Abstract: An original image signal, which represents an original image and is made up of a series of original image signal components Yij, is obtained. Corresponding interpolation coefficients Bij and Cij, which are set for each of the original image signal components Yij, in two different interpolating functions f and g, represented by Formulas (1) and (2), for obtaining two interpolation images having different levels of sharpness are linearly combined with each other by using Formula (3). A new interpolation coefficient Aij is thereby obtained. An interpolating operation is carried out on the original image signal components Yij with an interpolating function h, which has the new interpolation coefficient Aij and is represented by Formula (4). An interpolation image signal is thereby obtained, which is made up of a series of image signal components occurring at intervals different from those of the original image signal components Yij,f=.SIGMA.Bij.multidot.Yij (1)g=.SIGMA.Cij.multidot.Yij (2)Aij=(1-.alpha.)Bij+.

Abstract: A fundamental gradation curve is enlarged or reduced such that the minimum density and the maximum density represented by the fundamental gradation curve may be changed respectively to a desired minimum density and a desired maximum density. The enlarged or reduced fundamental gradation curve is translated such that a point corresponding to a predetermined density may be shifted to a point representing a desired density. The translated fundamental gradation curve is rotated around the point corresponding to the desired density such that this point may represent a desired contrast.