IMAGE FORMING APPARATUS AND METHOD FOR ELECTRIFYING AND DEVELOPING BIAS CONTROL FEATURES

An engine controller adjusts an image density of the toner image to a target density by controlling an electrifying bias and a development bias. The engine controller determines an optimal development bias which is needed to obtain the target density based on densities of first patch images which are formed in the following bias condition: The electrifying bias is fixed at the most recent optimal electrifying bias which is stored in a RAM; and the development bias is gradually changing based on the most recent optimal development bias which is stored in the RAM.