When we fish, we like to take pictures. For many, the grip -and-grin is the favorite shot. And, since trout live in beautiful places we also snap the scenes we see, to remember and share the beauty with our friends & family. However, many times the photo of the river scene is not as I remembered it. The exposure is not correct. Either the sky is way too bright or the sky is OK, but the ground is dark. Obviously, getting a better camera will fix that.
The new camera didn’t fix the problem.
I was running into a limitation of the “dynamic range” of the digital sensor. The dynamic range refers to the range between the darkest and brightest portions of the image. I learned that my new camera has a dynamic range of about 5 or 6 stops, while human vision has a range of 11 stops. That means the range between bright & dark that I can see with my eyes is twice what my camera can record.
The fancy new camera gave me a variety of options to choose the exposure, but the fundamental limitation of the dynamic range was still present.
One way around this limitation is a technique called “High Dynamic Range” Photography, or HDR for short. This technique involves taking multiple photos, at different exposures, and combining them in software on your computer.
Here are the 3 images that comprise the image above. Notice that in the first one, the river bank detail is present, but the sky is way over exposed. In the last, the sky is properly exposed, but the river banks are too dark . This sequence was taken at F8, with shutter speeds of 100, 350, and 1000. This is a great application for aperture priority mode (Av), and automatic exposure bracketing (-2, 0, +2).
The program that combines the images is called Photomatix. It uses a technique called tone-mapping to process all three photos and create a single image with the best parts of each. You can try this your-self, Photomatix can be downloaded and used for free, but it puts a watermark in the resulting photo until you purchase the unlock code.
I learned this technique from a really cool site called Stuck In Customs, by Trey Ratcliff. He wrote a step by step tutorial on his site, which includes a discount code to use if you purchase Photomatix.
There are other ways to combine multiple exposures using Photoshop and masking layers, but that is another blog post.