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 JPEGQTable
and 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 JPEGQTable
and
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 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.
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Field Summary
Fields declared in class javax.imageio.ImageReadParam
canSetSourceRenderSize, destination, destinationBands, minProgressivePass, numProgressivePasses, sourceRenderSize
Fields declared in class javax.imageio.IIOParam
controller, defaultController, destinationOffset, destinationType, sourceBands, sourceRegion, sourceXSubsampling, sourceYSubsampling, subsamplingXOffset, subsamplingYOffset
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Constructor Summary
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Method Summary
Modifier and TypeMethodDescriptionboolean
Returnstrue
if tables are currently set.Returns a copy of the array of AC Huffman tables set on the most recent call tosetDecodeTables
, ornull
if tables are not currently set.Returns a copy of the array of DC Huffman tables set on the most recent call tosetDecodeTables
, ornull
if tables are not currently set.Returns a copy of the array of quantization tables set on the most recent call tosetDecodeTables
, ornull
if tables are not currently set.void
setDecodeTables
(JPEGQTable[] qTables, JPEGHuffmanTable[] DCHuffmanTables, JPEGHuffmanTable[] ACHuffmanTables) Sets the quantization and Huffman tables to use in decoding abbreviated streams.void
Removes any quantization and Huffman tables that are currently set.Methods declared in class javax.imageio.ImageReadParam
canSetSourceRenderSize, getDestination, getDestinationBands, getSourceMaxProgressivePass, getSourceMinProgressivePass, getSourceNumProgressivePasses, getSourceRenderSize, setDestination, setDestinationBands, setSourceProgressivePasses, setSourceRenderSize
Methods declared in class javax.imageio.IIOParam
activateController, getController, getDefaultController, getDestinationOffset, getDestinationType, getSourceBands, getSourceRegion, getSourceXSubsampling, getSourceYSubsampling, getSubsamplingXOffset, getSubsamplingYOffset, hasController, setController, setDestinationOffset, setDestinationType, setSourceBands, setSourceRegion, setSourceSubsampling
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Constructor Details
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JPEGImageReadParam
public JPEGImageReadParam()Constructs aJPEGImageReadParam
.
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Method Details
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areTablesSet
public boolean areTablesSet()Returnstrue
if tables are currently set.- Returns:
true
if tables are present.
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setDecodeTables
public void setDecodeTables(JPEGQTable[] qTables, JPEGHuffmanTable[] DCHuffmanTables, 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.- Parameters:
qTables
- an array of quantization table objects.DCHuffmanTables
- an array of Huffman table objects.ACHuffmanTables
- an array of Huffman table objects.- Throws:
IllegalArgumentException
- if any of the arguments isnull
, has more than 4 elements, or if the numbers of DC and AC tables differ.- See Also:
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unsetDecodeTables
public void unsetDecodeTables()Removes any quantization and Huffman tables that are currently set.- See Also:
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getQTables
Returns a copy of the array of quantization tables set on the most recent call tosetDecodeTables
, ornull
if tables are not currently set.- Returns:
- an array of
JPEGQTable
objects, ornull
. - See Also:
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getDCHuffmanTables
Returns a copy of the array of DC Huffman tables set on the most recent call tosetDecodeTables
, ornull
if tables are not currently set.- Returns:
- an array of
JPEGHuffmanTable
objects, ornull
. - See Also:
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getACHuffmanTables
Returns a copy of the array of AC Huffman tables set on the most recent call tosetDecodeTables
, ornull
if tables are not currently set.- Returns:
- an array of
JPEGHuffmanTable
objects, ornull
. - See Also:
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