Hyperspectral environmental illumination maps: characterizing directional spectral variation in natural environments.

Takuma Morimoto,Sérgio M C Nascimento,João M M Linhares,Sho Kishigami,Hannah E Smithson

doi:10.1364/oe.27.032277

Takuma Morimoto, Sérgio M C Nascimento + Show 3 more

Open Access

https://doi.org/10.1364/oe.27.032277

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Abstract

Objects placed in real-world scenes receive incident light from every direction, and the spectral content of this light may vary from one direction to another. In computer graphics, environmental illumination is approximated using maps that specify illumination at a point as a function of incident angle. However, to-date, existing public databases of environmental illumination specify only three colour channels (RGB). We have captured a new set of 12 environmental illumination maps (eight outdoor scenes; four indoor scenes) using a hyperspectral imaging system with 33 spectral channels. The data reveal a striking directional variation of spectral distribution of lighting in natural environments. We discuss limitations of using daylight models to describe natural environmental illumination.

Highlights

The vast majority of objects do not themselves emit light and are visible only by virtue of the incident light they reflect
We report new hyperspectral measurements of environmental illumination, which specify the spectral content of incident light from every direction at a point in a scene
The mean chromaticity is slightly shifted toward lower values of S/(L+M)

Summary

Introduction

The vast majority of objects do not themselves emit light and are visible only by virtue of the incident light they reflect. Recent work has expanded these observations to twilight [5] The focus of these studies has been to characterize the dominant illumination in a scene. Such measurements have significantly advanced our understanding of the human visual system, especially of mechanisms underlying the perception of objects’ surface properties, such as colour and shape. If we imagine an object placed at a specific point in a scene, the spectral content of illumination hitting the object may vary significantly as a function of incident angle In computer graphics this directional dependency of illumination is approximated using an environmental illumination map [16], which, at each pixel in the map, stores the intensity of a light coming from a particular direction towards a single point in the scene (e.g. an object or an eye).

Hyperspectral imaging system

Measurement

Image processing

Results and discussion

Conclusion