Image forming apparatus having image signal discrimination device

摘要

The present invention provides an image forming apparatus having image signal discrimination device for discriminating whether an image density signal belongs to a line image portion or a natural image portion including a halftone image and outputting a discrimination signal, first image density conversion device having a first conversion property for converting the image density signal to a conversion signal and outputting the conversion signal, second image density conversion device having a second conversion property which is different from the first conversion property for converting a range of the image density signal corresponding to a low density portion to a conversion signal indicating a value within a range in which an image is not developed and outputting the conversion signal, selection device for alternately selecting the first and second image density conversion device with a predetermined period, pulse width modulation device for modulating pulse widths of the conversion signals output from the first and second image density signal conversion device and outputting a pulse width modulation signal, pulse width modulation signal period changing device for changing a period of the pulse width modulation signal output from the pulse width modulation device and the period of selection carried out by the selection device in accordance with the discrimination signal output from the image density signal discriminating device, and image formation device for forming an image in accordance with the pulse width modulation signal output from the pulse width modulation device.