JPEGImageReadParam


1   /*
2    * @(#)JPEGImageReadParam.java  1.11 03/12/19
3    *
4    * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
5    * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6    */
7   
8   package javax.imageio.plugins.jpeg;
9   
10  import javax.imageio.ImageReadParam  ;
11  
12  /**
13   * This class adds the ability to set JPEG quantization and Huffman
14   * tables when using the built-in JPEG reader plug-in.  An instance of
15   * this class will be returned from the
16   * <code>getDefaultImageReadParam</code> methods of the built-in JPEG
17   * <code>ImageReader</code>.
18   *
19   * <p> The sole purpose of these additions is to allow the
20   * specification of tables for use in decoding abbreviated streams.
21   * The built-in JPEG reader will also accept an ordinary
22   * <code>ImageReadParam</code>, which is sufficient for decoding
23   * non-abbreviated streams.
24   *
25   * <p> While tables for abbreviated streams are often obtained by
26   * first reading another abbreviated stream containing only the
27   * tables, in some applications the tables are fixed ahead of time.
28   * This class allows the tables to be specified directly from client
29   * code.  If no tables are specified either in the stream or in a
30   * <code>JPEGImageReadParam</code>, then the stream is presumed to use
31   * the "standard" visually lossless tables.  See {@link JPEGQTable
32   * <code>JPEGQTable</code>} and {@link JPEGHuffmanTable
33   * <code>JPEGHuffmanTable</code>} for more information on the default
34   * tables.
35   *
36   * <p> The default <code>JPEGImageReadParam</code> returned by the
37   * <code>getDefaultReadParam</code> method of the builtin JPEG reader
38   * contains no tables.  Default tables may be obtained from the table
39   * classes {@link JPEGQTable <code>JPEGQTable</code>} and {@link
40   * JPEGHuffmanTable <code>JPEGHuffmanTable</code>}.
41   *
42   * <p> If a stream does contain tables, the tables given in a
43   * <code>JPEGImageReadParam</code> are ignored.  Furthermore, if the
44   * first image in a stream does contain tables and subsequent ones do
45   * not, then the tables given in the first image are used for all the
46   * abbreviated images.  Once tables have been read from a stream, they
47   * can be overridden only by tables subsequently read from the same
48   * stream.  In order to specify new tables, the {@link
49   * javax.imageio.ImageReader#setInput <code>setInput</code>} method of
50   * the reader must be called to change the stream.
51   *
52   * <p> Note that this class does not provide a means for obtaining the
53   * tables found in a stream.  These may be extracted from a stream by
54   * consulting the <code>IIOMetadata</code> object returned by the
55   * reader.
56   *
57   * <p>
58   * For more information about the operation of the built-in JPEG plug-ins,
59   * see the <A HREF="../../metadata/doc-files/jpeg_metadata.html">JPEG
60   * metadata format specification and usage notes</A>.
61   *
62   * @version 0.5
63   */
64  public class JPEGImageReadParam extends ImageReadParam   {
65  
66      private JPEGQTable  [] qTables = null;
67      private JPEGHuffmanTable  [] DCHuffmanTables = null;
68      private JPEGHuffmanTable  [] ACHuffmanTables = null;
69  
70      /**
71       * Constructs a <code>JPEGImageReadParam</code>.
72       */
73      public JPEGImageReadParam() {
74          super();
75      }
76      
77      /**
78       * Returns <code>true</code> if tables are currently set.
79       *
80       * @return <code>true</code> if tables are present.
81       */
82      public boolean areTablesSet() {
83          return (qTables != null);
84      }
85  
86      /**
87       * Sets the quantization and Huffman tables to use in decoding
88       * abbreviated streams.  There may be a maximum of 4 tables of
89       * each type.  These tables are ignored once tables are
90       * encountered in the stream.  All arguments must be
91       * non-<code>null</code>.  The two arrays of Huffman tables must
92       * have the same number of elements.  The table specifiers in the
93       * frame and scan headers in the stream are assumed to be
94       * equivalent to indices into these arrays.  The argument arrays
95       * are copied by this method.
96       *
97       * @param qTables an array of quantization table objects.
98       * @param DCHuffmanTables an array of Huffman table objects.
99       * @param ACHuffmanTables an array of Huffman table objects.
100      *
101      * @exception IllegalArgumentException if any of the arguments
102      * is <code>null</code>, has more than 4 elements, or if the
103      * numbers of DC and AC tables differ.
104      *
105      * @see #unsetDecodeTables
106      */
107     public void setDecodeTables(JPEGQTable  [] qTables, 
108                                 JPEGHuffmanTable  [] DCHuffmanTables,
109                                 JPEGHuffmanTable  [] ACHuffmanTables) {
110         if ((qTables == null) ||
111             (DCHuffmanTables == null) ||
112             (ACHuffmanTables == null) ||
113             (qTables.length > 4) ||
114             (DCHuffmanTables.length > 4) ||
115             (ACHuffmanTables.length > 4) ||
116             (DCHuffmanTables.length != ACHuffmanTables.length)) {
117                 throw new IllegalArgumentException  
118                     ("Invalid JPEG table arrays");
119         }
120         this.qTables = (JPEGQTable  [])qTables.clone();
121         this.DCHuffmanTables = (JPEGHuffmanTable  [])DCHuffmanTables.clone();
122         this.ACHuffmanTables = (JPEGHuffmanTable  [])ACHuffmanTables.clone();
123     }
124 
125     /**
126      * Removes any quantization and Huffman tables that are currently
127      * set.
128      *
129      * @see #setDecodeTables
130      */
131     public void unsetDecodeTables() {
132         this.qTables = null;
133         this.DCHuffmanTables = null;
134         this.ACHuffmanTables = null;
135     }
136 
137     /**
138      * Returns a copy of the array of quantization tables set on the
139      * most recent call to <code>setDecodeTables</code>, or
140      * <code>null</code> if tables are not currently set.
141      *
142      * @return an array of <code>JPEGQTable</code> objects, or
143      * <code>null</code>.
144      *
145      * @see #setDecodeTables
146      */
147     public JPEGQTable  [] getQTables() {
148         return (qTables != null) ? (JPEGQTable  [])qTables.clone() : null;
149     }
150     
151     /**
152      * Returns a copy of the array of DC Huffman tables set on the
153      * most recent call to <code>setDecodeTables</code>, or
154      * <code>null</code> if tables are not currently set.
155      *
156      * @return an array of <code>JPEGHuffmanTable</code> objects, or
157      * <code>null</code>.
158      *
159      * @see #setDecodeTables
160      */
161     public JPEGHuffmanTable  [] getDCHuffmanTables() {
162         return (DCHuffmanTables != null)
163             ? (JPEGHuffmanTable  [])DCHuffmanTables.clone() 
164             : null;
165     }
166 
167     /**
168      * Returns a copy of the array of AC Huffman tables set on the
169      * most recent call to <code>setDecodeTables</code>, or
170      * <code>null</code> if tables are not currently set.
171      *
172      * @return an array of <code>JPEGHuffmanTable</code> objects, or
173      * <code>null</code>.
174      *
175      * @see #setDecodeTables
176      */
177     public JPEGHuffmanTable  [] getACHuffmanTables() {
178         return (ACHuffmanTables != null) 
179             ? (JPEGHuffmanTable  [])ACHuffmanTables.clone() 
180             : null;
181     }
182 }
183
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