Bracketing

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A still camera technique for ensuring correct exposure. To bracket manually, one picture is taken at the estimated exposure setting; another slightly underexposed and a third slightly overexposed. One of the three images typically looks better than the rest. Cameras may also feature automatic bracketing, which takes several different exposures one after the other. Autobracketing is automatic bracketing by using a setting on the camera to take several bracketed shots (in contrast to the photographer altering the settings by hand between each shot).

Types of bracketing

Exposure bracketing

Without further qualifications, the term bracketing usually refers to exposure bracketing: the photographer chooses to take one picture at a given exposure, one or two brighter, and one or two darker, in order to select the most satisfactory image. Many professional and advanced amateur cameras, including digital cameras, can automatically shoot a bracketed series of pictures. Exposure bracketing is indicated when dealing with high-contrast subjects and/or media with limited dynamic range, such as transparency film or CCD sensors in many digital cameras.

When shooting using print film, the person printing the pictures to paper must not compensate for the deliberately underexposed and overexposed pictures. If a set of photos are bracketed but are then printed using automated equipment, the equipment may assume that the camera or photographer made an error and automatically "correct" the shots it determines are "improperly" done.

Focus bracketing

A series of images demonstrating a focus bracket. The image on the left shows a single shot taken at f/11 with the features of the spider closest to the camera. The center image shows the features farthest from the camera. The image on the right shows focus stacking: a sequence of 8 incrementally focused images of the spider assembled to make a composite image in Photoshop. The magnification had to be changed by a factor of 0.5% between each image (first image at 100%, next at 100.5%, next at 101%, etc.).

An animation of the fourteen shots used to create a picture using focus bracketing (on left), next to the final image (right)

Focus bracketing is useful in situations with limited depth of field, such as macro photography, where one may want to make a series of exposures with different positions of the focal plane and then choose the one in which the largest portion of the subject is in focus, or combine the in-focus portions of multiple exposures digitally (focus stacking). Focus stacking is challenging, in that the subject (as in all brackets) must stay still and that as the focal point changes, the magnification (and position) of the images change. This must then be corrected in a suitable application by transforming the image.

White balance bracketing

White balance bracketing, which is specific to digital photography, provides a way of dealing with mixed lighting by having the camera make several images with different white points for one exposure taken, often ranging from bluish images to reddish images.

White balance bracketing doesn't require actual multiple exposures, but merely reprocesses the same raw sensor data with different white balance settings. When shooting in a camera's RAW format (if supported), white balance can be arbitrarily changed later, so white balance bracketing is unnecessary.

Flash bracketing

Flash bracketing is a technique of working with electronic flash, especially when used as fill flash in combination with existing light. The amount of light provided by the flash is varied in a bracketed series in order to find the most pleasing combination of ambient light and fill flash.

Autobracketing

Autobracketing is a feature of some more advanced cameras, whether film or digital cameras, particularly single-lens reflex cameras, where the camera will take several successive shots (usually three) with slightly different settings. Later, the best-looking pictures can be picked from the batch. When the photographer achieves the same result by changing the camera settings between each shot, this is simply called bracketing.

The most common type of autobracketing is exposure autobracketing, where the camera is set to capture the same image several times with slightly different exposure settings, both over-exposed and under-exposed (lighter and darker) compared to the current setting on the camera. Depending on the camera, the difference between each of the autobracketed shots could be anywhere up to two stops in each direction, in half-stop or one-third stop increments.

Cameras can perform autobracketing by adjusting either the shutter speed or the aperture setting, but not both at the same time. Exposure autobracketing is most commonly used with color reversal film (slide film) because of its small exposure latitude compared with print film (which has a wide exposure latitude) and digital cameras (which enable the photographer to review the captured image). In digital photography, autobracketing is convenient to shoot pictures for High dynamic range imaging.

Another common form of autobracketing is white balance autobracketing; this applies only to digital cameras, not to film cameras. This setting causes the camera to capture the same image several times with slightly different white balance settings, with both higher and lower color temperatures (bluer and redder) compared to the current setting on the camera.

Bracketing

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