Hyperspectral Document Imaging: Challenges and Perspectives

Hyperspectral imaging provides measurement of a scene in contiguous bands across the electromagnetic spectrum. It is an effective sensing technology having vast applications in agriculture, archeology, surveillance, medicine and forensics. Traditional document imaging has been centered around monochromatic or trichromatic (RGB) sensing often through a scanning device. Cameras have emerged in the last decade as an alternative to scanners for capturing document images. However, the focus has remained on mono-/tri-chromatic imaging. In this paper, we explore the new paradigm of hyperspectral imaging for document capture. We outline and discuss the key components of a hyperspectral document imaging system, which offers new challenges and perspectives. We discuss the issues of filter transmittance and spatial/spectral non-uniformity of the illumination and propose possible solutions via pre and post processing. As a sample application, the proposed imaging system is applied to the task of writing ink mismatch detection in documents on a newly collected database (UWA Writing Ink Hyperspectral Image Database http://​www.​csse.​uwa.​edu.​au/​%7Eajmal/​databases.​html). The results demonstrate the strength of hyperspectral imaging in capturing minute differences in spectra of different inks that are very hard to distinguish using traditional RGB imaging.