1 /*
2 * Copyright (c) 2000, 2001, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package javax.imageio.plugins.jpeg;
27
28 import javax.imageio.ImageReadParam;
29
30 /**
31 * This class adds the ability to set JPEG quantization and Huffman
32 * tables when using the built-in JPEG reader plug-in. An instance of
33 * this class will be returned from the
34 * <code>getDefaultImageReadParam</code> methods of the built-in JPEG
35 * <code>ImageReader</code>.
36 *
37 * <p> The sole purpose of these additions is to allow the
38 * specification of tables for use in decoding abbreviated streams.
39 * The built-in JPEG reader will also accept an ordinary
40 * <code>ImageReadParam</code>, which is sufficient for decoding
41 * non-abbreviated streams.
42 *
43 * <p> While tables for abbreviated streams are often obtained by
44 * first reading another abbreviated stream containing only the
45 * tables, in some applications the tables are fixed ahead of time.
46 * This class allows the tables to be specified directly from client
47 * code. If no tables are specified either in the stream or in a
48 * <code>JPEGImageReadParam</code>, then the stream is presumed to use
49 * the "standard" visually lossless tables. See {@link JPEGQTable JPEGQTable}
50 * and {@link JPEGHuffmanTable JPEGHuffmanTable} for more information
51 * on the default tables.
52 *
53 * <p> The default <code>JPEGImageReadParam</code> returned by the
54 * <code>getDefaultReadParam</code> method of the builtin JPEG reader
55 * contains no tables. Default tables may be obtained from the table
56 * classes {@link JPEGQTable JPEGQTable} and
57 * {@link JPEGHuffmanTable JPEGHuffmanTable}.
58 *
59 * <p> If a stream does contain tables, the tables given in a
60 * <code>JPEGImageReadParam</code> are ignored. Furthermore, if the
61 * first image in a stream does contain tables and subsequent ones do
62 * not, then the tables given in the first image are used for all the
63 * abbreviated images. Once tables have been read from a stream, they
64 * can be overridden only by tables subsequently read from the same
65 * stream. In order to specify new tables, the {@link
66 * javax.imageio.ImageReader#setInput setInput} method of
67 * the reader must be called to change the stream.
68 *
69 * <p> Note that this class does not provide a means for obtaining the
70 * tables found in a stream. These may be extracted from a stream by
71 * consulting the IIOMetadata object returned by the reader.
72 *
73 * <p>
74 * For more information about the operation of the built-in JPEG plug-ins,
75 * see the <A HREF="../../metadata/doc-files/jpeg_metadata.html">JPEG
76 * metadata format specification and usage notes</A>.
77 *
78 */
79 public class JPEGImageReadParam extends ImageReadParam {
80
81 private JPEGQTable[] qTables = null;
82 private JPEGHuffmanTable[] DCHuffmanTables = null;
83 private JPEGHuffmanTable[] ACHuffmanTables = null;
84
85 /**
86 * Constructs a <code>JPEGImageReadParam</code>.
87 */
88 public JPEGImageReadParam() {
89 super();
90 }
91
92 /**
93 * Returns <code>true</code> if tables are currently set.
94 *
95 * @return <code>true</code> if tables are present.
96 */
97 public boolean areTablesSet() {
98 return (qTables != null);
99 }
100
101 /**
102 * Sets the quantization and Huffman tables to use in decoding
103 * abbreviated streams. There may be a maximum of 4 tables of
104 * each type. These tables are ignored once tables are
105 * encountered in the stream. All arguments must be
106 * non-<code>null</code>. The two arrays of Huffman tables must
107 * have the same number of elements. The table specifiers in the
108 * frame and scan headers in the stream are assumed to be
109 * equivalent to indices into these arrays. The argument arrays
110 * are copied by this method.
111 *
112 * @param qTables an array of quantization table objects.
113 * @param DCHuffmanTables an array of Huffman table objects.
114 * @param ACHuffmanTables an array of Huffman table objects.
115 *
116 * @exception IllegalArgumentException if any of the arguments
117 * is <code>null</code>, has more than 4 elements, or if the
118 * numbers of DC and AC tables differ.
119 *
120 * @see #unsetDecodeTables
121 */
122 public void setDecodeTables(JPEGQTable[] qTables,
123 JPEGHuffmanTable[] DCHuffmanTables,
124 JPEGHuffmanTable[] ACHuffmanTables) {
125 if ((qTables == null) ||
126 (DCHuffmanTables == null) ||
127 (ACHuffmanTables == null) ||
128 (qTables.length > 4) ||
129 (DCHuffmanTables.length > 4) ||
130 (ACHuffmanTables.length > 4) ||
131 (DCHuffmanTables.length != ACHuffmanTables.length)) {
132 throw new IllegalArgumentException
133 ("Invalid JPEG table arrays");
134 }
135 this.qTables = (JPEGQTable[])qTables.clone();
136 this.DCHuffmanTables = (JPEGHuffmanTable[])DCHuffmanTables.clone();
137 this.ACHuffmanTables = (JPEGHuffmanTable[])ACHuffmanTables.clone();
138 }
139
140 /**
141 * Removes any quantization and Huffman tables that are currently
142 * set.
143 *
144 * @see #setDecodeTables
145 */
146 public void unsetDecodeTables() {
147 this.qTables = null;
148 this.DCHuffmanTables = null;
149 this.ACHuffmanTables = null;
150 }
151
152 /**
153 * Returns a copy of the array of quantization tables set on the
154 * most recent call to <code>setDecodeTables</code>, or
155 * <code>null</code> if tables are not currently set.
156 *
157 * @return an array of <code>JPEGQTable</code> objects, or
158 * <code>null</code>.
159 *
160 * @see #setDecodeTables
161 */
162 public JPEGQTable[] getQTables() {
163 return (qTables != null) ? (JPEGQTable[])qTables.clone() : null;
164 }
165
166 /**
167 * Returns a copy of the array of DC Huffman tables set on the
168 * most recent call to <code>setDecodeTables</code>, or
169 * <code>null</code> if tables are not currently set.
170 *
171 * @return an array of <code>JPEGHuffmanTable</code> objects, or
172 * <code>null</code>.
173 *
174 * @see #setDecodeTables
175 */
176 public JPEGHuffmanTable[] getDCHuffmanTables() {
177 return (DCHuffmanTables != null)
178 ? (JPEGHuffmanTable[])DCHuffmanTables.clone()
179 : null;
180 }
181
182 /**
183 * Returns a copy of the array of AC Huffman tables set on the
184 * most recent call to <code>setDecodeTables</code>, or
185 * <code>null</code> if tables are not currently set.
186 *
187 * @return an array of <code>JPEGHuffmanTable</code> objects, or
188 * <code>null</code>.
189 *
190 * @see #setDecodeTables
191 */
192 public JPEGHuffmanTable[] getACHuffmanTables() {
193 return (ACHuffmanTables != null)
194 ? (JPEGHuffmanTable[])ACHuffmanTables.clone()
195 : null;
196 }
197 }