The modulation transfer function (MTF) describes the ability of a detector to retain the contrast (signal amplitude) of an object. It also measures how much spatial frequency is transferred from the object to an image ⁸. This is because each detector has its own limiting spatial resolution.

MTF is defined as the Fourier transform (FT) of the point spread function (PSF). This concept applies to a linear system that is shift invariant. In practice, MTF is usually measured in two orthogonal directions using FT of the line spread function.

The modulation transfer function (MTF) is the most widely accepted measure of the spatial resolution response of medical x-ray imaging detectors and has proved to be a valuable tool for determining and comparing detector performance.

MTF and CTF are applicable to almost any printing technology. Contrast Transfer Function (CTF) is the preferred term for printed sample measurements. The term MTF is really more appropriate for optical components characterization. There are three components in CTF, 1) contrast, 2) transfer, and 3) function.