High-Dynamic Range Sunset Over the Mountains

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This is a reasonably colorful image of sunset in Boulder, CO on June 17, 2007.

Modern photography is based upon a detector that can only hold a certain amount of brightness information (or bit-depth). In general, the pixels usually hold 16-bit information, which provides 216-1≈65,000 levels of brightness. For many applications, this is perfectly fine. But for scenes that have a large range of brightnesses - a high dynamic range - this doesn't work as well because either some parts will be completely saturated (meaning that the recorded brightness is simply as bright as the pixel can record) or be completely under-exposed (like having a brightness of 0).

A "high-dynamic range" (or HDR) photograph attempts to solve this. It is accomplished by taking 2 or more exposures with different shutter speeds while keeping the camera stationary. The photos are then merged in special computer software (PhotoMax and Adobe PhotoShop are the two primary ones) that creates a composite image of a greater bit-depth (usually 32, providing 232-1≈2.1 billion levels of brightness). And hence this photograph.