# Class ImageReadParam

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

Direct Known Subclasses:
  `JPEGImageReadParam, TIFFImageReadParam`

public class ImageReadParam extends IIOParam
A class describing how a stream is to be decoded. Instances of this class or its subclasses are used to supply prescriptive "how-to" information to instances of `ImageReader`.

An image encoded as part of a file or stream may be thought of extending out in multiple dimensions: the spatial dimensions of width and height, a number of bands, and a number of progressive decoding passes. This class allows a contiguous (hyper)rectangular subarea of the image in all of these dimensions to be selected for decoding. Additionally, the spatial dimensions may be subsampled discontinuously. Finally, color and format conversions may be specified by controlling the `ColorModel` and `SampleModel` of the destination image, either by providing a `BufferedImage` or by using an `ImageTypeSpecifier`.

An `ImageReadParam` object is used to specify how an image, or a set of images, will be converted on input from a stream in the context of the Java Image I/O framework. A plug-in for a specific image format will return instances of `ImageReadParam` from the `getDefaultReadParam` method of its `ImageReader` implementation.

The state maintained by an instance of `ImageReadParam` is independent of any particular image being decoded. When actual decoding takes place, the values set in the read param are combined with the actual properties of the image being decoded from the stream and the destination `BufferedImage` that will receive the decoded pixel data. For example, the source region set using `setSourceRegion` will first be intersected with the actual valid source area. The result will be translated by the value returned by `getDestinationOffset`, and the resulting rectangle intersected with the actual valid destination area to yield the destination area that will be written.

The parameters specified by an `ImageReadParam` are applied to an image as follows. First, if a rendering size has been set by `setSourceRenderSize`, the entire decoded image is rendered at the size given by `getSourceRenderSize`. Otherwise, the image has its natural size given by `ImageReader.getWidth` and `ImageReader.getHeight`.

Next, the image is clipped against the source region specified by `getSourceXOffset`, `getSourceYOffset`, `getSourceWidth`, and `getSourceHeight`.

The resulting region is then subsampled according to the factors given in `IIOParam.setSourceSubsampling`. The first pixel, the number of pixels per row, and the number of rows all depend on the subsampling settings. Call the minimum X and Y coordinates of the resulting rectangle (`minX`, `minY`), its width `w` and its height `h`.

This rectangle is offset by (`getDestinationOffset().x`, `getDestinationOffset().y`) and clipped against the destination bounds. If no destination image has been set, the destination is defined to have a width of `getDestinationOffset().x` + `w`, and a height of `getDestinationOffset().y` + `h` so that all pixels of the source region may be written to the destination.

Pixels that land, after subsampling, within the destination image, and that are written in one of the progressive passes specified by `getSourceMinProgressivePass` and `getSourceNumProgressivePasses` are passed along to the next step.

Finally, the source samples of each pixel are mapped into destination bands according to the algorithm described in the comment for `setDestinationBands`.

Plug-in writers may extend the functionality of `ImageReadParam` by providing a subclass that implements additional, plug-in specific interfaces. It is up to the plug-in to document what interfaces are available and how they are to be used. Readers will silently ignore any extended features of an `ImageReadParam` subclass of which they are not aware. Also, they may ignore any optional features that they normally disable when creating their own `ImageReadParam` instances via `getDefaultReadParam`.

Note that unless a query method exists for a capability, it must be supported by all `ImageReader` implementations (e.g. source render size is optional, but subsampling must be supported).

See Also:
  - `ImageReader`
  - `ImageWriter`
  - `ImageWriteParam`

- ## Field Summary

  Fields
  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`

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `ImageReadParam()`
  Constructs an `ImageReadParam`.

- ## Method Summary

  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`

  ### Methods declared in class Object

  `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- ## Field Details

  - ### canSetSourceRenderSize

    protected boolean canSetSourceRenderSize
    `true` if this `ImageReadParam` allows the source rendering dimensions to be set. By default, the value is `false`. Subclasses must set this value manually.

    `ImageReader`s that do not support setting of the source render size should set this value to `false`.

  - ### sourceRenderSize

    protected Dimension sourceRenderSize
    The desired rendering width and height of the source, if `canSetSourceRenderSize` is `true`, or `null`.

    `ImageReader`s that do not support setting of the source render size may ignore this value.

  - ### destination

    protected BufferedImage destination
    The current destination `BufferedImage`, or `null` if none has been set. By default, the value is `null`.

  - ### destinationBands

    protected int[] destinationBands
    The set of destination bands to be used, as an array of `int`s. By default, the value is `null`, indicating all destination bands should be written in order.

  - ### minProgressivePass

    protected int minProgressivePass
    The minimum index of a progressive pass to read from the source. By default, the value is set to 0, which indicates that passes starting with the first available pass should be decoded.

    Subclasses should ensure that this value is non-negative.

  - ### numProgressivePasses

    protected int numProgressivePasses
    The maximum number of progressive passes to read from the source. By default, the value is set to `Integer.MAX_VALUE`, which indicates that passes up to and including the last available pass should be decoded.

    Subclasses should ensure that this value is positive. Additionally, if the value is not `Integer.MAX_VALUE`, then `minProgressivePass + numProgressivePasses - 1` should not exceed `Integer.MAX_VALUE`.

- ## Constructor Details

  - ### ImageReadParam

    public ImageReadParam()
    Constructs an `ImageReadParam`.

- ## Method Details

  - ### setDestination

    public void setDestination(BufferedImage destination)
    Supplies a `BufferedImage` to be used as the destination for decoded pixel data. The currently set image will be written to by the `read`, `readAll`, and `readRaster` methods, and a reference to it will be returned by those methods.

    Pixel data from the aforementioned methods will be written starting at the offset specified by `getDestinationOffset`.

    If `destination` is `null`, a newly-created `BufferedImage` will be returned by those methods.

    At the time of reading, the image is checked to verify that its `ColorModel` and `SampleModel` correspond to one of the `ImageTypeSpecifier`s returned from the `ImageReader`'s `getImageTypes` method. If it does not, the reader will throw an `IIOException`.

    Parameters:
      `destination` - the BufferedImage to be written to, or `null`.
    See Also:
      - `getDestination()`

  - ### getDestination

    public BufferedImage getDestination()
    Returns the `BufferedImage` currently set by the `setDestination` method, or `null` if none is set.
    Returns:
      the BufferedImage to be written to.
    See Also:
      - `setDestination(BufferedImage)`

  - ### setDestinationBands

    public void setDestinationBands(int[] destinationBands)
    Sets the indices of the destination bands where data will be placed. Duplicate indices are not allowed.

    A `null` value indicates that all destination bands will be used.

    Choosing a destination band subset will not affect the number of bands in the output image of a read if no destination image is specified; the created destination image will still have the same number of bands as if this method had never been called. If a different number of bands in the destination image is desired, an image must be supplied using the `ImageReadParam.setDestination` method.

    At the time of reading or writing, an `IllegalArgumentException` will be thrown by the reader or writer if a value larger than the largest destination band index has been specified, or if the number of source bands and destination bands to be used differ. The `ImageReader.checkReadParamBandSettings` method may be used to automate this test.

    Parameters:
      `destinationBands` - an array of integer band indices to be used.
    Throws:
      `IllegalArgumentException` - if `destinationBands` contains a negative or duplicate value.
    See Also:
      - `getDestinationBands()`
      - `IIOParam.getSourceBands()`
      - `ImageReader.checkReadParamBandSettings(ImageReadParam, int, int)`

  - ### getDestinationBands

    public int[] getDestinationBands()
    Returns the set of band indices where data will be placed. If no value has been set, `null` is returned to indicate that all destination bands will be used.
    Returns:
      the indices of the destination bands to be used, or `null`.
    See Also:
      - `setDestinationBands(int[])`

  - ### canSetSourceRenderSize

    public 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. If this method returns `false`, calls to `setSourceRenderSize` will throw an `UnsupportedOperationException`.
    Returns:
      `true` if setting source rendering size is supported.
    See Also:
      - `setSourceRenderSize(Dimension)`

  - ### setSourceRenderSize

    public void setSourceRenderSize(Dimension size) throws UnsupportedOperationException
    If the image is able to be rendered at an arbitrary size, sets the source width and height to the supplied values. Note that the values returned from the `getWidth` and `getHeight` methods on `ImageReader` are not affected by this method; they will continue to return the default size for the image. Similarly, if the image is also tiled the tile width and height are given in terms of the default size.

    Typically, the width and height should be chosen such that the ratio of width to height closely approximates the aspect ratio of the image, as returned from `ImageReader.getAspectRatio`.

    If this plug-in does not allow the rendering size to be set, an `UnsupportedOperationException` will be thrown.

    To remove the render size setting, pass in a value of `null` for `size`.

    Parameters:
      `size` - a `Dimension` indicating the desired width and height.
    Throws:
      `IllegalArgumentException` - if either the width or the height is negative or 0.
      `UnsupportedOperationException` - if image resizing is not supported by this plug-in.
    See Also:
      - `getSourceRenderSize()`
      - `ImageReader.getWidth(int)`
      - `ImageReader.getHeight(int)`
      - `ImageReader.getAspectRatio(int)`

  - ### getSourceRenderSize

    public 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. A `null` value indicates that no setting has been made.
    Returns:
      the rendered width and height of the source image as a `Dimension`.
    See Also:
      - `setSourceRenderSize(Dimension)`

  - ### setSourceProgressivePasses

    public void setSourceProgressivePasses(int minPass, int numPasses)
    Sets the range of progressive passes that will be decoded. Passes outside of this range will be ignored.

    A progressive pass is a re-encoding of the entire image, generally at progressively higher effective resolutions, but requiring greater transmission bandwidth. The most common use of progressive encoding is found in the JPEG format, where successive passes include more detailed representations of the high-frequency image content.

    The actual number of passes to be decoded is determined during decoding, based on the number of actual passes available in the stream. Thus if `minPass + numPasses - 1` is larger than the index of the last available passes, decoding will end with that pass.

    A value of `numPasses` of `Integer.MAX_VALUE` indicates that all passes from `minPass` forward should be read. Otherwise, the index of the last pass (i.e., `minPass + numPasses - 1`) must not exceed `Integer.MAX_VALUE`.

    There is no `unsetSourceProgressivePasses` method; the same effect may be obtained by calling `setSourceProgressivePasses(0, Integer.MAX_VALUE)`.

    Parameters:
      `minPass` - the index of the first pass to be decoded.
      `numPasses` - the maximum number of passes to be decoded.
    Throws:
      `IllegalArgumentException` - if `minPass` is negative, `numPasses` is negative or 0, or `numPasses` is smaller than `Integer.MAX_VALUE` but `minPass + numPasses - 1` is greater than `INTEGER.MAX_VALUE`.
    See Also:
      - `getSourceMinProgressivePass()`
      - `getSourceMaxProgressivePass()`

  - ### getSourceMinProgressivePass

    public int getSourceMinProgressivePass()
    Returns the index of the first progressive pass that will be decoded. If no value has been set, 0 will be returned (which is the correct value).
    Returns:
      the index of the first pass that will be decoded.
    See Also:
      - `setSourceProgressivePasses(int, int)`
      - `getSourceNumProgressivePasses()`

  - ### getSourceMaxProgressivePass

    public int getSourceMaxProgressivePass()
    If `getSourceNumProgressivePasses` is equal to `Integer.MAX_VALUE`, returns `Integer.MAX_VALUE`. Otherwise, returns `getSourceMinProgressivePass() + getSourceNumProgressivePasses() - 1`.
    Returns:
      the index of the last pass to be read, or `Integer.MAX_VALUE`.

  - ### getSourceNumProgressivePasses

    public int getSourceNumProgressivePasses()
    Returns the number of the progressive passes that will be decoded. If no value has been set, `Integer.MAX_VALUE` will be returned (which is the correct value).
    Returns:
      the number of the passes that will be decoded.
    See Also:
      - `setSourceProgressivePasses(int, int)`
      - `getSourceMinProgressivePass()`