PURPOSE: To easily correct the shape of a white plate graphic to an adjacent original graphic to an adequate shape.

CONSTITUTION: The original graphic of the thinning white plate graphic is extracted as a noticed graphic and the original graphic adjacent to this noticed graphic is extracted. The noticed graphic and the adjacent graphic are ORed the white plate graphic corresponding to the adjacent graphic is the thinning or thickening white plate graphic. Logic computation of the graphics with each other is then executed, by which the white plate graphic corresponding to the noticed graphic is corrected. A slipping in graphic is formed if the white plate graphic corresponding to the adjacent graphic is the drop-out white plate graphic or the white plate graphic of the same shape as the original shape. This graphic is then added to the white plate graphic corresponding to the noticed graphic, by which the white plate graphic is corrected.