This work focuses on the compensation of motion artefacts that may occur during a line scan acquisition and can be detected with our multi-line scan imaging system [10]. These artefacts are caused by fluctuations of the transport velocity that are not correctly reflected by the camera trigger, and are especially visible at high magnifications. We reduce such artefacts by analyzing the light field acquired with our system. Specifically, we use a variational formulation to design a warping function, such that lines that are acquired too early or too late are stretched or squeezed appropriately. To this end, we exploit the information comprised in the light field, i.e., control the estimation of the warping function by comparing light field views and enforce uniform spacing between line acquisitions. The proposed approach enables our system to perform the multi-line scan light field imaging at virtually any magnification independent from the transport and trigger quality. We demonstrate the capabilities of our approach for various objects by comparing 3D reconstructions from unprocessed acquisitions and our corrected acquisitions. Our approach significantly reduces artefacts in light fields and in 3D reconstructions that are generated from them.
Multi-line scan systems have been introduced as linear light field cameras and subsequently for 3D ranging for industrial inline applications. Up to now there have been no viable calibration methods to determine intrinsic and extrinsic parameters of such a system which would allow (i) metric measurements and (ii) line-scan image geometric rectification. Our work closes the gap by exploiting special properties of a typical multi-line scan setup, which internally uses a fast area-scan sensor that can also be operated in the line-scan mode. This allows the use of standard calibration approaches to determine the intrinsic camera parameters. We introduce a novel method to compute extrinsic camera parameters w.r.t. the transport direction. Consecutively, the images are rectified for all constructed line-scan views. This takes into account estimated camera model parameters in order to generate an EPI-corrected linear light field that is suitable for accurate 3D reconstructions. Furthermore, we introduce a novel calibration target that is characteristic by an asymmetric central element as well as a tailored fast detection algorithm. The proposed method significantly improves the 3D reconstruction quality and allows for absolute 3D measurements in metric units using the multi-line scan setup. The performance of the proposed method is demonstrated on several representative real world examples.