quant.c

h.263 c编码源码。目录下有input。qcif原始未压缩文件

/*************************************************
 * libr263: fast H.263 encoder library
 *
 * Copyright (C) 1996, Roalt Aalmoes, Twente University
 * SPA multimedia group
 *
 * Based on Telenor TMN 1.6 encoder (Copyright (C) 1995, Telenor R&D)
 * created by Karl Lillevold 
 *
 * Author encoder: Roalt Aalmoes, <[e-mail]>
 * 
 * Date: 31-07-96
 **************************************************/

#include"sim.h"

/* For q=8, a "speedy" version is integrated */
// 量化,后系数存入qcoeff, 并找到CBP 63个AC系数(qcoeff有非零值时,CBP=CBP_Mask 32,16,8,4,2,1 分别对应6个8*8块)

int QuantAndFindCBP(int *coeff, int *qcoeff, int QP, int Mode, int CBP_Mask)
{
  int i;
  int level;
  int tempje;
  int CBP = 0;

  if (Mode == MODE_INTRA) /* Intra */
  { 
    qcoeff[0] = mmax(1,mmin(254,coeff[0] >> 3)); /* was: /8 *///DC ,除以8,  并限定到1到255

    if(QP == 8) 
	{
      for(i = 1; i < 64; i++) {	/* QP == 8 */
	     level = (abs(coeff[i])) >> 4;                        //AC,除以16,
	     qcoeff[i] = mmin(127, mmax(-127,sign(coeff[i]) * level));
	     if(qcoeff[i])
	        CBP = CBP_Mask; //32
      }
    } else 
	{			/* QP != 8 */
      for(i = 1; i < 64; i++) {

		level = (abs(coeff[i])) / (2*QP);
		qcoeff[i] =  mmin(127,mmax(-127,sign(coeff[i]) * level));
		if(qcoeff[i])
	       CBP = CBP_Mask;
      }

    }	/* End intra QP == 8 */
  }
  else { /* non Intra */
    if(QP == 8) {
      for(i = 0; i < 64; i++) {
	tempje = abs(coeff[i]) - 4;
	if(tempje < 0) {
	  *(qcoeff++) = 0;
	} else {
	  level = tempje >> 4; /* Note 2*QP == 2*8 = 2^4 == ">>4" */
	  if((*(qcoeff++) = mmin(127,mmax(-127,(sign(coeff[i]) > 0) ?level :-level))) != 0)
	    CBP = CBP_Mask;
	}
      }
      
    } else {			/* QP != 8 */
      
      for (i = 0; i < 64; i++) {
	  level = (abs(coeff[i])-QP/2)  / (2*QP);
	  if((*(qcoeff++) = mmin(127,mmax(-127,sign(coeff[i]) * level)))!= 0)
	  CBP = CBP_Mask;
      }
      
    } /* End QP == 8 */
    
  }  
  return CBP;
}


void Dequant(int *qcoeff, int *rcoeff, int QP, int Mode)
{
  int i;
  
  if (QP) {
    for (i = 0; i < 64; i++) {
      if (qcoeff[i]) {
	if ((QP % 2) == 1)
	  rcoeff[i] = QP * (2*abs(qcoeff[i]) + 1);
	else
	  rcoeff[i] = QP * (2*abs(qcoeff[i]) + 1) - 1;
	rcoeff[i] = sign(qcoeff[i]) * rcoeff[i];
      }
      else
	rcoeff[i] = 0;
    }
    if (Mode == MODE_INTRA) { /* Intra */
      rcoeff[0] = qcoeff[0]*8;
    }
  }
  else {
    /* No quantizing at all */
    for (i = 0; i < 64; i++) {
      rcoeff[i] = qcoeff[i];
    }
  }
  return;
}