High Dynamic Range Images Made Easy with Photomatix™
From the early days, one of the things that intrigued me about digital imaging was the possibility of displaying a wider dynamic range in photography. Our tastes can tend toward contrasty images, partly because they are often more interesting.
The human eye is a pretty amazing piece of
technology and can see a very wide range of light (“dynamic range”) from very bright to almost complete darkness, even in the same scene. No photographic medium is yet capable of capturing and displaying that range. I say yet, because I believe that in my lifetime, I will not only see it done, but we will see digital sensors routinely installed in cameras that will capture that range. But we are not there yet.
Photographers think in terms of either “F stops” (if you are old like me), or the more modern and probably more technically correct terminology, “Exposure Values” (EV). Either way, the concept is the same. It is a measurement of the quantity of light which is allowed to strike the sensor or film surface (see the Tutorial, “How F Stops Work”). Film was capable, at best, of capturing maybe 3-5 full stops of EV, depending on the condition. Modern digital sensors may be able to add about 2 more. If you have ever experimented on a very contrasty scene, you know that isn’t very much. Indeed, it is rarely enough.
With film technology, capturing these of scenes was, at best, a compromise. Depending on the type of film you used, you had to choose either a highlight or a dark area that was important in the scene and let the other areas fall wherever they did. Sometimes, the result was disappointing. Often it was just not possible to capture the scene.
One method that could be used with some success was the combining of more than one image, using the “best” from each. This would allow you to make a “correct” exposure of the dark areas and another “correct” exposure of the bright areas, letting the other parts fall where they might, even at unacceptable levels. In the days of film, this was virtually impossible without sophisticated darkroom equipment and skills, or expensive custom lab work, in which you had to rely on the technician for interpretation. There was a technique called “contrast masking” or “silver masking” in which the darkroom technician would make, in effect, another “negative” that would create a mask of certain areas of the photograph. This would allow the light from the darkroom lamp to fall on some parts of the photograph more strongly than others (a very sophisticated “dodge and burn” process). I have one photograph that a very talented lab in California “saved.” But it still isn’t up to what I could do today with a digital image in Photoshop.
But these techniques didn’t really change the dynamic range equation. Until digital capture came along. We now have the technology to display greater dynamic range (the ability for sensors to capture it is coming — believe me). In the early years, working in Photoshop to extend the range was very difficult and much of it was done by eye. There are some unbelievably sophisticated processes “under the hood” of Photoshop. They are mostly beyond the capability of my own grey matter. They also take some serious computing power in many cases.
Some pretty talented minds and artists over the years developed blending, masking, and combining techniques. I have tried my hand at some of them. The “downside” is that it takes a long time to learn and develop the techniques, and you can then spend hours and hours on one photograph, trying to get things right. A few years back, several talents in the industry started to look more seriously at the concept of capture and display of so-called “High Dynamic Range Imagery” (known alternately as “HDR” or “HDRI”). Over those years, a couple of them have developed software for combining images that does all the “math” under hood for us. Last Winter, I decided it was time to start learning about HDRI. I bought and read a couple books (The HDRI Handbook, Christian Bloch, Rocky Nook Publishers, 2007; and Complete Guide to High Dynamic Range Digital Photography, Ferrell McCollough, Lark Books, 2008) from cover to cover, and on my last couple outings, purposefully took images designed to be combined at a later time.
There are a number of available HDRI softwares available. Photoshop actually has an HDRI algorithm built in. No surprise there. The surprise is that unlike almost all of the rest of PS, it isn’t very good! I suspect what will happen is that sooner or later, as they have done in other cases, Adobe will buy one of the available technologies and build it into Photoshop. There are two popular HDRI programs in use by many photographers today, FDR Tools and Photomatix. I liked the look of the FDR Tools in the books I read. To me, the results shown in the books seemed more “photorealistic” (if that term has any useful meaning). But I found the user interface to be clunky and difficult to use.
Both FDR Tools and Photomatix have downloadable trial versions, which I have tried. I have settled, or now, on Photomatix. The trial version leaves a “waternark” on the photo. I have left that on the illustrative photo here, so you can see what you get when you download the trial version. When you purchase the software, you are given a license key, which removes the watermark.
The first of these two shots appears severely “overexposed” and the second, severely “underexposed.” But both of them have parts of the scene that are properly exposed. That is the compromise. Neither the digital sensor in my Nikon D200, nor any film I ever shot, could come close to capturing this scene the way my eyes saw it that bright, sunny morning. But the HDRI result does!
I won’t spend any more time here talking about how it works. If you go to the D-TV site which is linked here, Matt Kloskowski offers a short, very good, video tutorial on Photomatix which is well worth watching. After a very quick run-through of just one image with Photomatix, I am persuaded. I bought the license key, and am looking forward to making more images from my “saved” collection of exposures.
I hope you found this review interesting and useful. I would love to hear your comments and experiences with HDRI, the software you use, and what you like and dislike about it.