Brightness normalization

bn.c

/*
 * author: Maciej Ciemborowicz
 * Jagiellonian University
 * ZGK 2011/2012
 * 
 * gcc gd_wewy.o bn.c -o bn -lgd -ansi -Wall -pedantic
 */

#include <stdio.h>
#include <math.h>
#include <gd.h>
#include "gd_wewy.h"

#define MIN(a,b) ((a)<(b)?(a):(b))
#define MAX(a,b) ((a)>(b)?(a):(b))

typedef struct rgb {
  float r, g, b;
} RGB;

typedef struct hsv {
  float h, s, v;
} HSV;

/* based on: http://www.algorytm.org/modele-barw/transformacja-hsv-rgb/hsv-rgb-c.html */
RGB hsv2rgb(float hue, float sat, float val) {
  
  float red, grn, blu;
  float i, f, p, q, t;
  RGB result;

  if(val==0) {
    red = 0;
    grn = 0;
    blu = 0;
  } 
  else {
    hue/=60;
    i = floor(hue);
    f = hue-i;
    p = val*(1-sat);
    q = val*(1-(sat*f));
    t = val*(1-(sat*(1-f)));
    if (i==0) {red=val; grn=t; blu=p;}
    else if (i==1) {red=q; grn=val; blu=p;}
    else if (i==2) {red=p; grn=val; blu=t;}
    else if (i==3) {red=p; grn=q; blu=val;}
    else if (i==4) {red=t; grn=p; blu=val;}
    else if (i==5) {red=val; grn=p; blu=q;}
  }
  
  result.r = red;
  result.g = grn;
  result.b = blu;
  
  return result;
  
}

/* based on: http://www.algorytm.org/modele-barw/transformacja-hsv-rgb/hsv-rgb-c.html */
HSV rgb2hsv(float red, float grn, float blu){
  
  float hue, sat, val;
  float x, f, i;
  
  HSV result;
    
  x = MIN(MIN(red, grn), blu);
  val = MAX(MAX(red, grn), blu);
  
  if (x == val){
    hue = 0;
    sat = 0;
  }
  else {
    f = (red == x) ? grn-blu : ((grn == x) ? blu-red : red-grn);
    i = (red == x) ? 3 : ((grn == x) ? 5 : 1);
    hue = fmod((i-f/(val-x))*60, 360);
    sat = ((val-x)/val);
  }
  
  result.h = hue;
  result.s = sat;
  result.v = val;
  
  return result;

}
  
/* ****************************************************************** */
  
int main(int argc, char * argv[]) {

  int i, j, k, x, y;
  gdImagePtr img;
  int color;
  HSV color_hsv;
  RGB color_rgb;
  float min_brightness = 255;
  float max_brightness = 0;
  
  /* **************************************************************** */
  
  if (argc < 2) {
    fprintf(stderr, "Error: No argument!\n");
    return 1;
  }
  
  /* **************************************************************** */

  for (k=1; k<argc; ++k) {
     
    img = wczytajPng(argv[k]);
    
    if (img == NULL) {
      fprintf(stderr, "Error: Can't read %s!\n", argv[k]);
    }
    else {

      x = gdImageSX(img);
      y = gdImageSY(img);
      
      /* find brightness range */
      for (i=0; i<x; ++i) {
        for (j=0; j<y; ++j) {
          
          color = gdImageGetPixel(img, i, j);
          
          color_hsv = rgb2hsv((float) gdImageRed(img, color), 
                              (float) gdImageGreen(img, color), 
                              (float) gdImageBlue(img, color));
          
          min_brightness = MIN(min_brightness,color_hsv.v);
          max_brightness = MAX(max_brightness,color_hsv.v);

        }
      }
      
      /* normalize image brightness */
      for (i=0; i<x; ++i) {
        for (j=0; j<y; ++j) {
          
          color = gdImageGetPixel(img, i, j);
          
          color_hsv = rgb2hsv((float) gdImageRed(img, color), 
                              (float) gdImageGreen(img, color), 
                              (float) gdImageBlue(img, color));
          
          color_hsv.v =  (color_hsv.v - min_brightness) * (255. / (max_brightness - min_brightness));

          color_rgb = hsv2rgb(color_hsv.h, color_hsv.s, color_hsv.v);
          
          color = gdTrueColor((int) color_rgb.r, 
                              (int) color_rgb.g, 
                              (int) color_rgb.b);
          
          gdImageSetPixel(img, i, j, color);

        }
      }
      
      zapiszPng(img, argv[k]);
      gdImageDestroy(img);
      
    }
  
  }
  
  return 0;
}