ce, also known as luma), colour (chrominance, also known as chroma) and the shapes and patterns of objects within our field of vision. Our eyes have a remarkable dynamic range and can tolerate and process visual information in anything between direct sunlight (+100 000 lux) to a moonlit night (fractions of a lux). There are various tricks that help us increase this dynamic range, for instance we just see things in black and white at very low light levels. We also have autowhite colour balancing as part of our natural visual tool set. White has a green tinge in daylight, a yellow tinge under fluorescent light and an orange tinge under incandescent light, but the tinge disappears courtesy of our natural image processing chain. These dynamic range and colour-capture and colour-correction capabilities have to be recreated in artificial image processing systems. In addition, our natural image processing system is incredibly efficient at sorting out the entropy in the viewed image (the useful information) and redundant information that can be effectively ignored and discarded. This process is also adaptive. If you are hurtling down a hill on a mountain bike, your brain will just be processing the visual information relevant to the task in hand (staying on the bike and not hitting any trees in the process). These compression capabilities and adaptive pattern recognition capabilities have to be recreated in artificial image processing systems. We are also naturally adept at pattern recog- nition, recognising a face in a crowd for example. These pattern-recognition capabilities have to be recreated in artificial image processing systems. Each component in an artificial image processing chain has a required function and a 'wanted effect'. Unfortunately, most components also produce 'unwanted effects' that introduce im- pairments. We can, however, go some way towards cancelling out or at least concealing these effects, as described in the following sections. 8.2.1 The Lens The wanted effect in a lens is optical quality, the