Complex sentence: Vignetting is sometimes used for creative effect (e.g. to draw attention to the center of the frame), and are then deliberately introduced by the photographer by the use of special filters or post-processing procedures.
Split into simpler sentences: Vignetting is sometimes used for creative effect (e.g. to draw attention to the center of the frame). It is deliberately introduced by the photographer by the use of special filters or post-processing procedures.