Automatic thresholding of gray-level using multistage approach

A multistage approach is presented for thresholding document images, along with its application. The proposed method is based on two stages. Global thresholding is used in the first stage to give a preliminary result. A second stage then refines the threshold value based on local spatial characteristics of the regions formed in the first stage. It automatically customizes the thresholding of regions that have specific and consistent characteristics but are different to other regions in the image. This technique works well for both simple images, in which the background and foreground are distinct and separable and complex images containing multiple regions with different shading/textures. A typical application is postal envelope analysis. The results of evaluation show significant improvement compared to several other global and local thresholding techniques.