Class HCompress

java.lang.Object

nom.tam.fits.compression.algorithm.hcompress.HCompress

public class HCompress
extends Object

The original compression code was written by Richard White at the STScI and included (ported to c and adapted) in cfitsio by William Pence, NASA/GSFC. That code was then ported to java by R. van Nieuwenhoven. Later it was massively refactored to harmonize the different compression algorithms and reduce the duplicate code pieces without obscuring the algorithm itself as far as possible. The original site for the algorithm is

See Also:

• http://www.stsci.edu/software/hcompress.html

Field Summary

Fields

Modifier and Type	Field	Description
private int	bitbuffer	variables for bit output to buffer when Huffman coding
private static final int[]	BITS_MASK
protected static final int	BITS_OF_1_BYTE
protected static final int	BITS_OF_1_NYBBLE
private int	bitsToGo2	Number of bits free in buffer
private int	bitsToGo3
private int	buffer2	Bits buffered for output
protected static final int	BYTE_MASK
private static final int[]	CODE
private static final byte[]	CODE_MAGIC
private static final int	HTRANS_START_MASK
private static final int	N3	to be refactored to a good name.
private static final int[]	NCODE
protected static final int	NYBBLE_MASK
protected static final double	ROUNDING_HALF

Constructor Summary

Constructors

Constructor	Description
HCompress()

Method Summary

Modifier and Type	Method	Description
private int	b2i(boolean b)
private int	bufcopy(byte[] a, int n, byte[] buffer, int b, long bmax)
protected void	compress(long[] aa, int ny, int nx, int scale, ByteBuffer output)
private LongBuffer	copy(LongBuffer a, int i)
private void	digitize(LongBuffer a, int aOffset, int nx, int ny, long scale)
private void	doEncode(ByteBuffer compressedBytes, LongBuffer pixels, int nx, int ny, byte[] nbitplanes)	encode pixels.
private void	doneOutputtingBits(ByteBuffer outfile)
private int	encode(ByteBuffer compressedBytes, LongBuffer a, int nx, int ny, int scale)
private int	htrans(long[] a, int nx, int ny)
private int	log2n(int nqmax)
private void	outputNbits(ByteBuffer outfile, int bits, int n)
private void	outputNnybble(ByteBuffer outfile, int n, byte[] array)
private void	outputNybble(ByteBuffer outfile, int bits)
private int	qtreeEncode(ByteBuffer outfile, LongBuffer a, int n, int nqx, int nqy, int nbitplanes)	macros to write out 4-bit nybble, Huffman code for this value
private void	qtreeOnebit(LongBuffer a, int n, int nx, int ny, byte[] b, int bit)
private void	qtreeReduce(byte[] a, int n, int nx, int ny, byte[] b)
private void	shuffle(long[] a, int aOffset, int n, int n2, long[] tmp)
private void	startOutputtingBits()
private void	writeBdirect(ByteBuffer outfile, LongBuffer a, int n, int nqx, int nqy, byte[] scratch, int bit)

Methods inherited from class Object

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

Field Details

HTRANS_START_MASK

private static final int HTRANS_START_MASK

See Also:

• Constant Field Values

ROUNDING_HALF

protected static final double ROUNDING_HALF

See Also:

• Constant Field Values

BITS_OF_1_BYTE

protected static final int BITS_OF_1_BYTE

See Also:

• Constant Field Values

BITS_OF_1_NYBBLE

protected static final int BITS_OF_1_NYBBLE

See Also:

• Constant Field Values

BYTE_MASK

protected static final int BYTE_MASK

See Also:

• Constant Field Values

NYBBLE_MASK

protected static final int NYBBLE_MASK

See Also:

• Constant Field Values

N3

private static final int N3

to be refactored to a good name.

See Also:

• Constant Field Values

BITS_MASK

private static final int[] BITS_MASK

CODE

private static final int[] CODE

CODE_MAGIC

private static final byte[] CODE_MAGIC

NCODE

private static final int[] NCODE

bitbuffer

private int bitbuffer

variables for bit output to buffer when Huffman coding

bitsToGo2

private int bitsToGo2

Number of bits free in buffer

bitsToGo3

private int bitsToGo3

buffer2

private int buffer2

Bits buffered for output

Constructor Details

HCompress

public HCompress()

Method Details

b2i

private int b2i(boolean b)

bufcopy

private int bufcopy(byte[] a,
 int n,
 byte[] buffer,
 int b,
 long bmax)

compress

protected void compress(long[] aa,
 int ny,
 int nx,
 int scale,
 ByteBuffer output)

copy

private LongBuffer copy(LongBuffer a,
 int i)

digitize

private void digitize(LongBuffer a,
 int aOffset,
 int nx,
 int ny,
 long scale)

doEncode

private void doEncode(ByteBuffer compressedBytes,
 LongBuffer pixels,
 int nx,
 int ny,
 byte[] nbitplanes)

encode pixels.

Parameters:

compressedBytes - compressed data

pixels - pixels to compress

nx - image width dimension

ny - image height dimension

nbitplanes - Number of bit planes in quadrants

doneOutputtingBits

private void doneOutputtingBits(ByteBuffer outfile)

encode

private int encode(ByteBuffer compressedBytes,
 LongBuffer a,
 int nx,
 int ny,
 int scale)

htrans

private int htrans(long[] a,
 int nx,
 int ny)

log2n

private int log2n(int nqmax)

outputNbits

private void outputNbits(ByteBuffer outfile,
 int bits,
 int n)

outputNnybble

private void outputNnybble(ByteBuffer outfile,
 int n,
 byte[] array)

outputNybble

private void outputNybble(ByteBuffer outfile,
 int bits)

qtreeEncode

private int qtreeEncode(ByteBuffer outfile,
 LongBuffer a,
 int n,
 int nqx,
 int nqy,
 int nbitplanes)

macros to write out 4-bit nybble, Huffman code for this value

qtreeOnebit

private void qtreeOnebit(LongBuffer a,
 int n,
 int nx,
 int ny,
 byte[] b,
 int bit)

qtreeReduce

private void qtreeReduce(byte[] a,
 int n,
 int nx,
 int ny,
 byte[] b)

shuffle

private void shuffle(long[] a,
 int aOffset,
 int n,
 int n2,
 long[] tmp)

startOutputtingBits

private void startOutputtingBits()

writeBdirect

private void writeBdirect(ByteBuffer outfile,
 LongBuffer a,
 int n,
 int nqx,
 int nqy,
 byte[] scratch,
 int bit)