A novel preprocessing method for hectography prints based on independent component analysis

Archives and cultural facilities consists of vast spectra of different document classes, many of which are not encountered today anymore. The digitization therefore calls for image enhancement and preprocessing solutions so far not required and hence unsolved. A prominent document class in this context is hectography, which was a inexpensive printing and duplication method, widely used throughout the 20th century. The major challenge with hectography is poor contrast on the one side and multiple degradation effects on the other side.In this paper a novel preprocessing method for hectography duplicates is proposed which leads to better Optical Character Recognition (OCR) results compared to traditional methods that operate on grayscale images. The proposed method is based on the model confo rm with the independent component analysis. The problem of unwanted Gaussian noise components is considered as well

A Novel Approach to the Design of Oversampling Low-Delay Complex-Modulated Filter Bank Pairs

In this contribution we present a method to design prototype filters of oversampling uniform complex-modulated FIR filter bank pairs. Especially, we present a noniterative two-step procedure: (i) design of analysis prototype filter with minimum group delay and approximately linear-phase frequency response in the passband and the transition band and (ii) Design of synthesis prototype filter such that the filter bank pairs distortion function approximates a linear-phase allpass function. Both aliasing and imaging are controlled by introducing sophisticated stopband constraints in both steps. Moreover, we investigate the delay properties of oversampling uniform complex-modulated FIR filter bank pairs in order to achieve the lowest possible filter bank delay. An illustrative design example demonstrates the potential of the design approach