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The mapping between source and destination Y coordinates is given by the equations:

 dx = (sx - sourceXOffset)/subsampleX + dstXOffset;
 dy = (sy - sourceYOffset)/subsampleY + dstYOffset;
 

 sx = (dx - dstXOffset)*subsampleX + sourceXOffset;
 sy = (dy - dstYOffset)*subsampleY + sourceYOffset;
 

Decompressors may be written with various levels of complexity. The most complex decompressors will override the decode method, and will perform all the work of decoding, subsampling, offsetting, clipping, and format conversion. This approach may be the most efficient, since it is possible to avoid the use of extra image buffers, and it may be possible to avoid decoding portions of the image that will not be copied into the destination.

Less ambitious decompressors may override the decodeRaw method, which is responsible for decompressing the entire tile or strip into a byte array (or other appropriate datatype). The default implementation of decode will perform all necessary setup of buffers, call decodeRaw to perform the actual decoding, perform subsampling, and copy the results into the final destination image. Where possible, it will pass the real image buffer to decodeRaw in order to avoid making an extra copy.

Slightly more ambitious decompressors may override decodeRaw, but avoid writing pixels that will be discarded in the subsampling phase.

The default implementation analyzes the destination image to determine if it is suitable as the destination for the decodeRaw method.

If this method is called, the beginDecoding method must be called prior to calling any of the decode methods.
Parameters:
  compression - the compression type.

If this method is called, the beginDecoding method must be called prior to calling any of the decode methods.
Parameters:
  dstMinX - the minimum X coordinate of the destinationregion.

The active source height will always be equal to (dstHeight - 1)*subsampleY + 1.

The pixels in the source region to be copied are those with X coordinates of the form activeSrcMinX + k*subsampleX, where k is an integer such that 0 <= k < dstWidth.

The pixels in the source region to be copied are those with Y coordinates of the form activeSrcMinY + k*subsampleY, where k is an integer such that 0 <= k < dstHeight.

The active source width will always be equal to (dstWidth - 1)*subsampleX + 1.

The default implementation computes tables used by the decode method to rescale components to different bit depths. Thus, if this method is overridden, it is important for the subclass method to call super(), unless it overrides decode as well.

The default implementation calls getRawImageType, and calls the resulting ImageTypeSpecifier's createBufferedImage method. a BufferedImage whose underlying dataarray has the same format as the raw source pixel data, ornull if it is not possible to create such animage.

The default implementation analyzes the destination image to determine if it is suitable as the destination for the decodeRaw method. If not, a suitable image is created. Next, decodeRaw is called to perform the actual decoding, and the results are copied into the destination image if necessary. Subsampling and offsetting are performed automatically.

The precise responsibilities of this routine are as follows. The input bit stream is defined by the instance variables stream, offset, and byteCount. These bits contain the data for the region of the source image defined by srcMinX, srcMinY, srcWidth, and srcHeight.

The source data is required to be subsampling, starting at the sourceXOffsetth column and including every subsampleXth pixel thereafter (and similarly for sourceYOffset and subsampleY).

Pixels are copied into the destination with an addition shift of (dstXOffset, dstYOffset). The complete set of formulas relating the source and destination coordinate spaces are:

 dx = (sx - sourceXOffset)/subsampleX + dstXOffset;
 dy = (sy - sourceYOffset)/subsampleY + dstYOffset; 
 

The inverse mapping, from destination to source coordinates, is one-to-one:

 sx = (dx - dstXOffset)*subsampleX + sourceXOffset;
 sy = (dy - dstYOffset)*subsampleY + sourceYOffset;
 

The region of the destination image to be updated is given by the instance variables dstMinX, dstMinY, dstWidth, and dstHeight.

It is possible that not all of the source data being read will contribute to the destination image. For example, the destination offsets could be set such that some of the source pixels land outside of the bounds of the image. As a convenience, the bounds of the active source region (that is, the region of the strip or tile being read that actually contributes to the destination image, taking clipping into account) are available as activeSrcMinX, activeSrcMinY, activeSrcWidth and activeSrcHeight. Thus, the source pixel at (activeSrcMinX, activeSrcMinY) will map to the destination pixel (dstMinX, dstMinY).

The sequence of source bands given by sourceBands are to be copied into the sequence of bands in the destination given by destinationBands.

Some standard tag information is provided the instance variables photometricInterpretation, compression, samplesPerPixel, bitsPerSample, sampleFormat, extraSamples, and colorMap.

In practice, unless there is a significant performance advantage to be gained by overriding this routine, most users will prefer to use the default implementation of this routine, and instead override the decodeRaw and/or getRawImageType methods.
exception:
  IOException - if an error occurs indecodeRaw.

The default implementation calls decodeRaw(byte[] b, ...) and copies the resulting data into s.
Parameters:
  s - a short array to be written.
Parameters:
  dstOffset - the starting offset in s to bewritten.
Parameters:
  bitsPerPixel - the number of bits for each pixel.
Parameters:
  scanlineStride - the number of shorts toadvance between that starting pixels of each scanline.
throws:
  IOException - if an error occurs reading from the sourceImageInputStream.

The default implementation calls decodeRaw(byte[] b, ...) and copies the resulting data into i.
Parameters:
  i - an int array to be written.
Parameters:
  dstOffset - the starting offset in i to bewritten.
Parameters:
  bitsPerPixel - the number of bits for each pixel.
Parameters:
  scanlineStride - the number of ints toadvance between that starting pixels of each scanline.
throws:
  IOException - if an error occurs reading from the sourceImageInputStream.

The default implementation calls decodeRaw(byte[] b, ...) and copies the resulting data into f.
Parameters:
  f - a float array to be written.
Parameters:
  dstOffset - the starting offset in f to bewritten.
Parameters:
  bitsPerPixel - the number of bits for each pixel.
Parameters:
  scanlineStride - the number of floats toadvance between that starting pixels of each scanline.
throws:
  IOException - if an error occurs reading from the sourceImageInputStream.

If this method is called, the beginDecoding method must be called prior to calling any of the decode methods.
Parameters:
  activeSrcHeight - the height of the active source region.

If this method is called, the beginDecoding method must be called prior to calling any of the decode methods.
Parameters:
  activeSrcMinX - the minimum X coordinate of the activesource region.

If this method is called, the beginDecoding method must be called prior to calling any of the decode methods.
Parameters:
  activeSrcMinY - the minimum Y coordinate of the activesource region.

If this method is called, the beginDecoding method must be called prior to calling any of the decode methods.
Parameters:
  activeSrcWidth - the width of the active source region.

If this method is called, the beginDecoding method must be called prior to calling any of the decode methods.
Parameters:
  bitsPerSample - the number of bits for each source imagesample.

If this method is called, the beginDecoding method must be called prior to calling any of the decode methods.
Parameters:
  byteCount - the number of bytes of compressed data.

If this method is called, the beginDecoding method must be called prior to calling any of the decode methods.
Parameters:
  colorMap - the color map to apply to the source data,as an array of chars.

If this method is called, the beginDecoding method must be called prior to calling any of the decode methods.
Parameters:
  compression - the compression type.

If this method is called, the beginDecoding method must be called prior to calling any of the decode methods.
Parameters:
  destinationBands - an array of intsspecifying the destination bands to be written.

If this method is called, the beginDecoding method must be called prior to calling any of the decode methods.
Parameters:
  dstHeight - the height of the destination region.

If this method is called, the beginDecoding method must be called prior to calling any of the decode methods.
Parameters:
  dstMinX - the minimum X coordinate of the destinationregion.

If this method is called, the beginDecoding method must be called prior to calling any of the decode methods.
Parameters:
  dstMinY - the minimum Y coordinate of the destinationregion.

If this method is called, the beginDecoding method must be called prior to calling any of the decode methods.
Parameters:
  dstWidth - the width of the destination region.

If this method is called, the beginDecoding method must be called prior to calling any of the decode methods.
Parameters:
  dstXOffset - the horizontal destination offset to beused when mapping between source and destination coordinates.

If this method is called, the beginDecoding method must be called prior to calling any of the decode methods.
Parameters:
  dstYOffset - the vertical destination offset to beused when mapping between source and destination coordinates.

If this method is called, the beginDecoding method must be called prior to calling any of the decode methods.
Parameters:
  extraSamples - the interpretation of any samples in thesource file beyond those used for basic color or grayscaleinformation.

If this method is called, the beginDecoding method must be called prior to calling any of the decode methods.
Parameters:
  image - the destination BufferedImage.

If this method is called, the beginDecoding method must be called prior to calling any of the decode methods.
Parameters:
  metadata - the IIOMetadata object for theimage being read.

If this method is called, the beginDecoding method must be called prior to calling any of the decode methods.
Parameters:
  offset - the offset of the beginning of the compresseddata.

If this method is called, the beginDecoding method must be called prior to calling any of the decode methods.
Parameters:
  photometricInterpretation - the photometric interpretationvalue.

If this method is called, the beginDecoding method must be called prior to calling any of the decode methods.
Parameters:
  planar - true if the image to be decoded isstored in planar format.

If this method is called, the beginDecoding method must be called prior to calling any of the decode methods.
Parameters:
  reader - the current ImageReader.

If this method is called, the beginDecoding method must be called prior to calling any of the decode methods.
Parameters:
  sampleFormat - the format of the source image data,for example unsigned integer or floating-point.

If this method is called, the beginDecoding method must be called prior to calling any of the decode methods.
Parameters:
  samplesPerPixel - the number of samples in each sourcepixel.

If this method is called, the beginDecoding method must be called prior to calling any of the decode methods.
Parameters:
  sourceBands - an array of intsspecifying the source bands to be read.

If this method is called, the beginDecoding method must be called prior to calling any of the decode methods.
Parameters:
  sourceXOffset - the horizontal source offset to be used whenmapping between source and destination coordinates.

If this method is called, the beginDecoding method must be called prior to calling any of the decode methods.
Parameters:
  sourceYOffset - the vertical source offset to be used whenmapping between source and destination coordinates.

If this method is called, the beginDecoding method must be called prior to calling any of the decode methods.
Parameters:
  srcHeight - the height of the source region being decoded,irrespective of how it will be copied into the destination.

If this method is called, the beginDecoding method must be called prior to calling any of the decode methods.
Parameters:
  srcMinX - the minimum X coordinate of the source regionbeing decoded, irrespective of how it will be copied into thedestination.

If this method is called, the beginDecoding method must be called prior to calling any of the decode methods.
Parameters:
  srcMinY - the minimum Y coordinate of the source regionbeing decoded, irrespective of how it will be copied into thedestination.

If this method is called, the beginDecoding method must be called prior to calling any of the decode methods.
Parameters:
  srcWidth - the width of the source region being decoded,irrespective of how it will be copied into the destination.

If this method is called, the beginDecoding method must be called prior to calling any of the decode methods.
Parameters:
  stream - the ImageInputStream to be read.

If this method is called, the beginDecoding method must be called prior to calling any of the decode methods.
Parameters:
  subsampleX - the horizontal subsampling factor.
throws:
  IllegalArgumentException - if subsampleX isless than or equal to 0.

If this method is called, the beginDecoding method must be called prior to calling any of the decode methods.
Parameters:
  subsampleY - the vertical subsampling factor.
throws:
  IllegalArgumentException - if subsampleY isless than or equal to 0.