Patent ID: 6947178
Filing Date: 2005-09-20
Classification: G06T,H04N

Abstract:
1. A method for converting halftone images into continuous-tone images, comprising: obtaining a halftone image; defining a two-stage filter, wherein a first stage is a smoothing filter and a second stage is a sigma filter connected to the smoothing filter; defining parameters for the smoothing filter and the sigma filter, which includes an intensity difference delta; inputting the halftone image into a smoothing filter to derive an intermediate image; sweeping a window across said halftone image and the corresponding intermediate image, and within a window, selecting those pixels that have an intermediate gray value within said intensity difference delta of a center window pixel; applying a sigma filter to pixels from said halftone image that correspond to pixels selected in said sweeping step; and outputting from said sigma filter a continuous-tone image which is piecewise-smooth and has preserved edges.