Color image processing apparatus capable of suppressing moire

Details Color image processing apparatus capable of suppressing moire Color image processing apparatus capable of suppressing moire

1994-06-22

1996-11-05

Boudreau, Leo

Image analysis

Color image processing

Drop-out color in image

358454, 358533, H04N 140

Patent

active

055726003

ABSTRACT:
An image data generating circuit of a color image processing apparatus generates multivalued image data for each color in accordance with density of each color of magenta (M), cyan (C) and yellow (Y). An M-screen threshold value generating circuit outputs a plurality of first threshold values, a C-screen threshold value generating circuit outputs a plurality of second threshold values, and a Y-screen threshold value generating circuit for outputting a plurality of third threshold values. A comparing circuit compares the multivalued image data outputted from the image data generating circuit with the first to third threshold values outputted from the M-, C- and Y- screen generating circuits for each color to output a comparison result in the form of a binary signal. The first and second threshold values is assigned to each pixel of an M multi-cell and a C multi-cell constituted by square matrixes having screen angles of .+-.tan.sup.-1 (q/p) and each side of .beta..multidot.p.multidot.q, respectively. For preventing coarse moire, p and q are any value of (11,3), (15,4) and (19,5), and the M multi-cell and the C multi-cell consist of N (=p.sup.2 +q.sup.2) sub-cells arrayed continuously in the directions of the screen angles of .+-.tan.sup.-1 (q/p) and having threshold values in accordance with the predetermined number of gradations. The third threshold value is assigned to a Y multi-cell constituted by a square matrix having a screen angle of 45 degrees and each side of .beta..multidot.p.multidot.q. The Y multi-cell consists of 2(p-q).sup.2 sub-cells arrayed continuously in the direction of the screen angle of 45 degrees. The first to fourth threshold values are repeatedly outputted in a cycle of .beta..multidot.p.multidot.q in synchronism with the multivalued image data of each color.

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"PostScript Screening" by Peter Frink, published by Adobe Systems Incorporated, 1992, pp. 42-98.
European Search Report.

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