| 摘要 |
<p>An electrostatographic machine is provided with a manually operable switch for changing the output of a pre-transfer corona discharge device depending upon the contrast characteristic of an original document to be copied. If the pre-transfer device is energized by an A.C. signal biased to a preselected D.C. level, this D.C. bias level may be changed in accordance with contrast quality of the original document to vary the image density at which transition from transfer suppression to transfer enhancement takes place. Alternatively the A.C. excitation level may be varied to change the point at which transition from transfer enhancement to transfer suppression occurs.</p> |
