jpegimagereadparam.java

java1.6众多例子参考

/*
 * @(#)JPEGImageReadParam.java	1.12 05/11/17
 *
 * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package javax.imageio.plugins.jpeg;

import javax.imageio.ImageReadParam;

/**
 * This class adds the ability to set JPEG quantization and Huffman
 * tables when using the built-in JPEG reader plug-in.  An instance of
 * this class will be returned from the
 * <code>getDefaultImageReadParam</code> methods of the built-in JPEG
 * <code>ImageReader</code>.
 *
 * <p> The sole purpose of these additions is to allow the
 * specification of tables for use in decoding abbreviated streams.
 * The built-in JPEG reader will also accept an ordinary
 * <code>ImageReadParam</code>, which is sufficient for decoding
 * non-abbreviated streams.
 *
 * <p> While tables for abbreviated streams are often obtained by
 * first reading another abbreviated stream containing only the
 * tables, in some applications the tables are fixed ahead of time.
 * This class allows the tables to be specified directly from client
 * code.  If no tables are specified either in the stream or in a
 * <code>JPEGImageReadParam</code>, then the stream is presumed to use
 * the "standard" visually lossless tables.  See {@link JPEGQTable
 * <code>JPEGQTable</code>} and {@link JPEGHuffmanTable
 * <code>JPEGHuffmanTable</code>} for more information on the default
 * tables.
 *
 * <p> The default <code>JPEGImageReadParam</code> returned by the
 * <code>getDefaultReadParam</code> method of the builtin JPEG reader
 * contains no tables.  Default tables may be obtained from the table
 * classes {@link JPEGQTable <code>JPEGQTable</code>} and {@link
 * JPEGHuffmanTable <code>JPEGHuffmanTable</code>}.
 *
 * <p> If a stream does contain tables, the tables given in a
 * <code>JPEGImageReadParam</code> are ignored.  Furthermore, if the
 * first image in a stream does contain tables and subsequent ones do
 * not, then the tables given in the first image are used for all the
 * abbreviated images.  Once tables have been read from a stream, they
 * can be overridden only by tables subsequently read from the same
 * stream.  In order to specify new tables, the {@link
 * javax.imageio.ImageReader#setInput <code>setInput</code>} method of
 * the reader must be called to change the stream.
 *
 * <p> Note that this class does not provide a means for obtaining the
 * tables found in a stream.  These may be extracted from a stream by
 * consulting the <code>IIOMetadata</code> object returned by the
 * reader.
 *
 * <p>
 * For more information about the operation of the built-in JPEG plug-ins,
 * see the <A HREF="../../metadata/doc-files/jpeg_metadata.html">JPEG
 * metadata format specification and usage notes</A>.
 *
 * @version 0.5
 */
public class JPEGImageReadParam extends ImageReadParam {

    private JPEGQTable[] qTables = null;
    private JPEGHuffmanTable[] DCHuffmanTables = null;
    private JPEGHuffmanTable[] ACHuffmanTables = null;

    /**
     * Constructs a <code>JPEGImageReadParam</code>.
     */
    public JPEGImageReadParam() {
        super();
    }
    
    /**
     * Returns <code>true</code> if tables are currently set.
     *
     * @return <code>true</code> if tables are present.
     */
    public boolean areTablesSet() {
        return (qTables != null);
    }

    /**
     * Sets the quantization and Huffman tables to use in decoding
     * abbreviated streams.  There may be a maximum of 4 tables of
     * each type.  These tables are ignored once tables are
     * encountered in the stream.  All arguments must be
     * non-<code>null</code>.  The two arrays of Huffman tables must
     * have the same number of elements.  The table specifiers in the
     * frame and scan headers in the stream are assumed to be
     * equivalent to indices into these arrays.  The argument arrays
     * are copied by this method.
     *
     * @param qTables an array of quantization table objects.
     * @param DCHuffmanTables an array of Huffman table objects.
     * @param ACHuffmanTables an array of Huffman table objects.
     *
     * @exception IllegalArgumentException if any of the arguments
     * is <code>null</code>, has more than 4 elements, or if the
     * numbers of DC and AC tables differ.
     *
     * @see #unsetDecodeTables
     */
    public void setDecodeTables(JPEGQTable[] qTables, 
                                JPEGHuffmanTable[] DCHuffmanTables,
                                JPEGHuffmanTable[] ACHuffmanTables) {
        if ((qTables == null) ||
            (DCHuffmanTables == null) ||
            (ACHuffmanTables == null) ||
            (qTables.length > 4) ||
            (DCHuffmanTables.length > 4) ||
            (ACHuffmanTables.length > 4) ||
            (DCHuffmanTables.length != ACHuffmanTables.length)) {
                throw new IllegalArgumentException
                    ("Invalid JPEG table arrays");
        }
        this.qTables = (JPEGQTable[])qTables.clone();
        this.DCHuffmanTables = (JPEGHuffmanTable[])DCHuffmanTables.clone();
        this.ACHuffmanTables = (JPEGHuffmanTable[])ACHuffmanTables.clone();
    }

    /**
     * Removes any quantization and Huffman tables that are currently
     * set.
     *
     * @see #setDecodeTables
     */
    public void unsetDecodeTables() {
        this.qTables = null;
        this.DCHuffmanTables = null;
        this.ACHuffmanTables = null;
    }

    /**
     * Returns a copy of the array of quantization tables set on the
     * most recent call to <code>setDecodeTables</code>, or
     * <code>null</code> if tables are not currently set.
     *
     * @return an array of <code>JPEGQTable</code> objects, or
     * <code>null</code>.
     *
     * @see #setDecodeTables
     */
    public JPEGQTable[] getQTables() {
        return (qTables != null) ? (JPEGQTable[])qTables.clone() : null;
    }
    
    /**
     * Returns a copy of the array of DC Huffman tables set on the
     * most recent call to <code>setDecodeTables</code>, or
     * <code>null</code> if tables are not currently set.
     *
     * @return an array of <code>JPEGHuffmanTable</code> objects, or
     * <code>null</code>.
     *
     * @see #setDecodeTables
     */
    public JPEGHuffmanTable[] getDCHuffmanTables() {
        return (DCHuffmanTables != null)
            ? (JPEGHuffmanTable[])DCHuffmanTables.clone() 
            : null;
    }

    /**
     * Returns a copy of the array of AC Huffman tables set on the
     * most recent call to <code>setDecodeTables</code>, or
     * <code>null</code> if tables are not currently set.
     *
     * @return an array of <code>JPEGHuffmanTable</code> objects, or
     * <code>null</code>.
     *
     * @see #setDecodeTables
     */
    public JPEGHuffmanTable[] getACHuffmanTables() {
        return (ACHuffmanTables != null) 
            ? (JPEGHuffmanTable[])ACHuffmanTables.clone() 
            : null;
    }
}