Color digital halftoning using black and secondary color replace

Details Color digital halftoning using black and secondary color replace Color digital halftoning using black and secondary color replace

1997-08-11

1999-06-29

Rogers, Scott

Image analysis

Histogram processing

For setting a threshold

382167, 358502, 358518, 358523, 358534, H04N 152, H04N 156, H04N 160

Patent

active

059179945

ABSTRACT:
This system selectively enables a printer to deposit primary or black color dots at pixel locations on a sheet to produce a color image--in such a way as to increase the overall number of dots used in the image, thereby minimizing contrast between dots on the sheet and adjacent areas and so providing a better simulation of a continuous-tone image. The result is print quality often near that of error diffusion, usually better than any dither technique, but with the greater speed of a dither technique. The system includes a memory for storing a first color vector for each pixel in the image, respectively, and a processor coupled to the memory for determining a second color vector from each of the first vectors, respectively. The processor accomplishes this determination by replacing a fraction of the black color component of the first vector with primary colors. Preferably the processor also removes from the first color vector a quantity of white, in conjunction with the black replacement; in this case the processor sets the fraction of the black component to a value between zero and one inclusive, depending on the quantity of white that is available, in the first color vector, for removal. Preferably the fraction is the smaller of (1) the quantity of black present and (2) a certain fraction of the quantity of white available for removal. Analogously a fraction of the secondary color component of a color vector is replaced with primary colors.

REFERENCES:
patent: 5473446 (1995-12-01), Perumal, Jr. et al.
patent: 5657137 (1997-08-01), Perumal, Jr. et al.

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