
  84:     for (int i = 0; i < 3; i++)
  85:       out[0] = (float) (temp[i] * coeff[i]);
  86:     return out;
  87:   }
  88: 
  89:   public float[] fromRGB(float[] in)
  90:   {
  91:     float[] out = new float[1];
  92: 
  93:     // Convert non-linear RGB coordinates to linear ones,
  94:     //  numbers from the w3 spec.
  95:     out[0] = 0;
  96:     for (int i = 0; i < 3; i++)
  97:       {
  98:         float n = in[i];
  99:         if (n < 0)
 100:           n = 0f;
 101:         if (n > 1)
 102:           n = 1f;
 103:         if (n <= 0.03928f)
 104:           out[0] += (float) (coeff[i] * n / 12.92);
 105:         else
 106:           out[0] += (float) (coeff[i] * Math.exp(2.4 * Math.log((n + 0.055) / 1.055)));
 107:       }
 108:     return out;
 109:   }
 110: }