A | HDR : HIGH DYNAMIC RANGE

The imaging high dynamic range(High dynamic range imaging or HDRI) ou HDRI) includes a set of digital techniques to obtain a large dynamic range in an image. His interest is to represent or to memorize many levels of intensity light in an image. This technique takes longer to assign values to a single pixel. First developed for computer-generated images, this technique was then adapted to digital photography. :

The digital image is encoded on traditional values 256 (between 0 and 255) on each red green and blue, ie to 24 bits per pixel (3 x 8 bits). The luminous intensity gap between the pixel and the brighter the pixel the lowest, not black, that is 255. But in reality, it is common that the dynamics between the areas brightest and darkest a scene is greater. The HDR images using more bits per pixel images that conventional and can store a dynamic broadly higher. The most common is to store the images with a floating by color (96 bits per pixel), but there are also images HDR to 32 bits per pixel, as the format of Radiance RGBE or format LogLuv SGI.

In photography, image HDR has no interest if not converted into a standard format displayable (24 bits per pixel or less for example). That is why an artifice, "Tone Mapping," must be used properly to reveal the image. This algorithm creates, from a HDR image, a photo where all the elements are properly exposed. Without any overexposure or under-exposure, the picture becomes much more detail in both dark areas and highlight areas. The record is often very realistic, including landscapes and environments cloudy night.

Photography made from an image on a large dynamic range after Tone Mapping: :

Photograph showing the level of detail made possible with HDR (see the window)..