PHP-GD调色技巧：色相饱和度调整方法

function hslToRgb($h, $s, $l) {
   $c = (1 - abs(2 $l - 1)) $s;
   $x = $c (1 - abs(fmod($h / 60, 2) - 1));
   $m = $l - $c / 2;
   if ($h < 60) {
      $r = $c; $g = $x; $b = 0;
   } else if ($h < 120) {
      $r = $x; $g = $c; $b = 0;
   } else if ($h < 180) {
      $r = 0; $g = $c; $b = $x;
   } else if ($h < 240) {
      $r = 0; $g = $x; $b = $c;
   } else if ($h < 300) {
      $r = $x; $g = 0; $b = $c;
   } else {
      $r = $c; $g = 0; $b = $x;
   }
   return [
      round(($r + $m) 255),
      round(($g + $m) 255),
      round(($b + $m) 255)
   ];
}

function adjustHueSaturation($image, $hueShift = 0, $satAdjust = 0) {
   $width = imagesx($image);
   $height = imagesy($image);
   for ($x = 0; $x < $width; $x++) {
      for ($y = 0; $y < $height; $y++) {
         $colorIndex = imagecolorat($image, $x, $y);
         $r = ($colorIndex >> 16) & 0xFF;
         $g = ($colorIndex >> 8) & 0xFF;
         $b = $colorIndex & 0xFF;

         list($h, $s, $l) = rgbToHsl($r, $g, $b);

         $h = ($h + $hueShift) % 360;
         $s = max(0, min(1, $s + $satAdjust));

         list($nr, $ng, $nb) = hslToRgb($h, $s, $l);
         $newColor = imagecolorallocate($image, $nr, $ng, $nb);
         imagesetpixel($image, $x, $y, $newColor);
      }
   }
}