Patent ID: 7869726

Claim:
An image forming apparatus that performs printing image data of a print job received from a host apparatus on a print medium, the image forming apparatus comprising: an image bearing body on which an electrostatic latent image is formed; a charging member that charges the image bearing body; a developer material bearing body that supplies a developer material to the electrostatic latent image to form a developer image; a developer material supplying member that supplies the developer material to the developer material bearing body; a first power supply that applies a first voltage to the developer material bearing body; a second power supply that applies a second voltage to the developer material supplying member; a third power supply that applies a third voltage to the charging member; a dividing section that divides the image data into a plurality of sub data areas, each of the sub data areas extending from the beginning of the entire image data to the end of the entire image data; a dot counter that counts a number of dots in a corresponding one of the plurality of sub data areas; a computing section that computes a print duty for each of the plurality of sub data areas based on the number of dots counted by the dot counter and a total number of printable dots in a printable area for the print job, a total number of print duties in the print job being equal in number to the plurality of sub data areas; a memory that holds a reference and the print duty; a comparing section that compares the print duty with the reference; and a controller that controls the second power supply to increase a voltage difference between the first voltage and the second voltage while maintaining the third voltage and the first voltage, the voltage difference being increased when the print duty is larger than the reference.