Noise and Other Artifacts in OTF Derived from Image Scanning.
Image scanning here means measuring intensity distribution in the image of a pinhole or slit target with a moving knife edge or slit, with data recorded digitally. With the aid of some established methods for empirically estimating noise power spectra, combined with prior knowledge of the spectrum of a dominant noise process (usually shot noise of the PM tube), quantitative statistical formulae are developed that relate the magnitude of the fluctuating part of the answers to the several instrumental parameters that must be chosen in planning a measurement: the scan length, scanning speed, choice of target and choice of scanner, sampling rate, etc. Another noise mechanism, essentially peculiar to the computational method, is also examined briefly. The predictive formulae are compared statistically with a mass of experimental data, and it is concluded that they do predict, to within better than a factor of 2, the outcome of an actual measurement. Some sources of systematic error are also briefly discussed.
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