The success of near infrared spectroscopy is based on the penetration of the radiation in solid and turbid inhomogeneous materials, giving diffuse transmission or diffuse reflection. For hyperspectral near infrared imaging where a pixel may be 0.2 mm × 0.2 mm or smaller, the same diffusion processes may give interaction over a number of pixels. Transmission experiments using pinholes show that both objective flare and diffusion of radiation lead to a smearing of information over neighbouring pixels over distances of 0.7 to 2 mm, leading to the conclusion that a pixel in a near-infrared image is not an isolated sample cell.

Keywords: hyperspectral NIR imaging, diffuse reflection, diffuse transmission, pinhole, information depth