Term: Modulation Transfer Function
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Term: Modulation Transfer Function
- Definition:
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). 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. Note: There are also other methods for measuring MTF and/or SFR.
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.
Note: In the 2022 revision of the Technical Guidelines for Digitizing Cultural Heritage Materials, SFR is a surrogate metric to MTF. There are some very minor differences between SFR and MTF. In the purest sense SFR may not give the same results due to assumptions about linearity and the response at the zero frequency. For simplicity the Guidelines use SFR as the evaluation metric as SFR is much easier to calculate for field use.
- Category:
- Image
- Resource:
- Norman Koren tutorial on MTF
http://www.normankoren.com/Tutorials/MTF.html - See also:
- SFR