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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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
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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 }