001    /* JPEGQTable.java --
002     Copyright (C)  2006  Free Software Foundation, Inc.
003    
004     This file is part of GNU Classpath.
005    
006     GNU Classpath is free software; you can redistribute it and/or modify
007     it under the terms of the GNU General Public License as published by
008     the Free Software Foundation; either version 2, or (at your option)
009     any later version.
010    
011     GNU Classpath is distributed in the hope that it will be useful, but
012     WITHOUT ANY WARRANTY; without even the implied warranty of
013     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014     General Public License for more details.
015    
016     You should have received a copy of the GNU General Public License
017     along with GNU Classpath; see the file COPYING.  If not, write to the
018     Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
019     02110-1301 USA.
020    
021     Linking this library statically or dynamically with other modules is
022     making a combined work based on this library.  Thus, the terms and
023     conditions of the GNU General Public License cover the whole
024     combination.
025    
026     As a special exception, the copyright holders of this library give you
027     permission to link this library with independent modules to produce an
028     executable, regardless of the license terms of these independent
029     modules, and to copy and distribute the resulting executable under
030     terms of your choice, provided that you also meet, for each linked
031     independent module, the terms and conditions of the license of that
032     module.  An independent module is a module which is not derived from
033     or based on this library.  If you modify this library, you may extend
034     this exception to your version of the library, but you are not
035     obligated to do so.  If you do not wish to do so, delete this
036     exception statement from your version. */
037    
038    
039    package javax.imageio.plugins.jpeg;
040    
041    import gnu.java.lang.CPStringBuilder;
042    
043    /**
044     * The JPEGQTable class represents a quantization table that can be
045     * used to encode or decode a JPEG stream.  The standard JPEG
046     * luminance and chrominance quantization tables are provided as
047     * static fields.  Table entries are stored in natural order, not
048     * zig-zag order.
049     */
050    public class JPEGQTable
051    {
052      /**
053       * The table entries, stored in natural order.
054       */
055      private int[] table;
056    
057      /**
058       * The standard JPEG luminance quantization table.  Values are
059       * stored in natural order.
060       */
061      public static final JPEGQTable K1Luminance = new JPEGQTable(new int[]
062          {
063            16, 11, 10, 16,  24,  40,  51,  61,
064            12, 12, 14, 19,  26,  58,  60,  55,
065            14, 13, 16, 24,  40,  57,  69,  56,
066            14, 17, 22, 29,  51,  87,  80,  62,
067            18, 22, 37, 56,  68, 109, 103,  77,
068            24, 35, 55, 64,  81, 104, 113,  92,
069            49, 64, 78, 87, 103, 121, 120, 101,
070            72, 92, 95, 98, 112, 100, 103,  99
071          }, false);
072    
073      /**
074       * The standard JPEG luminance quantization table, scaled by
075       * one-half.  Values are stored in natural order.
076       */
077      public static final JPEGQTable K1Div2Luminance =
078        K1Luminance.getScaledInstance(0.5f, true);
079    
080      /**
081       * The standard JPEG chrominance quantization table.  Values are
082       * stored in natural order.
083       */
084      public static final JPEGQTable K2Chrominance = new JPEGQTable(new int[]
085          {
086            17, 18, 24, 47, 99, 99, 99, 99,
087            18, 21, 26, 66, 99, 99, 99, 99,
088            24, 26, 56, 99, 99, 99, 99, 99,
089            47, 66, 99, 99, 99, 99, 99, 99,
090            99, 99, 99, 99, 99, 99, 99, 99,
091            99, 99, 99, 99, 99, 99, 99, 99,
092            99, 99, 99, 99, 99, 99, 99, 99,
093            99, 99, 99, 99, 99, 99, 99, 99
094          }, false);
095    
096      /**
097       * The standard JPEG chrominance quantization table, scaled by
098       * one-half.  Values are stored in natural order.
099       */
100      public static final JPEGQTable K2Div2Chrominance =
101        K2Chrominance.getScaledInstance(0.5f, true);
102    
103      /**
104       * Construct a new JPEG quantization table.  A copy is created of
105       * the table argument.
106       *
107       * @param table the 64-element value table, stored in natural order
108       *
109       * @throws IllegalArgumentException if the table is null or if
110       * table's length is not equal to 64.
111       */
112      public JPEGQTable(int[] table)
113      {
114        this(checkTable(table), true);
115      }
116    
117      /**
118       * Private constructor that avoids unnecessary copying and argument
119       * checking.
120       *
121       * @param table the 64-element value table, stored in natural order
122       * @param copy true if a copy should be created of the given table
123       */
124      private JPEGQTable(int[] table, boolean copy)
125      {
126        this.table = copy ? (int[]) table.clone() : table;
127      }
128    
129      private static int[] checkTable(int[] table)
130      {
131        if (table == null || table.length != 64)
132          throw new IllegalArgumentException("invalid JPEG quantization table");
133    
134        return table;
135      }
136    
137      /**
138       * Retrieve a copy of the quantization values for this table.
139       *
140       * @return a copy of the quantization value array
141       */
142      public int[] getTable()
143      {
144        return (int[]) table.clone();
145      }
146    
147      /**
148       * Retrieve a copy of this JPEG quantization table with every value
149       * scaled by the given scale factor, and clamped from 1 to 255
150       * baseline or from 1 to 32767 otherwise.
151       *
152       * @param scaleFactor the factor by which to scale this table
153       * @param forceBaseline clamp scaled values to a maximum of 255 if
154       * true, 32767 if false
155       *
156       * @return a new scaled JPEG quantization table
157       */
158      public JPEGQTable getScaledInstance(float scaleFactor,
159                                          boolean forceBaseline)
160      {
161        int[] scaledTable = getTable();
162        int max = forceBaseline ? 255 : 32767;
163    
164        for (int i = 0; i < scaledTable.length; i++)
165          {
166            scaledTable[i] = Math.round (scaleFactor * (float) scaledTable[i]);
167            if (scaledTable[i] < 1)
168              scaledTable[i] = 1;
169            else if (scaledTable[i] > max)
170              scaledTable[i] = max;
171          }
172    
173        // Do not copy scaledTable.  It is already a copy because we used
174        // getTable to retrieve it.
175        return new JPEGQTable(scaledTable, false);
176      }
177    
178      /**
179       * Create a string representing this JPEG quantization table.
180       */
181      public String toString()
182      {
183        CPStringBuilder buffer = new CPStringBuilder();
184    
185        buffer.append("JPEGQTable:\n");
186        for (int i = 0; i < 8; i++)
187          {
188            buffer.append("        ");
189            for (int j = 0; j < 8; j++)
190              {
191                buffer.append(table[i * 8 + j] + " ");
192              }
193            buffer.append("\n");
194          }
195    
196        return buffer.toString();
197      }
198    }