| 摘要 |
PURPOSE: To emphasize a bright or dark tone according to the selection of a halftone level by selecting one set of quadruplets obtained by combining a halftone two- reflectivity gray level and a black and white pixel level so as to minimize the generation of the black and white pixel level in each of halftone cells. CONSTITUTION: A linear scanning array 70 converts the image of each line of a document to an analogue image signal and this signal is converted to a pixel by a pre- processing part 76. A processing part 78 outputs the control signal of many bits showing halftone cells to be printed to a power supply control part 81 according to forms at every lines and pixels and a power operating signal operating power supply devices 83, 84, 85 selectively is supplied to lines 82-1, 82-2, 82-3. The power supply devices 83, 84, 85 output powers different in level to drive a laser 25 and expose a photoelectric receptor 20 to supply a latent electrostatic image according to the image content of the image signal from the linear scanning array 70. The number of gray pixels and that of black pixels in the halftone cells are compared mutually and the best result is achieved by an average gray level maximizing the use of the gray scale level of black and white pixels and minimizing the use of the halftone gray level. |
