This control works at the other end of the brightness scale, and can reduce the brightest areas only. With most digital images it’s usually possible to bring out more detail of darker under-exposed areas than it is to recover detail in over-exposed areas. In other words it’s better to have under-exposed images than over-exposed ones. For more information on this control see the Shadows and Highlights Brightness tutorial.
Sometimes called Cross-process, this effect simulates a photographic processing technique which historically used the ‘wrong’ chemicals to develop film - thus resulting in some dramatic or less dramatic (depends on the values you set) contrast and saturation effects. Sometimes referred to as a ‘faded old-world photo’ look. Use the slider to experiment.