Playing with HDR and pano photos
I got up this morning to try some pre-dawn photos from the Horsetooth reservoir dam. I've spent some time each weekend coming up to speed on Photoshop CS3, and I've been wanting to play with panoramas and High Dynamic Range (HDR) photos.
There are a lot of pretty amazing HDR images on Flickr. Some of them look pretty bizarre, but are cool nonetheless. I wanted to try a high contrast shot, where I could get a relatively natural looking image without the harsh shadows. I thought the pre-dawn contrast of residential lights, plus the bright sky against the very dark ground would make for an interesting challenge.
According to Kelby, it is important to capture enough range with multiple exposures that you don't have any areas clipped throughout all the exposures. I thought I'd try 7 images with one baseline exposure, three over-exposed (1-stop each) and three underexposed (1 stop each). My first test shot from the tripod reminded me that I had image stabilization turned on (I *hate* it when I do that). I turned it off and shot the seven images. As I shot the darkest one, I thought that I might still be capturing too much light on the individual town lights and at the horizon, so I kept reducing the exposure by 1 stop and shooting for a total of 11 images. I combined the images into a single, 32-bit per channel HDR image. After reducing this to 16-bits per channel by using local contrast and some curve adjustments, I ended up with this.
There were a couple of other challenges along the way. First, because the lighting was so poor, each exposure was long, and I had the ISO up to about 800 -- this caused some interesting problems with noise and stuck pixels. The HDR process actually reduced the noise across exposures somewhat, and Noise Ninja corrected the rest of it. I used a healing brush on the stuck pixels. Also, there were a couple of cars that were moving on the road in a couple of images, but not in the others. Instead of getting a ghost image, I ended up with some really blown out lights where the cars were. I used a healing brush on these as well.
I think the result is okay. I like the fact that I can see a lot of detail in the dark areas of the photo, without having an extremely unnatural look to the photo.
While I was up there, I walked across the road to face the reservoir on the other side, which was receiving some of the dawn (or pre-dawn) light. I thought this might be a good time to try a panorama. Using Kelby's advice, I selected a consistent aperature for the shot (f/8 in this case), set my focus to manual, metered for the sky, and then set exposure to manual and overlapped the photos by about 20% or so. Photoshop CS3 made combining these photos a snap, and I ended up with a pretty nice shot.
You can see the light coming from behind at a very low angle. Also, due to the long exposure times, you can see that the water is a bit blurred. I'm glad I did this. I need to practice these kinds of shots before my vacation at Lake Powell. I'd like to use these techniques to get some nice vista shots while I'm there.
