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.
We present a hybrid multi-line scan approach which enables simultaneous acquisition of light field & photometric stereo data. While light fields capture mostly large-scale surface deviations and rely on visible surface structures, photometric stereo is primarily sensitive to fine surface deviations and does not rely on visible structures. The combination of both approaches yields a solid performance for a large variety of depths, ranging from macro- to microscopic scales. Contrary to traditional photometric stereo, that relies on a strobed illumination, our approach uses two constant light sources which, however, generate multiple illumination geometries in different portions of the camera's field of view. Our object is moving on a conveyor belt during the acquisition process. Due to our multi-line scan sensor the object is observed from several viewing angles. The object's movement is causing each object point to be illuminated under several illumination directions. Hence, during our acquisition process the object points are captured under all feasible viewing angles and lighting conditions. In our system, surface normals are derived making use of the Lambert's cosine law. However, due to the lack of illuminations spanning orthogonally to the transport direction, the surface normals can be inferred only in the transport direction. We present a variational approach for 3D depth reconstruction designed specifically for our hybrid setup that jointly takes into account the light field as well as photometric stereo depth cues and provides one globally consistent solution. Depth maps obtained by the proposed algorithm show both the large-scale accuracy as well as sensitivity to fine surface details.