Two-dimensional measurement of the lens optical transfer function from a digital image

We present a novel method for accurately measuring the optical transfer function (OTF) of a camera lens by digitally imaging a tartan test pattern containing sinusoidal functions with multiple frequencies and orientations. The tartan pattern can be tuned to optimize the measurement accuracy for an adjustable set of sparse spatial frequencies. The measurement method is designed to be accurate, reliable, and fast in a wide range of measurement conditions, including uncontrolled lighting. We describe the design of the tartan pattern and the algorithm for estimating the OTF accurately from a captured digital image. Simulation results show that the tartan method has significantly better accuracy for measuring the modulus of the OTF (the modulation transfer function, or MTF) than the ISO 12233 standard slanted-edge method, especially at high spatial frequencies. With 1% simulated imaging noise, the root mean square (RMS) error of the tartan method is on average 5 times smaller than the RMS error of the slanted-edge method. Experiments with a printed tartan chart show good agreement (0.05 RMS) with MTFs measured using the slanted-edge method and that, like the slanted-edge method, our method is tolerant to wide variations in illumination conditions.