Hand-guided qualitative deflectometry with a mobile device

Abstract

We introduce a system that exploits the screen and front-facing camera of a mobile device to perform three-dimensional deflectometry-based surface measurements. In contrast to current mobile deflectometry systems, our method can capture surfaces with large normal variation and wide field of view (FoV). We achieve this by applying automated multi-view panoramic stitching algorithms to produce a large FoV normal map from a hand-guided capture process without the need for external tracking systems, like robot arms or fiducials. The presented work enables 3D surface measurements of specular objects ’in the wild’ with a system accessible to users with little to no technical imaging experience. We demonstrate high-quality 3D surface measurements without the need for a calibration procedure. We provide experimental results with our prototype Deflectometry system and discuss applications for computer vision tasks such as object detection and recognition.

Reflections about holographic and non-holographic acquisition of surface topography

“…This is because (well designed) slope measurement methods exploit a perfect source encoding: the OTF represents the spatial derivative (or at least an approximation,for shearing methods). Among the spatially differentiating methods we find the so called phase-measuring de-flectometry (pmd) [44][45][46] which is completely incoherent, and we find classical shearing interferometry [47].…”

“…As starters, a brief explanation of incoherent phasemeasuring deflectometry for a later comparison with holography and other coherent methods [44][45][46]:…”

Surface Measurement of a Large Inflatable Reflector in Cryogenic Vacuum

“…Taking advantage of total internal reflection at a water-air interface, PMD has also been used to measure disturbances of a fluid surface [15]. Willomitzer et al introduced stitched panoramic measurements of stained-glass windows with a mobile device [16]. PMD for more traditional technical surfaces is well-described in recent literature reviews [17,18].…”

Skinscan: Low-Cost 3D-Scanning for Dermatologic Diagnosis and Documentation

“…All these so-called "reflectance-based" methods are highly dependent on the reflective properties of the objects of interest. For specular objects, Willomitzer et al [14] proposed the idea of utilizing a tablet to perform deflectometry measurements using the screen and front camera. However, this system is not tailored to measure rather diffuse objects like human skin.…”