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 with slightly different settings. The images may be automatically combined, for example into one high dynamic range image, or they may be stored separately so the best-looking pictures can be picked later from the batch. When the photographer achieves the same result by changing the camera settings between each shot, this is simply called bracketing.
Parameter altered
The bracketing is typically for one specific parameter:
Exposure
Exposure autobracketing is the most common form. In this, the camera is set to capture the same image several times with different exposure settings, both over-exposed and under-exposed compared to the current setting on the camera, which may already include exposure compensation. Depending on the camera, the difference between each of the autobracketed shots could be anywhere from one-quarter up to three full stops in each direction, in full, half, third or quarter stop increments, ranging from two up to nine shots in series. Sometimes it is possible to either define the order, in which the shots will be taken, or to give an offset as a start-point of the bracketing series. More sophisticated equipment allows auto-exposure bracketing to be combined with timer and intervalometer functions as well. Cameras can perform autobracketing by adjusting either the shutter speed or the aperture setting. In programmed exposure mode, many cameras will alter both parameters at the same time. Some cameras allow to swap the parameter used for shifting in manual mode. Digital cameras may also alter the ISO setting if auto-ISO is enabled. Exposure autobracketing is most commonly used with color reversal film because of its small exposure latitude compared with print film and digital cameras. In digital photography, autobracketing is convenient to shoot pictures for high dynamic range imaging.
Flash
Automatic flash bracketing is typically performed by altering the flash output of a connected dedicated flash accordingly. Using non-dedicated studio flashes, for example on the PC socket, flash bracketing can be carried out by altering the aperture, however, this will also affect ambient light and the depth of field. If, in manual mode, a camera defaults to alter the shutter speed, it might be necessary to swap the parameters used for shifting in order for the camera to alter the aperture instead. Since the flash may need time to recharge between the shots, some cameras fall back to single-advance drive mode during auto flash bracketing, even if they are otherwise configured for continuous-advance drive.
ISO
Automatic ISO bracketing simulates exposure bracketing by altering the ISO or signal gain prior to conversion of the image to JPEG or other image file format. The actual exposure values are usually kept constant. Auto ISO bracketing is not a common feature of digital cameras.
White-balance
Another common form of autobracketing is white balance autobracketing ; this applies only to digital cameras, not to film cameras. This function provides a way of dealing with mixed lighting by having the camera take one shot and process the raw sensor data several times for slightly different white point settings, with both higher and lower color temperatures compared to the current setting on the camera. Typically, the amount of offset can be configured. Since shooting in a camera's raw format the white balance can be arbitrarily changed in postprocessing as well at a later stage, white balance bracketing is particularly useful for reviewing different white balance settings in the field.
