| 摘要 |
<p>A digital halftone output image is rendered from a continuous tone input image having a plurality of input pixels which have been digitized as gray scale values. A page frame buffer (32) for storing a pixel representation of the halftone output image is defined in terms of a plurality of clustered-dot cells (50), each clustered-dot cell (50) encompassing a unique set of output pixels (52) in the page frame buffer (32). A number of interactive gray scale patterns (60) are defined for use in the clustered-dot dithering process in terms of the same number of output pixels (50) that define a single clustered-dot cell (50). Each interactive gray scale pattern (60) is capable of producing a unique gray scale value when applied to the clustered-dot cell (50). A computer processor (34) produces the halftone output image by dithering each input pixel of the continuous tone input image to produce a unique clustered-dot cell (50) in the page frame buffer (32) which is filled with one of the interactive gray scale patterns (60) closest to the gray scale value of that input pixel. Unlike classical ordered dithering techniques which use a series of ordered gray scale patterns, the use of the series of interactive gray scale patterns (60) results in more output gray scale values than there are output pixels (52) in the clustered-dot cell (50). The interactive gray scale patterns (60) utilize the interaction among output pixels (52) in order to generate gray scale patterns which have the same number of output pixels (52) turned on, but which produce different gray scale values when printed. Because the interaction among ouptut pixels (52) is most prominent in those types of laser printers and the like which cannot produce individually discrete output pixels or which have output pixels (52) with unequal horizontal and vertical dimensions, the effectiveness of the present invention is greatest among these types of graphic display devices.</p> |
