Laurie asked about HDR images in my first post on my London trip yesterday. Here is a very brief explanation on making HDR images.
HDR stands for High Dynamic Range and is a technique for manipulating digital photographs in a way that it shows a wider dynamic range of exposures. The simplest way to describe is this: you take three identical shots of a picture with different exposure settings and then use a software to tone map the images into a single image which combines the best of each of the three images. Know what I mean?
I just went out this afternoon to take some pictures to demonstrate this technique. Here is the typical picture I took with my camera with the setting set to “P” (auto mode). The picture is not bad. However, you notice the following … the tree at the back is under exposed and looked dark. The pine needles on the ground were over exposed giving a light orangey tone and the grass in the background was over exposed.
By manipulating the picture I get the following results: The tree in the back, the pine needles on the ground and the grass in the background is now properly exposed. Can you see the difference? It’s kind of hard to see the real difference with this daylight shot. So, how was this done?
Well, like I said, I take three shots of the scene with the following stops -2, 0 and +2. My camera is equipped to take such Exposure Bracketed shots. Basically, I take one shot with 2 stops under exposed, one at normal exposure and another with 2 stops over exposed … like this:
I then used a software to generate and tone map the three images into one. I used a software called Photomatix (try googling photomatix and download a trial copy) to tone map the images. It’s really simple.
Here is another set of pictures taken a moment ago of my desk. See the difference. With the HDR Image you can see the house outside the window, the carpet below the desk and the natural warm glow of the table top. You may click on each of the images below to get a bigger size image.
What is more dramatic is with shots taken at low light. See this one I took of the Eiffel — ain’t it gorgeous?
But wait, there are a little bit more to it. A few quick remarks:
- You will want to use a good sturdy TRIPOD to take identical pictures. Although the software is able to align, to a certain degree, hand held shots, nothing beats using a tripod.
- HDR is good only for stationary pictures … i.e. if you have people moving in between the three shots, you will get “ghosts”.
- Your camera should have the feature to fix the aperture. It is because you want all three shots to be taken at the same aperture (but with different time exposure). In other words, it should have a manual mode.
- You want to set the ISO setting to something like 100 or 200. Noise at high ISO shows badly on HDR images.
So, Laurie, does this help? If you want to find out more, just google either “high dynamic range” or “HDR”.