Resolution Enhancement Techniques for Halftoned Images

摘要

Recently, speed and resolution of electrophotographic printer engine have been significantly improved. In today's market, it is not difficult to find low to mid-end electrophotographic printers with the spatial resolution greater than 600 dpi and/or bit-depth resolution more than 1 bit. Printing speed is determined by the processing time at computer, data transmission time between computer and printer, and processing and printing time at printer. When halftoning is performed at computer side, halftoned data would be compressed and sent to printer. In this case, increase in the spatial and bit-depth resolution would increase data size to be transmitted and memory size at printer. For a high-speed printer, increased transmission time may limit the throughput in imaging chain. One of possible solutions to this problem is to develop resolution enhancement techniques. In this paper, a fast and efficient spatial resolution enhancement technique is proposed. Objectives of the proposed technique are to reduce the data size for transmission and minimize image quality deterioration. In the proposed technique, number of black pixels in the halftoned data is binary coded for data reduction. At printer, black pixel placement algorithm is applied to binary coded data. For non-edge area, screen order is utilized for the black pixel placement. When identified as edge area, locations of black pixels are selected by the edge order designed by genetic algorithm.