Structured light in scattering media

Abstract

Virtually all structured light methods assume that the scene and the sources are immersed in pure air and that light is neither scattered nor absorbed. Recently, however, structured lighting has found growing application in underwater and aerial imaging, where scattering effects cannot be ignored. In this paper, we present a comprehensive analysis of two representative methods -light stripe range scanning and photometric stereo -in the presence of scattering. For both methods, we derive physical models for the appearances of a surface immersed in a scattering medium. Based on these models, we present results on (a) the condition for object detectability in light striping and (b) the number of sources required for photometric stereo. In both cases, we demonstrate that while traditional methods fail when scattering is significant, our methods accurately recover the scene (depths, normals, albedos) as well as the properties of the medium. These results are in turn used to restore the appearances of scenes as if they were captured in clear air. Although we have focused on light striping and photometric stereo, our approach can also be extended to other methods such as grid coding, gated and active polarization imaging.

Time-to-Contact in Scattering Media

“…In order to avoid these difficulties, previous works approach the problem by attempting to eliminate the effect of scattering media [4]- [11]. These approaches consider the scattering media as an obstacle for observing proper images, and attempt to eliminate the effect of the scattering media in the image by using image enhancement and color correction techniques [8], [10].…”

“…These methods often do not aim to obtain a precise estimation of the original image outside of scattering media, instead it attempts to make the image clearer and more suitable to the human observers. For recovering the original images accurately, Narasimhan et al [11] tried to control the light conditions with hardware solutions using a controllable light source such as projector, and eliminate the effect of scattering media. Although this approach is very useful with promising results, it requires a controllable light source, and thus it cannot be used in ordinary environments.…”

“…Then the behavior of light rays in scattering media can be represented by using a single scattering model [11]. In the single scattering model, every light ray that comes into contact with a micro-particle is reflected only once.…”

“…The α represents the angle between the input light ray and reflected direction as shown in Fig. 4 [11]. By using the phase function P, the observed intensity of light reflected by a media can be described as follows:…”

Python and MatPlotLib based Open Source Software System for Simulating Images with point Light Sources in Attenuating and Scattering Media

“…When the medium is also scattering, if we assume it is homogeneous and not highly dense, as in smoky welding environment or murky water, we can use single scattering model ( Figure 3) [5].…”