PHP中的RGB到HSV

function rgbToHsv($r, $g, $b) {
    $r /= 255;
    $g /= 255;
    $b /= 255;

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

    $h, $s, $v = 0;

    $d = $max - $min;
    $s = $max == 0 ? 0 : $d / $max;

    if ($max == $min) {
        $h = 0;
    } else {
        switch ($max) {
            case $r:
                $h = ($g - $b) / $d + ($g < $b ? 6 : 0);
                break;
            case $g:
                $h = ($b - $r) / $d + 2;
                break;
            case $b:
                $h = ($r - $g) / $d + 4;
                break;
        }
        $h /= 6;
    }

    return array($h, $s, $v);
}

$rgb = array(255, 0, 0); // 红色
list($h, $s, $v) = rgbToHsv($rgb[0], $rgb[1], $rgb[2]);
echo "HSV: ($h, $s, $v)";

HSV: (0, 1, 1)