run_mode.cpp

基于块方向的图像无损压缩代码

/*++*
* Copyright (c) 1997 University of British Columbia. All rights reserved.
*
*       File:           regular_mode.c
*       Pourpose:       contains the main routins used in the run mode.
*
*       Author:         Ismaeil R. Ismaeil, Aug. 1997
*
*--*/

#include "stdafx.h"
#include "globals.h"
#include "prototypes.h"

int RUNindex_prev;

void RunModeProcessing()
{
	int glimit;

	/* Scanning */
	RUNval = Ra;
	RUNcnt = 0;

	while(Ix == RUNval)
	{
		RUNcnt += 1;
		Rx = RUNval;
		if(EOLine == 1)
			break;
		else
			GetNextSample();
	}

	/* Encoding of run segments of length rm */
	while(RUNcnt >= (1<<J[RUNindex]))
	{
		AppendToBitStream(1,1);
		RUNcnt -= (1<<J[RUNindex]);
		if(RUNindex < 31)
		{
			RUNindex_prev = RUNindex;
			RUNindex++;
		}
	}

	/* Encoding of run segments of length less than rm */
	if(Ra != Ix)
	{
		AppendToBitStream(0,1);
		AppendToBitStream(RUNcnt, J[RUNindex]);
		if(RUNindex>0)
		{
			RUNindex_prev = RUNindex;
			RUNindex = RUNindex - 1;
		}
	}
	else if(RUNcnt > 0)
		AppendToBitStream(1,1);

	/* Run interruption sample encoding */
	if(Ra != Ix)
	{
		/* Index computation */
		if(Ra == Rb)
			RItype = 1;
		else
			RItype = 0;
 
		/* Prediction error for a run interruption sample */
		if(RItype == 1)
			Errval = Ix - Ra;
		else
			Errval = Ix - Rb;

		/* Error computation for a run interruption sample */
		if((RItype == 0) && (Ra>Rb)) 
		{
			Errval = -Errval;
			SIGN = -1;
		}
		else
			SIGN = 1;

		if(NEAR_LOSSLESS > 0)
		{
			Errval = Quantize(Errval);
			Rx = ComputeRx();
		}
		else
			Rx = Ix;

		Errval = ModRange(Errval, RANGE);
 
		/* Computation of auxiliary variable in Golomb parameter */
		if(RItype == 0)
			TEMP = A[365];
		else
			TEMP = A[366]+(N[366]>>1);
 
		q = RItype + 365;

		for(k=0; (N[q]<<k)<TEMP; k++);

		/* Computation of map for Errval mapping */
		if((k==0) && (Errval>0) && (2*Nn[q]<N[q]))
			map = 1;
		else if((Errval < 0) && (2*Nn[q] >= N[q]))
			map = 1;
		else if((Errval < 0) && (k != 0))
			map = 1;
		else 
			map = 0;
  
		/* Errval mapping for run interuption sample */
		EMErrval = 2*(ABS(Errval)) - RItype - map;

		/* Mapped-error encoding */
		glimit = LIMIT - J[RUNindex_prev] - 1;

		GolombCoding(EMErrval, k, glimit); 

		/* update of parameters for run interruption sample */

		if(Errval < 0)
			Nn[q] = Nn[q] + 1;
		A[q] = A[q] + ((EMErrval+1-RItype)>>1);
		if(N[q] == RESET)
		{
			A[q] = A[q]>>1;
			N[q] = N[q]>>1;
			Nn[q] = Nn[q]>>1;
		}
		N[q] = N[q] + 1;
	}

	return;
}