PURPOSE: To prevent the whole extracted image (especially an internal image) from being unclear in an anti-aliasing processing method for quieting the peripheral part of an extracted image.

CONSTITUTION: In image synthesis for integrating an extracted image in an area corresponding to a background image, identifying labels Lk ('1' e.g.), Lc ('2' e.g.) are allocated to boundary picture elements and picture elements in the inside extracted image as shown in figures (a), (b), outline image elements are detected by using the boundary image elements of the label Lk, the density value of each outline image element is substituted by the mean value of density values of 8 peripheral image elements, a label Lr ('3' e.g.) are allocated to the substituted picture elements as shown in a figure (c), and then the density value of each boundary image element of the label Lk is substituted by a weighted mean value between the density values of 8 peripheral picture elements and the density value of the picture element itself (e.g. twice the density value of the picture element itself is weighted). An image corresponding to the picture elements of the labels Lr, Lk, Lc is displayed as an anti-aliasing picture.