IMAGE DENSITY CORRECTING METHOD

PROBLEM TO BE SOLVED: To form a patch having high stability and always the same halftone density and to stably obtain excellent copied image density irrespective of using circumstances by forming a patch for correcting gradation of halftone without being influenced by an illuminating lamp and correcting gradation. SOLUTION: The halftone patch image is formed without performing exposure which becomes an unstable element so as to correct the gradation. Namely, grid potential by a scorotron electrifier 11 is lowered to form a latent image by unexposure which is not influenced by light quantity, and the latent image is developed with developer to form the halftone (optical density 0.4) developed patch image on a photoreceptor drum 10. The density of the developed patch image is measured. In the case of judging that the density is higher than the previously set density, a gradation correction mode (γ mode) is started to correct the gradation. The same density sensor SD is used for the density detection of the patch image for measuring toner density and that of the patch image (γ patch) for correcting the gradation.