1. A method of approximating an image by decreasing an amount of image data used to create the image, wherein said image data defines a polygonal framework, said framework being composed of line segments drawn between vertices, said method comprising: evaluating a degree of importance of each line segment of said framework; removing at least one unnecessary line segment from said framework which is identified based on said evaluation of said degree of importance of each line segment; and determining a position of a vertex after said unnecessary line segment is removed , wherein said framework is drawn on a display apparatus .