1. A computer usable medium having embodied thereon a computer program for restoring a reduced binary image, reduced from an original binary image by down sampling, into the original binary image, comprising the steps of: (a) calculating a predicted value of an interpolated pixel based on values of object pixels A, B, C and D around the interpolated pixel using the following equation: EQU INP(P)=A.multidot.(1-h)(1-v)+B.multidot.(1-h)v+C.multidot.h(1-v)+D.multidot .hv, where h and v of each term represent horizontal and vertical distances between the object pixel and the interpolated pixel included in the corresponding term; (b) calculating a context C.sub.P, representing a state value of reference pixels around the object pixels, by concatenation of the reference pixel values using the following equation: ##EQU2## wherein P represents the position of the interpolated pixel, C.sub.k represents the reference pixel and k is an index of reference pixels; (c) obtaining a threshold value, THRc(t), corresponding to the context C.sub.P which is changed in each interpolated pixel based on its context; and (d) determining the interpolated pixel as "1" if the predicted value in step (a) is greater than the threshold value in step (c), and setting the pixel value of the interpolated pixel as "0" otherwise.