(PECL imagick 2.0.0)
Imagick::contrastImage — Change the contrast of the image
$sharpen
   )Enhances the intensity differences between the lighter and darker elements of the image. Set sharpen to a value other than 0 to increase the image contrast otherwise the contrast is reduced.
sharpenThe sharpen value
   Restituisce TRUE in caso di successo.
  
Lancia una ImagickException in caso di errore.