Pixel-wise calibration for a multi-focus microscopic 3D imaging system

Abstract

This paper presents a novel pixel-wise calibration method for a multi-focus microscopic structured light (MF-MSL) three-dimensional (3D) system with the camera being attached an electronically tunable lens (ETL). The method begins with a conventional stereo calibration performed at a selected focus. Next, a pixel-wise relationship between the continuous focus settings and corresponding phase values is established using a stationary white plane as the reference. By translating the white plane across the depth range defined by the ETL's continuous focus, a pixel-wise relationship between the phase difference (i.e., the deviation from the reference phase) and the 3D coordinates is derived. This process ultimately yields a direct mapping between the continuous focus values and 3D coordinates at each pixel. Since the proposed pixel-wise calibration method mitigates lens artifacts during focus variations, it greatly improved the calibration accuracy. Experimental results demonstrated that, comparing to the traditional stereo method, the proposed method reduced the root-mean-square error (rmse) by more than 50% for our 10× extended depth of field (DoF) system.