Corner cases and limitations using a DOE based geometric camera calibration

Abstract

Several 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: <list list-type="order"> <list-item>Calibration of extreme wide field of view cameras > 140°.</list-item> <list-item>Calibration of cameras/lens combinations with a large entrance pupil.</list-item> <list-item>Increased camera DOE distance to, e.g., measure cameras behind a windshield in automotive applications.</list-item> <list-item>Camera pairs with a stereo base significantly exceeding 60 mm.</list-item> <list-item>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.</list-item> </list>There are also a few limitations compared to the conventional methods: <list list-type="lower-alpha"> <list-item>Measurement at infinity only</list-item> <list-item>Stereo basis cannot be measured due to translation invariance of the method</list-item> <list-item>Determination of chromatic aberration</list-item> <list-item>Limited application of a single DOE (due to resolution of the camera and field of view)</list-item> </list>All these desires and limitations are discussed, and solutions are presented where possible.