SimpleImagick: simple PHP wrapper for ImageMagick

<?php
class SimpleImagick {
    public $image;

    public function __construct($filename)
    {
        $this->load($filename);
    }
    public function load($filename)
    {
        if (!class_exists('Imagick')) throw new Exception('Imagick not found');
        $this->image = new Imagick();
        $ping_result = $this->image->pingImage($filename);
        $this->image->readImage($filename);
    }
    public function save(
        $filename,
        $image_type = IMAGETYPE_JPEG,
        $compression = 75,
        $permissions = null
    ) {
        $this->image->setCompressionQuality($compression);
        $this->image->setFormat($image_type);
        $this->image->writeImage($filename);
        if ($permissions != null) {
            chmod($filename, $permissions);
        }
    }
    public function output($image_type = IMAGETYPE_JPEG, $compression = 90)
    {
        $this->image->setCompressionQuality($compression);
        $format = $this->image->setFormat($image_type);
        header('Content-type: image/'.$format);
        echo $this->image;
    }
    public function getWidth()
    {
        return $this->image->getImageWidth();
    }
    public function getHeight()
    {
        return $this->image->getImageHeight();
    }
    public function resizeToHeight($height)
    {
        $this->image->thumbnailImage(null, $height);
    }
    public function resizeToWidth($width)
    {
        $this->image->thumbnailImage($width, null);
    }
    public function scale($scale)
    {
        $width = $this->getWidth() * $scale / 100;
        $height = $this->getheight() * $scale / 100;
        $this->image->scaleImage(round($width), round($height));
    }
    public function resize($width, $height)
    {
        $this->image->scaleImage($width, $height);
    }
    public function crop($width, $height)
    {
        $src_x = round(($this->getWidth()  - $width)  / 2);
        $src_y = round(($this->getHeight() - $height) / 2);
        $this->image->cropImage($width, $height, $src_x, $src_y);
    }
    private function setFormat($image_type)
    {
        switch ($image_type) {
            case IMAGETYPE_JPEG: $format = 'jpeg'; break;
            case IMAGETYPE_PNG:  $format = 'png';  break;
            case IMAGETYPE_GIF:  $format = 'gif';  break;
            default:             $format = 'jpeg';
        }
        $this->image->setImageFormat($format);
        return $format;
    }
}