Conversion Between Sine Wave and Square Wave Spatial Frequency Response of an Imaging System

摘要

The spatial frequency response of an imaging system, known as the Modulation Transfer Function (MTF), is a primary image quality metric that is commonly measured with a sine wave target. The FBI certification program for commercial fingerprint capture devices, which MITRE actively supports, has an MTF requirement. In some cases, however, a square wave ('bar target') must be used in testing, which results in a similar quantity called the Contrast Transfer Function (CTF). This document reports on an investigation of the mathematical relationship between the MTF and CTF, methods for converting between the two, and derives an equivalent CTF from the given spec MTF, for use in the FBI certification program. The methodology presented is applicable to the general case, i.e., whenever conversion between the MTF and CTF of an imaging system is needed.