Method for detecting an image edge within a dithered image

摘要

A method for detecting an image edge within a dithered image. A pixel within a support region is selected for processing. The differences between pixel values in the region and the selected pixel are computed to form a current difference map. Whether the selected pixel in the region differ by no more than one resolution level from any other pixel of the region is determined from the current difference map. An edge is determined not to exist within the region if the difference map for a region contains no values differing by more than one resolution level. An edge is determined to exist within a region if the difference map for the selected pixel and region contain values differing by more than one resolution level. Alternatively, a difference map for the selected region of support is determined and compared to a table of all possible valid difference maps. If a corresponding difference map is found within the table then an edge does not exist within the presently processed region of support. If no corresponding difference map is found within the table then an edge exists within the region of support. Alternatively, the number of valid difference maps to be compared for each region may be reduced by selecting only the difference maps based on the dither template as originally applied to the image. All valid difference maps which do not contain values based on the original dither template are excluded from comparison.