US 5,685,652 A · Method of preparing threshold matrix and method of and apparatus for generating halftone image

Abstract

The present invention is made to effectively prevents the occurrence of undesirable dot patterns in the process of FM screening. Threshold values in an M1.times.M2 threshold matrix are determined using a plurality of fundamental tiles of 2.times.2 dots in size. The method of the invention arranges the plurality of fundamental tiles in the M1.times.M2 threshold matrix region, while not allowing the fundamental tiles to have preset forbidden arrangements. This gives a 50% dot pattern including 50% black dots and 50% white dots. The values `0` and `1` are assigned as the upper-most paired bits of digital data representing a threshold value to the positions of two black dots in each fundamental tile, and the values `2` and `3` are assigned as the upper-most paired bits to the positions of two white dots. The values of the other paired bits included in the digital data representing a threshold value are determined by successively dividing the M1.times.M2 threshold matrix region into four equal parts and allocating different values of `0` through `3` to the four divisional matrix regions.

Claims20

Dependent claims

A method of producing a threshold matrix used in a halftone process of multi-tone image data, said method comprising the steps of:

(a) providing a plurality of fundamental tiles each having a size of 2.times.2 dots in which two black dots and two white dots are arranged in parallel;
(b) arranging said plurality of fundamental tiles in a threshold matrix region while preventing said fundamental tiles to form a predetermined forbidden arrangement, thereby determining an array of black dots and white dots in a 50%-halftone image in said threshold matrix region, said 50%-halftone image having an area rate of 50% for both of black dots and white dots;
and
(c) determining threshold values in said threshold matrix region based on the arrangement of said plurality of fundamental tiles in said threshold matrix region, thereby producing said threshold matrix.

1 more element

A method of generating a halftone image by comparing multi-tone image data with a threshold matrix, said method comprising the steps of:

(a) providing a first memory for storing a threshold matrix, said threshold matrix being prepared by
(i) providing a plurality of fundamental tiles each having a size of 2.times.2 dots in which two black dots and two white dots are arranged in parallel;
(ii) arranging said plurality of fundamental tiles in a threshold matrix region while preventing said fundamental tiles to form a predetermined forbidden arrangement, thereby determining an array of black dots and white dots in a 50%-halftone image in said threshold matrix region, said 50%-halftone image having an area rate of 50% for both of black dots and white dots;
and
(iii) determining threshold values in said threshold matrix region based on the arrangement of said plurality of fundamental tiles in said threshold matrix region, thereby producing said threshold matrix;
(b) comparing multi-tone image data with a threshold value read out of said first memory, thereby converting said multi-tone image data to a recording signal representing a halftone image;
and
(c) producing said halftone image in response to said recording signal.

5 more elements

An apparatus for generating a halftone image by comparing multi-tone image data with a threshold matrix, said apparatus comprising:

a memory for storing a threshold matrix, said threshold matrix being prepared by
(i) providing a plurality of fundamental tiles each having a size of 2.times.2 dots in which two black dots and two white dots are arranged in parallel;
(ii) arranging said plurality of fundamental tiles in a threshold matrix region while preventing said fundamental tiles to form a predetermined forbidden arrangement, thereby determining an array of black dots and white dots in a 50%-halftone image in said threshold matrix region, said 50%-halftone image having an area rate of 50% for both of black dots and white dots;
and
(iii) determining threshold values in said threshold matrix region based on the arrangement of said plurality of fundamental tiles in said threshold matrix region, thereby producing said threshold matrix;
means for reading out a threshold value from said memory;
and
a comparator for comparing multi-tone image data with the threshold value read out of said memory, thereby converting said multi-tone image data to a recording signal representing a halftone image;
and
recording means for producing said halftone image in response to said recording signal.

7 more elements

Dependencies are inferred from the claim text.

Method of preparing threshold matrix and method of and apparatus for generating halftone image

Life of this patent

Method of preparing threshold matrix and method of and apparatus for generating halftone image

Life of this patent

Abstract

Claims20