A system for generating images for display, the system comprising a content identification unit operable to identify content to be displayed, an overlay identification unit operable to identify an overlay to be applied to at least a portion of the content to be displayed, a rasterization rate determining unit operable to determine, in dependence upon the identified overlay, a rasterization rate to be applied to each of two or more areas of at least a frame of the content to be displayed, a rendering unit operable to render the content to be displayed in accordance with the determined rasterization rates, and an overlay applying unit operable to generate an image by applying the overlay to the rendered image.