Information AboutHdri |
| CATEGORIES ABOUT HIGH DYNAMIC RANGE IMAGING | |
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HDRI example showing stained glass windows in south alcove of Old Saint Paul's , Wellington , New Zealand .]] In Computer Graphics and Cinematography , high dynamic range imaging (HDRI for short) is a set of techniques that allow a far greater Dynamic Range of exposures than normal digital imaging techniques. The intention is to accurately represent the wide range of intensity levels found in real scenes, ranging from direct sunlight to the deepest shadows. This provides the opportunity to shoot a scene and have total control of the final imaging from the beginning to the end of the photography project. An example would be that it provides the possibility to re-expose. One can capture as wide a range of information as possible on location and choose what is wanted later. Gregory Ward is widely considered to be the founder of the file format for high dynamic range imaging. The use of high dynamic range imaging in computer graphics has been pioneered by Paul Debevec . He is considered to be the first person to create computer graphic images using HDRI maps to realistically light and animate CG objects. When preparing for display, a high dynamic range image is often Tone Mapped and combined with several Full Screen Effect s. DIFFERENCE BETWEEN HIGH DYNAMIC RANGE AND TRADITIONAL DIGITAL IMAGES Information stored in high dynamic range (HDR) images usually corresponds to the physical values of Luminance or Radiance that can be observed in the real world. This is different from traditional Digital Images , which represent colors that should appear on a monitor or a paper print. Therefore HDR image formats are often called scene-referred, in contrast to traditional digital images, which are device-referred or output-referred. Furthermore, traditional images are usually encoded for the human Visual System (maximizing the visual information stored in the fixed number of bits), which is usually called gamma encoding or Gamma Correction . The values stored for HDR images are linear, which means that they represent relative or absolute values of radiance or luminance (gamma 1.0). HDR images require a higher number of bits per color channel than traditional images, both because of the linear encoding and because they need to represent values from to (the range of visible luminance values) or more. 16-bit (" Half Precision ") or 32-bit Floating Point numbers are often used to represent HDR pixels. However, when the appropriate Transfer Function is used, HDR pixels for some applications can be represented with as few as 10-12 bits for luminance and 8 bits for Chrominance without introducing any visible quantization artifacts [http://www.mpi-sb.mpg.de/resources/hdrvideo/ . EXAMPLE HDR IMAGES , Wellington , New Zealand . Eight exposures ranging from 1/20th of a second to 30 seconds]] SEE ALSO
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