The optical transfer function ( OTF ) describes the spatial (angular) variation as a function of spatial (angular) frequency. When the image is projected onto a flat plane, such as photographic film or a solid state detector, spatial frequency is the preferred domain, but when the image is referred to the lens alone, angular frequency is preferred. OTF may be broken down into the magnitude and phase components as follows:
where
and (ξ,η) are spatial frequency in the x- and y-plane, respectively.
The OTF accounts for aberration. The magnitude is known as the Modulation Transfer Function (MTF) and the phase portion is known as the Phase Transfer Function (PTF) .
In imaging systems, the phase component is typically not captured by the sensor. Thus, the important measure with respect to imaging systems is the MTF.
Another related quantity is the Contrast Transfer Function (CTF). MTF describes the response of an optical system to an image decomposed into sine waves. CTF describes the response of an optical system to an image decomposed into square waves.
Phase is critically important to adaptive optics and holographic systems.
The OTF is the Fourier transform of the Point Spread Function.
The modulation transfer function represents the Bode plot of an imaging system (such as a microscope or the human eye), and thus depicts the filtering characteristic of the imaging system. The human eye, for instance, acts as a low-pass filter, meaning that very high-frequency components (sharp edges) cannot be perfectly perceived.
Photography
In photography, certain cameras (such as the Pentax K10D) feature an "MTF autoexposure" mode, where the choice of aperture is optimised for maximum sharpness. Typically this means somewhere in the middle of the aperture range.
See also
- Strehl ratio
- Optical resolution
- Transfer function
- Wavefront coding
- Modulation transfer function (infrared imaging)
- Signal to noise ratio (image processing)
- Signal transfer function
References
- ^ B2BVideoSource.com:
Modulation transfer function
Another concept that may be new to neophyte vision people is that of modulation transfer function. Most lenses including the human lens are not perfect optical systems.
Modulation Transfer Function
Author: Jeffrey Kuhn (jkuhn@ccwf.cc.utexas.edu) The University of Texas at Austin Date: 2000/8/22: Source: MeasureMTF_.java: API: MeasureMTF_.html: Installation:
Nikon MicroscopyU | Modulation Transfer Function
The modulation transfer function of a lens, microscope objective, or other optical system is a measurement of its ability to transfer contrast at a particular reolution level from ...
Modulation Transfer Function (MTF)
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Optical transfer function - Wikipedia, the free encyclopedia
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