Optical EngineeringImaging system fundamentals
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Point-and-shoot, TV studio broadcast, and thermal infrared imaging cameras have significantly different applications. A parameter that applies to all imaging systems is Fλ/d, where F is the focal ratio, λ is the wavelength, and d is the detector size. Fλ/d uniquely defines the shape of the camera modulation transfer function. When Fλ/d<2, aliased signal corrupts the imagery. Mathematically, the worst case analysis assumes that the scene contains all spatial frequencies with equal amplitudes. This quantifies the potential for aliasing and is called the spurious response. Digital data cannot be seen; it resides in a computer. Cathode ray tubes, flat panel displays, and printers convert the data into an analog format and are called reconstruction filters. The human visual system is an additional reconstruction filter. Different displays and variable viewing distance affect the perceived image quality. Simulated imagery illustrates different Fλ/d ratios, displays, and sampling artifacts. Since the human visual system is primarily sensitive to intensity variations, aliasing (a spatial frequency phenomenon) is not considered bothersome in most situations.