Direct imaging process with feed back control by measuring the amount of toner deposited

A method of detecting an amount of toner deposited on a surface area of an image forming element, the method comprising:

• measuring a change in an impedance or capacitance of an electrode extending over said surface area, and the impedance or capacitance of the electrode is measured by changing a potential of the electrode by a predetermined voltage and detecting an amount of charge flowing to or from the electrode in response to the change in the potential,
• wherein the measuring step includes the steps of:
• connecting the electrode to a first predetermined potential of a voltage source until the electrode is charged to this potential;
• disconnecting the electrode from the voltage source and then connecting the electrode, through an integrator, to a second predetermined potential, so that the electrode is discharged with a low discharge resistance through the integrator;
• and
• integrating a discharge current flowing through the integrator until the electrode is discharged to the second predetermined potential.

An image forming device comprising:

• an image forming element moving past an image forming station in which a toner is deposited on a surface of the image forming element, said image forming element having at least one electrode extending over a predetermined surface area of the image forming element;
• and
• at least one measuring circuit measuring an amount of toner deposited on said predetermined surface area on the basis of a resulting change in an impedance or capacitance of the electrode,
• wherein the image forming element is a drum having a plurality of electrodes extending circumferentially on or below an outer surface of the drum and corresponding each to a row of pixels of a toner image to be formed, wherein each of said electrodes of the drum is electrically connectable to one of said measuring circuits.