Efficient Gonio-spectral Imaging for Diffuse Objects Based on Optical Reflectance Properties

摘要

Precise color and texture reproduction based on gonio-spectral reflectance properties of object is required in many fields such as E-commerce, digital archives, criminal investigation and so on. However, spectral imaging at all geometries requires much measurement tasks and huge data storage. In this paper, efficient gonio-spectral imaging was performed for diffuse objects of Lambertian-like reflection by taking account of its optical reflectance properties. The proposed method assumes relative spectral distribution of reflected light could be regarded being constant, and only the power changes. This is preserved for wide range of geometries, except for neighbor of specular direction. Therefore, gonio-spectral images were created from only one basic spectral image at certain geometry. It was achieved by modulating power of the basic spectral image at each pixel with relative power change between illumination geometries. The relative power change was calculated from grayscale data of image reproduction geometry and that of basic spectral imaging. And also, spatial resolution was enhanced by recording grayscale images at higher resolution than basic spectral image. Experiments were performed to Japanese washi paper and cloth. Basic spectral data was obtained at geometry 45/0, and grayscale images were taken at geometry 81/0 and 87/0. From created spectral images, color images were reproduced under illuminant A and D65. Light-and-shade induced by surface textures were precisely represented together with color information based on spectral data. Good correspondence between appearance of real sample and reproduced images was achieved with smaller number of sampling points and less data amount than the previous method.