# Class JPEGImageReadParam

java.lang.Object
javax.imageio.IIOParam
javax.imageio.ImageReadParam
javax.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 `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.

## Field Summary

### Fields declared in class ImageReadParam

`canSetSourceRenderSize, destination, destinationBands, minProgressivePass, numProgressivePasses, sourceRenderSize`
Modifier and Type
Field
Description
`protected boolean`
`canSetSourceRenderSize`
`true` if this `ImageReadParam` allows the source rendering dimensions to be set.
`protected BufferedImage`
`destination`
The current destination `BufferedImage`, or `null` if none has been set.
`protected int[]`
`destinationBands`
The set of destination bands to be used, as an array of `int`s.
`protected int`
`minProgressivePass`
The minimum index of a progressive pass to read from the source.
`protected int`
`numProgressivePasses`
The maximum number of progressive passes to read from the source.
`protected Dimension`
`sourceRenderSize`
The desired rendering width and height of the source, if `canSetSourceRenderSize` is `true`, or `null`.

### Fields declared in class IIOParam

`controller, defaultController, destinationOffset, destinationType, sourceBands, sourceRegion, sourceXSubsampling, sourceYSubsampling, subsamplingXOffset, subsamplingYOffset`
Modifier and Type
Field
Description
`protected IIOParamController`
`controller`
The `IIOParamController` that will be used to provide settings for this `IIOParam` object when the `activateController` method is called.
`protected IIOParamController`
`defaultController`
The default `IIOParamController` that will be used to provide settings for this `IIOParam` object when the `activateController` method is called.
`protected Point`
`destinationOffset`
The offset in the destination where the upper-left decoded pixel should be placed.
`protected ImageTypeSpecifier`
`destinationType`
An `ImageTypeSpecifier` to be used to generate a destination image when reading, or to set the output color type when writing.
`protected int[]`
`sourceBands`
An array of `int`s indicating which source bands will be used, or `null`.
`protected Rectangle`
`sourceRegion`
The source region, on `null` if none is set.
`protected int`
`sourceXSubsampling`
The decimation subsampling to be applied in the horizontal direction.
`protected int`
`sourceYSubsampling`
The decimation subsampling to be applied in the vertical direction.
`protected int`
`subsamplingXOffset`
A horizontal offset to be applied to the subsampling grid before subsampling.
`protected int`
`subsamplingYOffset`
A vertical offset to be applied to the subsampling grid before subsampling.

## Constructor Summary

Constructors
Constructor
Description
`JPEGImageReadParam()`
Constructs a `JPEGImageReadParam`.

## Method Summary

Modifier and Type
Method
Description
`boolean`
`areTablesSet()`
Returns `true` if tables are currently set.
`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.
`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.
`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.
`void`
`setDecodeTables(JPEGQTable[] qTables, JPEGHuffmanTable[] DCHuffmanTables, JPEGHuffmanTable[] ACHuffmanTables)`
Sets the quantization and Huffman tables to use in decoding abbreviated streams.
`void`
`unsetDecodeTables()`
Removes any quantization and Huffman tables that are currently set.

### Methods declared in class ImageReadParam

`canSetSourceRenderSize, getDestination, getDestinationBands, getSourceMaxProgressivePass, getSourceMinProgressivePass, getSourceNumProgressivePasses, getSourceRenderSize, setDestination, setDestinationBands, setSourceProgressivePasses, setSourceRenderSize`
Modifier and Type
Method
Description
`boolean`
`canSetSourceRenderSize()`
Returns `true` if this reader allows the source image to be rendered at an arbitrary size as part of the decoding process, by means of the `setSourceRenderSize` method.
`BufferedImage`
`getDestination()`
Returns the `BufferedImage` currently set by the `setDestination` method, or `null` if none is set.
`int[]`
`getDestinationBands()`
Returns the set of band indices where data will be placed.
`int`
`getSourceMaxProgressivePass()`
If `getSourceNumProgressivePasses` is equal to `Integer.MAX_VALUE`, returns `Integer.MAX_VALUE`.
`int`
`getSourceMinProgressivePass()`
Returns the index of the first progressive pass that will be decoded.
`int`
`getSourceNumProgressivePasses()`
Returns the number of the progressive passes that will be decoded.
`Dimension`
`getSourceRenderSize()`
Returns the width and height of the source image as it will be rendered during decoding, if they have been set via the `setSourceRenderSize` method.
`void`
`setDestination(BufferedImage destination)`
Supplies a `BufferedImage` to be used as the destination for decoded pixel data.
`void`
`setDestinationBands(int[] destinationBands)`
Sets the indices of the destination bands where data will be placed.
`void`
`setSourceProgressivePasses(int minPass, int numPasses)`
Sets the range of progressive passes that will be decoded.
`void`
`setSourceRenderSize(Dimension size)`
If the image is able to be rendered at an arbitrary size, sets the source width and height to the supplied values.

### Methods declared in class IIOParam

`activateController, getController, getDefaultController, getDestinationOffset, getDestinationType, getSourceBands, getSourceRegion, getSourceXSubsampling, getSourceYSubsampling, getSubsamplingXOffset, getSubsamplingYOffset, hasController, setController, setDestinationOffset, setDestinationType, setSourceBands, setSourceRegion, setSourceSubsampling`
Modifier and Type
Method
Description
`boolean`
`activateController()`
Activates the installed `IIOParamController` for this `IIOParam` object and returns the resulting value.
`IIOParamController`
`getController()`
Returns whatever `IIOParamController` is currently installed.
`IIOParamController`
`getDefaultController()`
Returns the default `IIOParamController`, if there is one, regardless of the currently installed controller.
`Point`
`getDestinationOffset()`
Returns the offset in the destination image at which pixels are to be placed.
`ImageTypeSpecifier`
`getDestinationType()`
Returns the type of image to be returned by the read, if one was set by a call to `setDestination(ImageTypeSpecifier)`, as an `ImageTypeSpecifier`.
`int[]`
`getSourceBands()`
Returns the set of source bands to be used.
`Rectangle`
`getSourceRegion()`
Returns the source region to be used.
`int`
`getSourceXSubsampling()`
Returns the number of source columns to advance for each pixel.
`int`
`getSourceYSubsampling()`
Returns the number of rows to advance for each pixel.
`int`
`getSubsamplingXOffset()`
Returns the horizontal offset of the subsampling grid.
`int`
`getSubsamplingYOffset()`
Returns the vertical offset of the subsampling grid.
`boolean`
`hasController()`
Returns `true` if there is a controller installed for this `IIOParam` object.
`void`
`setController(IIOParamController controller)`
Sets the `IIOParamController` to be used to provide settings for this `IIOParam` object when the `activateController` method is called, overriding any default controller.
`void`
`setDestinationOffset(Point destinationOffset)`
Specifies the offset in the destination image at which future decoded pixels are to be placed, when reading, or where a region will be written, when writing.
`void`
`setDestinationType(ImageTypeSpecifier destinationType)`
Sets the desired image type for the destination image, using an `ImageTypeSpecifier`.
`void`
`setSourceBands(int[] sourceBands)`
Sets the indices of the source bands to be used.
`void`
`setSourceRegion(Rectangle sourceRegion)`
Sets the source region of interest.
`void`
`setSourceSubsampling(int sourceXSubsampling, int sourceYSubsampling, int subsamplingXOffset, int subsamplingYOffset)`
Specifies a decimation subsampling to apply on I/O.

### Methods declared in class Object

`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`
Modifier and Type
Method
Description
`protected Object`
`clone()`
Creates and returns a copy of this object.
`boolean`
`equals(Object obj)`
Indicates whether some other object is "equal to" this one.
`protected void`
`finalize()`
Deprecated, for removal: This API element is subject to removal in a future version.
Finalization is deprecated and subject to removal in a future release.
`final Class<?>`
`getClass()`
Returns the runtime class of this `Object`.
`int`
`hashCode()`
Returns a hash code value for this object.
`final void`
`notify()`
Wakes up a single thread that is waiting on this object's monitor.
`final void`
`notifyAll()`
Wakes up all threads that are waiting on this object's monitor.
`String`
`toString()`
Returns a string representation of the object.
`final void`
`wait()`
Causes the current thread to wait until it is awakened, typically by being notified or interrupted.
`final void`
`wait(long timeoutMillis)`
Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
`final void`
`wait(long timeoutMillis, int nanos)`
Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.

## Constructor Details

### JPEGImageReadParam

public JPEGImageReadParam()
Constructs a `JPEGImageReadParam`.

## Method Details

### areTablesSet

public boolean areTablesSet()
Returns `true` if tables are currently set.

Returns:
  `true` if tables are present.

### 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 is `null`, has more than 4 elements, or if the numbers of DC and AC tables differ.
See Also:
  - `unsetDecodeTables()`

### unsetDecodeTables

public void unsetDecodeTables()
Removes any quantization and Huffman tables that are currently set.

See Also:
  - `setDecodeTables(JPEGQTable[], JPEGHuffmanTable[], JPEGHuffmanTable[])`

### getQTables

public 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.

Returns:
  an array of `JPEGQTable` objects, or `null`.
See Also:
  - `setDecodeTables(JPEGQTable[], JPEGHuffmanTable[], JPEGHuffmanTable[])`

### getDCHuffmanTables

public 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.

Returns:
  an array of `JPEGHuffmanTable` objects, or `null`.
See Also:
  - `setDecodeTables(JPEGQTable[], JPEGHuffmanTable[], JPEGHuffmanTable[])`

### getACHuffmanTables

public 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.

Returns:
  an array of `JPEGHuffmanTable` objects, or `null`.
See Also:
  - `setDecodeTables(JPEGQTable[], JPEGHuffmanTable[], JPEGHuffmanTable[])`