| 摘要 |
PURPOSE:To keep a shade quality constant in an image printed on printing paper by a method wherein a density of a printing developing agent applied to a photosensitive body is detected based on a light receiving level of a gradation signal to a predetermined level-and an output timing of the gradation signal CONSTITUTION:A detection light Ls emitted from a light emission means 31 is emitted to a photosensitive body 2. The detection light Ls reflected by the photosensitive body 2 is received by a light-receiving means 32. The light- receiving means 32 converts the received detection light Ls to an electric signal Si in accordance with the light receiving level thereof. At this time, the output of the detection light is controlled by a pulse width modulation in a blanking period Tb between an information signal Sv and a gradation signal. Ss by a level setting means. The light receiving level by the light-receiving means 32 is set to a predetermined level Lc. In a density detection means 33, a density of a printing developing agent applied to the photosensitive body 2 is detected based on a light receiving level of a gradation signal component S to the predetermined level Lc and an output timing of the gradation signal component S. |
