dct_2d.c

DCT算法的实现和测试

#include <stdio.h>
#include <math.h>
#include <stdlib.h>

#define invroot2 0.7071067814

#define VERBOSE 0

static double *g= NULL;
static double two_over_sqrtncolsnrows = 0.0;
static int ncolsvalue = 0;
static int nrowsvalue = 0;

static void initfct2d(int nrows, int ncols){
  if(VERBOSE) printf("FCT2D -- Initialising for new nrows=%d\n",nrows);
  if ((nrows<=0)||(ncols<0)){
    printf("FCT2D -- ncols=%d or nrows=%d is <=0\n",nrows,ncols);
    exit(1);
  }
  if(g != NULL) free(g);
  g = (double *)calloc(nrows,sizeof(double));
  if(g == NULL){
    printf("FCT2D -- Unable to allocate g array\n");
    exit(1);
  }
  ncolsvalue = ncols;
  nrowsvalue = nrows;
  two_over_sqrtncolsnrows = 2.0/sqrt(ncols*1.0*nrows);
}

void fct2d(double f[], int nrows, int ncols)
/* CALL THIS FOR FORWARD 2d DCT DON-MONRO PREFERRED SCALING */
{
  int u,v;

  if ((ncols!=ncolsvalue)||(nrows!=nrowsvalue)){
    initfct2d(nrows,ncols);
  }
  for (u=0; u<=nrows-1; u++){
    fct_noscale(&f[u*ncols],ncols);
  }
  for (v=0; v<=ncols-1; v++){
    for (u=0; u<=nrows-1; u++){
       g[u] = f[u*ncols+v];
    }
    fct_noscale(g,nrows);
    for (u=0; u<=nrows-1; u++){
      f[u*ncols+v] = g[u]*two_over_sqrtncolsnrows;
    }
  }
}

void ifct2d(double f[], int nrows, int ncols)
/* CALL THIS FOR INVERSE 2d DCT DON-MONRO PREFERRED SCALING */
{
  int u,v;

  if ((ncols!=ncolsvalue)||(nrows!=nrowsvalue)){
    initfct2d(nrows,ncols);
  }
  for (u=0; u<=nrows-1; u++){
    ifct_noscale(&f[u*ncols],ncols);
  }
  for (v=0; v<=ncols-1; v++){
    for (u=0; u<=nrows-1; u++){
       g[u] = f[u*ncols+v];
    }
    ifct_noscale(g,nrows);
    for (u=0; u<=nrows-1; u++){
       f[u*ncols+v] = g[u]*two_over_sqrtncolsnrows;
    }
  }
}