PHP HSV to RGB formula comprehension

Question

I can convert RGB values to HSV with the following code...

 $r = $r/255;
 $g = $g/255;
 $b = $b/255;

 $h = 0;
 $s = 0;
 $v = 0;

 $min = min(min($r, $g),$b);
 $max = max(max($r, $g),$b);

 $r = $max-$min;
 $v = $max;


 if($r == 0){
  $h = 0;
  $s = 0;
 }
 else {
  $s = $r / $max;

  $hr = ((($max - $r) / 6) + ($r / 2)) / $r;
  $hg = ((($max - $g) / 6) + ($r / 2)) / $r;
  $hb = ((($max - $b) / 6) + ($r / 2)) / $r;

  if ($r == $max) $h = $hb - $hg;
  else if($g == $max) $h = (1/3) + $hr - $hb;
  else if ($b == $max) $h = (2/3) + $hg - $hr;

  if ($h < 0)$h += 1;
  if ($h > 1)$h -= 1;
 }

But how do you convert HSV to RGB in PHP???

The following is on wikipedia but I don't understand it,

I'm guessing it's pretty obvious

alt text

There are formulas here: http://en.wikipedia.org/wiki/HSV_color_space#Conversion_from_RGB_to_HSL_or_HSV — NullUserException, Aug 30 '10 at 02:12
Is this formula **REALLY** working for you? Because you re-introduced $r variable (nothing like dynamic language...). — greenoldman, Jun 17 '11 at 12:18
Does this answer your question? [PHP function to convert HSL to RGB or Hex](https://stackoverflow.com/questions/20423641/php-function-to-convert-hsl-to-rgb-or-hex) — SMJ, May 19 '20 at 08:32

score 15 · Accepted Answer · edited Feb 14 '15 at 21:43

15

This is for the the HSV values in the range [0,1] (and giving RGB values in the range [0,1], instead of {0, 1, ..., 255}:

function HSVtoRGB(array $hsv) {
    list($H,$S,$V) = $hsv;
    //1
    $H *= 6;
    //2
    $I = floor($H);
    $F = $H - $I;
    //3
    $M = $V * (1 - $S);
    $N = $V * (1 - $S * $F);
    $K = $V * (1 - $S * (1 - $F));
    //4
    switch ($I) {
        case 0:
            list($R,$G,$B) = array($V,$K,$M);
            break;
        case 1:
            list($R,$G,$B) = array($N,$V,$M);
            break;
        case 2:
            list($R,$G,$B) = array($M,$V,$K);
            break;
        case 3:
            list($R,$G,$B) = array($M,$N,$V);
            break;
        case 4:
            list($R,$G,$B) = array($K,$M,$V);
            break;
        case 5:
        case 6: //for when $H=1 is given
            list($R,$G,$B) = array($V,$M,$N);
            break;
    }
    return array($R, $G, $B);
}

edited Feb 14 '15 at 21:43

Jonathan Bredo Christensen

75
12

answered Aug 30 '10 at 02:15

Artefacto

96,375
17
202
225

What do you mean by This is for the the HSV values in the range [0,1] (and giving RGB values in the range [0,1], instead of {0, 1, ..., 255} Please explain – Mark Lalor Aug 30 '10 at 02:21
I mean the values must be between 0 and 1. – Artefacto Aug 30 '10 at 02:22
1

Ohhh so instead of h:0, s:100 and v: 100 it should be h:0 s:1 v:1 – Mark Lalor Aug 30 '10 at 02:26
The simplest approach I've seen so far. – Reactgular Sep 08 '13 at 15:02
To translate from Deg/Perc/Perc, like you're used to, to [0,1], divide the hue by 60, and sat and lum by 100. – Cullub Dec 19 '15 at 02:40

score 5 · Answer 2 · edited Aug 04 '12 at 01:56

Translation of rolls answer for HSL from C to PHP

function ColorHSLToRGB($h, $s, $l){

        $r = $l;
        $g = $l;
        $b = $l;
        $v = ($l <= 0.5) ? ($l * (1.0 + $s)) : ($l + $s - $l * $s);
        if ($v > 0){
              $m;
              $sv;
              $sextant;
              $fract;
              $vsf;
              $mid1;
              $mid2;

              $m = $l + $l - $v;
              $sv = ($v - $m ) / $v;
              $h *= 6.0;
              $sextant = floor($h);
              $fract = $h - $sextant;
              $vsf = $v * $sv * $fract;
              $mid1 = $m + $vsf;
              $mid2 = $v - $vsf;

              switch ($sextant)
              {
                    case 0:
                          $r = $v;
                          $g = $mid1;
                          $b = $m;
                          break;
                    case 1:
                          $r = $mid2;
                          $g = $v;
                          $b = $m;
                          break;
                    case 2:
                          $r = $m;
                          $g = $v;
                          $b = $mid1;
                          break;
                    case 3:
                          $r = $m;
                          $g = $mid2;
                          $b = $v;
                          break;
                    case 4:
                          $r = $mid1;
                          $g = $m;
                          $b = $v;
                          break;
                    case 5:
                          $r = $v;
                          $g = $m;
                          $b = $mid2;
                          break;
              }
        }
        return array('r' => $r * 255.0, 'g' => $g * 255.0, 'b' => $b * 255.0);
}

See [this answer](http://stackoverflow.com/a/34363975/3437608) for the reverse to this function, and added capabilities. — Cullub, Dec 19 '15 at 02:38

Teson · Answer 3 · 2018-04-24T20:21:05.783

Found this post too late, my alternate take on it:

hsv2rgb function PHP

hue: 0-360, sat: 0-100, val: 0-100

  function hsv2rgb($hue,$sat,$val) {;
    $rgb = array(0,0,0);
    //calc rgb for 100% SV, go +1 for BR-range
    for($i=0;$i<4;$i++) {
      if (abs($hue - $i*120)<120) {
        $distance = max(60,abs($hue - $i*120));
        $rgb[$i % 3] = 1 - (($distance-60) / 60);
      }
    }
    //desaturate by increasing lower levels
    $max = max($rgb);
    $factor = 255 * ($val/100);
    for($i=0;$i<3;$i++) {
      //use distance between 0 and max (1) and multiply with value
      $rgb[$i] = round(($rgb[$i] + ($max - $rgb[$i]) * (1 - $sat/100)) * $factor);
    }
    $rgb['html'] = sprintf('#%02X%02X%02X', $rgb[0], $rgb[1], $rgb[2]);
    return $rgb;
  }

score 1 · Answer 4 · edited Aug 30 '10 at 02:16

private class HSLPixel{
        double hue;
        double saturation;
        double lightness;

        .... your code
}

public Color HSLToRGB(HSLPixel pixel){

            double v;
            double r,g,b;
            double l = pixel.lightness;
            double h = pixel.hue;
            double s = pixel.saturation;

            r = l;   // default to gray
            g = l;
            b = l;
            v = (l <= 0.5) ? (l * (1.0 + s)) : (l + s - l * s);
            if (v > 0){
                  double m;
                  double sv;
                  int sextant;
                  double fract, vsf, mid1, mid2;

                  m = l + l - v;
                  sv = (v - m ) / v;
                  h *= 6.0;
                  sextant = (int)h;
                  fract = h - sextant;
                  vsf = v * sv * fract;
                  mid1 = m + vsf;
                  mid2 = v - vsf;

                  switch (sextant)
                  {
                        case 0:
                              r = v;
                              g = mid1;
                              b = m;
                              break;
                        case 1:
                              r = mid2;
                              g = v;
                              b = m;
                              break;
                        case 2:
                              r = m;
                              g = v;
                              b = mid1;
                              break;
                        case 3:
                              r = m;
                              g = mid2;
                              b = v;
                              break;
                        case 4:
                              r = mid1;
                              g = m;
                              b = v;
                              break;
                        case 5:
                              r = v;
                              g = m;
                              b = mid2;
                              break;
                  }
            }
            Color rgb = new Color((int)(r * 255.0), (int)(g * 255.0), (int)(b * 255.0));
            return rgb;
    }

score 1 · Answer 5 · answered Oct 10 '10 at 16:59

1

ColorJizz allows you to convert from/to many formats. There is a PHP version too.

answered Oct 10 '10 at 16:59

Mikee

2,403
2
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score 0 · Answer 6 · answered Aug 30 '10 at 02:28

0

of course you can, just change the function definitions to php style, change all the variables etc but keep the core code the same, shouldn't take you more than 30 minutes to do that and test it.

answered Aug 30 '10 at 02:28

rollsch

2,518
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give it a shot and the lines you get stuck on ask us, I've never really done php before. – rollsch Aug 30 '10 at 02:43
I'm stuck at the start, but this is a very good example! I'll upvote it – Mark Lalor Aug 30 '10 at 02:51
anything in particular that is tripping you up? I can try and explain it for you. – rollsch Aug 30 '10 at 03:51

PHP HSV to RGB formula comprehension

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