Single View Reflectance Capture using Multiplexed Scattering and Time-of-flight Im

晃晃

Single View Reflectance Capture using Multip***d Scattering and Time-of-flight Imaging

Nikhil Naik  Shuang Zhao  Andreas Velten  Ramesh Raskar   Kavita Bala

MIT Media Lab Cornell University







Abstract

This paper introduces the concept of time-of-flight reflectance esti-

mation, and demonstrates a new technique that allows a camera to

rapidly acquire reflectance properties of objects from a single view-

point, over relatively long distances and without encircling equip-

ment. We measure material properties by indirectly illuminating

an object by a laser source, and observing its reflected light indi-

rectly using a time-of-flight camera. The configuration collectively

acquires dense angular, but low spatial sampling, within a limited

solid angle range - all from a single viewpoint. Our ultra-fast imag-

ing approach captures space-time “streak images" that can separate

out different bounces of light based on path length. Entanglements

arise in the streak images mixing signals from multiple paths if they

have the same total path length. We show how reflectances can be

recovered by solving for a linear system of equations and assuming

parametric material models; fitting to lower dimensional reflectance

models enables us to disentangle measurements.

We demonstrate proof-of-concept results of parametric reflectance

models for homogeneous and discretized heterogeneous patches,

both using simulation and experimental hardware. As compared

to lengthy or highly calibrated BRDF acquisition techniques, we

demonstrate a device that can rapidly, on the order of seconds, cap-

ture meaningful reflectance information. We expect hardware ad-

vances to improve the portability and speed of this device.

Keywords: computational photography, multipath light transport,

reflectance acquisition, global illumination, time of flight

1 Introduction

Acquiring material properties of real-world materials has a long

and rich history in computer graphics; existing techniques di-

rectly image the sample being measured to acquire different proper-

ties including tabulated reflectance functions, spatially varying re-

flectances, and parametric models (see [Weyrich et al. 2009] for a

survey of state-of-the-art techniques.). These reflectance functions,

are necessary for relighting, material editing, and rendering, as well

as for matching and material identification.

In this paper, we present a new acquisition approach to reflectance

measurement. Our approach is unique in two ways: we exploit

ultra-fast time-of-flight (ToF) imaging to achieve rapid acquisition

of materials; and we use indirect observation to acquire many sam-

ples simultaneously, and in fact, even permit around-the-corner

measurement of reflectance properties. The key insight of this re-

search is to exploit ultra-fast imaging to measure individual light

transport paths, based on the distance traveled at the speed of light.

This capability uniquely lets us separately measure the direct (0-

bounce), 1-bounce, 2-bounce, and more, light paths; in comparison,

traditional approaches use controlled laboratory settings to mini-

mize the impact of multi-bounce light transport, or must explicitly

separate direct and indirect lighting from all bounces.

We make the following contributions:

a) We present a new technique for reflectance acquisition by sep-

arating light multip***d along different transport paths. Our ap-

proach uses indirect viewing with 3-bounce scattering coupled

with time-of-flight imaging to capture reflectances. Our proof-of-

concept system demonstrates first steps towards rapid material ac-

quisition.









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奇

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晃晃

先顶上去，偶要高亮加精鸟！

晃晃

精典，学习了！

tc

顶!学习了!阅!

tc

精典，学习了！

菜刀吻电线

发了那么多，我都不知道该用哪个给你回帖了，呵呵

奇

不错不错，收藏了

菜刀吻电线

有意思！学习了！

晃晃

其实楼主所说的这些，俺支很少用！