Functional image crop in PHP with GD

imageAutocrop.php

<?php

/**
 * Functional approach of automatic image cropping, pass a file path and a color callback, which evaluates if a color is below the crop threshold or not.
 * @param $path The path to the file
 * @param $colorFilter Clojure, the function takes 1 parameter: $color is the hex value of the color to evaluate
 * Code Example:
 * <code>
 * $newImg = $imageAutocrop($path, function($color) { return $color > 0xF0FFFF || $color === 0;});
 * </code>
 */
$imageAutocrop = function($path, $colorFilter) {

	if(!file_exists($path)) {
		throw new Exception("File not found.");
	}

	$size = getimagesize($path);

	if(!$size) {
		throw new Exception("Not an image: $path");
	}

	switch($size["mime"]){
		case "image/jpeg":
			$img = imagecreatefromjpeg($path); //jpeg file
		break;
		case "image/gif":
			$img = imagecreatefromgif($path); //gif file
		break;
		case "image/png":
			$img = imagecreatefrompng($path); //png file
		break;
		default: 
			$img = false;
		break;
	}

	if(!$img) {
		throw new Exception('Given file is not a valid image.');
	}

	/**
	 * Inner function, used to search for the offsets to crop at.
	 * @param $img The GD resource
	 * @param $colorFilter The callback to evaluate colors
	 * @param $h The height of the image
	 * @param $w The width of the image
	 * @param $xFn Callback to calculate the X-Coordinate to search for each point
	 * @param $yFn Callback to calculate the Y-Coordinate to search for each point
	 */
	$getOffset = function($img, $colorFilter, $h, $w, $xFn, $yFn) {
		for($y = 0;$y < $h;$y++) {
			for($x = 0;$x < $w;$x++) {
				$c = imagecolorat($img, $xFn($w, $h, $x, $y), $yFn($w, $h, $x, $y));
				if(!$colorFilter($c)) {
					return $y;
				}
			}
		}
	};

	$h = imagesy($img);
	$w = imagesx($img);

	$offsetTop    = $getOffset($img, $colorFilter, $h, $w, function($w, $h, $x, $y) { return $x;          }, function($w, $h, $x, $y) { return $y;          });
	$offsetBottom = $getOffset($img, $colorFilter, $h, $w, function($w, $h, $x, $y) { return $w - 1 - $x; }, function($w, $h, $x, $y) { return $h - 1 - $y; });
	$offsetLeft   = $getOffset($img, $colorFilter, $w, $h, function($w, $h, $x, $y) { return $y;          }, function($w, $h, $x, $y) { return $x;          });
	$offsetRight  = $getOffset($img, $colorFilter, $w, $h, function($w, $h, $x, $y) { return $w - 1 - $y; }, function($w, $h, $x, $y) { return $h - 1 - $x; });
	
	$newH = $h - ($offsetTop + $offsetBottom);
	$newW = $w - ($offsetLeft + $offsetRight);
	$newImg = imagecreatetruecolor($newW, $newH);
	imagecopy($newImg, $img, 0, 0, $offsetLeft, $offsetTop, $newW, $newH);
	return $newImg;
};

?>