Multithresholding of mixed-type documents

Mixed type documents include text, drawings and graphics regions. It is obvious that a technique that can reduce the number of the gray-levels in accordance to the type of each document region could be important for many document applications, such as storage, transmission and recognition. To solve this problem this paper proposes a new method that is called the document multithresholding technique. The method is based on a Page Layout Analysis (PLA) technique and on a neural network multilevel threshold selection approach. In the final document the different block types are stored with the appropriate and limited number of gray-level values. In text and line-drawing blocks, only one threshold is determined whereas in the graphics blocks the optimal number of thresholds is first determined. The performance of the method was extensively tested on a variety of documents