1. A method for edge direction detection in an image, comprising the steps of: selecting a pixel in an area of the image that is on a center line and defining the pixel as the selected pixel; calculating a vector value from a plurality of pixels being related to the selected pixel, the vector value being associated with a selected direction; using the vector value to determine whether the selected pixel is in a non-selected direction edge area; if the selected pixel is in the non-selected direction edge area, then determining a correlation between the non-selected direction edge area and the selected direction, such that if the correlation is low, then the area of the image is considered to not include an edge in the selected direction, wherein the step of determining the correlation further includes the steps of: calculating at least two candidate edge directions based on a plurality of small-angle vector values each associated with a direction having a small-angle certain angle from the selected direction; if one of the at least two candidate edge directions is associated with a preferred direction, verifying that the one of the at least two candidate edge directions is consistent with an additional candidate edge direction of the at least two candidate edge directions; when neither of the at least two candidate edge directions is associated with the preferred direction, then performing a direction detection process based solely on big-angle vector values associated with directions having bigger angles from the selected direction than the small-angle.