Information International, Inc.

Robert W Waller

Dean W Anschultz

Halftone images are formed from dots selected from a dot character font memory storing information representing halftone dots of different sizes and shapes corresponding to different gray scale tone values or image densities. An original image is first scanned to sample its tone values at minute intervals exceeding the desired dot resolution of the reproduction. These sample values are digitized by an A/D converter which converts them to multibit binary numbers. Adjacent samples are compared to determine the average image density in a particular area, as well as the rapidity of rate of change of image density within that area. If the rate of change of image density in a given area is below a selected threshold value, the area is designated as low detail and the multibit binary number representing the result of the average density calculation over the area is used to select a dot character from the font memory for reproducing that area of the image. If, however, the rate of change of image density exceeds the selected threshold value, indicating an area of relatively high detail, the area samples are used to select special dot shapes and positions for use in reproducing that sampled area. This technique achieves a higher resolution halftone image for a given amount of stored data than prior techniques, as well as achieving a higher 'apparent' resolution to the observer.

Method and apparatus for forming high resolution halftone images

In a film reader, a system is provided for deriving a dynamic reference signal proportional to the intensity of light in a flying spot scanner without obstructing any radiation from the scanner to a film being read comprising light guides each disposed with one end in an annular bracket which surrounds the flux path to the film and the other end of all light guides bundled together at the face of an auxiliary photometer. The one end of each guide is held in the annular bracket with its viewing axis pointing back toward the scanner. The viewing axes of the guides are evenly spaced and arranged to pass through a circle centered on the emitting surface of the flying spot scanner. The circle is preferably of greater diameter than the scanner.

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Northridge, CA, United States of America

Robert W Waller