High Dynamic Range Imaging, or HDR, is an interesting concept that has come with the advent of Photoshop and digital imaging, specifically when Adobe released it’s built in “merge to HDR” function in 2005 with Photoshop CS2. Explaining what Dynamic Range is would take a long time. But basically, it is a scene’s range in brightness from completely black to the completely bright. For Ansel Adams fans, it’s Zone 0 to Zone 9. HDR imagine could roughly be translated to the traditional B+W photography and printing techniques of dodging and burning although there are some differences.
Let’s talk about why HDR imaging came about. Photography is an often frustrating give and take experience in getting a exposure. If you have one part of your picture perfectly exposed, another part may be under or over exposed. An example: Imagine someone under a tree when it is bright outside; obviously it will be darker under the shade than scenes not under the shade. If you properly expose the person under the shade, then everything not under the shade will be overexposed. This may seem confusing for those not immersed in photography because our eyes are amazing and see a broad dynamic range of light with no problem, so you may not have observed this. But on film, it is a problem.
Take the below as an example. The middle image “n” is the original photo. The exposure is relatively balanced. But the sky is a little too bright, and the subject, Andrew Brackman, a little too dark. “N-1” (read as “n minus one”) is a one f/stop darker. That is, it is one half as bright as the original photo. The sky and field-house in the back is now at the proper exposure, but Brack is too dark. “N+1” is one f/stop brighter, or twice as bright as “n”. Now Brack is at the proper exposure but the sky is blown out to a white where there is no discernible detail. So we have multiple pictures where the exposure is right is some areas and bad in others. The miracle of HDR puts all the photos together and more or less flattens the dynamic range to get rid of the dark and bright areas.
(Side note: The different exposures were created from one Canon Raw file; the exposure was manipulated in the software to create 3 different files. It would be impossible to take multiple exposures when doing action scenes.)