Edge-based modulation transfer function measurement method using a variable oversampling ratio

Abstract

The ISO 12233 edge-based method approximates the modulation transfer function (MTF) as a function of horizontal or vertical spatial frequency by analyzing a 1D supersampled edge gradient obtained from the captured image of a near-vertical or near-horizontal bi-tonal edge, respectively. The method involves the slanted projection of pixels in a square array into a linear array of subpixel-wide bins. It can be modified to accommodate diagonal MTF measurements; however, using a fixed integer oversampling ratio degrades the accuracy and precision of diagonal MTF estimates due to periodic misalignment between the projection paths and the bin array. In this study, an edge-based method—called OMNI-sine—is proposed to counter the misalignment and improve MTF estimates by using a variable oversampling ratio dependent on the slant angle.