ccontrast.c

image processing including fourier,wavelet,segmentation etc.

/*--------------------------- Commande MegaWave -----------------------------*/
/* mwcommand
  name = {ccontrast};
  version = {"1.0"};
  author = {"Lionel Moisan"};
  function = {"Contrast improvment by histogram adjusting"};
  usage = {
	   'g':g->g [0.0,1e20]  "gamma factor (visual correction)",
           input->in            "source image",
           output<-out          "processed image"
          };
*/
/*-- MegaWave2 - Copyright (C) 1994 Jacques Froment. All Rights Reserved. --*/

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

/* Include always the MegaWave2 Library */
#include "mw.h"
 
/***** gamma correction [0,1]->[0,1] *****/

float fgamma(g,x)
float g,x;
{
    return (float)pow((double)x,1.0/(double)g);
}


/****************************** CONTRAST ******************************/

void ccontrast(in,out,g)
Cimage in;
Cimage out;
float *g;
{
    int *histo, h;
    int adr,i,x2,size,ofs;
    unsigned char *new,y;
    float yd;

    /* Allocate memory */
    out = mw_change_cimage(out,in->nrow,in->ncol);
    size = in->nrow*in->ncol;
    histo = (int *)calloc(256,sizeof(int));
    new = (unsigned char *)calloc(256,sizeof(unsigned char));
    if (!out || !histo || !new) 
      mwerror(FATAL,1,"Not enough memory !\n");

    /* Compute the old histogram */
    for (adr=0;adr<size;adr++) 
      histo[(unsigned int)(in->gray[adr])]++;

    /* Compute the new histogram */
    ofs = 0; x2 = 0;
    for (i=0;i<256;i++) if (h=histo[i]) {
	/* grey level 0 correction */
	if (x2==0) ofs = -h;
	yd = (float)(x2 + ofs +h)*0.5/size;
	/* gamma correction if any */
	if (g) yd = fgamma(*g,yd);
	y = (int)(yd*256.0);
	/* grey level 255 correction */
	if (x2+h==size<<1 || y>255) y = 255;
	x2 += 2*h;
	new[i] = y;
	mwdebug("gray %d -> %d\n",i,y);
    }
    
    /* Process image */
    for (adr=0;adr<size;adr++) 
      out->gray[adr] = new[in->gray[adr]];
}