High Dynamic Range Images (HDR)
Since the last camera upgrade last year (details here), I've been experimenting with the HDR techniques. My previous cameras did not have the exposure auto-bracketing function, and this function was one of the reasons why I have decided to buy a Canon 450D.
HDR comes from Higy Dynamic Range images and refers to images having a greater dynamic range of luminance between the light and darker part of a scene than normal photography techniques. Its intention is to more accurately render the wide range of light intensity levels found in real scenes (from direct sunlight to shadows for example). Although most of the time over-processing that looks fake is associated with this technique, its scope is to render an image closer to how it is perceived by our eyes.
This technique was first developed around 1930s and 1940s, but the first applications in digital photography appeared in 1993. A HDR image can be considered even the raw file of the most recent digital cameras, as one pixel is defined in 24 bits (having thus a wider range of luminance), but on its display on the screens (camera and computer screens) it looses information as the pixel-depth is only 8 bits. Tone-mapping techniques have been introduced to convert a 24 bits image to 8 bits, in an attempt to differentially map the luminance levels of each pixel. Different algorithms are available on the market to make this conversion, the most notable being the one included in the most recent Photoshop releases or from the specialized software for HDR - Photomatix.
The tone-mapping technique can be apply to a raw image or at least 2 jpeg images of the same scene taken with different exposures, with comparable results. Many parameters of this technique influence the final result. The following results can be noted: details in both shadows and direct sunlight or both the sky and subject and enhanced color rendering.
To create my own HDR images I take 3 shots of the same scene with different exposures (bracketing +/-(1+1/4) usually). I use the tone-mapping algorithm from Photomatix and set the parameters so that the final results to look as real as possible. However, the images obtained this way look different than normal exposed photographs.
Here are some examples with comments:
I am continuing to experiment with HDR techniques. Some more images are even on the pending line... Let me direct you to a personal gallery of HDR images, where my further experiments will be found.
Photo credits: Mihai-bogdan Lazar.