A graphics processing apparatus performs tile based compositing operations. Tile metadata includes flag data, such as transparency and/or intensity flag data, indicating whether a given input graphics tile makes less than a predetermined first threshold level of contribution or more than a second predetermined threshold level of contribution to a corresponding output graphics tile. For example, if an input graphics tile is transparent, then its reading from a memory and/or subsequent processing may be suppressed. If a given input graphics tile is opaque, then underlying input graphics tiles that are obscured may have their reading and/or further processing suppressed.