Abstract: The invention is for use with a visible medium capable of light reflection etc., and for use with a color-image source that defines a desired color. Here a device for causing the medium to appear colored includes a gray-scale subsystem to achromatically suppress a stated fraction of the reflection; and at least two device-primary subsystems to cause selective reflection of light of two associated device-primary colors. Even if the device, as originally made, in effect uses the gray-scale subsystem to help construct colors, or the device-primary subsystems to help form gray-scale "values", such cross-dependency is essentially removed. A programmed processor resolves the desired-rendition information into Fraction-Black, Fraction-Colorant, and hue.

Abstract: A media advance system for swath-type printers for precisely positioning the media for successive swath printing. A dual photodiode line sensor is mounted on the print head. The diode active areas are separated by less than the line widths of lines printed in the media margin. Circuitry is provided to provide a signal indicative of the difference between the photocurrents produced by each photodiode. For the first swath of the page or plot, marginal lines are drawn by the first and Nth print device of the print head. Without moving the media, the line sensor is positioned over the marginal line printed by the first device, and the resulting difference signal is saved as a reference value. The media is then advanced until the same value of the difference signal is obtained from the line image of the marginal line drawn by the Nth print device. The media is then advanced a predetermined amount to precisely position the media for the next successive swath to be printed.