You all have at sometime seen a photo where the sky is overexposed and the rest of the image is well exposed, or opposite. And you may have experienced the difficulty of taking a well exposed photo without overexposing the sky and light areas, or underexposing dark areas.
The solution to this is HDR photography.
HDR means High Dynamic Range and consists of two or more different exposed images. The result is a image with more information in the light and dark areas.
The file can become very large because of this (32 bit image vs. 8 bit standard image) but tonemapping or blending, teqhniques I am going to blog about later, let you "compress" the image to the way you want it to look on the monitor and paper.
You can also make HDR looking images with one standard exposed photo or a RAW file, but it is not true HDR as it only simulates the look. There is a ongoing discussion about RAW though.
HDR is most interesting when there is sunlight and/or big contrasts.
The trick is to use different shutter speeds and exposure value (EV) on your digital camera to create a HDR image. The easiest method is to use auto bracketing where you can choose the EV interval. A interval of -2EV, 0 and 2EV will get a good result for making a HDR image, but more exposures with shorter intervals will get more presise results. Typically HDR images consists of 3, 5 and more images. For the image above I used auto bracketing with three exposures and 2EV interval on my Canon EOS 400D/Rebel XTi.
Make sure you are holding the camera steady or use a tripod or monopod, as u have to take the pictures at the exact same place for all exposures. It is easier the higher shutter speed you can get in the lightning condition. Turn up the ISO rate if necessary and if your camera can shoot and process images with low noise at higher rates.
When you got two or more pictures with different exposures so that you can see the clouds on the sky clearly in some and dark areas well exposed in other you are ready to do image editing.
Photoshop is one choice. Here you can blend the pictures together using layers and masks. The output can be a very good natural looking HDR image.
But the choice that gives the most instant satisfaction is Photomatix and tonemapping, which I am going to blog about soon in the image editing catagory.
(to be continued soon..)