JP3944711B2 - Dither matrix generation method and printer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is a dither matrix creation method for creating a dither matrix that inputs a multi-value gradation signal and converts it into a binarized signal based on the screen line. The present invention relates to a dither matrix generation method and a printer for generating, as a blue noise mask, the arrangement order of dot nuclei in a dither matrix that determines the shape of dot nuclei to be determined and the arrangement of dot nuclei that determines the screen angle.
[0002]
[Prior art]
In a binary image recording system such as a laser printer, when printing multi-tone recording such as an electronic document, the density information of the document is printed by gradation processing such as dithering. A process of replacing dots with coarse and dense is necessary.
[0003]
A conventional technique will be described with reference to FIGS. A halftone cell 1 is shown in a portion surrounded by a thick line in FIG. A small square 2 indicates a square having one minimum dot that can be printed by the printer. A plurality of small cells 2 are collected to constitute one cell. In the case of a binary printer, the number of gradations that can be theoretically expressed is determined by the minimum number of dots 2 that can be printed by the printer that constitutes one halftone cell 1. For example, the number of dots 2 constituting the halftone cell 1 of FIG. 1 is 32, and the number of gradations that can be theoretically expressed is
32 + 1 (no dot is written) = 33 gradations can be expressed.
[0004]
However, in order to express a smooth gradation, it is required to express at least 64 gradations (ideally 256 gradations). As means for expressing 64 gradations or more, a method of setting the number of dots constituting a halftone cell to 64 dots or more, and using a plurality of halftone cells as shown in FIG. 2, the total number of dots is 64 dots or more. There is a way to make it. (This method is hereinafter referred to as a supertone cell.) This method is disclosed in Japanese Patent Laid-Open No. 10-75375.
[0005]
[Problems to be solved by the invention]
In the above-described conventional supertone cell method for expressing intermediate gradations, even if the number of screen lines is increased, 256 gradations can be expressed regardless of the number of screen lines if 256 or more threshold matrixes are used. However, if the arrangement order of dots serving as the core of the screen is arranged in a fixed pattern, a different pattern is generated depending on the gradation. For example, low gradation representations of the threshold matrix shown in FIGS. 1 and 2 are shown in FIG. 3 matrix (a) and matrix (b).
[0006]
FIG. 3 shows an example of printing at a low gradation of a certain gradation among inputs from 0 (white) to 255 (black). When the input value is 5, 10, 15, 20 and the threshold value matrix is FIG. 1, the printing result when the threshold value matrix is FIG. 3 is shown in FIG. 3A, and when the threshold value matrix is FIG. Shown in b). Since the printing result of the matrix (a) in FIG. 3 can express only 33 gradations, it cannot be printed when the input value = 5, and the input value = 15 and the input value = 20 are the same printing result. . However, since all of the halftone cell dots are added in the same way, the dot area of each halftone cell dot is constant and appears as a uniform halftone. On the other hand, since the result of the matrix (b) in FIG. 3 can express 129 gradations, a change in gradation can be expressed when the input value changes by 5; however, the number of dots in the halftone cell has a periodicity. A difference occurs in the dot area of each halftone cell dot. When input = 5, there are halftone cells in which no dots are generated and halftone cells in which one dot is generated. When input = 10, there are halftone cells in which 1 dot is generated and halftone cells in which 2 dots are generated. Therefore, when input = 5, the screen angle becomes 0 °, and when input value = 10, it appears as 45 °. As described above, when there is a periodicity in the difference in the dot area of the halftone cell (difference in the number of generated dots), it appears as a unique pattern.
[0007]
[Means for Solving the Problems]
In order to solve the above-described problem, in the present invention, in a dither matrix creating method for creating a dither matrix that inputs a multi-value gradation signal and converts it into a binarized signal based on the screen line, dots for creating a screen line , The shape of the dot nuclei that changes according to the gradation, the dither matrix setting unit that determines the arrangement of the dot nuclei that determines the screen angle, and the arrangement order of the dot nuclei of the dither matrix is generated as a blue noise mask. A dot nucleus array generation unit , and the dot nucleus array generation unit is arranged so that the difference between the number of dot nuclei arranged vertically and the number of dot nuclei arranged horizontally is within ± 1. It is characterized by.
Further, in a dither matrix creating method for creating a dither matrix for inputting a multi-value gradation signal and converting it into a binarized signal based on a screen line, a dot nucleus for creating a screen line and a dot that changes depending on the gradation A dither matrix setting unit for determining the arrangement of dot nuclei for determining the screen angle, and a dot nucleus arrangement generating unit for generating the arrangement order of the dot nuclei of the dither matrix as a blue noise mask, The dot nucleus arrangement generation unit arranges the dot nuclei in order from the dot nuclei farthest from the predetermined position reference of all the dot nuclei, and the difference between the number of dot nuclei arranged vertically and the number of dot nuclei arranged horizontally is ± 1 It arranges so that it may become within a piece.
And a storage unit that stores a dither matrix created by using the dither matrix generation method, and a conversion unit that converts a multilevel signal into a binary or multilevel signal using the dither matrix. To do.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to FIGS. Here, a screen with a screen angle of 45 ° will be described as an example.
[0009]
FIG. 4 shows a dither matrix generation method according to an embodiment of the present invention. A plurality of minimum dots 4 that can be printed by the printer are gathered to form a halftone cell 3, and a plurality of halftone cells 3 are gathered to create the dither matrix of the present invention.
[0010]
The dither matrix of the present invention is arranged so that the halftone cells 3 can be packed at a screen angle of 45 °. The halftone cell 3 is composed of 32 dots 4 that can be expressed by a printer. The dot arrangement order in the halftone cell 3 is arranged so as to spread from the center. This arrangement order is generally called a screen shape, and there are a method of spreading in a round shape, a method of spreading in a diamond shape, or a method of spreading in a lattice shape. This arrangement order may be variously changed depending on the printer performance, the image to be printed, and the like.
[0011]
As a technique for expressing the gradation, the minimum dot 4 that can be printed by the printer is expressed by 64 × 64 dots, and 128 halftone cells 3 are arranged therein. The halftone cells 3 are arranged so that the screen angle is 45 °. As shown in FIG. 4, the 64 × 64 dot blocks are continuously arranged vertically and horizontally during printing. Although 64 × 64 dots are used as an example, there is no limitation on the number of dots used. In addition, although the number of halftone cells is 32 as an example, other numbers may be used.
[0012]
The order of printing on the 128 halftone cells 3 is determined. As in claim 2, an arbitrary halftone cell 3 is determined and the halftone cell located farthest from the first cell is defined as the first cell. Cell 3 is the second cell. Next, the halftone cell 3 farthest from both the cells 1 and 2 is set as the third cell, and then the halftone cell 3 furthest from the cells 1, 2, and 3 is set as the fourth cell.
[0013]
As a condition for determining the arrangement order of the halftone cells 3, the difference between the determined number of halftone cells 3 in each column and the determined number of arranged halftone cells in each row is within ± 1. It is necessary to arrange so that it becomes.
[0014]
FIG. 5 shows an arrangement example of the halftone cell 3. The columns are a to p and the rows are A to P. Columns a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p 16 columns, columns A, B, C, D, E, F, G, The number of determined cells in each of 16 columns of H, I, J, K, L, M, N, O, and P is counted. For example, as shown in FIG. 6, the cell (a · A) is the first cell. At that time, row a and column A are counted as 1. Next, as shown in FIG. 7, the second cell is the farthest cell (i.I) from the first cell. At that time, i row and I column are 1 count. Next, as shown in FIG. 8, the third cell is the cell (a.I) which is the farthest from the first and second cells, but the a row and the I column are already 1 count, In addition, since there are 0 count rows and columns, arrangement at that position is prohibited. Therefore, as shown in FIG. 9, the cell (b.H) farthest from the first and second cells other than a, i rows, A and I columns is the third cell. In this way, the order from 1 to 128 is determined for all the cells.
[0015]
The method of determining the order of all cells uses the blue noise method, and the details are performed by the method described in Japanese Patent No. 2622429.
[0016]
In the halftone cell 3, the dot arrangement order is determined as shown in FIG. The dot arrangement order is arranged so as to spread from the center. This arrangement order is generally called a screen shape, and there are a method of spreading in a round shape, a method of spreading in a diamond shape, and the like. This arrangement order may be changed according to the performance of the printer, the image to be printed, or the like.
[0017]
The order of the dither matrix within 64 × 64 dots is 1 in the cell in the order 1 of the halftone cell 3 determined using the blue noise method, and 1 in the cell in the order 2 of the halftone cell 3. Order in order of 2nd. The first of the cells in the order 128 of the halftone cell 3 is 128, and then the second of the cells in the order 1 of the halftone cell 3 is 129. Finally, 4096 is the 32nd cell in the 128 cells in the order 128 of the halftone cell 3. This can also be expressed by the following formula.
[0018]
The print dot order in each cell is
(Order of halftone cell 3 (1 to 128) × (dot order in cell (1 to 32)) + 1)
It becomes.
[0019]
In addition, when the dither matrix order is desired to be expressed by numbers up to 255, it can be dealt with by rounding the numerical values obtained in the order of (255 ÷ maximum matrix number (4096)) × dot order (1 to 4096) to an integer. .
[0020]
If gradation is expressed in such a dot arrangement order (dither matrix), it is possible to prevent periodic patterns in the gradation part by high gradation screen processing with the number of screen lines. A high-quality printer can be obtained by incorporating the dither matrix into the printer.
[0021]
In addition, this invention is not limited to said Example, Various modifications for achieving the objective are included.
[0022]
【The invention's effect】
According to the present invention, in order to realize a high gradation expression number while maintaining a high screen line number, the dot nucleus for creating the screen line, the shape of the dot nucleus that changes according to the gradation, and the dot that determines the screen angle By using a dither matrix generation method that generates the dot arrangement order of the dither matrix, which determines the arrangement of the nuclei, as a blue noise mask, eliminate the periodicity of the dot arrangement and prevent the appearance of appearance patterns. This solves the problem of pattern generation in the gradation portion and enables printing with high image quality.
[Brief description of the drawings]
FIG. 1 is a dither matrix diagram according to the prior art.
FIG. 2 is a dither matrix diagram according to a conventional technique.
FIG. 3 is a diagram showing a printing result in the dither matrix shown in FIGS. 1 and 2;
FIG. 4 is a matrix diagram according to the present invention.
FIG. 5 is a matrix diagram according to the present invention.
FIG. 6 is a first cell diagram according to the present invention.
FIG. 7 shows a second cell example according to the present invention.
FIG. 8 is a third cell prediction example diagram according to the present invention.
FIG. 9 shows a third cell example according to the present invention.
FIG. 10 is a cell example diagram according to the present invention.
[Explanation of symbols]
3 is a halftone cell, and 4 is a dot.

Claims (3)

In a dither matrix creation method for creating a dither matrix for inputting a multi-value gradation signal and converting it into a binarized signal based on a screen line, a dot nucleus for creating a screen line and a dot nucleus that changes according to the gradation with the shape, the dither matrix setting unit which determines the arrangement of the nuclear dots determining the screen angle, and a dot core sequence generator for generating an order of arrangement of the nuclear dots in the dither matrix as a blue noise mask, the dot nuclei The dither matrix generation method characterized in that the arrangement generation unit arranges so that a difference between the number of dot nuclei arranged vertically and the number of dot nuclei arranged horizontally is within ± 1 . In a dither matrix creation method for creating a dither matrix for inputting a multi-value gradation signal and converting it into a binarized signal based on a screen line, a dot nucleus for creating a screen line and a dot nucleus that changes according to the gradation A dither matrix setting unit for determining the arrangement of dot nuclei for determining the screen angle, and a dot nucleus array generating unit for generating the arrangement order of the dot nuclei of the dither matrix as a blue noise mask. The array generator arranges all the dot nuclei in order from the dot nuclei farthest from the predetermined position reference, and the difference between the number of dot nuclei arranged vertically and the number of dot nuclei arranged horizontally is within ± 1 A dither matrix generation method , characterized by being arranged so that A storage unit that stores a dither matrix created by using the dither matrix generation method according to claim 1 and a conversion unit that converts a multilevel signal into a binary or multilevel signal using the dither matrix. A printer characterized by that .

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