To solve this problem, the edge image is decomposed by the edge direction, and the text regions, which makes outliers,are removed. Each boundary line of a rectangular white paper has different direction. If there is no perspective distortion, the boundary lines of the opposite side of a paper has the direction with the difference of 180 degree as shown in Fig.3.
However, the captured image has some perspective distortions practically. We decompose the edge plane into eight separate
edge planes as follows.