Image Processing Reference
In-Depth Information
Figure2.10 Visible (left) and MWIR (3-5 mm) (right) images of a man sitting in a car.
Figure2.11 Visible (left) and MWIR (3-5 mm) (right) images of a man reflected in a
brushed stainless steel refrigerator door. (CourtesyofFLIRandPatrickStanbro)
as a video signal to a display or recording device, just like a standard video
camera. Because of the difficulty of building FPAs with the same number of pixels
as conventional visible-light video cameras, thermal images taken with standard
commercial FPA cameras have tended to be grainy in appearance compared to
conventional video images. We now have commercially-available one-megapixel
thermal imaging cameras that produce incredible imagery. Even bigger thermal IR
FPAs have been built for satellite remote sensing and astronomical telescopes.
Figure 2.12 shows an infrared camera that is sensitive to energy in the MWIR
waveband. The camera is about the size of a large loaf of bread. The FPA in
this particular camera is made of the semiconductor material indium antimonide,
which needs to be cooled to liquid nitrogen temperatures (77 K or321 : 07 F) to
reduce detector noise (which is very temperature dependent) to workable levels.
A small closed-cycle cooler cools the FPA. Note the green color of the lens—
this is an antireflection coating on a germanium lens. The lens is totally opaque to
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