PHP: HEX to CMYK

Question

How do I convert a HEX color value to CMYK equivalent in php?

I want to write a function that does that. But Ive got no clue how to convert hex to CMYK

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Answer 1

I just came across this because I was looking for a conversion script. However, the rgb2cmyk function in the answer by Mark Baker doesn’t seem to be calculating the correct values. I compared the results with multiple online calculators and in order to get the correct values I had to modify the function like this:

function rgb2cmyk($var1,$g=0,$b=0) {
    if (is_array($var1)) {
            $r = $var1['r'];
            $g = $var1['g'];
            $b = $var1['b'];
    } else {
            $r = $var1;
    }
    $cyan = 1 - $r/255;
    $magenta = 1 - $g/255;
    $yellow = 1 - $b/255;
    $black = min($cyan, $magenta, $yellow);
    $cyan = @round(($cyan - $black) / (1 - $black) * 100);
    $magenta = @round(($magenta - $black) / (1 - $black) * 100);
    $yellow = @round(($yellow - $black) / (1 - $black) * 100);
    $black = round($black * 100);
    return array(
            'c' => $cyan,
            'm' => $magenta,
            'y' => $yellow,
            'k' => $black,
    );
}

Now, I don’t fully understand what I did here but it appears to output the correct values (compared to all the other online calculators).

Answer 2

function hex2rgb($hex) {
   $color = str_replace('#','',$hex);
   $rgb = array(
      'r' => hexdec(substr($color,0,2)),
      'g' => hexdec(substr($color,2,2)),
      'b' => hexdec(substr($color,4,2)),
   );
   return $rgb;
}

function rgb2cmyk($var1,$g=0,$b=0) {
   if (is_array($var1)) {
      $r = $var1['r'];
      $g = $var1['g'];
      $b = $var1['b'];
   } else {
      $r = $var1;
   }
   $cyan = 255 - $r;
   $magenta = 255 - $g;
   $yellow = 255 - $b;
   $black = min($cyan, $magenta, $yellow);
   $cyan = @(($cyan    - $black) / (255 - $black));
   $magenta = @(($magenta - $black) / (255 - $black));
   $yellow = @(($yellow  - $black) / (255 - $black));
   return array(
      'c' => $cyan,
      'm' => $magenta,
      'y' => $yellow,
      'k' => $black,
   );
}

$color=rgb2cmyk(hex2rgb('#FF0000'));