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THE HDRI PROCESS

HDR stands for High Dynamic Range. It's a relatively new technology to many amateur photographers. It has been popularized by the advent of digital cameras and easy to use desktop software. Dynamic range is the levels of light a camera can capture in a single shot. Real world scenes have light ranges exceeding 50,000:1 while some of the most powerful cameras can available capture up to 300:1 light range. This necessitates the use of HDR technology for some images.

If you use a camera with a low dynamic range to shoot a picture with one very bright scene, such as a city at night or a sunset, the sun will be clearly visible while the rest of the picture will be dark shadows. HDR is the digital process which is used to develop the raw images that have been captured. It involves separating different exposures of the same scene and then putting all the properly exposed parts into one final image. This involves the use of third party photography software that adjusts both shadows and highlights such as the bright sun.

When capturing a HDR image, have a stand/ tripod for your camera, a fast lens camera with an optical stabilizer if possible and of course the software. The most commonly used software is photomatix pro or Photoshop CS3. The camera should be able to record 14bit raw images and bracket exposures. Create a sequence for capturing different exposures; this will help you to capture just the right amount of dynamic range. It's important to maintain pixels throughout the shooting since combining different exposure increases image noise.

One of the main advantages of HDR imaging is that it allows the photographer to record a greater range of tonal detail in a photo than he could by just using his camera. It's commonly used in real estate marketing due to the need to display room and window simultaneously. It is only advisable to use HDR imaging if the scene's brightness distribution cannot be easily blended using a graduated neutral density GND filter which extends dynamic range and also maintains local contrast. Scenes which are ideally suited for GND are usually landscape photography. Since HDR imaging is a process you need to be ready for a lot of trial and errors before you get the final perfect image, also do not expect HDR to change those bright highlights or deep shadows greatly it may actually lead to a washed out image or one that doesn't make sense . However do not just give up try redoing it differently until you get the desired results.

douglas kanuri
Mon, 13 Apr 2009 22:09:27 +0000

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