PURPOSE: To correctly detect the tilt of a mark sheet by using a round guide mark.
CONSTITUTION: When the effective number of lines is set at 15 for both mark tables m1 and m2, m1 (L) and m2 (L) mean a series which defines L as an argument (L=1-15) and also serve as the histograms of left and right guide marks 41 and 42. If a stain 43 is detected, the centers of both marks 41 and 42 are shifted from each other. Therefore, the noises are emphasized for the reading of marks. In this connection, the areas of both marks 41 and 42 are calculated as the total number of pixels. Then, the lines positioned at 1/2 area of each mark are defined as center lines C1 and C2. A line error (h) is calculated from the difference between both lines C1 and C2 as h=C1-C2, and a tilt angle θ is calculated from the error (h) and the distance (w) between both marks as tanθ=h/w. Based on the angle θ, the mark positions are calculated for the subsequent reading of marks. Thus, the reading mark areas are properly recognized.
YASHIKI SEISHI
KONO KOJI
