This work presents a method to characterize the 2D modulation transfer function (MTF) of electronic imaging systems using a setup that enables single-pixel illumination. The method is based on direct capture of point-spread function (PSF) images; therefore, it allows a higher level of accuracy than methods that derive PSF from multiple line-spread function measurements with a slanted-edge or another macro-target. The work presents a design of a measurement setup for PSF characterization, and a simulation test bench that can be used to simulate PSF. It shows simulated PSF images of 1.1 μm pixel pitch monochrome image sensors with and without μ-lenses, and the 2D-MTF plots that were calculated from these results. It also presents PSF images that were obtained from experimental work with these sensors and the 2D-MTF plots that were calculated for them. 1D-MTF results of the two sensors, as obtained from the slanted edge method, are compared to their cross-section 2D-MTF results, as obtained from PSF measurements. Comparison shows that there is a good agreement between the two methods, specifically, for measurements that are done with green light, and that the 2D-MTF method is more sensitive to spectral variations of the illumination.
This paper proposes several adjustments to the ISO 12233 slanted edge algorithm for estimating camera MTF. First, the Ridler-Calvard binary image segmentation method is used to find the line. Secondly, total least squares, rather than ordinary least squares, is used to compute the line parameters. Finally, the pixel values are projected in the reverse direction from the 1D array to the 2D image, rather than from the 2D image to the 1D array. Together, these changes yield an algorithm that exhibits significantly less variation than existing techniques when applied to real images. In particular, the proposed algorithm is largely invariant to the rotation angle of the edge as well as to the size of the image crop.