Image forming apparatus and program executed by computer of image forming apparatus

An electrophotographic image forming apparatus comprising:

• an image carrier that is rotatable and carries and conveys a toner image;
• a charging member that is arranged in contact with or close to the image carrier;
• a charging power supply that charges the image carrier by applying a charging bias to the charging member;
• an exposurer that forms a latent image on the charged image carrier;
• a developing member that is arranged close to the image carrier;
• a developing power supply that develops the latent image and forms a toner image on the image carrier by applying a developing bias to the developing member;
• a transfer member that transfers the toner image formed on the image carrier to a medium by receiving an applied transfer bias;
• and
• a hardware processor that controls the image forming apparatus, wherein
• the hardware processor
• obtains a potential of an exposure part where the latent image is formed and a potential of a non-exposure part where the latent image is not formed, on the image carrier after the toner image has been transferred to the medium,
• determines the charging bias based on a difference between the obtained potentials of the exposure part and the non-exposure part so that a potential on the image carrier becomes uniform after the toner image has been transferred to the medium, and
• determines the developing bias based on the determined charging bias.