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
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013 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014 General Public License for more details.
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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
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036 exception statement from your version. */
037
038
039package javax.imageio.plugins.jpeg;
040
041import 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 */
050public 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}