Measurement of the spatial frequency response (SFR) of digital still-picture cameras using a modified slanted edge method

摘要

Spatial resolution is one of the main characteristics of electronic imaging devices such as the digital still-picture camera. It describes the capability of a device to resolve the spatial details of an image formed by the incoming optical information. The overall resolving capability is of great interest although there are various factors, contributed by camera components and signal processing algorithms, affectign the spatial resolution. The spatial frequency response (SFR), analogous to the MTF of an optical imaging system, is one of the four measurements for analysis of spatial resolution defined in ISO/FDIS 12233, and it provides a complete profile of the spatial response of digital still-picture cameras. In that document, a test chart is employed to estimate the spatial resolving capability. The calculations of SFR were conducted by using the slanted edge method in which a scence with a black-to-white or white-to-black edge tilted at a specified angle is captured. An algorithm is used to find the line spread function as well as the sFR. We will present a modified algorithm in which no prior information of the angle of the tilted black-to-white edge is needed. The tilted angle was estimated by assuming that a region around the center of the transition between black and white regions is linear. At a tilted angle of 8 degree the minimum estimation error is about 3percent. The advantages of the modified slanted edge method are high accuracy, flexible use, and low cost.