METHOD OF AND APPARATUS FOR CHANGING THE PIXEL DENSITY OF A BINARY IMAGE USING AVERAGE VALUES CALCULATED FROM SETS OF REFERENCE PIXELS SELECTED FROM THE BINARY IMAGE

A image processing apparatus includes a dither processor, which converts an electrical signal representing a continuous-tone input image into a binary image singal by a dither method using a dither matrix. The binary image signal is stored in a memory, and supplied to a pixel-density conversion processor, which converts a pixel density of the binary image signal at a predetermined ratio, and generates a converted image with the pixel coordinates as defined by the conversion ratio. A pixel coordinate calculator calculates a coordinate position of each pixel of the converted image in the binary image, and selects a fiducial pixel. A reference pixel selector defines a window area on the binary image containing the fiducial pixel and corresponding in size to the dither matrix size, and extracts reference picture elements in the window area. A calculator calculates an average image-density of the reference picture elements and generates density data, which is binarized by a second dither processor by using a second dither matrix.