predic.c

JPEG压缩和解压程序和一些相关的说明文档 内容比较全

/*This file include programe accomplish the prediction discribed in JPEG_LS standard.
 *The author is Fujian Shi,email [e-mail].
 */
#include "commondecls.h"




#define   PIXEL  unsigned char 
#define   UNI_TYPE int
#define T1 3
#define T2 7
#define T3 21
#define NEAR 6

#define PREDICTION(Rb, Ra, Rc,Px)	\
{	\
	register PIXEL minx;	\
	register PIXEL maxx;	\
	\
	if (Rb > Ra) {	\
		minx = Ra;	\
		maxx = Rb;	\
	} else {	\
		maxx = Ra;	\
		minx = Rb;	\
	}	\
	if (Rc >= maxx)	\
		Px = minx;	\
	else if (Rc <= minx)	\
		Px = maxx;	\
	else	\
		Px = Ra + Rb - Rc;	\
}


#define   QUAN_GRAD(D,q) if (D<=-T3)q=-4;\
else if (D<=-T2) q=-3;\
else if (D<=-T1) q=-2;\
else if (D< -NEAR) q=-1;\
else if (D<=NEAR) q=0;\
else if (D<T1) q=1;\
else if (D<T2) q=2;\
else if (D<T3) q=3;\
else q=4


#define PO_OR_NE(Q)  *sign_ptr= Q >= 0 ? 1 : (-1)
#define MAKE_FIRST_POSITIVE(Q1,Q2,Q3)       Q1 *=*sign_ptr;Q2 *=*sign_ptr;Q3 *=*sign_ptr
#define ABS(Q) Q >= 0 ? Q : -Q
LOCAL(int) 
find_bin(UNI_TYPE Q1,UNI_TYPE Q2,UNI_TYPE Q3,UNI_TYPE *sign_ptr)
{
  int position=0;
  
  if (Q1 != 0) {
    PO_OR_NE(Q1);
    MAKE_FIRST_POSITIVE(Q1,Q2,Q3);
    position +=41;
    Q1--;
    if (Q2 < 0) {
      position +=45;
      Q2 = ABS(Q2)-1;
    }
    if (Q3 <0) {
      position +=5;
      Q3 =ABS(Q3)-1;
    }
    position +=81*Q1 + 9*Q2 + Q3;
  }else if (Q2 != 0) {
    PO_OR_NE(Q2);
    MAKE_FIRST_POSITIVE(Q1,Q2,Q3);
    position +=5;
    Q2--;
    if (Q3 < 0) {
      position +=5;
      Q3 =ABS(Q3)-1;
    }
    position +=9*Q2 + Q3;
  }else {
    PO_OR_NE(Q3);
    MAKE_FIRST_POSITIVE(Q1,Q2,Q3);
    position +=Q3;
  }
  return position;
  
}


 
int
get_errval(j_compress_ptr cinfo,int Ra, PIXEL Rb, int Rc,PIXEL  Rd,PIXEL *x)
{
  UNI_TYPE D1,D2,D3;
  UNI_TYPE Q1,Q2,Q3,Q;
  int px;

  UNI_TYPE sign=1,errval,errval_coded;
  predic_structure_ptr pre=&cinfo->pre;

  /*Caculate the context bin and the predic value px.*/
  D1=Rd-Rb;
  D2=Rb-Rc;
  D3=Rc-Ra;
  QUAN_GRAD(D1,Q1);
  QUAN_GRAD(D2,Q2);
  QUAN_GRAD(D3,Q3);
  Q=find_bin(Q1,Q2,Q3,&sign);
  PREDICTION(Rb,Ra,Rc,px)

  /*Correct the prediction*/
  px +=sign*pre->C[Q];
  if (px >255) px=255;
  if (px<0) px=0;
  errval=(*x - px)*sign;
  if (errval >=0) errval=(errval+NEAR)/(2*NEAR+1);
  else errval=-(NEAR-errval)/(2*NEAR+1);
  errval_coded=errval;
  px=px+sign*errval*(2*NEAR+1);
  if (px<0) px=0;
  if (px>255) px=255;
  *x=px;
  if (errval<0 ) errval +=256;
  if (errval >= 128) errval -=256;

  /*Update the N[Q], B[Q],C[Q]to accomplish  context self-adaption*/
  pre->B[Q] +=errval*(2*NEAR+1);
  if (pre->N[Q]==pre->reset) {
    pre->B[Q] >>=1;
    pre->N[Q] >>=1;
  }
  pre->N[Q] +=1;

  /* Do bias estimation for NEXT pixel */
  /* Bias cancelation tries to put error in (-1,0] (A.6.2)*/	
  if  ( pre->B[Q] <= -pre->N[Q] ) {
    if (pre->C[Q] > -128)
      --pre->C[Q];
    if ( (pre->B[Q] += pre->N[Q]) <= -pre->N[Q] ) 
			pre->B[Q] = -pre->N[Q]+1;
  } else if ( pre->B[Q] > 0 ) {
           if (pre->C[Q] < 127)
             ++pre->C[Q];
	   if ( (pre->B[Q] -= pre->N[Q]) > 0 )
	     pre->B[Q] = 0;
  }
  /*printf("C[%d]=%d\n",Q,pre->C[Q]);*/
  return errval_coded;
}