Until the early 20th century, infrared photography was not possible because silver halide emulsions are not sensitive to longer wavelengths than that of blue light (and to a lesser extent, green light) without the addition of a dye to act as a color sensitizer. These wavelengths also penetrate a few millimeters into skin and give a milky look to portraits, although eyes often look black. The dark skies, in turn, result in less infrared light in shadows and dark reflections of those skies from water, and clouds will stand out strongly. The other attributes of infrared photographs include very dark skies and penetration of atmospheric haze, caused by reduced Rayleigh scattering and Mie scattering, respectively, compared to visible light. Wood, and not after the material wood, which does not strongly reflect infrared. The effect is named after the infrared photography pioneer Robert W. There is a small contribution from chlorophyll fluorescence, but this is marginal and is not the real cause of the brightness seen in infrared photographs. When these filters are used together with infrared-sensitive film or sensors, " in-camera effects" can be obtained false-color or black-and-white images with a dreamlike or sometimes lurid appearance known as the "Wood Effect," an effect mainly caused by foliage (such as tree leaves and grass) strongly reflecting in the same way visible light is reflected from snow. ("Infrared filter" may refer either to this type of filter or to one that blocks infrared but passes other wavelengths.) Film is usually sensitive to visible light too, so an infrared-passing filter is used this lets infrared (IR) light pass through to the camera, but blocks all or most of the visible light spectrum (the filter thus looks black or deep red). Wavelengths used for photography range from about 700 nm to about 900 nm. The part of the spectrum used is referred to as near-infrared to distinguish it from far-infrared, which is the domain of thermal imaging. In infrared photography, the film or image sensor used is sensitive to infrared light. Taken from a passenger airplane within seconds apart using a Sony H-9 Digital camera. Infrared (900 nm LP) Aerial Photography of Old Hickory Lake, Tennessee.
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