Multilevel color halftoning

A new high-speed color printer uses new image screening methods that lead to superior-quality images. The screen rulings as well as the screening angles are varied. The cyan, magenta, and yellow screens are around 200 lines per inch. The black screen starts at 212 lines per inch at 45 degrees and progresses to 300 lines per inch at zero degrees when half the pels in the basic cell are on. This improves the details in the black color plane without introducing significant moire patterns. Since the printer is capable of 4 bits/color, threshold matrices are used to determine onset of printing. The actual output intensities are selected from look-up-tables indexed by the input value minus the threshold. Experiments showed that the intermediate intensity values reproduced best as leading pels on vertical marks. Results for mixing halftones at significantly different screen rulings are illustrated.