CauStereo: Range from light in nature

Abstract

Underwater, natural illumination typically varies strongly temporally and spatially. The reason is that waves on the water surface refract light into the water in a spatiotemporally varying manner. The resulting underwater illumination field forms a caustic network and is known as flicker. This work shows that caustics can be useful for stereoscopic vision, naturally leading to range mapping of the scene. Range triangulation by stereoscopic vision requires the determination of correspondence between image points in different viewpoints, which is often a difficult problem. We show that the spatiotemporal caustic pattern very effectively establishes stereo correspondences. Thus, we term the use of this effect as CauStereo. The temporal radiance variations due to flicker are unique to each object point, thus disambiguating the correspondence, with very simple calculations. Theoretical limitations of the method are analyzed using ray-tracing simulations. The method is demonstrated by underwater in situ experiments.

Triangulation in Random Refractive Distortions

“…Refraction has been used and analyzed in the context of computational photography [20,31,33,40,47,48,49]. Theory about visual refraction through a WAI is described in Ref.…”

STELLA MARIS: Stellar marine refractive imaging sensor

“…An image of the Stella Maris Monastery was captured from the Haifa Bat-Galim beach. The monastery vista is distorted by a wavy WAI: the WAI is simulated as in [23,46] by a wind of 1.5m/s, and has peak-to-peak amplitude of 2cm. Sunrays project onto the WAI, refract, pass the pinhole array and irradiate the diffuser.…”

Improved Stereo Matching in Scattering Media by Incorporating a Backscatter Cue

“…Underwater 3-D reconstruction by stereovision has been explored over the last dozen years [1], [6], [15], [17], [20], [21], [32]. Some of these works employ the open-air dense matching techniques based on relaxing the brightness constancy assumption; e.g., [20].…”

“…Some of these works employ the open-air dense matching techniques based on relaxing the brightness constancy assumption; e.g., [20]. Others have applied feature-based methods to images acquired under good visibility, and thus negligible backscatter [6], [15], [21], [32]. Single image dehazing offers a possible approach for image contrast enhancement (and scene radiance recovery) [4], [8], [14], [33].…”