| 摘要 |
PURPOSE:To copying original images of different densities in background parts satisfactorily by changing the correlative relations between reference electrostatic latent image potential and developing bias potential in correspondence to the change in the quantity of exposure light. CONSTITUTION:The potential of the reference electrostatic latent image on a photosensitive drum 1 formed of reference charts 4a, 4b of medium contrast id detected with a surface potential detector 14. In accordance with this, a developing bias control circuit 43 controls an electric power supply 44 for developing bais, and supplies the developing bias of the potential having a constant correlative relation corresponding to the detected reference electrostatic latent image potential to a developing electrode 16. When the image exposure is adjusted, the circuit 43 changes the correlative relation cooperatively with the change in the quantity of exposure light, thereby changing the developing bias voltage. In this way, the image reproducibility in the low density parts is changed, and the original images of different densities in the background parts are copied satisfactorily. |
