[post revised on 2017-10-21]
Definition and explanation
Before describing different types of “image merging” workflows, I will explain some terms that I will be using in this blog. Today I will explain the meaning of bracketing.
Bracketing consists in acquiring a series of images with different camera settings. The word bracketing comes from the idea that we have a target value for the setting, say exposure, and we acquire images with this exact target setting and settings both at slightly large and slightly smaller values (bracketing both “sides” of the target). At least three images need to be acquired for the meaning to strictly apply, but in some exceptional cases even hundreds images are acquired.
Bracketing is an old term and an old idea, which of course can be used also with film cameras. Some automatic film cameras and advanced digital cameras can automate bracketing, at least for some parameters. Bracketing can also achieved by manually changing the settings through the acquisition of a series of images. Examples of parameters for which bracketing is frequently used: exposure, focus distance, and white balance. In the case of exposure, bracketing can be achieved by bracketing (diaphragm) aperture, shutter speed, or ISO setting.
The most basic approach is to just select the best image from the bracketed series, and use it. What I will discuss in some future posts is the merging of a series bracketed images into a single composite image which is “better” than any of the individual images.
Some examples of bracketing on different image acquisition parameters.
Here bracketing was done using 2 EV steps, in practice the step size used is almost always smaller, frequently as small as 1/3 EV. However, when images are merged, 2 EV is frequently.
The change in the focus plane is more difficult to see than for exposure above, as the subject has a depth of less than one centimetre.
Conclusion: Bracketing makes it possible to take photographs with optimal settings when we are uncertain of the optimal values for these settings.
All illustrations, text and measurements are of my own authorship, and copyrighted.
(c) 2015-2017 Pedro J. Aphalo