Corner cases and limitations using a DOE based geometric camera calibration

Diffractive‑optics–based geometric camera calibration has opened the door to highly compact, easy‑to‑use setups capable of capturing precise dot‑grid patterns from virtual infinity. This paper explores the method’s untapped potential, from extreme wide‑FOV calibration to large entrance pupils and automotive distances, while addressing key limitations such as infinity‑only measurement and chromatic constraints. Several practical solutions are presented to extend the technique beyond distortion measurement toward richer system characterization.

Abstract

Everal years ago, the geometric calibration of cameras based on diffractive optical elements was invented, and since October 2020 the first product is commercially available. A laser beam is expanded, and the plane wave falls onto a diffractive optical element. The DOE generates a regular grid of light dots that virtually originates from infinity. This structure is then captured with the device under test and the dot positions are detected. From the positions, the required values can be calculated. The potential of the method, the compactness of the setup and the ease of use have brought up many desires that so far had not been addressed.

Amongst these are:

1. Calibration of extreme wide field of view cameras > 140°.
2. Calibration of cameras/lens combinations with a large entrance pupil.
3. Increased camera DOE distance to, e.g., measure cameras behind a windshield in automotive applications.
4. Camera pairs with a stereo base significantly exceeding 60 mm.
5. Deriving the point spread function of the system at every light dot to use the method for more than just distortion measurement, e.g., MTF determination or visualization.

Author

Dietmar Wueller, Image Engineering, Kerpen, Germany 2021, Electronic Imaging Symposium