Real-time modulation transfer function measurement system

We developed a modulation transfer function (MTF) measurement system that analyzes the edge responses of a sampled imaging system in real time. The MTF can be continuously observed while operating the iris, focus, and zoom. This system accurately estimates the edge angle and selects a binning phase from a small number of binning phases to improve the precision of the MTF estimation. Furthermore, it incorporates a simplified method that approximates the MTF without edge angle estimation and the following subpixel binning, enabling the analysis of nonstraight edges. This system is applicable to multiple edges in arbitrary directions, unlike the conventional ISO 12233 edge-based method, in which only a near-vertical or near-horizontal edge is applicable. The analysis of edge responses on a starburst chart yields a contour plot of multidirectional MTFs that enables direct observation of the anisotropy due to the performance and conditions of the camera and lens (e.g., misalignment of the optical components), as well as the pixel arrangement of the image sensor and image processing method applied (e.g., Bayer color filter array demosaicing). Further, this system can also measure camera noise while adjusting the MTF with an edge enhancement filter.