Thresholding of badly illuminated document images through photometric correction

This paper presents a document image thresholding technique that binarizes badly illuminated document images by the photometric correction. Based on the observation that illumination normally varies smoothly and document images often contain a uniformly colored background, the global shading variation is estimated by using a two-dimensional Savitzky-Golay filter that fits a least square polynomial surface to the luminance of a badly illuminated document image. With the knowledge of the global shading variation, shading degradation is then corrected through a compensation process that produces animage with roughly uniform illumination. Badly illuminated document images are accordingly binarized through the global thresholding of the compensated ones. Experiments show that the proposed thresholding technique is fast, robust, and efficient for the binarization of badly illuminated document images.