What is HDR Photography?

by Al Hannigan on August 3, 2006

What in the world of digital is an HDR image? Oh … well now, here it is. High Dynamic Range Image ! Wow, now that clears up everything doesn’t it?

Duhhh, not really.

Well, let’s see if it can be turned into something that doesn’t require a dictionary, encyclopedia and a PHD in ??? …. well, in something related.

Note: If you are technically adept, familiar with this HDRI technology, then please don’t read what follows … and if you do read it, please don’t leave comments about what a feeble attempt I am making to explain this. It is not a tutorial, and there are links provided for more technical and accurate info on HDRI.

Actually, it is not all that difficult to understand HDR in simple terms, although actually doing it does present a few more challenges.

Dynamic range for our purposes here refers to the brightness of light in a scene from its highest intensity (the whites, or highlights) to its lowest intensity (the blacks or shadows). When you have a scene that contains a very large range of light intensity, that would be considered a high density range scene.

High dynamic range imageClick on this image to see a larger version.

In this example from Wikipedia the interior of this scene with the light streaming through the stained glass windows exceeds the range of brightness values that can be reproduced in a photograph or on a computer monitor.

The six individual exposures used to create the image above. Exposure times from top left are: 1/40sec, 1/10sec, 1/2sec, 1sec, 6sec, 25sec.

A long exposure to render the details and tonal values of the interior would totally blow out the stained glass windows … they would become white blobs with little or no color … as demonstrated in this series of 6 exposures.

The sixth image (lower right) does an excellent job of showing the wood interior, but look what happens to the windows. The shorter exposures that bring out the details and colors of the stained glass windows render everything else in the scene as black.

So how does a photographer create an image like the one above? It’s done using a process known as HDR imaging … basically, taking a series of bracketed exposures and then merging them together to produce a single final result that approximates the brightness range of the actual scene itself.

Because normal computer monitors and photographic printing papers cannot come close to reproducing the full range of brightnesses we can see with our eyes, much less the actual brightness range of light itself, HDRI is a compromise solution that attempts to create a visual likeness of what we see when viewing high dynamic range scenes.

Some common situations you’ve all likely encountered are brilliant sunsets, landscapes with dramatic cloud formations and even those brilliant night scenes that present a real challenge to photographers who attempt to capture such images.

More examples of HDR photography :

Click on the images to see the larger versions
High dynamic range image

  • HDR image by: Dean S. Pemberton
  • Canon 350D
  • f/8, ISO100
  • 18mm
  • 8 Exposures: 30″ 20″ 12″ 5″ 3″ 1″ 1/4″ 1/20″

HDR image of San Francisco at nightNighttime in San Francisco taken from an 8th floor hotel room using 3 exposures bracketed two stops apart. by Mathew Spolin

While some may write off HDR technology as the “latest hokey gimmick”, to me it opens up a potential level of creative photography that will be both challenging and exciting.

Having learned the Zone System as taught by Ansel Adams, as well as some of its variations pioneered in the early days of B&W photography, I see some strong similarities.

For those not familiar with the zone system, it was basically a way to transfer scene brightness to photographic printing paper in such a way as to make full use of the paper’s tonal ranges from pure white to pure black, while retaining the desired details in both the highlights and shadows.

When a scene had a wide range of brightness values (zones, or a high dynamic range) Adams would use a combination of exposure and processing to “compress” these values. This would allow him to reproduce the scene within the limits of photo paper.

The concept of “expose for the shadows, develop for the highlights” was perfected by Adams’ work in this area.

The Zone System could also be applied to expand the brightness range of a low contrast scene … like an overcast day for example … and produce more vibrant prints that still retained the “mood” or “character” of the light that was present.

Prints created with the Zone System formula are beautiful to see in real life. Reproductions can’t come close to revealing the true beauty and rich tonal ranges in the originals produced by those who truly mastered this concept.

Makes one wonder if these early pioneers were accused of messing with “hokey gimmicks”.

This compression or expansion control was one of the first things I learned when I began my training in B&W photography and why I came to love the sessions I spent in the darkroom.

Today, my darkroom is a computer and photoshop … admittedly, not quite as appealing as those early days in my chemical darkroom. But with the creative potential of HDR images, my digital darkroom promises to be very interesting.

Once I become more skilled in the technical aspects needed to create these images, I can begin to explore the full creative potential it offers … which is the main reason any wannabe artist must suffer through mastering technical skills in the first place.

For more on HDR imaging click on the links below or do a search for HDR photography.

Wikipedia.org-HDRI

Flickr: The HDR Pool

HDR Shop Home – HDR shop tutorials. They also offer a free trial download of their HDR Shop software.

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{ 1 comment }

1 Di October 6, 2009 at 12:58 am

I’m a very amateur photographer, but I’ve been seeing a ton of stuff about HDR lately, most of which is nonsensical to me. Thanks for the simple explanation.

Also congrats on the cute grandbaby on your front page. I just got my first nephew this year 😀

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