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Term: Modulation Transfer Function

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Term: Modulation Transfer Function

The sharpness of an imaging system can be characterized by its Modulation Transfer Function (MTF), which is generally equivalent to the Spatial Frequency Response (SFR). One approach to measuring this parameter employs a target with black and white bands of increasing spatial frequency (see examples at http://www.normankoren.com/Tutorials/MTF.html). (There are also other methods for measuring MTF and/or SFR.) As the bands get closer together, it becomes more and more difficult for an imaging system to reproduce them so that the bands can be distinguished: what had been black and white blurs into gray. On the image of the target, where the frequencies of the bands remain clear and distinct, the MTF is said to be 100 percent. When the contrast falls to one half of its original value, the MTF at that point on the target is 50 percent. Experts in fields like photography state that humans perceive high levels of image sharpness at the 50 percent point. In some other image-dependent scientific fields, however, the 10 percent point is used to determine the resolution of an imaging system.
Norman Koren tutorial on MTF
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