ADAPTIVE IMAGE SHARPENING METHOD USING EDGE SHARPNESS

This paper proposes a new method for automatic improvement in image qu ality through adjusting the image sharpness. This method does not need prior knowledge about image blur. To improve image quality, the sharp ness must be adjusted to an optimal value. This paper shows a new meth od to evaluate sharpness without MTF. It is considered that the human visual system judges image sharpness mainly based upon edge area featu res. Therefore, attention is paid to the high spatial frequency compon ents in the edge area. The value is defined by the average intensity o f the high spatial frequency components in the edge area. This is call ed the image ''edge sharpness'' value. Using several images, edge shar pness values are compared with experimental results for subjective sha rpness. According to the experiments, the calculated edge sharpness va lues show a good linear relation with subjective sharpness. Subjective image sharpness does not have a monotonic relation with subjective im age quality. If the edge sharpness value is in a particular range, the image quality is judged to be good. According to the subjective exper iments, an optimal edge sharpness value for image quality was obtained . This paper also shows an algorithm to alter an image into one which has another edge sharpness value. By altering the image, which achieve s optimal edge sharpness using this algorithm, image sharpness can be optimally adjusted automatically. This new image improving method was applied to several images obtained by scanning photographs. The experi mental results were quite good.