Hand-held Schlieren Photography with Light Field probes

Abstract

We introduce a new approach to capturing refraction in transparent media, which we call Light Field Background Oriented Schlieren Photography (LFBOS). By optically coding the locations and directions of light rays emerging from a light field probe, we can capture changes of the refractive index field between the probe and a camera or an observer. Rather than using complicated and expensive optical setups as in traditional Schlieren photography we employ commodity hardware; our prototype consists of a camera and a lenslet array. By carefully encoding the color and intensity variations of a 4D probe instead of a diffuse 2D background, we avoid expensive computational processing of the captured data, which is necessary for Background Oriented Schlieren imaging (BOS). We analyze the benefits and limitations of our approach and discuss application scenarios.

Angular domain reconstruction of dynamic 3D fluid surfaces

“…These angular domain normals cannot be directly mapped to spatial domain normals, i.e., we cannot perform raysurface intersection as the surface is unknown. Further, by using a wide aperture viewing camera, we can only recover the exit ray direction rather than the ray itself, i.e., we cannot perform ray-ray intersections [22]. We therefore derive a new angular-domain surface integration scheme.…”

Refraction Wiggles for Measuring Fluid Depth and Velocity from Video

“…To address the fact that the background must be in focus, Wetzstein et al [28] introduced light field BOS imaging in which the textured background is replaced by a light field probe. However, this comes at the cost of having to build a light field probe as large as the flow of interest.…”

Reconstructing Gas Flows Using Light-Path Approximation

“…The core of our approach is to acquire ray-ray correspondences using the LF-probe [28,29]. A LF-probe, as shown in Fig.…”

“…To obtain a dense set of correspondences, similar to [28,29], we use color-coded pattern to encrypt the 4D ray positions and directions emitted by the probe. In particular, we use a combination of horizontal red gradient and vertical blue gradient behind each microlens to discriminate rays of different directions.…”

“…Our solution exploits the light field probe (LF-Probe) [28,29] which serves as a view-dependent reference pattern. A LF-probe, in essence, is an "inverted" light field camera [22] where each pixel on the pattern maps to a unique ray.…”