slantededge

Slanted-edge, also referred to as the slanted-edge method or slantededge, is a practical technique used to characterize the spatial frequency response of cameras and other imaging systems. It relies on capturing an image of a high-contrast edge that is tilted relative to the image sensor's pixel grid.

The edge is typically oriented at a small angle, often several degrees, to avoid sampling artifacts. A flat, uniform target with a sharp luminance transition is imaged under stable exposure and focus conditions. After acquisition, the edge region is selected for processing, and the edge angle is measured or estimated.

Processing converts the raw image into a one-dimensional edge spread function (ESF) by averaging pixel values perpendicular to the edge. The ESF is differentiated to obtain the line spread function (LSF). The magnitude of the Fourier transform of the LSF yields the modulation transfer function (MTF) across spatial frequencies. Windowing and noise reduction techniques are commonly applied to improve accuracy.

ISO 12233 formalizes the slanted-edge procedure for MTF measurement and is widely used in camera testing and lens evaluation. The method enables rapid, repeatable estimates of sharpness from a single image and requires relatively simple equipment, such as a test target or even a printed edge.

Limitations include sensitivity to edge quality, lighting uniformity, and alignment. The measured MTF can be influenced by sensor sampling, color channels, and post-processing such as demosaicing. Proper calibration and consistent imaging conditions are essential for comparisons across devices.