| 摘要 |
PURPOSE:To set the quantity to be controlled corresponding to each even in case of copying a document having a large halftone or a document having strong contrast by setting the surface potential of a photosensitive body based on a ratio of a variation of gradation. CONSTITUTION:Prior to a copying process, a document 50 is brought to pre-scan, and in this case, an AE sensor 36 monitors the increase and decrease of image density, and at every section in which the density increases continuously and at every section in which the density decreases continuously, its density variation quantity and length of its section are measured. Subsequently, at every section, the variation ratio is calculated by calculating the variation quantity/length, the variation ratio of the whole document is calculated by totaling the variation ratios which have been calculated with regard to all the sections of the document 50, and based thereon, the electrostatic charging potential on the surface of a photosensitive body is controlled by a control part 48. In such a way, even the document having a complicated halftone and even the document having strong contrast can be copied faithfully, respectively. |
