PHP function to convert Hex to HSL (Not HSL to Hex)

[thara]

I am trying to convert colors from Hex to HSL (Not HSL to Hex). I am using a PHP function for this purpose. But It's not working properly for some colors. For example for #e04c4c the HSL should be (0, 70%, 59%) which it isn't the case with the function.

function hexToHsl($hex) {
    $red = hexdec(substr($hex, 0, 2)) / 255;
    $green = hexdec(substr($hex, 2, 2)) / 255;
    $blue = hexdec(substr($hex, 4, 2)) / 255;

    $cmin = min($red, $green, $blue);
    $cmax = max($red, $green, $blue);
    $delta = $cmax - $cmin;

    if ($delta === 0) {
        $hue = 0;
    } elseif ($cmax === $red) {
        $hue = (($green - $blue) / $delta) % 6;
    } elseif ($cmax === $green) {
        $hue = ($blue - $red) / $delta + 2;
    } else {
        $hue = ($red - $green) / $delta + 4;
    }

    $hue = round($hue * 60);
    if ($hue < 0) {
        $hue += 360;
    }

    $lightness = (($cmax + $cmin) / 2) * 100;
    $saturation = $delta === 0 ? 0 : ($delta / (1 - abs(2 * $lightness - 1))) * 100;
    if ($saturation < 0) {
        $saturation += 100;
    }

    $lightness = round($lightness);
    $saturation = round($saturation);

    //return "hsl(${hue}, ${saturation}%, ${lightness}%)";
    return array($hue, $saturation, $lightness);
}

This is how I used it:
 

$templatePrimaryColor = '#e04c4c';

$templatePrimaryColor = str_replace("#", "",$templatePrimaryColor);

list($h,$s,$l) = hexToHsl($templatePrimaryColor);

$primaryColor = "hsl(${h}, ${s}%, ${l}%)";

This is the output:

echo '<pre>',print_r(hexToHsl($templatePrimaryColor)).'</pre>';

Array
(
    [0] => 0
    [1] => 99
    [2] => 59
)
1

Does anyone know what is the problem there?

Thank you.

[requinix]

    $lightness = (($cmax + $cmin) / 2) * 100;
    $saturation = $delta === 0 ? 0 : ($delta / (1 - abs(2 * $lightness - 1))) * 100;

You're multiplying the lightness by 100 too early. This throws off the saturation calculation.

Leave it as $cmax+$cmin/2 and multiply when you do the round() later.

[Barand]

Your method has a fatal problem with greys (ie when R = G = B)

[requinix]

24 minutes ago, Barand said:

Your method has a fatal problem with greys (ie when R = G = B)

You mean when $delta === 0?

[Barand]

Yes, if all 3 components are equal then $delta is zero, giving a division by zero error.

[requinix]

In the $hue calculations? The first branch handles the $delta=0 case.

[Barand]

$templatePrimaryColor = '555555';
echo '<pre>',print_r(hexToHsl($templatePrimaryColor)).'</pre>';

->

Warning:  Division by zero in C:\inetpub\wwwroot\test\winuser\noname3.php on line 14

 

[Barand]

43 minutes ago, requinix said:

The first branch handles the $delta=0 case.

Not quite.

var_dump($delta) gives float(0), therefore the first branch needs to be either

if ($delta === 0.0) {

or

if ($delta == 0) {