JPH09200518A - Dot threshold level setting method and binary data generator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent moire stripes from being produced on an output image by deciding a threshold level to be assigned to each picture element in a dot cell in response to a specific black level processing order. SOLUTION: A super-cell S is divided into dot cells Hh each centered around a highlight point. Furthermore, the same super-cell S is divided into dot cells Hs each centered around a shadow point. The apex of each dot cell Hs is coincident with a center of each dot cell Hh. Then to which dot cell Hh and to which dot cell Hs each pixel P belongs is decided. A different random number from each dot cell is added to a coordinate of each pixel P to decide the black level sequencing is decided. Then a threshold level assigned to each pixel P in the dot cell Hh centered around a highlight point and a threshold level assigned to each pixel P in the dot cell Hs centered around a shadow point are alternately decided to decide a threshold level of a super-cell threshold level template.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a halftone dot threshold value setting method and a binary data creating device suitable for application to an image recording device or the like for creating a halftone dot image film.

[0002]

2. Description of the Related Art Recently, a supercell is set on a pixel grid determined by output resolution, the set supercell is divided into halftone dot cells, and a threshold value is assigned to each pixel in the divided halftone dot cells. A halftone dot generation technique for setting a halftone dot threshold is known.

As a reference for a technique for generating halftone dots in relation to such a super cell, for example, "Book Name: Postscript Screening, Author: Peter Fink, Publisher: MDI Corporation, Issue Date : August 11, 1994, first edition, first printing ”.

By considering a super cell composed of a plurality of halftone dot cells, the screen ruling and halftone angle can be changed more finely, and a value closer to the designated screen ruling and halftone angle can be obtained. Has the advantage that

The pixel grid is a group of pixels that are blackening units. Therefore, the pixel grid may be imagined as a state in which pixels are arranged vertically and horizontally.

As shown in FIG. 12A, the halftone dot cells are, for example, 10 on the pixel grid (actually, for example, 256 dots are formed corresponding to the gradation of the image). It is composed of pixels P, and is represented by a square as shown by a chain line in the figure. The halftone dot cell H is usually represented by a square.

FIG. 12A shows a halftone dot cell H having a halftone angle of (1/3) [rational tangent RT {RT = (1/3)}].

FIG. 13A shows a halftone dot cell H having a halftone angle of 0 ° (0/3) [rational tangent RT (RT = 0)].

The threshold value (not shown) assigned to each pixel of the halftone dot cell H is as described later in detail.
Since a large value is set gradually from the center of the halftone dot cell H to the outside, the blackening order (blackening order) of the pixel P at the center of the halftone dot cell H becomes the first. Become. FIG.
In A, a state in which only the pixel P having the first blackening order is blackened is indicated by hatching.

In the following description, a halftone dot cell H which is blackened from the center is represented by drawing a hatched circle in a square as shown in FIG. 13B corresponding to FIG. 13A. . In this case, the halftone dot cell H shown in FIG. 12A is displayed tilted by the same halftone angle as shown in FIG. 12B.

FIG. 14 shows a schematic structure of a super cell S composed of nine halftone dot cells H1 to H9.
The four vertices 2 to 5 of the super cell S must match the vertices of the pixel P, but the vertices 6, 7, 8 and the like shared by the halftone cells H1 to H9 are the vertices of the pixel P. It does not have to match.

In the case of the supercell S in the example of FIG. 14, when the number of pixels on the x-axis is m and the number of pixels on the y-axis is n on the xy axes that are orthogonal to each other, the rational tangent RT corresponding to the halftone angle is obtained.
Becomes RT = (n / m).

[0013]

By the way, the halftone dot cell H
For each of 1 to H9, for example, a threshold value is set to 0, 1, 2, ...

Here, the halftone dot cells H1 to H9 in which the threshold values are set corresponding to the pixels P are referred to as halftone dot cell threshold templates for convenience. Therefore, the supercell S having a threshold value set corresponding to the pixel P is referred to as a supercell threshold value template.

For the sake of simplification, a blackening process by the so-called density pattern method is considered, in which the size of the pixel of the original image to which this supercell threshold template is applied is the same as the size of the halftone dot cell H. I shall.

When the image data values of the original image are all close to 255, which is a value of 100%, for example, the halftone dot cells H1 to H9 are almost blackened. .

In this case, the halftone dot cells H1 to H9 in which the threshold values are arranged as described above are blackened from the vicinity of the center thereof,
Since the highlight point (value 0 in the above example) is arranged near the center, the halftone dot cell at the center of the highlight point (or, generally, the blackened point of the halftone dot cell on the highlight side is Since it is small, it is called a dot cell with a small dot center. The halftone dot cell H shown in FIGS. 12B and 13B is also a halftone dot cell centered on the highlight point.

However, the supercell S composed of the halftone dot cells H1 to H9 at the center of such a highlight point as described above.
Then, in the vicinity of the vertices 2 to 8 of each halftone dot cell H1 to H9, the number of pixels that are not blackened periodically, that is, the number of blank pixels varies. As a specific and extreme example, the vertex 6 is blackened, the vertex 7 is blank, and the vertex 8 is blackened.

Within the supercell S, each halftone dot cell H1.
The number of blackened pixels in H9 is distributed almost uniformly, but the number of whiteout pixels is not controlled and varies periodically in each halftone dot cell H1 to H9. There is a problem that this is visually recognized as a grid-shaped or striped moire on the output image. This can be considered as a moire of the frequency of the halftone dots and the output resolution.

FIG. 15A shows an example of a concrete simulation image of moire fringes generated on the output image 9 at the time of outputting a high halftone percentage (shadow portion). It can be seen that moire fringes are prominent in the direction of arrow 10. In addition, in FIG. 15A, a square portion denoted by reference numeral 11 is a blank portion, and the other portions are blackened portions.

The present applicant has proposed a technique for reducing the above-mentioned moire fringes in Japanese Patent Application No. 7-123922.
This technique divides the supercell into halftone dot cells by dividing them into halftone dot cells centered on the highlight point, and also divides them into halftone dot cells centered on the shadow point. The threshold assigned to the pixel, eg 0,
1, 2, 3, ..., Thresholds assigned to each pixel in the halftone dot cell at the center of the shadow point, that is, N, N-1, N-
This is a technique for alternately setting 2, ... (0 → N → 1 → N-1
→ ... → 3 → N-3. ).

According to this technique, it is possible to considerably reduce the moire fringes caused by the above-mentioned causes. However, even with this technique, it has been found that the moire may be visible especially under the condition that the striped moire related to the scanning pitch of the halftone dots and the laser beam is conspicuous.

The present invention has been made on the premise of this technique, and an object of the present invention is to provide a halftone dot threshold setting method and a binary data creating apparatus in which moire fringes do not occur on an output image.

[0024]

According to a first aspect of the present invention, a supercell is set on a pixel grid determined by an output resolution, the set supercell is divided into halftone dot cells, and each of the divided halftone dot cells is divided into halftone dot cells. In the halftone dot threshold value setting method of assigning a threshold value to each pixel to set a halftone dot threshold value, when dividing the super cell into halftone dot cells, the supercell is divided into halftone dot cells centered on the highlight point and the shadow point center The halftone dot cells at the center of the shadow point so that the vertices of the halftone dot cells at the center of the shadow point coincide with the centers of the halftone dot cells at the highlight point, and When calculating the blackening order of pixels in each halftone dot cell in the center of the shadow point, a different random number for each halftone dot cell is added to the coordinates of each pixel to determine the blackening order. In this blackening order Flip with a threshold value assigned to each pixel in the highlight point centers of halftone cells, characterized in that defined alternately threshold assigned to each pixel in the halftone cell of the shadows point center.

In a second aspect of the present invention, the random number to be added is
The feature is that the size of the random number and the number of halftone cells to be added can be controlled.

A third aspect of the present invention is characterized in that the size of the random number to be added is equal to or smaller than the size of the pixel.

A fourth aspect of the present invention compares original image data with a supercell threshold template to obtain binary data.
The value data creating device is characterized in that the supercell threshold template is created as in the first invention.

According to the present invention, in the coordinate calculation for determining the blackening order of pixels in each of the halftone dot cell at the center of the highlight point and the halftone dot cell at the center of the shadow point, the coordinates of each pixel are calculated. A different random number is added to each halftone dot cell to determine the blackening order, and the threshold assigned to each pixel in the halftone dot cell at the highlight point and the halftone dot centered dot according to the determined blackening order. By alternately setting the threshold value assigned to each pixel in the point cell, it is possible to prevent moire fringes from occurring on the output image.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. In the drawings referred to below, those corresponding to those shown in FIGS. 12 to 15 are designated by the same reference numerals and detailed description thereof will be omitted, but these drawings are also referred to as necessary. Explain.

1 and 2 show a schematic configuration of an image plate making system 31 to which an embodiment of the present invention is applied, and a binary data creating device 41 constituting the image plate making system 31.

In FIG. 1, an original image 32 such as a photograph is supplied to an image input section 33, and an image scanner forming the image input section 33 causes, for example, 8-bit digital image data (hereinafter, simply referred to as image data). .) DA
It is said. The image processing unit 34 for this image data DA
Thus, various image processes such as color correction process and sharpness process are performed to create an image data DB.

The image data DB is supplied to the binary data creating device 41 which constitutes the image recording unit 35.

In FIG. 2, the image data G supplied to the binary data creating device 41 is supplied to the comparison input of the comparison section 43 through the input port 42. Further, the address calculation unit 44 calculates the address AD (x, y) representing the x-axis address and the y-axis address (see FIG. 14 for the x-axis and the y-axis) on the supercell threshold template 45 from the image data G. . Supercell threshold template 45
Reads the threshold value A (in this case, 8-bit threshold value data) A stored in the memory cell corresponding to the specified address AD and supplies it to the reference input of the comparison unit 43.
In practice, the supercell threshold template 45 is, for example, a ROM, and the read subject is the CPU.

The comparison section 43 performs a binary data conversion process represented by the following equations (1) and (2).

G ≧ A → 1 (blackened) (1) G <A → 0 (blank: non-blackened) (2) The binary data B created by the comparison unit 43 is output to the output port 4
It is supplied to the exposure unit 36 (see FIG. 1) through 6.

In the exposure section 36, a halftone image is exposed and recorded as a latent image on the film by a laser beam to form and output a halftone image film F.

The output halftone dot image film F is developed, and then a printing plate and a PS plate are prepared. By mounting this PS plate on a printing machine and transferring the image onto a sheet, a desired image can be obtained. You will get a hard copy.

Next, the supercell threshold template 45
A method of creating the threshold value set in step 1 will be described in detail with reference to the flowchart of FIG.

First, the calculation input parameters (m, n, k, L) corresponding to the output conditions of the halftone dot image film F are set (step S1).

The order of determining the parameters (m, n, k, L) is not particularly limited. For example, first, the parameters (m, n) relating to the halftone angle (rational tangent RT) are determined. In this case, the mesh angle that can be actually set for the desired mesh angle is
A value obtained by dividing the number of pixels n on the y-axis shown in FIG. 14 by the number of pixels m on the x-axis is {(n / m) = rational tangent RT}. This rational tangent RT (= n / m) is set so as to have a value closest to a desired halftone angle in relation to the length L of one side of the supercell S. The rational tangent RT is represented by θ = arctan (n / m), where θ is the angle. In order to realize the angle θ = 15 ° used in printing, the rational tangent RT = n / m is set and n / m = 3/11, 4/15, 7
/ 26, 11/41, 15/56, ... May be used.

Next, the length L of one side of the supercell S and one length for obtaining the desired number of lines (for example, the length Q of one side of the halftone dot cell H in FIG. 4, which will be described later). A combination (L, k) of the number k of halftone cells H that form the supercell S is determined in consideration of the output resolution (these are determined at the same time).

That is, the length L of one side of the supercell S
, The actual length of the supercell S is known, and the number k of halftone dot cells Hh included in the supercell S is determined by determining the number k which is a parameter. The length Q of one side of the point cell H is determined. In this embodiment, the number k of halftone dot cells H in one supercell S is k = 10.

Next, the supercell S is expressed by the following equation (3),
The line group defined by the equation (4) is used to divide into the halftone dot cells Hh at the center of the highlight points (step S2).

Nx-my + (p-n) L = 0 {p =-(n-1) to (n-1)} (3) mx-ny-qL = 0 {q = 0 to (m + n-1) )} (4) In FIG. 4, a supercell S having a side length of L is (3)
A straight line based on the equation (4) is used to divide a halftone dot cell Hh having a side length Q into a highlight point center. The halftone dot cells Hh1 to Hh10 at the center of the highlight point are
Each is represented by a circle with a hatch in the center. This indicates that, as described above, the blackening starts from the center corresponding to the change from the small threshold to the large threshold.

Further, in step S2, the same super cell S is divided into halftone dot cells Hs centering on shadow points.

In FIG. 5, the length of one side of the supercell S is Q.
It is shown that the cell is divided into halftone dot cells Hs centered on the shadow point. Halftone dot cells Hs1 to Hs10 around the shadow point
Indicates the portions other than the central circle by hatching. As will be described later in detail, this is because the blackening is outside (each halftone dot cell Hs
1 to the outside of Hs10). The straight line group for partitioning the halftone dot cells Hs1 to Hs10 at the center of the shadow point is y = y + (1 /
6) In equation (4) where L is set, y = y + (1 /
2) It is represented by the formula L. This results in each straight line being shifted by half the length Q / 2 of the halftone dot cell (Hh or Hs) length Q / 2 in the x-axis direction and the y-axis direction.

As a result, the positions of the halftone dot cells Hs1 to Hs10 at the center of each shadow point are shaded in the direction of the straight line of the formula (3) with reference to the positions of the halftone dot cells Hh1 to Hh10 at the center of each highlight point. Half the length Q of the point cell Q / 2
Only half of the half length Q / 2 of the halftone dot cell is shifted in the direction of the straight line of the formula (4) from the shifted position.
It will move to the shifted position.

In FIG. 6, the halftone dot cell Hh centered on the highlight point is drawn by a solid line on the divided supercell S, and the halftone dot cell Hs centered on the shadow point is drawn by a dotted line so as to overlap this.

As can be seen from FIG. 6, as a result, the apex of the halftone dot cell Hs centered on the shadow point coincides with the center of the halftone dot cell Hh centered on the highlight point. Further, as can be seen from the position of the pixel P schematically drawn, each pixel P has one halftone dot cell Hh at the highlight point center and one halftone dot cell Hs at the shadow point center (two in total). Belongs to a point cell. The pixel P in FIG. 6 belongs to the halftone dot cell Hh6 centered on the highlight point and the halftone dot cell Hs6 centered on the shadow point.

Then, next, letting the coordinates of each pixel P in the supercell S be (x, y), which pixel (pixel) P belongs to which halftone dot cell Hh1 to Hh10 at the center of the highlight point, and Halftone dot cell Hs1 centered on which shadow point
It is determined whether it belongs to Hs10 (step S3).

Next, the blackening order of each pixel P is determined for each halftone dot cell Hh, Hs (step S4). The blackening order is defined by a common spot function f (u, v) for each halftone dot cell Hh, Hs. Spot function f (u,
v) is a function that defines the shape of the blackened halftone dot, that is, a function that represents the blackening order of the pixel P in one halftone dot cell Hh, Hs. In this embodiment, the spot function f (u, v) is represented by the center coordinate (0.5) of each halftone dot cell Hh, Hs in the uv coordinate system shown in FIG. , 0.5) to increase the blackened portion in a circular shape.

F (u, v) = (u−0.5) ² + (v−0.5) ² (5) Here, variables (coordinates) u and v are respectively the following (6)
Equation (7) is given.

U = u + rand_u (Hh_n or Hs_n) (6) v = v + rand_v (Hh_n or Hs_n) (7) Random numbers rand_u and rand_v are independent random numbers in the u-axis and v-axis directions. And, therefore,
Expressions (6) and (7) in which independent random numbers random_u and land_v are added to the variables u and v on the right side of Expressions (6) and (7) are variables (5) on the left side of Expression (7). Of the spot function f (u, v). In addition, the random number random_u (Hh_n
Or Hs_n), random number random_v (Hh_n
Or Hs_n) are halftone dot cells Hh and Hs, respectively.
It indicates that a random number that takes a different value for each halftone dot cell is used. Generation of random numbers rand_u, rand_v
Any known random number generation method may be used, such as generating a random number using an M-sequence code.

The magnitudes of the values of the random numbers rand_u and rand_v can be controlled to any magnitudes, and for example, they can be controlled to vary depending on the size of the halftone dot cell H or the pixel P. It is possible. However, the random number ra
If the values of nd_u and rand_v are too large, it is possible to eliminate the striped moire shown in FIG. 15A that occurs in the image, but on the other hand, the so-called graininess becomes noticeable and the image quality deteriorates.

Therefore, a random number random for eliminating the striped moire and making the rough feeling inconspicuous.
Maximum value of _u and land_v (+ direction and-direction)
Is preferably set to be equal to or smaller than the size of the pixel P (the length of the diagonal line of the pixel P shown in FIG. 6). When the net is a so-called coarse net, the random numbers rand_u and rand_v having larger values than those of the net having a high number of lines may be used.

The number of halftone dot cells (Hh_0 to Hh_n or Hs_0 to H) included in the supercell S to which the random numbers random_u and random_v can be added.
s_n), the number of halftone dot cells is random number random_u,
It is also possible to control whether to add rand_v. That is, the halftone dot cell to which a random number is added is
Any number may be determined from the number (N + 1) of threshold values described later.

Each value of the spot function f (u, v) may be actually calculated based on the equations (6) and (7), and it may be prepared as a two-dimensional lookup table. Good.

Next, the threshold A (see FIG. 2) of the supercell threshold template 45 (see FIG. 2) is determined according to the blackening order determined by the spot function f (u, v) (step S5). . The super cell threshold template 45 is
It has the same size as the super cell S, and in that sense is called a super cell threshold template 45. The supercell threshold template 45 is a table in which the threshold A is set to 1: 1 for each pixel position.

FIG. 8 is a detailed flowchart for determining the threshold value.

In this embodiment, the threshold value A takes values 0, 1, ..., N. In practice, for example,
The values are 0, 1, ..., 255.

Therefore, first, the threshold value A for the halftone dot cell Hh at the highlight point is represented by the threshold value HL (A = HL), and the threshold value A for the halftone dot cell Hs at the shadow point center is represented by the threshold value SD (A = SD), and as their initial value, the threshold value HL = 0,
The threshold value SD = N is set (step S11). Further, pixels forming the halftone dot cell Hh are represented by Ph, and pixels forming the halftone dot cell Hs are represented by Ps. When the threshold value HL is set for the pixel Ph, the pixel Ph = HL, or more simply, in consideration of the fact that the position of the pixel Ph is determined by the coordinates (x, y), the pixel Ph (x, y) = HL.

Next, the supercell threshold template 45
Among the unprocessed pixels (pixels whose thresholds are not determined) in the halftone dot cell Hh, the pixel in the earliest blackening order Ph (x, y),
Among the unprocessed pixels in the supercell threshold template 45, the pixel Ps (x, y) with the latest blackening order in the halftone dot cell Hs.
Is selected (step S12).

Next, it is confirmed that the selected pixel Ph (x, y) and pixel Ps (x, y) are not isolated pixels, just in case (step S13). As shown in FIG. 9, whether the selected pixel P is the pixel P
When (x, y), the four pixels P above, below, left and right
(X, y + 1), P (x, y-1), P (x-1,
If any one of the pixels y) and P (x + 1, y) is a pixel for which the threshold value A has been determined (a pixel for which the threshold value A has been determined is a processing pixel), then it is not an isolated pixel. I can judge.

When the determination in step S13 is established, the threshold values A of the selected pixel Ph (x, y) and pixel Ps (x, y) are set to pixel Ph (x, y) = HL and pixel Ps, respectively.
(X, y) = SD is set (step S14).

Next, it is determined whether there is any unprocessed pixel for which the threshold A has not been determined (step S15).

If there are unprocessed pixels, the threshold value HL,
The value of SD is set to the threshold value HL = HL + 1 (in this case, H
L = 1), threshold SD = SD-1 (in this case, SD = N-
Change to 1) (step S16).

Then, the processing from step S12 to step S16 is repeated again, and step S1
In other words, the threshold value A of all the pixels Ph (x, y) and Ps (x, y) is determined until the determination of 5 is not established.

In FIG. 10, the threshold function HL of the halftone dot cell Hh at the center of the highlight point is set as the threshold value HL by the threshold value determination process in step S5, and the spot function f that determines the blackening order is provided to facilitate understanding of this embodiment. (U, v) random number rand_
Up to HL = 0, 1, 2, and 3 when u and land_v are considered to be zero values, SD = N, N-1, N-2, as the threshold SD of the halftone dot cell Hs at the center of the shadow point.
Up to N-3, the supercell threshold value template 45 in a state in which four points are respectively determined is schematically shown.

As can be seen from FIG. 10, the thresholds HL and SD
From the center of the halftone dot cell Hh at the highlight point center, HL =
It is determined as 0, 1, 2, 3, and SD = N, N-1, N- from the center of the halftone dot cell Hs at the center of the shadow point.
2, N-3 will be decided. In detail, 0 → N
→ 1 → N-1 → …… → 3 → N-3
Will be decided.

The spot function f that determines the blackening order
The threshold HL of the halftone dot cell Hh at the center of the highlight point when the random numbers random_u and random_v are added to (u, v)
11 schematically shows the supercell threshold template 45A in a state in which the threshold SD of the halftone dot cell Hs at the center of the shadow point is determined to be 4 points.

In the case where the threshold value A is alternately determined in this way, when assigning a value near the threshold value A = N / 2, the pixel Ph in the halftone dot cell Hh at the highlight point center is assigned.
When the position of (x, y) coincides with the position of the pixel Ps (x, y) in the halftone dot cell Hs at the center of the shadow point, the pixel P (x of the halftone dot cell previously assigned is , Y) is prioritized and a value near the threshold value A = N / 2 is assigned.

By this procedure, all thresholds A of the supercell threshold template 45A are determined. The supercell threshold template 45A for which the threshold A is determined is R
It is stored in a storage device such as an OM and is used for the binary data creation device 41 as shown in FIG.

As described above, according to the above-described embodiment, when the supercell S is divided into the halftone dot cells H, it is divided into the halftone dot cells Hh centered on the highlight points and the halftone dot cells Hs centered on the shadow points. When the coordinate calculation for determining the blackening order of the pixel P in each of the halftone dot cell Hh centered on the highlight point and the halftone dot cell Hs centered on the shadow point is performed, Random number ran that differs for each halftone dot cell
The blackening order is determined by adding d_u and land_v, and the halftone dot cell Hh at the center of the highlight point is determined according to the determined blackening order.
, The threshold value HL assigned to each pixel Ph and the threshold value SD assigned to each pixel Ps in the halftone dot cell Hs at the center of the shadow point are alternately determined. Therefore, when the density of the original image in which moire fringes are likely to appear is high, in other words, when the halftone dot percentage is, for example, about 90% or more, the blackened pixel in the halftone dot cell Hh at the center of the highlight point is considered. The number is equal to the number of blank pixels in the halftone dot cell Hs at the center of the shadow point, and the effect that moire fringes are not generated is achieved.

FIG. 15B is a simulation image 9'at the time of high halftone output, to which this embodiment produced corresponding to FIG. 15A is applied. In FIG. 15B, the quadrangle portion denoted by reference numeral 11 'is a blank portion, and the other portions are blackened portions. FIG.
It is understood from B that the moire fringes are not generated.

The present invention is not limited to the above-mentioned embodiments, and it goes without saying that various configurations can be adopted without departing from the gist of the present invention.

For example, in addition to the application to the supercell having the inclination of 0 ° shown in FIG. 4, the application to the inclined supercell S shown in FIG. 14 is also possible.

[0077]

As described above, according to the present invention, when a supercell is divided into halftone dot cells, it is divided into halftone dot cells centering on highlight points and also halftone dot cells centering on shadow points. However, when calculating the blackening order of pixels in each of the halftone dot cell at the highlight point and the halftone dot center at the shadow point, the coordinate of each pixel is different for each halftone dot cell. Add a random number to determine the blackening order,
The threshold value assigned to each pixel in the halftone dot cell at the center of the highlight point and the threshold value assigned to each pixel in the halftone dot cell at the center of the shadow point are alternately determined according to the determined blackening order. Therefore, when the density of the original image is high, in other words, when the halftone dot percentage is, for example, about 90% or more, the number of blackening pixels in the halftone dot cell at the highlight point center and the shadow point center The number of blank pixels in each halftone dot cell becomes equal in each halftone dot cell in each supercell, and the effect that moire fringes are not generated is achieved.

By comparison of the features of the present invention with respect to the prior art, as a prior art that uses a random number to eliminate moire, for example, Japanese Patent Publication No. 6-57049, "halftone dot forming method". (First prior art), Japanese Unexamined Patent Publication No. 6-30250, "Method for adjusting dot size in digital halftoning by multi-cell threshold array" (second prior art), and There is a technology (third prior art) disclosed in Japanese Patent Application Laid-Open No. 7-38755 "Halftone screen forming device, halftone screen and method for forming the same".

These first to third prior arts are similar to the present invention in that they use random numbers when determining the threshold array in the threshold template.

However, the first prior art is a method in which the unit halftone dot area is divided into divided areas consisting of a predetermined number of elements, and a random number is set as a deviation amount for each divided area, and the second prior art is In the calculation of the coordinates supplied to the spot function, an offset vector is introduced, and this offset vector is generated by a random number generator. The third prior art introduces a random phase vector in the coordinate calculation. However, when dividing a super cell into halftone dot cells, which is a part of the characteristic part of the present invention, each of them is divided into halftone dot cells centered on highlight points, There is no suggestion that the vertex of the dot cell centered on the shadow point coincides with the center of the dot cell centered on the highlight point, with the division into point cells.

The random number generation disclosed in the inventions according to the first to third prior arts can be applied to the present invention.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of an image plate making system to which an embodiment of the present invention is applied.

FIG. 2 is a block diagram showing a schematic configuration of a binary data creation device that constitutes the image plate making system of the example of FIG.

FIG. 3 is a flowchart showing an algorithm for determining a threshold of a super cell threshold template.

FIG. 4 is a diagram showing a configuration of a super cell divided into halftone dot cells centered on a highlight point.

FIG. 5 is a diagram showing a configuration of a super cell divided into halftone dot cells centered on a shadow point.

FIG. 6 is a diagram provided for explaining the definition of the existing position of a pixel.

FIG. 7 is a diagram provided for explaining a spot function.

FIG. 8 is a flowchart showing a detailed algorithm for determining a threshold value.

FIG. 9 is a diagram provided for explaining an unprocessed pixel for which a threshold value has not been determined.

FIG. 10 is a diagram showing an example of a threshold template in which thresholds are set.

FIG. 11 is a diagram showing an example of a threshold template in which a threshold is set according to an added random number.

FIG. 12A is a diagram for explaining a relationship between a tilted halftone dot cell and a pixel, and FIG. 12B is a diagram for explaining a tilted halftone dot cell.

13A is a diagram for explaining a relationship between a non-tilted halftone dot cell and a pixel, and FIG. 13B is a diagram for explaining a non-tilted halftone dot cell.

FIG. 14 is a diagram provided for explaining a configuration of a super cell.

FIG. 15A is a diagram according to the related art for explaining a case where moire fringes are generated at high halftone percentage, and FIG. 15B is a moire fringe is generated at high halftone percentage. It is a figure concerning this invention provided for explanation when there is no.

[Explanation of symbols]

41 ... Binary data creation device 45, 45A ... Supercell threshold template A ... Threshold (threshold data) B ... Binary data F ... Halftone dot image film G ... Image data H ... Halftone dot cell HL ... Halftone dot centered net Threshold value for dot cell Hh ... Halftone dot cell at highlight point Hs ... Halftone dot cell at shadow point center P ... Pixel S ... Super cell SD ... Threshold value for halftone dot cell at shadow point center

Claims (6)

[Claims] 1. A supercell is set on a pixel grid determined by an output resolution, the set supercell is divided into halftone dot cells, and a threshold value is assigned to each pixel in the divided halftone dot cell to assign a halftone dot. In a halftone dot threshold value setting method for setting a threshold value, when dividing the supercell into halftone dot cells, while dividing into halftone dot cells centering on highlight points, and dividing into halftone dot cells centering on shadow points, at that time, The apex of the halftone dot cell at the center of the shadow point is aligned with the center of the halftone dot cell at the highlight point center, and the respective halftone dot cells at the highlight point center and the shadow point center When calculating the blackening order of the pixels in the point cells, a different random number is added to the coordinates of each pixel for each halftone dot cell to determine the blackening order, and the highlighting is performed according to the blacking order. Dot-centered net The threshold value assigned to each pixel in the cell, halftone threshold setting method characterized by defining alternating threshold assigned to each pixel in the halftone cell of the shadows point center. 2. The halftone dot threshold value setting method according to claim 1, wherein the random number to be added can control the size of the random number and the number of halftone dot cells to be added. 3. The halftone dot threshold value setting method according to claim 1, wherein the size of the random number to be added is equal to or smaller than the size of the pixel. 4. A binary data creation apparatus for obtaining binary data by comparing original image data with a supercell threshold template, wherein the supercell threshold template sets a supercell on a pixel grid determined by an output resolution, Divide the set super cell into halftone cells,
In the case of assigning a threshold value to each pixel in the divided halftone dot cells and setting the halftone dot threshold value, when dividing the super cell into the halftone dot cells, the supercell is divided into the halftone dot cells at the center of the highlight points. , The shadow point center halftone dot cell, wherein the vertex of the shadow point center halftone dot cell coincides with the center of the highlight point center halftone dot cell, At the time of coordinate calculation for determining the blackening order of pixels in each dot cell and each dot cell at the center of the shadow point, different random numbers are added to the coordinates of each pixel for blackening The order is determined, and the threshold value assigned to each pixel in the halftone dot cell at the center of the highlight point and the threshold value assigned to each pixel in the halftone dot cell at the center of the shadow point are alternately set according to the blackening order. Created as determined And binary data generating device, characterized in that are. 5. The binary data creating apparatus according to claim 4, wherein the random number to be added is capable of controlling the size of the random number and the number of halftone dot cells to be added. 6. The binary data creation device according to claim 4, wherein the size of the random number to be added is equal to or smaller than the size of the pixel.