Change saturation (university homework - libgd)

saturation.c

// author: Maciej Ciemborowicz
// Jagiellonian University
// ZGK 2011/2012

#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))

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

  //////////////////////////////////////////////////////////////////////

  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;
  }
  
  // set saturation of rgb color, return gdTrueColor
  int set_saturation(float r, float g, float b, int percent) {
  
    RGB rgb;
    HSV hsv;

    hsv = rgb2hsv(r, g, b);
          
    if ((hsv.s * ((float)percent / 100)) < 1)
      hsv.s *= (float)percent / 100;
    else
      hsv.s = 1;
          
    rgb = hsv2rgb(hsv.h, hsv.s, hsv.v);

    return gdTrueColor((int) rgb.r, (int) rgb.g, (int) rgb.b);
  
  }

  //////////////////////////////////////////////////////////////////////

  int i, j, k, x, y;
  gdImagePtr img;
  int color;

  //////////////////////////////////////////////////////////////////////

  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);
        
      for (i=0; i<x; ++i) {
        for (j=0; j<y; ++j) {
          
          color = gdImageGetPixel(img, i, j);
          
          color = set_saturation((float) gdImageRed(img, color), 
                                 (float) gdImageGreen(img, color), 
                                 (float) gdImageBlue(img, color), 
                                 175);
          
          gdImageSetPixel(img, i, j, color);

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

  return 0;
}