Edge sharpening through ramp width reduction

摘要

Edge sharpness is very important to the visual quality of an image. Most commonly adopted methods increase the contrast of the edges to achieve sharpening. However, for wider ramp edges, increasing contrast alone brings very limited sharpening effect. In this paper, we propose a new method which sharpens an edge by reducing its width. Based on the intensity of a pixel and that of its neighbors, we derive three intensity indices and three gradient indices for the pixel. The three intensity indices are used to suggest whether the pixel is on an intensity ramp. The three gradient indices further indicate the location of the pixel relative to the ramp's centerline. If it is located above the centerline on the ramp, we increase the pixel's intensity. If it is located below the centerline, we reduce its intensity. If it is on or near the ramp's centerline, we leave the pixel's intensity unchanged. In this way the width of a ramp edge may be reduced and visually the edge becomes sharper.