High dynamic range photography by Michael Williams

Written in August, 2007

I walked into a photography shop in Paris in 2005 and saw a photograph of the Italian coastline that looked almost three-dimensional. I thought it might have been taken with a large format camera because of the detail in both highlights and shadows, but the shopkeeper informed me it was a technique called high dynamic range photography and tone mapping. His English was better than my French but I did not understand much else he said about this technique.

Therefore, I began to study this technique in detail in December of 2006. The purpose of this article is to introduce the concept to some who may not be familiar with it. I would like to impress upon everyone how easy it is to do, and how much it can enhance certain kinds of scenes that photographers take. I also believe it has commercial as well as artistic value. While it has been used for several years now in Europe, it is now increasing its popularity in the United States, South America, Australia and Japan. I am a member of an international HDR listserv and Americans are definitely in the minority here.

I am not going to get into a debate about whether Photoshop CS3 version is better than the stand-alone Photomatix version that I purchased last January for $99. Photomatix was designed and is maintained by a French company called HDRsoft, which develops software in the field of high dynamic range imaging for photography. The first version of Photomatix was released in July 2002.

So what? What can it do? All photographers know that typically when you photograph high contrast scenes you get blown out highlights and ugly shadows. This is because of the tonal ratio between the brightest and darkest parts of the scene, a ratio that can be as high as 100,000:1. Try taking a photo in your kitchen on a bright day and expose for the interior of the house. You know what happens. The windows will be blown out, and if you try to expose for the windows, the room will be dark. There are some traditional methods photographers use to ameliorate this kind of situation, but time does not permit discussing here.

By taking several shots of the same scene at different exposure ranges, you can reduce if not eliminate this contrast using the HDR-tone mapping technique. Here’s how:

1. Mount your camera on a tripod.

2. Set your camera to manual exposure mode. Select the appropriate aperture for your scene (e.g. f/8 or less if you need more depth of field) and I use the lowest ISO settings on my camera, which are 100 for Nikon’s D200 and 200 for Nikon’s D300.

3. Keep a constant aperture and ISO. Control image exposure by changing the shutter speed only. Measure the light in the brightest part of the scene and the darkest part of the scene. (I use the spot metering mode on the camera to take these measurements. There are a number of ways to do it including using Av mode.)

4. Determine the number and value of exposures necessary. For this, use the exposure time measured to give you the brightest source image from your measurements in step 3. (A little overexposure is likely here). Multiply this number by four to find the next exposure with a stop spacing of 2 exposure values. Multiply by 4 in successive exposures until you pass the exposure that will give you the darkest source image, again based on your measurements. (A little underexposure is likely here.)

The suggested exposure increment is +/-2 for optimal exposure range, although I use less (never more) when experimenting sometimes. For typical outdoor scenes, three exposures may be all that is needed. Let us say you are shooting a statue of George Washington outdoors. Let’s say we noted from our measurements that our scene has a range of tonal values from 1/30 of a second to 1/500 of a second.

I do this manually by multiplying the exposure values in my head by a factor of four (remember you are trying for a range of 2 exposure increments for each exposure). 1/30x4= 1/120 (nearest shutter speed is 125). That will become the second exposure. Multiply 1/125x4= 1/500, hence the third and final exposure for this scene. Yes, you can use your camera’s auto exposure bracket if your camera offers a range of +/-2 exposures. Be sure to check your histogram to make sure you are covering the entire tonal range of the scene.

With a little practice and experimentation that is about all there is for the first part. Now using some sound digital workflow techniques, be sure to keep your differently exposed source images in a folder correctly labeled so you have them separated from other source images.

To create your final HDR photograph using Photomatix, you will have to do the following two-step process, which I have simplified, but is effective even if you never used the other aspects which time does not permit me to get into in this article.

1. The first step is to merge your differently exposed source images into a single 32-bit HDR image. Because of its high dynamic range, a true 32-bit HDR image will not display properly on conventional monitors. Nor will they print nor do much of anything else.
2. In the second step, this 32-bit HDR image is then processed, or ‘developed,’ via the tone-mapping tool. This tool allows the dynamic range captured in the HDR image, and produces an image, which can be properly displayed and printed on conventional LDR monitors and printers using 8-bit jpeg.or 16-bit tiff. images.

I would say emphatically that after tone mapping an image, it is still necessary to edit the image further in Photoshop or some other editing program. Whenever I have not done so, I have not gotten optimum results. This program is far from perfect. Experimentation and many updates to this program in the past two years have made me realize there is much more to this technique to be learned. It is not a cure all for photography any more than any other technique. Sometimes you want high contrast and shadows. Sometimes you do not want images to look tone mapped.

I have left out many things in this article but the essentials are all here. The rest can be learned and there is lots of information on this subject. I have created several binders filled with articles and documentation already. Please remember that I am not a technical person by any means and that I spent a great deal more time studying this technique than many of you would have to do to use it effectively. I consider myself a creative and lucky photographer, so if I can do this anyone can.

NOTE: Both images are good example of HDR. The first one I shot one very bright Sunday in an old and dark parking garage in downtown Macon. It may not be particularly interesting, but you can see how it handled the exposure issue.

The second one is a photo of Manarola, Italy, that won 1^st place in the scenic class in the National Fair this year. It was also judged print of the year in the PSA print competition for 2007.