CADI.Common.LogicalTarget.JPEG2000.Decode
Class MQDecoder

java.lang.Object
  CADI.Common.LogicalTarget.JPEG2000.Decode.MQDecoder

All Implemented Interfaces:

Decoder

public class MQDecoder
extends java.lang.Object
implements Decoder

This class decodes bits for the fractional bit plane decoder of JPEG2000, decoding them with the MQ decoder. This class allows the use of the following MQ options: restart, reset, bypass. Usage example:
construct
decodeBit
decodeBit
decodeBit
swapInputByteStream
reset
restart
decodeBit
decodeBit
...

Version:

1.2

Author:

Group on Interactive Coding of Images (GICI)

Field Summary

private int	A Interval range.
private int	C Lower down interval.
private ByteStream	inputByteStream Bytestream from which the MQ decoder reads data.
private int	L Number of bytes transferred to the outputByteStream.
private int	numContexts Number of contexts (defined by JPEG2000).
private int[][]	statesMPS State and Most Probable Symbol of each context.
private int[][]	stateSymbolInit MQ context state initialization (defined by JPEG2000 standard).
private int[][]	stateTrans MQ probability state transition (defined by JPEG2000 standard).
private int	t Number of bits to transfer (down counter).
private int	Tr Byte to transfer.

Constructor Summary

MQDecoder()
Constructor that initializes internal registers of the MQ decoder but does not initialize the inputByteStream.

MQDecoder(ByteStream inputByteStream)
Constructor that initializes internal registers of the MQ decoder.

Method Summary

boolean	decodeBit() Decode a bit using the context 18 (equivalent probabilities).
boolean	decodeBit(int context) Decode a bit.
private void	fillLSB() Fill the C register with a new byte of inputByteStream.
void	reset() Reset the context probabilities of the decoder, if any.
void	restart() Start the value of the internal variables A, C, ... of the MQ decoder filling them with the values of the inputByteStream.
void	swapInputByteStream(ByteStream inputByteStream) Swaps the current inputByteStream.

Methods inherited from class java.lang.Object

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

Field Detail

inputByteStream

private ByteStream inputByteStream

Bytestream from which the MQ decoder reads data.

The content must be understood as a ByteStream.

numContexts

private final int numContexts

Number of contexts (defined by JPEG2000).

Positive number.

See Also:

Constant Field Values

stateSymbolInit

private final int[][] stateSymbolInit

MQ context state initialization (defined by JPEG2000 standard).

First array index represents the context and second is: (p.e. [2][0] is the initial state of context 2)

• 0 - Initial state for the context
• 1 - Initial expected symbol for the context

stateTrans

private final int[][] stateTrans

MQ probability state transition (defined by JPEG2000 standard).

First array index represents the current state and second is: (i.e. [1][0] is the transition to do when code a MPS symbol and the state of the context is 1)

• 0 - MPS transition
• 1 - LPS transition
• 2 - If 1 change MPS by LPS, nothing otherwise
• 3 - estimation (probability is--> 0xXXX / (2^16 * alpha) -alpha usually is 0.708-)

A

private int A

Interval range.

From right to left: 8 register bits, 3 spacer bits, 8 partial code byte, 1 carry bit.

C

private int C

Lower down interval.

From right to left: 8 register bits, 3 spacer bits, 8 partial code byte, 1 carry bit.

t

private int t

Number of bits to transfer (down counter).

Usually it is initialized to 8, unless carry situations that it initilized to 7. Then count down until 0.

Tr

private int Tr

Byte to transfer.

Byte flushed to the outputByteStream.

L

private int L

Number of bytes transferred to the outputByteStream.

Byte flushed to the output ByteStream.

statesMPS

private int[][] statesMPS

State and Most Probable Symbol of each context.

Array index is the context and the State [context][0] or MPS [context][1]. It must correspond to some stateTrans.

Constructor Detail

MQDecoder

public MQDecoder()

Constructor that initializes internal registers of the MQ decoder but does not initialize the inputByteStream. Before using the MQ decoder the function swapInputByteStream should be called.

MQDecoder

public MQDecoder(ByteStream inputByteStream)
          throws ErrorException

Constructor that initializes internal registers of the MQ decoder.

Parameters:

inputByteStream - the input stream of bytes

Throws:

ErrorException - when end of ByteStream is reached

Method Detail

decodeBit

public boolean decodeBit()
                  throws ErrorException

Decode a bit using the context 18 (equivalent probabilities).

Specified by:

decodeBit in interface Decoder

Returns:

a boolean indicating the bit decoded

Throws:

ErrorException - when trying to read after the end of the inputByteStream

decodeBit

public boolean decodeBit(int context)
                  throws ErrorException

Decode a bit.

Specified by:

decodeBit in interface Decoder

Parameters:

context - a byte that indicates the context of the decoded bit

Returns:

a boolean indicating the bit decoded

Throws:

ErrorException - when trying to read after the end of the inputByteStream

fillLSB

private void fillLSB()
              throws ErrorException

Fill the C register with a new byte of inputByteStream. If the end of the ByteStream is reached, then this function fills the new byte with a value of 0xFF.

Throws:

ErrorException - when trying to read after the end of the inputByteStream

swapInputByteStream

public void swapInputByteStream(ByteStream inputByteStream)

Swaps the current inputByteStream. After the call of this function you should restart de MQ decoder calling the restart function (it fills the internal registers with the bytes of the new inputByteStream).

Specified by:

swapInputByteStream in interface Decoder

Parameters:

inputByteStream - the input stream of bytes

reset

public void reset()

Description copied from interface: Decoder

Reset the context probabilities of the decoder, if any.

Specified by:

reset in interface Decoder

restart

public void restart()
             throws ErrorException

Start the value of the internal variables A, C, ... of the MQ decoder filling them with the values of the inputByteStream. The context probabilities are maintained. This function should be called every time a new ByteStream is passed to the decoder.

Specified by:

restart in interface Decoder

Throws:

ErrorException - when end of ByteStream is reached