PHP - GD editing

<?php
//Report all errors
ini_set("display_errors", "1");
error_reporting(E_ALL);
function imagecolorfilter($im){
    $height = imagesy($im);
    $width = imagesx($im);
    for($x=0; $x<$width; $x++){
        for($y=0; $y<$height; $y++){
            $rgb = ImageColorAt($im, $x, $y);
            $r = ($rgb >> 16) & 0xFF;
            $g = ($rgb >> 8) & 0xFF;
            $b = $rgb & 0xFF;
            $c=($r+$g+$b)/3;
            if($r<$g+10 || $r<$b){$r=$c;$g=$c; $b=$c;}//only red
        imagesetpixel($im, $x, $y,imagecolorallocate($im, $r,$g,$b));
        }
    }
}

if(isset($_GET['source'])){
    $image = filter_var($_GET['source'], FILTER_SANITIZE_STRING);

    $image = imagecreatefromjpeg($image);

    imagefilter($image, IMG_FILTER_MEAN_REMOVAL);
    imagefilter($image, IMG_FILTER_COLORIZE, 10, 10, 10);


    //bluring
    $gaussian = array(array(1.0, 2.0, 1.0), array(2.0, 4.0, 2.0), array(1.0, 2.0, 1.0));
    imageconvolution($image, $gaussian, 16, 0);
    imagecolorfilter($image);

    header('content-type: image/jpeg');

    imagejpeg($image, '', 10);
    imagedestroy($image);
}
?>