Originally Posted by
DanK
Since you are new to this, I think it's worth pointing out a distinction. Sometimes you have an situation where the image doesn't exceed the dynamic range of the sensor but where parts of the image are squished into the top or bottom of the histogram. I think that's what Geoff is referring to. The method he describes is one of several ways to try to make the best of this situation. However, sometimes you have a situation where the range of brightness in the scene exceeds what your camera can handle, and some of the image is pure black or pure white ("clipped" or "blown out"), with no data recorded other than the value for black (0) or white (255). In that case, Geoff's method won't work because you can't create detail where none exists. The solution in that case is to bracket exposures, regardless of which method you use to create the composite.
One fine point is that if you shoot raw, sometimes what appears to be blown out isn't quite, and you can recover detail that looked like it was lost. Geoff's method can work then. But when an area really is clipped and there are no data, there are no data.