An electrophotographic photosensitive drum for use in an electrophotographic image forming apparatus includes a cylinder and flanges provided on end portions in the axial direction of the cylinder. In a reset period, a reset pulse with a waveform of a sloped ramp pulse is applied to the scan electrode. The plurality of images is associated with compression values generated on compression of the plurality of images. The coverage model has the form of a sequence of Floating-Point commands with constraints on the input operands, intermediate result operand and the result operand.