Fourth order indirect diffusion coupled with shock filter and source for text binarization

Abstract

In this paper, we present a binarization method for degraded document images with contrast variation or low contrast, which couples a selective shock filter and a time-dependent source to a fourth order indirect diffusion process. The role of the selective shock filter is to enhance the edges as far as possible, while the time-dependent source plays an increasingly predominant role in the process of binarization. The fourth order indirect diffusion not only keeps the merit of noise immunity of the direct diffusion counterpart, but also preferably preserves the low-frequency components to avoid blur and dislocation of weak edges. We develop a novel numerical scheme for solving our model effectively and efficiently, by incorporating finite differencing with the parallel splitting up method in the literature. The proposed algorithm is tested on seven publicly available datasets (Document Image Binarization COmpetition (DIBCO) 2009 to 2014 and 2016). The experimental results indicate that our model is very effective for binarization of document images with contrast variation or low contrast, and has mostly the best effect for document images from the DIBCO datasets, compared with four partial differential equation (PDE) models and four benchmark and recent non-PDE methods.