Fill flash is a photographic

Photography

Photography is the art, science and practice of creating durable images by recording light or other electromagnetic radiation, either electronically by means of an image sensor or chemically by means of a light-sensitive material such as photographic film...

 technique used to brighten deep shadow areas, typically outdoors on sunny days, though the technique is useful any time the background is significantly brighter than the subject of the photograph, particularly in backlit

Backlighting (lighting design)

Backlighting refers to the process of illuminating the subject from the back. In other words, the lighting instrument and the viewer are facing towards each other, with the subject in between. This causes the edges of the subject to glow, while the other areas remain darker. The backlight can be a...

 subjects. To use fill flash, the aperture

Aperture

In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture of an optical system is the opening that determines the cone angle of a bundle of rays that come to a focus in the image plane. The aperture determines how collimated the admitted rays are,...

 and shutter speed

Shutter speed

In photography, shutter speed is a common term used to discuss exposure time, the effective length of time a camera's shutter is open....

 are adjusted to correctly expose

Exposure (photography)

In photography, exposure is the total amount of light allowed to fall on the photographic medium during the process of taking a photograph. Exposure is measured in lux seconds, and can be computed from exposure value and scene luminance over a specified area.In photographic jargon, an exposure...

 the background, and the flash

Flash (photography)

A flash is a device used in photography producing a flash of artificial light at a color temperature of about 5500 K to help illuminate a scene. A major purpose of a flash is to illuminate a dark scene. Other uses are capturing quickly moving objects or changing the quality of light...

 is fired to lighten the foreground.

Most point and shoot camera

Point and shoot camera

A point-and-shoot camera, also called a compact camera, is a still camera designed primarily for simple operation. Most use focus free lenses or autofocus for focusing, automatic systems for setting the exposure options, and have flash units built in....

s include a fill flash mode that forces the flash to fire, even in bright light.

Depending on the distance to the subject, using the full power of the flash may greatly overexpose the subject especially at close range. Certain cameras allow the level of flash to be manually adjusted e.g. 1/3, 1/2, or 1/8 power, so that both the foreground and background are correctly exposed, or allow an automatic flash exposure compensation

Exposure compensation

Exposure compensation is a technique for adjusting the exposure indicated by a photographic exposure meter, in consideration of factors that may cause the indicated exposure to result in a less-than-optimal image. Factors considered may include unusual lighting distribution, variations within a...

.