Sunday, March 6, 2011

HDR photography

High dynamic range - a technique in photography involving the execution of several exposures of the same frame, some of which are underexposed, overexposed and the remainder. It allows you to obtain a picture of the scene is characterized by a large tonal range. 
Using this technique, usually done three to five photographs (sometimes more - depending on the tonal range and dynamics of the camera frame) with a properly illuminated shadows and indirect light elements, such as the difference between 2 EV (can be 1 or even 3), then combines the images into one file. In order to obtain the source photography, the method bracketing or produces a RAW file with different parameters. 
HDR composite image is subjected to the mapping of luminance, so that compression is a global contrast of the image, but are observed local changes in brightness. This technique can also be used to improve the quality of individual photographs, and noise, which in this case usually is enhanced, can be removed using a bilateral filter. 
For the first time this technique was used in 1857 by Gustave Le Gray, on the one hand trying to photograph both the sea and the sky, although it exceeded the technical capabilities of contemporary cameras and films. Le Gray solved the problem by doing two separate images with different exposure time, and then used the different parts of the negatives to obtain a positive.