METHOD AND DEVICE FOR CORRECTING IMAGE DENSITY

PROBLEM TO BE SOLVED: To perform stable toner concn. control and concn. correction without being influenced by the fluctuation of the intensity of light illuminating a patch by electrifying a photoreceptor to different electrification potential by changing the grid voltage of an electrifying means, forming a patch image for controlling toner density and a patch image for correcting gradation, and performing the control of the toner concn. and the correction of the gradation. SOLUTION: A grid voltage control means by which the grid voltage of a scorotron electrifier 11 is switched to at least two or more values is provided to form the patch at the grid voltage different between at the time of forming the latent image of the patch for controlling the toner concn. and at the time of forming the latent image of the patch for correcting the gradation. Then, the patch image for controlling the toner concn. or correcting the gradation is formed at a position equivalent to the patch part on the photoreceptor drum 10 so as to control the toner concn. and correct the gradation. Thus, the accurate control and the accurate correction are performed without using a troublesome and complicated sensor or depending on a control means.