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JPEGImageReadParam.javaAPI DocJava SE 5 API6954Fri Aug 26 14:57:30 BST 2005javax.imageio.plugins.jpeg

JPEGImageReadParam

public class JPEGImageReadParam extends 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 getDefaultImageReadParam methods of the built-in JPEG ImageReader.

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 ImageReadParam, which is sufficient for decoding non-abbreviated streams.

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 JPEGImageReadParam, then the stream is presumed to use the "standard" visually lossless tables. See {@link JPEGQTable JPEGQTable} and {@link JPEGHuffmanTable JPEGHuffmanTable} for more information on the default tables.

The default JPEGImageReadParam returned by the getDefaultReadParam method of the builtin JPEG reader contains no tables. Default tables may be obtained from the table classes {@link JPEGQTable JPEGQTable} and {@link JPEGHuffmanTable JPEGHuffmanTable}.

If a stream does contain tables, the tables given in a JPEGImageReadParam 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 setInput} method of the reader must be called to change the stream.

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 IIOMetadata object returned by the reader.

For more information about the operation of the built-in JPEG plug-ins, see the JPEG metadata format specification and usage notes.

version
0.5

Fields Summary
private JPEGQTable[]
qTables
private JPEGHuffmanTable[]
DCHuffmanTables
private JPEGHuffmanTable[]
ACHuffmanTables
Constructors Summary
public JPEGImageReadParam()
Constructs a JPEGImageReadParam.


            
      
        super();
Methods Summary
public booleanareTablesSet()
Returns true if tables are currently set.

return
true if tables are present.

        return (qTables != null);
public javax.imageio.plugins.jpeg.JPEGHuffmanTable[]getACHuffmanTables()
Returns a copy of the array of AC Huffman tables set on the most recent call to setDecodeTables, or null if tables are not currently set.

return
an array of JPEGHuffmanTable objects, or null.
see
#setDecodeTables

        return (ACHuffmanTables != null) 
            ? (JPEGHuffmanTable[])ACHuffmanTables.clone() 
            : null;
public javax.imageio.plugins.jpeg.JPEGHuffmanTable[]getDCHuffmanTables()
Returns a copy of the array of DC Huffman tables set on the most recent call to setDecodeTables, or null if tables are not currently set.

return
an array of JPEGHuffmanTable objects, or null.
see
#setDecodeTables

        return (DCHuffmanTables != null)
            ? (JPEGHuffmanTable[])DCHuffmanTables.clone() 
            : null;
public javax.imageio.plugins.jpeg.JPEGQTable[]getQTables()
Returns a copy of the array of quantization tables set on the most recent call to setDecodeTables, or null if tables are not currently set.

return
an array of JPEGQTable objects, or null.
see
#setDecodeTables

        return (qTables != null) ? (JPEGQTable[])qTables.clone() : null;
public voidsetDecodeTables(javax.imageio.plugins.jpeg.JPEGQTable[] qTables, javax.imageio.plugins.jpeg.JPEGHuffmanTable[] DCHuffmanTables, javax.imageio.plugins.jpeg.JPEGHuffmanTable[] ACHuffmanTables)
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-null. 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 null, has more than 4 elements, or if the numbers of DC and AC tables differ.
see
#unsetDecodeTables

        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();
public voidunsetDecodeTables()
Removes any quantization and Huffman tables that are currently set.

see
#setDecodeTables

        this.qTables = null;
        this.DCHuffmanTables = null;
        this.ACHuffmanTables = null;