Constrained Energy Maximization and Self-Referencing Method for Invisible Ink Detection from Multispectral Historical Document Images

This article deals with a serious form of degradation that often affects the readability of historical document images: the invisibility of text or ink. Due to wear over long periods of storage, the ink may become invisible to the human eye, an undesirable situation for scholars (i.e. Indian Ocean World project (IOW¹, with whom we are working closely). Because only the class of ink is known a priori (reference), it can be considered as a target to be detected. This can be achieved by designing a linear filter that maximizes an energy function while minimizing the false detection of document image background elements. For each document image in which the ink is targeted, an internal reference is defined by a new self-referencing strategy. The proposed method is compared with a state-of-the-art methods, and validated on samples of real historical document images.