Types of Infrared Imaging
Illumination based Imaging: The SLRs and digital cameras featuring Infrared Night Vision in them often rely on the basic fact that the CCD and CMOS sensors used in them are sensitive to the Near Infrared region which comprises the non-thermal part. Thus, a nearby source of IR illumination during the night time, or the sun during day time serve as the primary source of IR radiation which is then reflected in varying degrees by the object being photographed producing an IR image. Infrared Filters are also used which block all other forms of visible light from reaching the film. Very interesting ‘in-camera- effects with dream like or lurid coloring appearances named as ‘Wood Effect’ after the IR photography pioneer Robert W. Wood takes place, based on reflection of IR rays from foliage. The sources of illumination can be Incandescent lamps with IR filter in front of them, LED illuminators or Laser type illuminators based on laser diode.
Thermal Imaging: The wider part of the IR band comprises of thermal IR, which are emitted from almost everything above absolute zero. Thus it also forms a major area of thrust in IR imaging apart from the Near IR band. This class of IR imaging works along the following steps:
1. The IR light emanating from the objects in the scene is focused by means of a special lens.
2. A phased array of IR detectors scans the light to create a detailed temperature pattern called thermogram.
3. This thermogram is converted into electrical impulses which are fed into a dedicated signal processing chip to convert the electrical data into a format suitable for viewing purposes.
4. This information is then sent to the display unit where it appears as an image.
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