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    /**
042     * The JPEGQTable class represents a quantization table that can be
043     * used to encode or decode a JPEG stream.  The standard JPEG
044     * luminance and chrominance quantization tables are provided as
045     * static fields.  Table entries are stored in natural order, not
046     * zig-zag order.
047     */
048    public class JPEGQTable
049    {
050      /**
051       * The table entries, stored in natural order.
052       */
053      private int[] table;
054    
055      /**
056       * The standard JPEG luminance quantization table.  Values are
057       * stored in natural order.
058       */
059      public static final JPEGQTable K1Luminance = new JPEGQTable(new int[]
060          {
061            16, 11, 10, 16,  24,  40,  51,  61,
062            12, 12, 14, 19,  26,  58,  60,  55,
063            14, 13, 16, 24,  40,  57,  69,  56,
064            14, 17, 22, 29,  51,  87,  80,  62,
065            18, 22, 37, 56,  68, 109, 103,  77,
066            24, 35, 55, 64,  81, 104, 113,  92,
067            49, 64, 78, 87, 103, 121, 120, 101,
068            72, 92, 95, 98, 112, 100, 103,  99
069          }, false);
070    
071      /**
072       * The standard JPEG luminance quantization table, scaled by
073       * one-half.  Values are stored in natural order.
074       */
075      public static final JPEGQTable K1Div2Luminance =
076        K1Luminance.getScaledInstance(0.5f, true);
077    
078      /**
079       * The standard JPEG chrominance quantization table.  Values are
080       * stored in natural order.
081       */
082      public static final JPEGQTable K2Chrominance = new JPEGQTable(new int[]
083          {
084            17, 18, 24, 47, 99, 99, 99, 99,
085            18, 21, 26, 66, 99, 99, 99, 99,
086            24, 26, 56, 99, 99, 99, 99, 99,
087            47, 66, 99, 99, 99, 99, 99, 99,
088            99, 99, 99, 99, 99, 99, 99, 99,
089            99, 99, 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          }, false);
093    
094      /**
095       * The standard JPEG chrominance quantization table, scaled by
096       * one-half.  Values are stored in natural order.
097       */
098      public static final JPEGQTable K2Div2Chrominance =
099        K2Chrominance.getScaledInstance(0.5f, true);
100    
101      /**
102       * Construct a new JPEG quantization table.  A copy is created of
103       * the table argument.
104       *
105       * @param table the 64-element value table, stored in natural order
106       *
107       * @throws IllegalArgumentException if the table is null or if
108       * table's length is not equal to 64.
109       */
110      public JPEGQTable(int[] table)
111      {
112        this(checkTable(table), true);
113      }
114    
115      /**
116       * Private constructor that avoids unnecessary copying and argument
117       * checking.
118       *
119       * @param table the 64-element value table, stored in natural order
120       * @param copy true if a copy should be created of the given table
121       */
122      private JPEGQTable(int[] table, boolean copy)
123      {
124        this.table = copy ? (int[]) table.clone() : table;
125      }
126    
127      private static int[] checkTable(int[] table)
128      {
129        if (table == null || table.length != 64)
130          throw new IllegalArgumentException("invalid JPEG quantization table");
131    
132        return table;
133      }
134    
135      /**
136       * Retrieve a copy of the quantization values for this table.
137       *
138       * @return a copy of the quantization value array
139       */
140      public int[] getTable()
141      {
142        return (int[]) table.clone();
143      }
144    
145      /**
146       * Retrieve a copy of this JPEG quantization table with every value
147       * scaled by the given scale factor, and clamped from 1 to 255
148       * baseline or from 1 to 32767 otherwise.
149       *
150       * @param scaleFactor the factor by which to scale this table
151       * @param forceBaseline clamp scaled values to a maximum of 255 if
152       * true, 32767 if false
153       *
154       * @return a new scaled JPEG quantization table
155       */
156      public JPEGQTable getScaledInstance(float scaleFactor,
157                                          boolean forceBaseline)
158      {
159        int[] scaledTable = getTable();
160        int max = forceBaseline ? 255 : 32767;
161    
162        for (int i = 0; i < scaledTable.length; i++)
163          {
164            scaledTable[i] = Math.round (scaleFactor * (float) scaledTable[i]);
165            if (scaledTable[i] < 1)
166              scaledTable[i] = 1;
167            else if (scaledTable[i] > max)
168              scaledTable[i] = max;
169          }
170    
171        // Do not copy scaledTable.  It is already a copy because we used
172        // getTable to retrieve it.
173        return new JPEGQTable(scaledTable, false);
174      }
175    
176      /**
177       * Create a string representing this JPEG quantization table.
178       */
179      public String toString()
180      {
181        StringBuffer buffer = new StringBuffer();
182    
183        buffer.append("JPEGQTable:\n");
184        for (int i = 0; i < 8; i++)
185          {
186            buffer.append("        ");
187            for (int j = 0; j < 8; j++)
188              {
189                buffer.append(table[i * 8 + j] + " ");
190              }
191            buffer.append("\n");
192          }
193    
194        return buffer.toString();
195      }
196    }