METHOD AND APPARATUS FOR ENLARGING OR REDUCING AN IMAGE ON THE BASIS OF PRE-CALCULATED REFERNCE PEL CONTRIBUTION RATE DATA AND TWO- DIMENSIONAL REFERENCE WINDOW SHIFTING AMOUNT DATA STORED IN A TABLE MEMORY

A method and apparatus for reducing or enlarging an image. More specifically, this invention can increase or decrease the magnification ratio of an image even while scanning each line. This invention involves converting a first image with a first pel density to a second image with a second pel density. The intensity P of a new pel at a point p of the second image is represented by ##EQU1## where m is the number of reference pels of the first image that are sampled and that are within a given two-dimensional reference window when it is in a predetermined position corresponding to the point p, where Ii is the intensity of the i-th pel of the m sampled reference pels, and where .alpha.i is a contribution rate indicating how much the i-th pel contributes to the intensity P. Pre-calculated contribution rate data (.alpha.i) and pre-calculated shifting amount data indicating the relative amount the reference window is to be shifted are stored in a memory. The shifting amount data is used to position the reference window to a predetermined position where the m reference pels are sampled, and the contribution rate data and the values of the m sampled pels are used to determine the intensity P.