1. An image processor comprising: image reading means for photoelectrically scanning image data of an original to obtain an input analog image signal; sampling means for A/D-converting the input analog image signal to sample the image data, thereby obtaining a sampled digital image signal; correcting means for linearly correcting the sampled digital image signal with respect to an image density between the original and a recording image in accordance with the image data of the original, wherein said correcting means performs a conversion to obtain an output Q.sub.i ' given by ##EQU3## where Q.sub.i is the sampled digital image signal Q.sub.iM is the value of the sampled digital image signal when D.sub.i =D.sub.iM HL is a predetermined black density of the original D.sub.OM is a recording density of black when a recording density of white is give as 0 D.sub.i is a density of a pixel of the original D.sub.iM is a density of the pixel of the original having the highest black density value; and processing image data generating means for generating a binary processing image signal in accordance with the output Q.sub.i ' from said correcting means.