Improving Image Matching by Reducing Surface Reflections Using Polarising Filter Techniques

Abstract

ABSTRACT:In dense stereo matching applications surface reflections may lead to incorrect measurements and blunders in the resulting point cloud.To overcome the problem of disturbing reflexions polarising filters can be mounted on the camera lens and light source. Reflections in the images can be suppressed by crossing the polarising direction of the filters leading to homogeneous illuminated images and better matching results.However, the filter may influence the camera's orientation parameters as well as the measuring accuracy. To quantify these effects, a calibration and an accuracy analysis is conducted within a spatial test arrangement according to the German guideline VDI/VDE 2634.1 (2002) using a DSLR with and without polarising filter. In a second test, the interior orientation is analysed in more detail. The results do not show significant changes of the measuring accuracy in object space and only very small changes of the interior orientation (c ≤ 4 µm) with the polarising filter in use.Since in medical applications many tiny reflections are present and impede robust surface measurements, a prototypic trinocular endoscope is equipped with polarising technique. The interior and relative orientation is determined and analysed. The advantage of the polarising technique for medical image matching is shown in an experiment with a moistened pig kidney. The accuracy and completeness of the resulting point cloud can be improved clearly when using polarising filters. Furthermore, an accuracy analysis using a laser triangulation system is performed and the special reflection properties of metallic surfaces are presented.

Multi-Variant TLS and SfM Photogrammetric Measurements Affected by Different Factors for Determining the Surface Shape of a Thin-Walled Dome

“…The matte spots gave a smaller distortion of the sphere and the regions with a glossy surface were covered with a bigger distortion or lack of measurement. It is an interpretation supported by research from other authors showing problems with reflections [ 24 , 27 ]. For Agisoft Photoscan, larger differences from the scanner occurred only in a narrow strip in the lower, central part of the back of the dome.…”

“…One of the factors influencing the accuracy of photogrammetric measurements, especially in the case of objects with smooth or wet surfaces, was reflections. In the publication [ 24 ], the authors investigated the use of a polarization filter to reduce reflections on photographed objects in medical applications. The study concluded that a polarization filter can be used on a standard camera in structure from motion (bundle adjustment).…”

Scan to Hbim for Complex Reflective Metal Artefacts. 3d Digitisation and Restoration

“…Therefore, the system has been disassembled and the main pieces, the structure, scenes and four caryatids (Fig. 4), have been acquired and restored for educational and research purposes and in collaboration with local authorities, according to the acquisition process based on the comparison between textured models and orthophotos, both processed by photographic acquisition with different cameras and lighting photographic sets (listed below according to different decreasing costs): Cross-polarization images improve photogrammetric reconstruction and measurement on reflective surfaces (Wells et al, 2005, Conen et al, 2018. However, no errors occurred during photo alignment, regardless of the photographic set.…”

The Digitalization of Ancient Egyptian Coffins: A Discussion Over Different Techniques for Recording Fine Details

“…Next to the tripod, there were two external flashlights (Godox QS600II) synchronized with the camera. As known, (Conen et al, 2018, Menna et al, 2016 the photogrammetric matching of reflective surfaces may result in incorrect measurements, blunders, and noise in the final point cloud. To solve the problem of cross-polarisation can be used: polarizing filters can be mounted both on the camera lens and on the light source.…”