The MTF, or Modulation Transfer Function, is defined as the ratio of the image contrast to the target contrast, expressed as a function of spatial frequency. That is, MTF(u) = C'(u) / C(u). C is the contrast in the target, C' is the corresponding contrast in the image.

A higher MTF value indicates better image quality and resolution. It is analogous to a high-resolution TV versus a pixelated low-resolution screen. The MTF is the ratio of relative image contrast divided by relative object contrast: Modulation transfer function = relative image contrast/relative object contrast.

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.

The modulation transfer function, or MTF, is a parameter used to evaluate the performance of a lens. MTF provides a quantitative and standardized way to characterize optical systems, so the metric is used by optical designers and microscopists alike to compare lenses and determine the ideal one for an imaging system.