Image forming apparatus

Abstract

In an image forming apparatus for forming an ordinary copy or a tonality image for an original image for a printing press, original image data is divided into data within a predetermined area and that outside the area, and pixel density within the area is subjected to a density conversion in accordance with screen half-toning information which will increase density information toward the approximate center of these pixels, by way of example. The original image data or the density-converted image data is converted into a binary-coded signal conforming to the density, and an output image is formed in accordance therewith. Preferably, plural types of non-linear correction tables are provided and a tone-conversion is performed selecting an appropriate correction table for each pixel, or for each line, of the density-converted image data. Preferably, the original image data is binary coded by a pattern signal having a long period, and the density-converted image data is binary coded by a pattern signal having a short period. The foregoing is applied to color-separated image data of each color. Preferably, the image data is divided, in accordance with color, into predetermined areas having the same or a different number of pixels, or into predetermined areas having a planar phase which differs for each color, and a screen angle is applied thereto.