Simple RGB to CMYK (0-255) ranges

rgb_to_cmyk.c

/*
  Based on: http://www.rapidtables.com/convert/color/rgb-to-cmyk.htm
*/

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

typedef struct RGB_t { unsigned char red, green, blue; } RGB;
typedef struct CMYK_t { unsigned char cyan, magenta, yellow, black; } CMYK;

void RgbToCMYK(struct RGB_t rgb, struct CMYK_t* outCmyk)
{
  float r, g, b;
  float c, m, y, k;
  
  r = rgb.red / 255.0f;
  g = rgb.green / 255.0f;
  b = rgb.blue / 255.0f;
  
  k = 1 - fmaxf(fmaxf(r, g), b);
  c = (1 - r - k) / (1 - k);
  m = (1 - g - k) / (1 - k);
  y = (1 - b - k) / (1 - k);
  
  outCmyk->cyan = c * 255;
  outCmyk->magenta = m * 255;
  outCmyk->yellow = y * 255;
  outCmyk->black = k * 255;
}

int main()
{
  struct RGB_t rgb = { 132, 34, 255};
  struct CMYK_t cmyk;
  
  RgbToCMYK(rgb, &cmyk);
  
  printf("RGB(%u,%u,%u) -> CMYK(%u,%u,%u,%u)\n", rgb.red, rgb.green, rgb.blue,
         cmyk.cyan, cmyk.magenta, cmyk.yellow, cmyk.black);
  // prints: RGB(132,34,255) -> CMYK(123, 221, 0, 0)

  struct RGB_t rgb_red = { 255, 0, 0};
  struct CMYK_t cmyk_red;
  
  RgbToCMYK(rgb_red, &cmyk_red);
  
  printf("RGB(%u,%u,%u) -> CMYK(%u,%u,%u,%u)\n", rgb_red.red, rgb_red.green, rgb_red.blue,
        cmyk_red.cyan, cmyk_red.magenta, cmyk_red.yellow, cmyk_red.black);
  // prints: RGB(255,0,0) -> CMYK(0, 255, 255, 0)
  
  return 0;
}