| 摘要 |
<p>An image signal (PS) or a screen threshold value (D) is converted by a plurality of conversion functions (Fi, Gi, fi, gi). The number (NST) of reference solid pixels, which should be exposed to attain a halftone area rate specified by a given image signal, is calculated for each quarter block (QB) which is a quarter of one unit block for one halftone dot. The numbers (NRS) of virtual solid pixels, which would be exposed if the converted image signal or the converted screen threshold value were used, are calculated concerning respective conversion functions for each quarter block. The number (NRS) of virtual solied pixels which is the closest to the number (NST) of reference solid pixels is selected and the conversion function corresponding to the selected number (NRS) is also selected for each quarter block (QB). Photosensitive film is exposed on the basis of the converted image signal or the converted screen threshold value converted by the selected copnversion function, whereby the halftone area rate specified by the given image signal is attained, and the line portion is prevented to be seen broken.</p> |
