TIFFDecodeParam
Date: 2016-04-28

org.apache.xmlgraphics.image.codec.tiff

## Class TIFFDecodeParam

- java.lang.Object
- - org.apache.xmlgraphics.image.codec.tiff.TIFFDecodeParam

- All Implemented Interfaces:
    java.io.Serializable, java.lang.Cloneable, ImageDecodeParam

      public class TIFFDecodeParam
      extends java.lang.Object
      implements ImageDecodeParam

  An instance of `ImageDecodeParam` for decoding images in the TIFF format.

  To determine the number of images present in a TIFF file, use the `getNumPages()` method on the `ImageDecoder` object that will be used to perform the decoding. The desired page number may be passed as an argument to the `ImageDecoder.decodeAsRaster)()` or `decodeAsRenderedImage()` methods.

  For TIFF Palette color images, the colorMap always has entries of short data type, the color Black being represented by 0,0,0 and White by 65536,65536,65536. In order to display these images, the default behavior is to dither the short values down to 8 bits. The dithering is done by calling the `decode16BitsTo8Bits` method for each short value that needs to be dithered. The method has the following implementation: `byte b; short s; s = s & 0xffff; b = (byte)((s >> 8) & 0xff);` If a different algorithm is to be used for the dithering, this class should be subclassed and an appropriate implementation should be provided for the `decode16BitsTo8Bits` method in the subclass.

  If the palette contains image data that is signed short, as specified by the SampleFormat tag, the dithering is done by calling `decodeSigned16BitsTo8Bits` instead. The method has the following implementation: `byte b; short s; b = (byte)((s + Short.MIN_VALUE) >> 8);` In order to use a different algorithm for the dithering, this class should be subclassed and the method overridden.

  If it is desired that the Palette be decoded such that the output image is of short data type and no dithering is performed, the `setDecodePaletteAsShorts` method should be used.

  This class is not a committed part of the JAI API. It may be removed or changed in future releases of JAI.

  See Also:
    `TIFFDirectory`, Serialized Form

- - ### Constructor Summary

    Constructors
    Constructor and Description
    `TIFFDecodeParam()` Constructs a default instance of `TIFFDecodeParam`.

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `byte` | `decode16BitsTo8Bits(int s)` Returns an unsigned 8 bit value computed by dithering the unsigned 16 bit value.
    `byte` | `decodeSigned16BitsTo8Bits(short s)` Returns an unsigned 8 bit value computed by dithering the signed 16 bit value.
    `boolean` | `getDecodePaletteAsShorts()` Returns `true` if palette entries will be decoded as shorts, resulting in an output image with short datatype.
    `java.lang.Long` | `getIFDOffset()` Returns the value set by `setIFDOffset()` or `null` if no value has been set.
    `boolean` | `getJPEGDecompressYCbCrToRGB()` Whether JPEG-compressed YCbCr data will be converted to RGB.
    `void` | `setDecodePaletteAsShorts(boolean decodePaletteAsShorts)` If set, the entries in the palette will be decoded as shorts and no short to byte lookup will be applied to them.
    `void` | `setIFDOffset(long offset)` Sets the offset in the stream from which to read the image.
    `void` | `setJPEGDecompressYCbCrToRGB(boolean convertJPEGYCbCrToRGB)` Sets a flag indicating whether to convert JPEG-compressed YCbCr data to RGB.

    - ### Methods inherited from class java.lang.Object

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

- - ### Constructor Detail

    - #### TIFFDecodeParam

          public TIFFDecodeParam()

      Constructs a default instance of `TIFFDecodeParam`.

  - ### Method Detail

    - #### setDecodePaletteAsShorts

          public void setDecodePaletteAsShorts(boolean decodePaletteAsShorts)

      If set, the entries in the palette will be decoded as shorts and no short to byte lookup will be applied to them.

    - #### getDecodePaletteAsShorts

          public boolean getDecodePaletteAsShorts()

      Returns `true` if palette entries will be decoded as shorts, resulting in an output image with short datatype.

    - #### decode16BitsTo8Bits

          public byte decode16BitsTo8Bits(int s)

      Returns an unsigned 8 bit value computed by dithering the unsigned 16 bit value. Note that the TIFF specified short datatype is an unsigned value, while Java's `short` datatype is a signed value. Therefore the Java `short` datatype cannot be used to store the TIFF specified short value. A Java `int` is used as input instead to this method. The method deals correctly only with 16 bit unsigned values.

    - #### decodeSigned16BitsTo8Bits

          public byte decodeSigned16BitsTo8Bits(short s)

      Returns an unsigned 8 bit value computed by dithering the signed 16 bit value. This method deals correctly only with values in the 16 bit signed range.

    - #### setIFDOffset

          public void setIFDOffset(long offset)

      Sets the offset in the stream from which to read the image. There must be an Image File Directory (IFD) at that position or an error will occur. If `setIFDOffset()` is never invoked then the decoder will assume that the TIFF stream is at the beginning of the 8-byte image header. If the directory offset is set and a page number is supplied to the TIFF `ImageDecoder` then the page will be the zero-relative index of the IFD in linked list of IFDs beginning at the specified offset with a page of zero indicating the directory at that offset.

    - #### getIFDOffset

          public java.lang.Long getIFDOffset()

      Returns the value set by `setIFDOffset()` or `null` if no value has been set.

    - #### setJPEGDecompressYCbCrToRGB

          public void setJPEGDecompressYCbCrToRGB(boolean convertJPEGYCbCrToRGB)

      Sets a flag indicating whether to convert JPEG-compressed YCbCr data to RGB. The default value is `true`. This flag is ignored if the image data are not JPEG-compressed.

    - #### getJPEGDecompressYCbCrToRGB

          public boolean getJPEGDecompressYCbCrToRGB()

      Whether JPEG-compressed YCbCr data will be converted to RGB.