This class adds the ability to set JPEG quantization and Huffman
tables when using the built-in JPEG writer plug-in, and to request that
optimized Huffman tables be computed for an image. An instance of
this class will be returned from the
getDefaultImageWriteParam methods of the built-in JPEG
ImageWriter.
The principal purpose of these additions is to allow the
specification of tables to use in encoding abbreviated streams.
The built-in JPEG writer will also accept an ordinary
ImageWriteParam, in which case the writer will
construct the necessary tables internally.
In either case, the quality setting in an ImageWriteParam
has the same meaning as for the underlying library: 1.00 means a
quantization table of all 1's, 0.75 means the "standard", visually
lossless quantization table, and 0.00 means aquantization table of
all 255's.
While tables for abbreviated streams are often specified by
first writing an 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.
Normally, the tables are specified in the
IIOMetadata objects passed in to the writer, and any
tables included in these objects are written to the stream.
If no tables are specified in the metadata, then an abbreviated
stream is written. If no tables are included in the metadata and
no tables are specified in a JPEGImageWriteParam, then
an abbreviated stream is encoded using the "standard" visually
lossless tables. This class is necessary for specifying tables
when an abbreviated stream must be written without writing any tables
to a stream first. In order to use this class, the metadata object
passed into the writer must contain no tables, and no stream metadata
must be provided. See
JPEGQTable JPEGQTable and
JPEGHuffmanTable JPEGHuffmanTable for more
information on the default tables.
The default JPEGImageWriteParam returned by the
getDefaultWriteParam method of the writer contains no
tables. Default tables are included in the default
IIOMetadata objects returned by the writer.
If the metadata does contain tables, the tables given in a
JPEGImageWriteParam are ignored. Furthermore, once a
set of tables has been written, only tables in the metadata can
override them for subsequent writes, whether to the same stream or
a different one. In order to specify new tables using this class,
the
javax.imageio.ImageWriter.reset reset method of the writer must be called.
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 | 
