Monday, January 21, 2008

HDR Headaches

I decided to try a foray into High Dynamic Range Imaging, or HDR imaging, recently. The Wikipedia reference explains the whole process.

In a nutshell, a DSLR's sensor can only capture a portion of the range of light in a scene. By bracketing exposures, the photographer can capture the majority of the range of light in teh field of view. By using applications that combine and tonal map the bracketed images into a single image with the range of all three.

In all, it's a fairly simple process that can result in a wide range of results. A HDR group I read had two recent threads on this particular subject: Thread 1, Thread 2. As you can see from the images in the posts, people have their own interpretations of what an image should look like. Honestly, some of the images I didn't care for and others I really liked.

The point is, HDR photography is pretty subjective because so many manipulations can be applied when generating the HDR image and then in post processing is Photoshop. Incidently, Photoshop is where most of the work on the image occurs.

This tutorial has been really helpful. But there is definitely a well developed skill and high degree of experience and knowledge required to produce these photographs. I'm beginning to get a handle on it, but I need a lot better understanding of the, dare I say this, mathematics behind the process. I've got a lot of reading to do on Sean T. McHugh's website. He has an exceptional series of tutorials on digital photography; it'll take me a month to digest everything he has in those tutorials. However, most of his photographs are done with neutral density filters and are not HDR images. Still, understanding the mathematics will be helpful.

I'd like to learn to produce quality HDR images like the ones referenced in Wikipedia (Photo 1, Photo 2, Photo 3).

After about 20 attempts at producing a good HDR image, I came up with the one above. It's five photos bracketed at 1 stop increments. The correct exposure was 1.5 seconds at f:8. The big glowing blur is the moon. My initial thought was that I could use Photoshop to mask the HDR image and reveal the correctly exposed moon from an additional image in the sequence. But, the long exposures on the negative side of the bracket produced too much of a burned out highlight.

I spent a few more days reading and studying the actual mathematics behind HDR imaging. That has given me a lot more insight into the whole process. I'll post up some more images soon. I still don't have much daylight after I get off work, so the majority of my shooting is limited to the weekends right now.


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