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
JPEGQTableJPEGQTable and
JPEGHuffmanTableJPEGHuffmanTable 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
JPEGQTable JPEGQTable and
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
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 | 
