One of the problems even more movies and digital sensors is their ability to render scenes with high contrast. This is characterized by high-lights burned and / or shadows completely blocked, while there, the eye can distinguish many more shades. The sensors have a dynamic effect (the ability to record differences in brightness) rather limited, inherent in the technology. We need in these cases the choice between a high emphasis on exposure-lights, shadows or otherwise. However, there are solutions, but which impose some constraints in terms of shooting. Here we will try to do an overview of HDR photography and its application fields.
First, let's define the term "HDR" or High Dynamic Range. I use these images myself in another field, computer graphics, where the format has emerged in the late 90s, thanks to the work of Paul Debevec. This format is now widely used in OpenEXR (developed by ILM, the famous studio of George Lucas) in rendering and compositing in this area. A pixel of an image is composed of three layers of colors, Red Green Blue, each layer can contain a number of nuances. 8bits in each layer is coded on 8 bits (or 8bpc for Bits Per Channel), or 256 shades of red, green, and blue. Indeed, computers are binary, it has 8 '0 'or '1' for encoding information, or 2 8 = 256 possibilities. Three layers (our R, G, B), we obtain 256 3 = 16,777,216 colors or 24bpp (Bit Per Pixel).
A file is actually a 32bit file 8bpc (24bpp then), but with a fourth layer, called alpha, containing information transparency. For example, a pixel is a pixel 100,100,100,128 dark gray, 50% transparency. This is to clarify, because we do not concern us here in the alpha channel. Digital cameras can take photographs of just a contrast of 1000:1 (ratio between the lowest and highest brightness level of representation), measures a real daylight scene, a contrast ratio of 100,000:1. It is therefore not surprising that dark areas on photos usually really drown in a black area or pull of the sun irradiated areas in white without markings. The camera cannot be such a wealth of information with a photo.
To get a realistic picture of a scene, you have to use a trick. With an exposure range in which the same motif deliberately over-exposed, normally exposed and under exposed images are created, both the drawings in the highlights and details will be kept in the shadows - at various individual images. Thanks to this exposure series can be used together with programs like Photoshop CS2 or Adobe Photomatix Pro HDRsoft a photo with high contrast - image with extremely fine color transitions - create an HDR.
On conventional screens, but is such a HDR image, not to its best advantage. A current monitor is the high contrast of the file is not present, it reduces the scene for output automatically. The same happened when printed on paper. In order to be considered on such so-called low-dynamic-range media (LDR-media) the detail of an HDR scene, it still requires an important second step. With a dynamic range compression (tone mapping) the contrast of the image is reduced controls. The result is a displayable file. This, of course not without losses. The user must decide what is important or can be omitted, for which he has several parameters to control the outcome - see photo gallery of this paragraph.
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