Basically you're taking a number of exposures (3 or more) and combining them. Each shot is taken at a different exposure, one underexposed, one overexposed, one correctly exposed. This allows you to get better detail in highlights and shadows.
I've heard of HDR being done with 1 exposure, but haven't seen it. You can do more than 3 exposures as well, in some cases people have done 5, 7 or more.
|