Question

Give an imaging system, what is the point spread function and optical transfer function useful measures off?

Answer 1

Ans:  

Point Spread Function (PSF): It is the 3D diffraction pattern of light emitted from an infinitely small point source in the specimen and transmitted to the image plane through a high numerical aperture objective, It is considered to be the fundamental unit of an image in theoretical models of image formation. When light is emitted from such a point object, a fraction of it is collected by the objective and focused at a corresponding point in the image plane.

An image is a convolution of the object and the PSF and can be represented as

Image = Object * PSF

Point Spread Function plays an important role in the image formation theory of the fluorescence microscope, The PSF of an optical device is the image of a single point object, The degree of spreading in the image of this point object is a measure for the quality of an optical system.

Optical Transfer Function (OTF): It is defined as the Fourier transform of the point-spread function, and represents the ratio of image contrast to specimen contrast when plotted as a function of spatial frequency.The optical transfer function is obtained by first acquiring the image of a point source, and applying the two-dimensional discrete Fourier transform to the sampled image