A note on where this fits today: I shoot 100MP medium format, whose sensor holds far more range in a single frame, so I largely don’t need the brackets. I still take them just in case. The explanation below still holds for when they are needed.
All cameras have limitations in how much information they can capture. One of these limits is how much light can be recorded in a single photograph. This “range” of light, from the brightest white to the darkest black is called the dynamic range. Sometimes the difference between the black and white is too much, and the camera cannot capture it all.
This is what a single photograph captured. The brightest clouds and the sidewalk are close to losing their detail, and the shade under the canopy and around the entryway is dark.
Just like panoramas, HDR simply requires taking multiple photographs. However, in this case, the camera is kept perfectly still. This time, we change the length of time the photographed is exposed.
When we shorten the time, the overall image becomes darker. This allows us to get details in the parts that were too bright (notice there is detail in the clouds and sidewalk). Of course, the rest of the photograph is nearly unusable its so dark.
Now that we have the whites. We need to get the detail back in the dark areas. We extend how long we expose the photograph so that the overall image becomes brighter. We now have details in the dark areas. We can start to see inside the building and the entryway doesn’t look so dark.
While three photographs may be sufficient, I usually take at least 5. It just depends how large the range is and how much of that range I want to capture. This range can be quite large when photographing interiors with views outdoors and its bright outside.
One thing that may not be obvious is that its extremely important that whatever you are photographing does not move. Otherwise when the photographs are stitched together, you will end up with what look like “ghosts”. (Yes, software can try to account for this, but the results aren’t as good).
Because of this, my GetOutCast forecast for architecture prefers the absence of wind.
There are a ton of tools out there that will create HDR images for you. I toggle between Photomatix and Photoshop.
