In the xerographic process, the photoreceptor serves as an intermediate receptor of the exposed image from the original document. It transfers this image onto paper to produce copies as we know them. Much like the film in a camera. In fact the difference between OPC and selenium photoreceptors is best explained using the same analogue. Just like the different chemical compositions in films of different brands, OPC and selenium are but different chemical formulations applied on an aluminium cylinder to form the photoreceptor. In black-and-white copiers this difference in composition has no discernible impact on copies though colour copiers almost invariably use OPC due to its sensitivity to a wider range of colours.