Backlight is the light behind the object of interest in a scene. This can be a major problem, especially in cameras with automatic iris control, because the camera will often adjust to keep the bright background within acceptable levels.
Think about a camera aimed at a door at the end of a dark hallway. When someone opens the door and steps into the hallway, the camera will try to compensate for the sudden bright exterior background. The result will be that the person in the doorway appears silhouetted and detail is lost in shadow. In extreme cases, there may be no discernable detail at all. Cameras must have backlight compensation to overcome this situation.
Backlight compensation is composed of camera circuitry that samples a scene and makes an assumption that objects in focus are the objects of interest, and that light levels should be optimized for these objects. Extremely high background light levels are selectively shut down while maintaining optimum levels on the objects of interest.
