Invariant representation for spectral reflectance images and its application

Abstract

Spectral images as well as color images observed from object surfaces are much influenced by various illumination conditions such as shading and specular highlight. Several invariant representations were proposed for these conditions using the standard dichromatic reflection model of dielectric materials. However, these representations are inadequate for other materials like metal. This article proposes an invariant representation that is derived from the standard dichromatic reflection model for dielectric and the extended dichromatic reflection model for metal. We show that a normalized surface-spectral reflectance by the minimum reflectance is invariant to highlights, shading, surface geometry, and illumination intensity. Here the illumination spectrum and the spectral sensitivity functions of the imaging system are measured in a separate way. As an application of the proposed invariant representation, a segmentation algorithm based on the proposed representation is presented for effectively segmenting spectral images of natural scenes and bare circuit boards.

Minimum removal and maximum normalization of VNIR hyperspectral image for shade and specular invariance

“…3 Ibrahim et al tried to solve the specular problem for metal materials. 4 Ashton et al proposed a shadow removal method in hyperspectral images. 5 Most HSI-based target detection methods use spectral preprocessing to reduce the illumination effects.…”

An Effective Method for Illumination-Invariant Representation of Color Images

“…In our previous studies, we proposed an invariant representation for a variety of real-world objects including metals and dielectrics [8]. We showed that the normalized surface spectral reflectance by the minimum reflectance was invariant to illumination effects and the representation was effective to spectral imaging applications [9]. However, the method requires an expensive and special measurement device such as a spectral imaging system and a standard white reference.…”