HDR
In computer graphics and photography, high dynamic range imaging (HDRI) is a set of techniques that allows a greater dynamic range of exposures (the range of values between light and dark areas) than normal digital imaging techniques. The intention of HDRI is to accurately represent the wide range of intensity levels found in real scenes ranging from direct sunlight to shadows.
HDRI was originally developed for use with purely computer-generated images. Later, methods were developed to produce a high dynamic range image from a set of photographs taken with a range of exposures. With the rising popularity of digital cameras and easy-to-use desktop software, the term "HDR" is now popularly used[1] to refer to the process of tone mapping together with bracketed exposures of normal digital images, giving the end result a high, often exaggerated dynamic range. This composite technique is different from, and generally of lower quality than, the production of an image from a single exposure of a sensor that has a native high dynamic range. Tone mapping is also used to display HDR images on devices with a low native dynamic range, such as a computer screen.
HDRI was originally developed for use with purely computer-generated images. Later, methods were developed to produce a high dynamic range image from a set of photographs taken with a range of exposures. With the rising popularity of digital cameras and easy-to-use desktop software, the term "HDR" is now popularly used[1] to refer to the process of tone mapping together with bracketed exposures of normal digital images, giving the end result a high, often exaggerated dynamic range. This composite technique is different from, and generally of lower quality than, the production of an image from a single exposure of a sensor that has a native high dynamic range. Tone mapping is also used to display HDR images on devices with a low native dynamic range, such as a computer screen.
Three exposures of the same image
Here the dynamic range of the image is demonstrated by adjusting the "exposure" when tone-mapping the HDR image into an LDR one for display. The above sequence uses an image rendered with Radiance using Paul Debevec's light probe of the Uffizi gallery. The rendering software produces a high dynamic range image. When making the JPEG images one sees, a part of that range is selected for display. This is similar to how a conventional camera captures only a portion of the dynamic range of a real physical scene.
The middle exposure is the desired exposure and is likely how this scene would normally be presented. The exposure to the left is 4 EV darker, showing some detail in the bright clouds in the sky. The exposure to the right is 3 EV lighter, showing some detail in the darker parts of the scene. This shows why compositing is desirable; a composite image can retain the interesting details from all three exposure settings.
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