US 5,398,118 A · Automatical generation of a periodic pattern without occurrence of moire

A method of generating a digital halftone screen comprising a plurality of periodic patterns which have a period of m pixels in an X-axis direction and a period of pixels in a Y-axis direction orthogonal to the X-axis direction on an integer coordinate where m and n represent integers, the method comprising the steps of:

determining a configuration of one of the periodic patterns that has a region enclosed by first through fourth sequences of pixels on the integer coordinate, the first sequence of pixels lying on a first jagged line segment between a first pixel having a first coordinate value (0, n) and a second pixel having a second coordinate value (m, 0), the second sequence of pixels lying on a second jagged line segment between the first pixel having the first coordinate value (0, n) and a third pixel having a third coordinate value (n, m+n), the third sequence of pixels lying on a third jagged line segment between the second pixel having the second coordinate value (m, 0) and a fourth pixel having a fourth coordinate value (m+n, m), the fourth sequence of pixels lying on a fourth jagged line segment between the third pixel having the third coordinate value (n, m+n) and the fourth pixel having the fourth coordinate value (m+n, m), the region including the first sequence of pixels, the second sequence of pixels, and the first pixel having the first coordinate value (0, n), the region excluding the third sequence of pixels, the fourth sequence of pixels, the second pixel having the second coordinate value (m, 0), the third pixel having the third coordinate value (n, m+n), and the fourth pixel having the fourth coordinate value (m+n, m);
calculating threshold values on all pixels in the region using a function defining a procedure for obtaining the threshold values;
and
when the afore-mentioned threshold values have discontinuous numbers, rearranging the threshold values so as to have continuous numbers, thereby generating rearranged threshold values as the periodic pattern in the digital halftone screen.

1 more element

A digital halftone screen generating device for generating a digital halftone screen comprising a plurality of periodic patterns which have a period of m pixels in an X-axis direction and a period of n pixels in a Y-axis direction orthogonal to the X-axis direction on an integer coordinate where m and n represent integers, said digital halftone screen generating device comprising:

a configuration determining section, supplied with periodic constants m and n, for determining a grid indicative of a configuration of one of the periodic patterns in the digital halftone screen by using the periodic constants m and n;
and
a threshold value distributing section, connected to said configuration determining section and supplied with the periodic constants and with a function defining a procedure for obtaining threshold values in a square area defined by:
-i.ltoreq.x.ltoreq.i, -i.ltoreq.y.ltoreq.i,
where i represents a real number for rotating the threshold values defined by the function by a screen angle .theta. given by:
.theta.=tan.sup.-1 (n/m),
said threshold value distributing section expanding on the grid threshold values enlarged by an enlargement ratio M given by:
M=(m.sup.2 +n.sup.2).sup.1/2 /(2i),
when the threshold values on the grid have discontinuous numbers, said threshold value distributing section rearranging the threshold values so as to have continuous numbers, said threshold value distributing section producing a periodic pattern signal indicative of the threshold values having the continuous numbers.

6 more elements

A digital halftone screen generating device for generating a digital halftone screen comprising a plurality of periodic patterns which have a period of m pixels in an X-axis direction and a period of n pixels in a Y-axis direction orthogonal to the X-axis direction on an integer coordinate where m and n represent integers, said digital halftone screen generating device comprising:

a periodic constant determining section, supplied with an input screen angle and an input number of intensity levels, for calculating periodic constants m and n using the input screen angle and the input number of intensity levels to produce the periodic constants m and n;
a configuration determining section, connected to said periodic constant determining section, for determining a grid indicative of a configuration of one of the periodic patterns in the digital halftone screen using the periodic constants m and n;
and
a threshold value distributing section, connected to said configuration determining section and said periodic constant determining section and supplied with a function defining a procedure for obtaining threshold values in a square area defined by;
-i.ltoreq.x.ltoreq.i, -1.ltoreq.y.ltoreq.i,
where i represents a real number for rotating the threshold values defined by the function by a screen angle .theta. given by:
.theta.=tan.sup.-1 (n/m),
said threshold value distributing section expanding on the grid threshold values enlarged by an enlargement ratio M given by:
M=(m.sup.2 +n.sup.2).sup.1/2 /(2i),
when the threshold values on the grid have discontinuous numbers, said threshold value distributing section rearranging the threshold values so as to have continuous numbers, said threshold value distributing section producing a periodic pattern signal indicative of the threshold values having the continuous numbers.

7 more elements

A digital halftone screen generating device for generating a digital halftone screen comprising a plurality of periodic patterns which have a period of m pixels in an X-axis direction and a period of n pixels in a Y-axis direction orthogonal to the X-axis direction on an integer coordinate where m and n represent integers, said digital halftone screen generating device comprising:

a configuration determining section, supplied with periodic constants m and n, for determining a grid indicative of a configuration of one of the periodic patterns in the digital halftone screen by using the periodic constants m and n;
a pattern storage for storing a plurality of functions each of which defines a procedure for obtaining threshold values in a square area defined by:
-.ltoreq. x.ltoreq.i, -1.ltoreq.y.ltoreq.i,
where i represents a real number;
and
a threshold value distributing section, connected to said configuration determining section and said pattern storage and supplied with the periodic constants and a pattern selection signal, for rotating the threshold values defined by one of the functions by a screen angle .theta. given by:
.theta.=tan.sup.-1 (n/m),
said threshold value distributing section expanding on the grid threshold values enlarged by an enlargement ratio M given by:
M=(m.sup.2 +n.sup.2).sup.1/2 /(2i),
when the threshold values on the grid have discontinuous numbers, said threshold value distributing section rearranging the threshold values so as to have continuous numbers, said threshold value distributing section producing a periodic pattern signal indicative of the threshold values having the continuous numbers.

7 more elements

A digital halftone screen generating device for generating a digital halftone screen comprising a plurality of periodic patterns which have a period of m pixels in an X-axis direction and a period of n pixels in a Y-axis direction orthogonal to the X-axis direction on an integer coordinate where m and n represent integers, said digital halftone screen generating device comprising:

a periodic constant determining section, supplied with an input screen angle and an input number of intensity levels, for calculating periodic constants m and n using the input screen angle and the input number of intensity levels to produce the periodic constants m and n;
a configuration determining section, connected to said periodic constant determining section, for determining a grid indicative of a configuration of one of the periodic patterns in the digital halftone screen using the periodic constants m and n;
a pattern storage for storing a plurality of functions each of which defines a procedure for obtaining threshold values in a square area defined by:
-1.ltoreq.x.ltoreq.1, -1.ltoreq.y.ltoreq.i,
where i represents a real number;
and
a threshold value distributing section, connected to said configuration determining section, said periodic constant determining section, and said pattern storage and supplied with a pattern selection signal, for rotating the threshold values defined by one of the functions by a screen angle .theta. given by:
.theta.=tan.sup.-1 (n/m),
said threshold value distributing section expanding on the grid threshold values enlarged by an enlargement ratio M given by:
M=(m.sup.2 +n.sup.2).sup.1/2 /(2i),
when the threshold values on the grid have discontinuous numbers, said threshold value distributing section rearranging the threshold values so as to have continuous numbers, said threshold value distributing section producing a periodic pattern signal indicative of the threshold values having the continuous numbers.

8 more elements

Automatical generation of a periodic pattern without occurrence of moire

Life of this patent

Automatical generation of a periodic pattern without occurrence of moire

Life of this patent

Abstract

Claims13