Abstract: Toner control system and method for an electrographic printer in which toner is delivered from a reservoir to a toner fountain and there applied to an electrostatically charged sheet to form an image. The visual quality of the image is monitored, and toner concentrate is added to the toner in response to the monitored quality to increase the amount of pigment particles in the toner and thereby maintain a substantially constant image quality. The concentrate is added to the toner in a return line between the fountain and the reservoir in relatively small, predetermined amounts, and it is mixed before being added. In the disclosed embodiments, a test image is formed outside the main image on the sheet, and the brightness of one or more predetermined colors in the test image is monitored. This system and method are applicable both to monochrome images and to multicolor images.

Abstract: A light concentrator, preferably for use with a color optical scanning device includes a reflector (34) with parabolic reflecting walls (36). Green LEDs (22), red LEDs (24), and blue LEDs (26) are situated at the base of the reflector (34) and a diffuser (30) is attached to the opposite end thereof. An electric switch (32) controls the LED array. When an input page is scanned, the switch (32) activates one type of LEDs at a time. The reflector (34) concentrates the emitted light at the surface of the diffuser (30). The photodetector array of the xerographic device receives three monochromatic images which are then superimposed to provide a color image.