Sharpness preserving image enlargement based on a ramp edge model

Abstract

In multimedia applications sometimes we need to enlarge an image for it to fit the overall page layout. The traditional pixel repetition method produces edges that are jagged, and the interpolation-based methods tend to produce blurry edges. In this paper, we present an approach that is able to maintain both the continuity and the sharpness of the edges when enlarging an image. In this approach, we first locate the edge pixels in an image. We then extract for each edge pixel five ramp parameter values. These five values together characterize locally the edge segment associated with the pixel and the location of the pixel on the edge. Next, we use the parameter values of the edge pixels in the original image to derive parameter values for the edge pixels in the enlarged image. The intensity of the edge pixels in the enlarged image can then be determined from their parameter values. If we keep the ramp width parameter values at the same level for the edge pixels in the enlarged image, the enlarged edges will be as sharp as the edges in the original. The experiments show that the suggested ramp model based approach indeed produces enlargements with continuous and well-defined edges.