APPARATUS AND METHOD FOR FORMING IMAGE USING HIGH GAMMA PHOTOSENSITIVE BODY

PROBLEM TO BE SOLVED: To vary a gradation pattern by virtue of a means for detecting a sensitivity of a photosensitive body in order to use it even when a characteristic of high gamma is degraded or lost therefrom. SOLUTION: Gradation expression of multiple exposure elements is executed by using a common reference signal and a surface voltage of an exposed region on a photosensitive body is monitored by means of a surface voltage sensor 1303 and is converted to digital data by an A/D converter 1306. The surface voltage data is inputted to a CPU 1307. At that time, when the photosensitive body has a good high gamma characteristic, the data inputted to the CPU 1307 may become 5/31. When the characteristic of sensitivity of the photosensitive body is deteriorated and high gamma characteristic is not maintained, it may become 7/31 because of gradation inverting phenomena. Therefore, it is preferable that a threshold level for sensitivity deterioration is set to 6/31. It is possible to eliminate the gradation inverting phenomena that is caused by variation of sensitivity of the photosensitive body having a characteristic of high gamma by providing a gradation pattern switching section.