The present invention concerns controlling a potential used to form an electrostatic image for image formation. According to the invention, an electrostatic latent image is formed on an image bearing member using, for example, a potential stored in a memory. The potential of the latent image is detected, and if the potential is not within a specified range, the potential is controlled (i.e., changed) to form another latent image with the changed potential. The latent image is then developed and the density of the developed image detected. In one embodiment, the amount of developer to be replenished is then controlled based upon the detected density and a target potential value, where the target potential value is determined and set based on the detected density and the potential used in the potential controlling step. In a related embodiment, when a result of the potential obtained after termination of a normal image formation process is out of a designated range, potential control is performed after termination of a next normal image formation process.
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