gomp-20050608-branch/libjava/classpath/gnu/java/awt/color/ToneReproductionCurve.java

   1 /* ToneReproductionCurve.java -- Representation of an ICC 'curv' type TRC
   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  * ToneReproductionCurve - TRCs are used to describe RGB
  43  * and Grayscale profiles. The TRC is essentially the gamma
  44  * function of the color space.
  45  *
  46  * For example, Apple RGB has a gamma of 1.8, most monitors are ~2.2,
  47  * sRGB is 2.4 with a small linear part near 0.
  48  * Linear spaces are of course 1.0.
  49  * (The exact function is implemented in SrgbConverter)
  50  *
  51  * The ICC specification allows the TRC to be described as a single
  52  * Gamma value, where the function is thus out = in**gamma.
  53  * Alternatively, the gamma function may be represented by a lookup table
  54  * of values, in which case linear interpolation is used.
  55  *
  56  * @author Sven de Marothy
  57  */
  58 public class ToneReproductionCurve
  59 {
  60   private float[] trc;
  61   private float gamma;
  62   private float[] reverseTrc;
  63
  64   /**
  65    * Constructs a TRC from a gamma values
  66    */
  67   public ToneReproductionCurve(float gamma)
  68   {
  69     trc = null;
  70     reverseTrc = null;
  71     this.gamma = gamma;
  72   }
  73
  74   /**
  75    * Constructs a TRC from a set of float values
  76    */
  77   public ToneReproductionCurve(float[] trcValues)
  78   {
  79     trc = new float[trcValues.length];
  80     System.arraycopy(trcValues, 0, trc, 0, trcValues.length);
  81     setupReverseTrc();
  82   }
  83
  84   /**
  85    * Constructs a TRC from a set of short values normalized to
  86    * the 0-65535 range (as in the ICC profile file).
  87    * (Note the values are treated as unsigned)
  88    */
  89   public ToneReproductionCurve(short[] trcValues)
  90   {
  91     trc = new float[trcValues.length];
  92     for (int i = 0; i < trcValues.length; i++)
  93       trc[i] = (float) ((int) trcValues[i] & (0xFFFF)) / 65535.0f;
  94     setupReverseTrc();
  95   }
  96
  97   /**
  98    * Performs a TRC lookup
  99    */
 100   public float lookup(float in)
 101   {
 102     float out;
 103
 104     if (trc == null)
 105       {
 106         if (in == 0f)
 107           return 0.0f;
 108         return (float) Math.exp(gamma * Math.log(in));
 109       }
 110     else
 111       {
 112         double alpha = in * (trc.length - 1);
 113         int index = (int) Math.floor(alpha);
 114         alpha = alpha - (double) index;
 115         if (index >= trc.length - 1)
 116           return trc[trc.length - 1];
 117         if (index <= 0)
 118           return trc[0];
 119         out = (float) (trc[index] * (1.0 - alpha) + trc[index + 1] * alpha);
 120       }
 121     return out;
 122   }
 123
 124   /**
 125    * Performs an reverse lookup
 126    */
 127   public float reverseLookup(float in)
 128   {
 129     float out;
 130
 131     if (trc == null)
 132       {
 133         if (in == 0f)
 134           return 0.0f;
 135         return (float) Math.exp((1.0 / gamma) * Math.log(in));
 136       }
 137     else
 138       {
 139         double alpha = in * (reverseTrc.length - 1);
 140         int index = (int) Math.floor(alpha);
 141         alpha = alpha - (double) index;
 142         if (index >= reverseTrc.length - 1)
 143           return reverseTrc[reverseTrc.length - 1];
 144         if (index <= 0)
 145           return reverseTrc[0];
 146         out = (float) (reverseTrc[index] * (1.0 - alpha)
 147               + reverseTrc[index + 1] * alpha);
 148       }
 149     return out;
 150   }
 151
 152   /**
 153    * Calculates a reverse-lookup table.
 154    * We use a whopping 10,000 entries.. This is should be more than any
 155    * real-life TRC table (typically around 256-1024) so we won't be losing
 156    * any precision.
 157    *
 158    * This will of course generate completely invalid results if the curve
 159    * is not monotonic and invertable. But what's the alternative?
 160    */
 161   public void setupReverseTrc()
 162   {
 163     reverseTrc = new float[10000];
 164     int j = 0;
 165     for (int i = 0; i < 10000; i++)
 166       {
 167         float n = ((float) i) / 10000f;
 168         while (trc[j + 1] < n && j < trc.length - 2)
 169           j++;
 170
 171         if (j == trc.length - 2)
 172           reverseTrc[i] = trc[trc.length - 1];
 173         else
 174           reverseTrc[i] = (j + (n - trc[j]) / (trc[j + 1] - trc[j])) / ((float) trc.length);
 175       }
 176   }
 177 }