Point spread function

The point spread, point spread function, point spread function or point spread function (English " point spread function ", short PSF) describes the radio frequency technology, optics and image processing, the effect of band-limiting factors such as:

• Diffraction at aperture
• Aberrations
• Influence of the sensor surface or aperture

It specifies how an idealized point-like object would be imaged by a system. Often the shape of the point spread function is independent of the original location of the ideal, point-like object. In this case one speaks of a linear system and the overall response of the system can be calculated as the sum of the item responses of the disassembled into its object points.

In light microscopy limited by diffraction maximum achievable resolution of a lens using the PSF can be determined. When resolution of a microscope is generally understood to mean the distance, must have the two point-like structures, so that they can (and not as a structure ) are recognized as separate structures.

But is taken Microscopically usually only the image of a small spherical structure, ie for example the microscopic image of very small fluorescent latex beads. To determine a measure of the achievable resolution in the x-, y -, or z-direction, brightness distribution along a profile of the lightest point is first determined in parallel to the desired axis. The width of the brightness distribution at half height between maximum intensity and Intensitätsminium (FWHM Full Width Half Maximum ) is conveniently often given as achievable resolution. Alternatively, the point spread function can be theoretically calculated for various experimental imaging scenarios.

While the width ( FWHM) of the point is the most important factor for the resolution, the actual achieved resolution of a microscopic image depends also on other factors such as the signal -to-noise ratio.