Binarization of document images using Hadamard multiresolution analysis

We propose a new method that combines the use of a global threshold and a window-based scheme for computing local thresholds. The latter scheme compares the contrast of gray values within a neighborhood whose size varies with the scale of the objects being examined. To compute the scale quantity, a new wavelet model entitled Hadamard multiresolution analysis is also proposed. When the window-based scheme is applied to the areas where the global threshold is likely to fail, we obtain uniformly better binary results than using a global threshold only. Significant improvements to OCR performance can also be achieved by our binary results.