Sharpness Improvement of Warped Document Images for Top View Book Scanners

This paper is aiming at improving the top view book scanner functionalities to the ability of depicting homogeneous sharpness across the output colour image. Typically, the opened book has a curved shape which results in a space-variant blur in the recorded image. A priori calibration filters are computed by taking an advantage of longitudinal chromatic aberration behaviour in the scanners. Hence, the sharpest channel on the focused plane is chosen as an exemplar to compute a restoration filter for the sharpest channel on each of the defocused planes. Assuming strong correlation between the channels, another filter is computed to reflect the sharpness of the restored channel to the other channels. In order to enhance spatial homogeneity of the scanned image, 3-D information is estimated from book contours. Results exhibit the possibility of having visually homogeneous sharpness in the entire scanned images.