1. A method for filtering an edge direction, the method which comprises: in a given row in an edge orientation map, selecting a given pixel having an edge direction; finding neighboring upper pixels having neighboring upper edge directions for the given pixel by traversing along the edge direction of the given pixel from the given pixel to a neighboring upper row of the edge orientation map; finding neighboring lower pixels having neighboring lower edge directions for the given pixel by traversing along the edge direction of the given pixel from the given pixel to a neighboring lower row of the edge orientation map; determining whether the edge direction of the given pixel can be extended to the neighboring upper row by checking an orientation similarity between the edge direction of the given pixel and the neighboring upper edge directions; determining whether the edge direction of the given pixel can be extended to the neighboring lower row by checking an orientation similarity between the edge direction of the given pixel and the neighboring lower edge directions; if the edge direction of the given pixel can be extended to both the neighboring upper row and the neighboring lower row, then assuming that the edge direction of the given pixel is valid; if the edge direction of the given pixel cannot be extended to the neighboring lower row, but the edge direction of the given pixel can be extended to one of the neighboring upper pixels, and a neighboring upper edge direction at the one of the neighboring upper pixels can be extended to a further neighboring upper row of the edge orientation map, then assuming that the edge direction of the given pixel is valid; if the edge direction of the given pixel cannot be extended to the neighboring upper row, but the edge direction of the given pixel can be extended to one of the neighboring lower pixels, and a neighboring lower edge direction at the one of the neighboring lower pixels can be extended to a further neighboring lower row of the edge orientation map, then assuming that the edge direction of the given pixel is valid; and otherwise, assuming that the edge direction of the given pixel is not valid.