Abstract: Forming a visible image of a sensor pattern on a photosensitive member for use in controlling image density of copies, wherein the sensor pattern of a reference density is placed substantially flush with a surface on which a document to be copied is placed; the surface of the photosensitive member is exposed to an optical image of the sensor pattern to form a latent image of the sensor pattern in a region of the photosensitive member outside a document image forming region; and the latent image is developed to obtain a visible image of the sensor pattern. The density sensed by a sensor element produces an electric signal used for controlling the density of an image.

Abstract: Light reflected from a reference pattern having a predetermined reflectivity is focused to a photoconductive element to form a latent image thereon. A degree of deposition of a toner on the latent image is sensed by a sensor and the toner supply to a developing unit is controlled in response to an output of the sensor. A fatigue standard is selected taking into account a fatigue characteristic particular to the photoconductor, so that a bias voltage applied to a developing roller in the developing unit is varied in response to the selected fatigue standard.

Abstract: A photoconductive drum (32) is charged, radiated with a light image of an original document (34) and developed to produce a toner image. The density of the toner image is sensed and additional toner fed to a developing unit (37) if the sensed density is below a predetermined value. The sensed toner density is compensated for variations in charge potential, light image intensity, electrostatic image potential, developing bias voltage, power supply voltage and/or sensor output so as to be independent of these variables.