During the large area image processing, when the image expands too big, the contour effect like mosaic will appear in the contour of the expanded image. To solve the problem,according to the invariance of the vector character, an effective way of the smooth and illimitable zoom of the image is brought forward as a example of binary image in this paper. First, extract the contour of the initial image. Second, according to the extracted contour ,find the corners of the contour using the Hough transform. Third, distinguish the line and curve using the corners and get the control points of the contour. After zooming in or zooming out the control points,the contour of the zoomed image is obtained using the control points. Last,fill the regions made of the contour of the zoomed image through the region-filling algorithm, Thus the smooth zoomed image and its contour are obtained, The contour effect is solved at the same time. The way is simple and effective, The way is also applied to the gray image and color image after they are segmented and form a series of regions.