/**
 * Used to only save a specific part of the full image.<br/>
 * Leave any value to NULL to disable it.
 * @param integer|null $left
 * @param integer|null $top
 * @param integer|null $width
 * @param integer|null $height
 */
public function set_crop($left=null,$top=null,$width=null,$height=null){
	$this->crop=array($left,$top,$width,$height);
}

/**
 * Set the output image file format.
 * @param string|null $format File format (see FMT_* constants).
 */
public function set_format($format=null){
	$this->format=$format;
}

/**
 * Number of milliseconds to wait for javascript to load.
 * @param integer|null $delay Delay in milliseconds, or a default of 200ms if null.
 */
public function set_delay($delay=null){
	$this->delay=$delay;
}

/**
 * Set authorization credentials (for HTTP Authentication only!!).
 * @param string|null $username The username.
 * @param string|null $password The password.
 */
public function set_credentials($username=null,$password=null){
	$this->login=($username || $password) ? array($username,$password) : null;
}

/**
 * Set output image quality (for lossy formats), lower quality *might* decrease file size.
 * @param integer|null $quality The quality between 0(low-quality) and 100(full quality).
 */
public function set_quality($quality=null){
	$this->quality=$quality;
}