Source for gnu.java.awt.color.LinearRGBConverter

   1: /* LinearRGBConverter.java -- conversion to a linear RGB color space
   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:  * LinearRGBConverter - conversion routines for a linear sRGB colorspace
  43:  * sRGB is a standard for RGB colorspaces, adopted by the w3c.
  44:  *
  45:  * The specification is available at:
  46:  * http://www.w3.org/Graphics/Color/sRGB.html
  47:  *
  48:  * @author Sven de Marothy
  49:  */
  50: public class LinearRGBConverter implements ColorSpaceConverter
  51: {
  52:   /**
  53:    * linear RGB --> sRGB
  54:    * Use the inverse gamma curve
  55:    */
  56:   public float[] toRGB(float[] in)
  57:   {
  58:     float[] out = new float[3];
  59:     for (int i = 0; i < 3; i++)
  60:       {
  61:         float n = in[i];
  62:         if (n < 0)
  63:           n = 0f;
  64:         if (n > 1)
  65:           n = 1f;
  66:         if (n <= 0.00304f)
  67:           out[i] = in[0] * 12.92f;
  68:         else
  69:           out[i] = 1.055f * ((float) Math.exp((1 / 2.4) * Math.log(n)))
  70:                    - 0.055f;
  71:       }
  72:     return out;
  73:   }
  74: 
  75:   /**
  76:    * sRGB --> linear RGB
  77:    * Use the gamma curve (gamma=2.4 in sRGB)
  78:    */
  79:   public float[] fromRGB(float[] in)
  80:   {
  81:     float[] out = new float[3];
  82: 
  83:     // Convert non-linear RGB coordinates to linear ones,
  84:     //  numbers from the w3 spec.
  85:     for (int i = 0; i < 3; i++)
  86:       {
  87:         float n = in[i];
  88:         if (n < 0)
  89:           n = 0f;
  90:         if (n > 1)
  91:           n = 1f;
  92:         if (n <= 0.03928f)
  93:           out[i] = (float) (n / 12.92);
  94:         else
  95:           out[i] = (float) (Math.exp(2.4 * Math.log((n + 0.055) / 1.055)));
  96:       }
  97:     return out;
  98:   }
  99: 
 100:   /**
 101:    * Linear RGB --> CIE XYZ (D50 relative)
 102:    * This is a simple matrix transform, the matrix (relative D65)
 103:    * is given in the sRGB spec. This has been combined with a
 104:    * linear Bradford transform for the D65-->D50 mapping, resulting
 105:    * in a single matrix which does the whole thing.
 106:    *
 107:    */
 108:   public float[] fromCIEXYZ(float[] in)
 109:   {
 110:     /*
 111:      * Note: The numbers which were used to calculate this only had four
 112:      * digits of accuracy. So don't be fooled by the number of digits here.
 113:      * If someone has more accurate source, feel free to update this.
 114:      */
 115:     float[] out = new float[3];
 116:     out[0] = (float) (3.13383065124221 * in[0] - 1.61711949411313 * in[1]
 117:              - 0.49071914111101 * in[2]);
 118:     out[1] = (float) (-0.97847026691142 * in[0] + 1.91597856031996 * in[1]
 119:              + 0.03340430640699 * in[2]);
 120:     out[2] = (float) (0.07203679486279 * in[0] - 0.22903073553113 * in[1]
 121:              + 1.40557835776234 * in[2]);
 122:     if (out[0] < 0)
 123:       out[0] = 0f;
 124:     if (out[1] < 0)
 125:       out[1] = 0f;
 126:     if (out[2] < 0)
 127:       out[2] = 0f;
 128:     if (out[0] > 1.0f)
 129:       out[0] = 1.0f;
 130:     if (out[1] > 1.0f)
 131:       out[1] = 1.0f;
 132:     if (out[2] > 1.0f)
 133:       out[2] = 1.0f;
 134:     return out;
 135:   }
 136: 
 137:   /**
 138:    * Linear RGB --> CIE XYZ (D50 relative)
 139:    * Uses the inverse of the above matrix.
 140:    */
 141:   public float[] toCIEXYZ(float[] in)
 142:   {
 143:     float[] out = new float[3];
 144:     out[0] = (float) (0.43606375022190 * in[0] + 0.38514960146481 * in[1]
 145:              + 0.14308641888799 * in[2]);
 146:     out[1] = (float) (0.22245089403542 * in[0] + 0.71692584775182 * in[1]
 147:              + 0.06062451125578 * in[2]);
 148:     out[2] = (float) (0.01389851860679 * in[0] + 0.09707969011198 * in[1]
 149:              + 0.71399604572506 * in[2]);
 150:     return out;
 151:   }
 152: }