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: Cyan, magenta, yellow and black ink are each used to print a color patch to obtain four color patches. Two of each pair of the three colorants cyan, magenta and yellow are used to print a red, a green and a blue patch. These seven color patches together with a patch formed by the printing medium with no colorant form eight color patches. A color monitor is adjusted until its screen color matches one of the eight color patches and the appearance values of the monitor are noted. This is repeated for each of the eight patches in order to compile a lookup table for the colors in each of the eight color patches. For softproofing, each square in a color grid pattern printed by the printer will contain portions, each of which has a color identical to one of the eight color patches. Using the lookup table, the values of the appearance signals corresponding to the colors of these portions in the square area are obtained for displaying a color patch on the color monitor of the same color.

Abstract: For highlight or dark areas of images, the error terms diffused to neighborhood pixels include components which are periodic with respect to a wavelength where the wavelength is a function of the density level of the pixels from which the error terms are diffused. In this manner, patterned artifacts or "worms" in the highlight or dark areas of the images are reduced or illuminated.