1. An image processing apparatus comprising: a vector detection unit which detects flow vectors of pixels in an inputted image; a vector-coherency calculation unit which calculates vector coherency based on the flow vectors detected by the vector detection unit; a deformation-characteristic computation unit which computes a deformation characteristic by using the vector coherency calculated by the vector-coherency calculation unit, the deformation characteristic being used for deforming a tap shape of a filter used for each of the pixels; and a painterly conversion unit which converts the inputted image based on the deformation characteristic computed by the deformation-characteristic computation unit.