JP2003158633A - Dot pattern generating method, correction method of threshold value matrix, data structure of the threshold value matrix, and recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dot pattern generating method, a correction method of threshold value matrix, a data structure of the threshold value matrix, and a recording medium that can eliminate or relax the periodicity (moire) caused in a dot pattern comprising multi-dot cells when only one dot cell has a dot different in growth by one pixel in the dot pattern. SOLUTION: Since the periodicity (moire) can easily be visually recognized in a dot pattern where one dot cell whose number of pixels is 19 or 17 (that is, more than or less than 18 pixels by one pixel) exists among dot patterns each comprising 8 dot cells each respectively comprising 18 pixels, for example, a threshold value 134 before correction is changed into a threshold value 133 after correction and a threshold value 136 before correction is revised into a threshold value 137 after correction in the vicinity of a gradation 135 of input image data in order to prevent the dot pattern as above from being produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image setter, a CTP (Computer to Plate) device, a CTC (Compu
ter to Cylinder) device, DDCP (Direct Digital Co)
Lor Proof) system and other halftone dot output devices in the field of printing, or electrophotographic or inkjet type continuous tone image output devices suitable for applying halftone dot pattern creation methods and threshold matrixes How to fix
The present invention relates to a threshold matrix data structure and a recording medium.

[0002]

2. Description of the Related Art In the field of printing plate making, when an original image is reproduced as a printed matter, ink is placed on a printing paper sheet through a printing plate mounted on a printing machine to form an image.

As a method of reproducing an original image on a printed matter,
An area gradation reproduction method is known in which an image to be formed is a halftone dot pattern (also referred to as a dot pattern) including a plurality of halftone dots (also referred to as dots).

In this case, a halftone dot pattern is also formed on the printing plate, and the printing plate is produced through a film output from the imagesetter or the CT.
It is created directly from the image data by the P device or the CTC device without passing through the film.

The halftone dot pattern formed on the film or the printing plate is created in advance by an image processing device such as a workstation.

FIG. 20 shows a state in which a schematic example of the halftone dot pattern 4 to be formed on the film or the printing plate is displayed on the display of the image processing apparatus.

The halftone dot pattern 4 is composed of 16 × 16 pixels, and, for example, values 0, 1, 2, ... 255.
The threshold values of the 16 × 16 threshold value array that is arranged corresponding to each pixel position are compared with the image data that takes a uniform value {here, the pixel value 239 (= 255-16)}. And the pixels in which the threshold values of the pixel value 239 or less are arranged are blackened and created.

In this case, a halftone dot cell 2 composed of 4 × 4 pixels
One halftone dot 3 is formed for each. A threshold array consisting of 4 × 4 pixels corresponding to the halftone dot cell 2 consisting of 4 × 4 pixels is called a halftone dot threshold cell. Therefore, the threshold matrix for creating the halftone dot pattern 4 in the example of FIG. 20 is composed of eight halftone dot threshold cells each having a threshold value of 4 × 4.

The halftone dot pattern 4 corresponding to these eight halftone dot threshold cells is a large cell of 16 × 16 pixels composed of eight halftone dot cells 2 of 4 × 4 pixels. Therefore, it is also called a multi-dot cell or a multi-dot cell.

In the example of FIG. 20, the halftone dot 3 of each halftone dot cell 2 forming the halftone dot pattern 4 of the multi-halftone dot cell is such that the pixel at the same position is a white pixel (also referred to as a white pixel). And all other pixels are black pixels. Here, the halftone dot% of each halftone dot cell 2 is about 9%.
The so-called shadow state is 3.8% (= 15 ÷ 16 × 100). Of course, the dot% as the dot pattern 4 is also about 93.8%.

[0011]

FIG. 21 shows a halftone dot pattern 6 in which four halftone dot patterns 4 shown in FIG. 20 are arranged vertically and horizontally.
Is shown. When this halftone dot pattern 6 is visually recognized, no new pattern is generated.

Actually, in the present invention, the output resolution is 2000 [pixels / inch] or less, so that the size of one pixel is, for example, one square pixel. The side length is 2.54 [c
m] /2000=12.7 [μm].

In practice, 1200 [pixel / inch] is adopted. Therefore, the actual pixel size is 21.
It is about 2 [μm] square.

Next, FIG. 22 shows eight halftone dot cells 2 of 18 pixels each having eight halftone dots 3 with a screen angle of 45 degrees and only one pixel at a specific position being a white pixel. 4 shows a halftone dot pattern 4. The total number of pixels of the halftone dot pattern 4 is 12 × 12 pixels = 144 pixels.

The corresponding threshold value matrix has a structure in which threshold values having values 0, 1, ..., 139 are arranged at corresponding positions of 12 × 12 pixels. This threshold matrix is also composed of eight halftone dot threshold cells, which is the same as the number of halftone dot cells 2.

In this case, as shown in FIG. 23, even when a halftone dot pattern 6 in which four halftone dot patterns 4 are arranged is created, a new pattern does not occur.

That is, when the halftone dots 3 in each halftone dot cell 2 constituting the halftone dot pattern 4 shown in the examples of FIGS. 20 and 22 have the same shape, the screen angle (0 ° in the example of FIG. 20). ) Or even if the total number of pixels forming the halftone dot cell 2 is different, no new pattern is generated on the halftone dot pattern 6 in which a plurality of halftone dot patterns 4 are arranged.

However, FIG. 24, FIG. 25, FIG.
As shown in FIG. 27, among the halftone dot patterns 4a (screen angle 0 degrees), 4b (screen angle 0 degrees), 4c (screen angle 45 degrees), and 4d (screen angle 45 degrees),
There may be halftone dot cells 2a, 2b, 2c, and 2d having halftone dots 3a, 3b, 3c, and 3d whose growth degree differs from the other halftone dot cells 1 by one pixel.

In this case, the corresponding FIG. 28,
Halftone dot pattern 4 as shown in FIGS. 29, 30, and 31.
Halftone dot pattern 6 including a, 4b, 4c and 4d
When a, 6b, 6c, and 6d are formed, the periodicity (moiré) occurs due to the presence of halftone dot cells 2a, 2b, 2c, and 2d having halftone dots 3a, 3b, 3c, and 3d having different growth conditions for only one pixel. The inventors of this application have found that there is a problem of being observed.

The present invention has been made in consideration of the above problem, and in a halftone dot pattern composed of multiple halftone dot cells, only one halftone dot cell has a halftone dot different in growth by one pixel. To provide a halftone dot pattern creation method, a threshold matrix correction method, a threshold matrix data structure, and a recording medium that have the periodicity (moiré) generated in a halftone dot pattern and can be alleviated. To aim.

[0021]

According to the present invention, the gradation of input image data is compared with the threshold value of a threshold matrix composed of at least four halftone dot threshold cells, and the same number of halftone dots as the halftone dot threshold cells. In the method of creating a halftone dot pattern, the halftone dots created by the at least four halftone dot threshold cells grow in substantially the same shape in accordance with an increase in gradation of the input image data. When the threshold matrix is created as described above, the halftone dot threshold cells are created for the image data of the next gradation of a certain gradation in which the shape of each halftone dot is a halftone dot of the same shape. The shape of each halftone dot holds the same shape as the halftone dot shape of a certain gradation, or two halftone dots in the shape of each halftone dot have the same shape as the halftone dot shape. Halftone dot shape with 1 pixel increase or 1 pixel decrease Tsu wherein the are (the invention according to claim 1).

According to the present invention, the shape of each halftone dot created by each halftone dot threshold cell is for the image data of the next gradation of a certain gradation in which the shape of each halftone dot is the same shape. , The same shape as the halftone dot shape of a certain gradation is maintained, or the shape of two halftone dots in the shape of each halftone dot is increased by one pixel or one pixel with respect to the halftone dot of the same shape. It has a reduced halftone dot shape. For this reason, one halftone dot in the halftone dot shape created by each halftone dot threshold cell for image data of a next gradation of a certain gradation in which the halftone dots have the same shape Since the shape does not become a halftone dot shape in which one pixel is increased or decreased by one pixel with respect to the halftone dot having the same shape, the periodicity (moiré) in the halftone dot pattern can be eliminated or alleviated.

In the present invention, the next gradation of a certain gradation is both the higher and lower gradations of a certain gradation (previous and subsequent gradations), or either one of the gradations. Means

The contents of the present invention will be described with reference to FIGS. 22, 26 and 2.
This will be described with reference to the halftone dot patterns 4, 4c and 4d of FIG.

Since the total number of pixels of the halftone dot patterns 4, 4c, and 4d is 12 × 12 = 144 pixels, the threshold value matrix (not shown) has pixel values of 0 to 143 before correction. It is arranged at the position corresponding to. In FIG. 32, it is described as a pre-correction threshold value. This pre-correction threshold corresponds to the gradation (0 to 143 gradation) of the input image data.

Whichever of the pre-correction threshold value and the post-correction threshold values A and B is used, if the value of the input image data is 0, for example, the number of black pixels is 0 and the number of white pixels is 144. A pattern is created. If the value of the input image data is 71, the number of black pixels is 72, which is the same as the number of white pixels. If the value of the input image data is 143, the number of black pixels is 144 and the number of white pixels is 0. Each halftone dot pattern is created.

Here, the halftone dot patterns 4, 4c and 4d in FIGS. 22, 26 and 27 are created with the pre-correction threshold values when the values of the input image data are 135, 136 and 134, respectively.

In this case, among the halftone dots formed by the eight halftone dot cells 2, one halftone dot whose pixel number has increased or decreased by 1 pixel is 1
Periodicity (moiré) with the existing halftone dot patterns 4c and 4d
Is easy to be visually recognized, such a halftone dot pattern 4c,
In order to prevent 4d from occurring, in the case of the corrected threshold value A, the uncorrected threshold value 134 is set as the corrected threshold value 133, and the uncorrected threshold value 136 is set as the corrected threshold value 137 (FIG. 32).
reference).

By doing so, the halftone dot pattern 4c shown in FIG. 26 becomes the two blackened halftone dots 3c shown in FIG.
The halftone dot pattern 4e shown in FIG. 27 is corrected to the halftone dot pattern 4e having 2
A halftone dot pattern 4f having three halftone dots 3d is modified.

In a halftone dot pattern in which a plurality of halftone dot patterns 4e and 4f are arranged vertically and horizontally, the occurrence of periodicity (moiré) is alleviated or eliminated.

In the conceptual diagram of FIG. 32, the circles indicate
The value of the input image data in which the number of pixels of each halftone dot 3 matches the shape, that is, the gradation, is shown.
A halftone dot pattern in which only one halftone dot has the shape of a halftone dot in which the number of pixels increases or decreases by 1 pixel with respect to the other halftone dots 2 is not adopted. In other words, it indicates that the threshold matrix (threshold array) for creating such a halftone dot pattern is not adopted.

The corrected threshold value is the corrected threshold value A in the upper row.
Instead of, for example, the pre-correction threshold value 136 is changed to the post-correction threshold value 1
The same effect can be obtained even if the modified threshold B is configured as shown in the lower part, such as 35.

Further, according to the present invention, the certain gradation is a dot%.
When the gradation is 50% or more, the halftone dot pattern in which the shapes of all the halftone dots created by the halftone dot threshold cells are all the same for the input image data of the gradation of 50% or more It is more preferable to use it in order to eliminate or alleviate the periodicity (moiré) in the halftone dot pattern (the invention according to claim 2).

In the conceptual diagram of FIG. 32, the threshold array is created so as to use such a halftone dot pattern.

Whether the shape of each halftone dot created by each halftone dot threshold cell is the same for the image data of the next gradation of the certain gradation at a gradation of 90% or more. Alternatively, by using a halftone dot pattern in which the shapes of two halftone dots are one dot increase or one pixel decrease with respect to the halftone dots of the same shape, the periodicity (moiré) is noticeable. It is easy to eliminate or alleviate the periodicity (moiré) in the shadow area.
Invention described).

In the conceptual diagram of FIG. 32, the threshold value is modified so that such a halftone dot pattern is used.
Is corrected to the corrected threshold 133, the pre-corrected threshold 136 is corrected to the corrected threshold 137 (corrected threshold A) or 135 (corrected threshold B), and the pre-corrected threshold 142 is corrected to the corrected threshold 141}.

Of course, the certain gradation is 50% in halftone dot%.
When the gradation is higher than that, be sure to use the halftone dot pattern in which the shapes of the respective halftone dots created by the respective halftone dot threshold cells are the same for the input image data of the gradation of 50% or more, In addition, the shape of each halftone dot created by each halftone dot threshold cell is the same for the image data of the next gradation of the certain gradation, or the shapes of two halftone dots are the same. It is not possible to use a halftone dot pattern in which the halftone dot pattern has one pixel increase or one pixel decrease with respect to the shape halftone dot
By setting the gradation to not less than%, the periodicity (moiré) in the halftone dot pattern can be more reliably eliminated or alleviated (the invention according to claim 4).

The present invention is suitable for application to a halftone dot pattern in which the number of halftone dots created by one halftone dot threshold cell is 100 or less (the invention according to claim 5).

Further, according to the present invention, the output resolution of the halftone dots is 2
It is suitable to be applied to a so-called low-resolution halftone dot pattern of 000 [pixels / inch] or less (the invention according to claim 6).

According to the present invention, the gradation of the input image data is compared with the threshold value of the threshold matrix consisting of at least four halftone dot threshold cells, and the halftone dot pattern consisting of the same number of halftone dots as the halftone dot threshold cells is formed. In the method of modifying the threshold value matrix used when creating, each halftone dot created by the at least four halftone dot threshold cells grows in substantially the same shape according to an increase in gradation of input image data. When the threshold matrix is created as described above, the halftone dot threshold cells are created for the image data of the next gradation of a certain gradation in which the shape of each halftone dot is a halftone dot of the same shape. The shape of each halftone dot holds the same shape as the halftone dot shape of a certain gradation, or two halftone dots in the shape of each halftone dot have the same shape as the halftone dot shape. Halftone dots with 1 pixel increase or 1 pixel decrease Modifying the threshold value constituting said threshold matrix such that Jo characterized (the invention described in claim 7).

By creating a halftone dot pattern using the modified threshold value matrix, it is possible to eliminate or reduce the periodicity (moiré) generated in the halftone dot pattern.

The present invention is a data structure of a threshold value matrix composed of a plurality of halftone dot threshold cells each having a plurality of threshold values, wherein each threshold value of the halftone dot threshold cells corresponds to an increase in gradation. , When the halftone dots are arranged to be large in a substantially uniform shape and the shape of each halftone dot created by each halftone dot threshold cell for a certain gradation of input image data is a halftone dot of the same shape, The shape of each halftone dot created by each halftone dot threshold cell for the image data of the next gradation of the certain gradation is
The same shape as the halftone dot shape of a certain gradation is maintained, or the shape of two halftone dots in the shape of each halftone dot is increased by 1 pixel or decreased by 1 pixel with respect to the halftone dot of the same shape. The threshold value is arranged so as to form the halftone dot shape (the invention according to claim 8).

According to the present invention, 1 in one multi-dot cell
Since only one halftone dot has halftone dots that differ in growth by one pixel, it is possible to eliminate or alleviate the periodicity (moiré) that occurs in the halftone dot pattern.

Further, such a threshold matrix data structure can be recorded in a recording medium and used (the invention according to claim 9).

[0045]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the basic construction of a plate making system 10 to which an embodiment of the present invention is applied.

The plate making system 10 basically has a halftone dot pattern data creating section 12 for creating halftone dot pattern data H from the input image data G supplied from the input terminal 11.
A threshold value matrix correction unit 14 that corrects a threshold value matrix from the created halftone dot pattern data H; a display unit 16 having a display or the like that displays an image corresponding to the created halftone dot pattern data H; And an image output machine 18 for producing a plate F such as a film or a printing plate from the halftone dot pattern data H.

Here, the halftone dot pattern data creation unit 12 and the threshold value matrix correction unit 14 are CPs as a control unit.
The functions achieved by a main body having a U (Central Processing Unit) and a workstation or a personal computer (each not shown) having an input device such as a keyboard are shown.

In the plate making system 10, a document image captured by a scanner, a digital camera or the like (not shown) and used as input image data G is a halftone dot composed of one or more black pixels (also referred to as blackened pixels). Plate F by a halftone dot pattern (also referred to as a dot pattern) which is a set pattern of
It is a system that reproduces.

Here, for convenience of understanding, it is assumed that the resolution of the input image data G matches the resolution of the image output machine 18. In this embodiment, the resolution of the image output device 18, that is, the output resolution is, for example, 1
It is assumed to be 200 [pixel / inch]. Further, the input image data G is continuous tone image data and has a value of 0,
1, ..., 399 shall be taken.

The halftone dot pattern data creating unit 12 includes a comparing unit 22, an address calculating unit 24, and a threshold matrix TM such as a supercell threshold template including at least four halftone dot threshold cells (the threshold matrix is the threshold data or the threshold array. Is also stored), and a network attribute input unit 28 as a selection means for selecting a desired threshold matrix TM from the threshold matrix TM stored in the threshold matrix storage unit 26.
It consists of and.

The input image data G supplied to the halftone dot pattern data creation unit 12 is supplied to the comparison input of the comparison unit 22. In addition, from the input image data G to the threshold matrix TM
Address AD = AD that represents the address of the upper x-axis and y-axis
The address calculator 24 calculates (x, y).

The threshold matrix TM is used by the address calculator 2
The threshold value T calculated at 4 and stored at the designated address AD is read out and supplied to the reference input of the comparison section 22. The threshold value T takes a value corresponding to the total gradation 0 to 399 of the input image data G, usually a value of 0, 1, ..., 399. It has been fixed.

As the threshold matrix TM, one corresponding to the halftone attributes (screen ruling, halftone angle and halftone shape) selected by the halftone attribute input unit 28 among the plurality of threshold matrices TM is used.

FIG. 2 shows a conceptual diagram of the threshold matrix 34 having a screen angle of 45 degrees selected by the network attribute input unit 28 in the threshold matrix TM. This threshold matrix 34 is 400 corresponding to 20 × 20 pixels in total.
It is composed of eight halftone dot threshold cells 32 each having a threshold value T and having a threshold value T for 50 pixels. From this meaning, the threshold matrix 34 is called a multi-dot threshold cell.

In practice, the threshold matrix TM (threshold matrix 34 as a concrete example) has a size corresponding to the size of the image of the input image data G when the halftone dot pattern data H is created. 26, a plurality of threshold matrixes 34 having a multi-halftone dot threshold cell configuration are arranged vertically and horizontally to create a threshold matrix TM having the image size of the input image data G.

The selected threshold matrix 34 shown in FIG.
Is at a position corresponding to each pixel of 20 × 20 pixels (= 400 pixels) in total, and the values 0, 1, 2,
A threshold value T that takes any value of 399 is arranged.

Each threshold T corresponds to an increase in gradation of the input image data G when the pixels corresponding to each halftone threshold cell 32 forming the threshold matrix 34 are blackened to form halftone dots. The threshold value T is assigned so that the halftone dots forming each halftone dot threshold cell 32 grow in the same shape.

The comparing section 22 compares the gradation value (pixel value) of the input image data G with each threshold value T forming the threshold matrix 34, and the pixel having the gradation value (pixel value) equal to or less than the threshold value T is black. The halftone dot pattern data H created by digitizing, that is, the gradation image data, is displayed on the display unit 16 such as a CRT monitor.
And to the image output machine 18.
Here, the image displayed on the display unit 16 according to the halftone dot pattern data H is a set pattern of halftone dots having halftone dots (dots) made up of 0 or 1 or more blackened pixels, that is, a halftone dot pattern (dots). It becomes a gradation image formed by a pattern).

On the other hand, in the image output machine 18, a plate F corresponding to this halftone dot pattern is created, and if the created plate F is a printing plate, it is mounted on the printing machine as it is, and the printing machine mounted on the printing machine is printed. Ink is applied to the plate. By applying (transferring) the ink attached to the printing plate onto the printing paper, it is possible to obtain a desired printed matter on which an image is formed by a halftone dot pattern on the printing paper.

The threshold matrix TM forming the halftone dot pattern data creating section 12 in the example of FIG.
It is possible to record on a recording medium 49 that is a supply medium such as a portable medium such as an optical disc that is a package medium such as a CDR or a DVD and can carry it. The threshold matrix TM can also be transmitted as data wirelessly or by wire.

In this embodiment, the threshold matrix TM used is one stored in a storage medium such as a hard disk mounted on a personal computer or the like.

The above is the description of the basic configuration of the plate making system 10 according to the embodiment of the present invention.

Next, a method for creating a halftone dot pattern for eliminating or mitigating the periodicity (moiré) that occurs on the halftone dot pattern as an image, a method for correcting a threshold matrix, and a threshold matrix TM (in this embodiment). Now, the data structure of the threshold matrix 34) will be described as an example.

First, an example of a halftone dot pattern corresponding to the halftone dot pattern data H created by the halftone dot pattern data creating unit 12 using the threshold value matrix 34 (see FIG. 2) selected from the threshold value matrix storage unit 26. Indicates.

For convenience of understanding, the threshold matrix 34
Image data G having the same size as the
Is supplied to the comparison unit 22 and the address calculation unit 24, and the halftone dot pattern data H corresponding thereto is created.

For example, if the value of the image data G is halftone dot 18
In the case of a gradation value (G = 72) corresponding to [%], if the halftone dot pattern data H appearing on the output side of the comparison unit 22 is halftone dot pattern data Ha, each halftone dot threshold value forming the threshold value matrix 34 In the cell 32, the pixel corresponding to the value (0 to 72) whose threshold T is T = 72 or less is blackened.

FIG. 3 shows a halftone dot pattern 60a displayed on the display unit 16 corresponding to the halftone dot pattern data Ha.

This halftone dot pattern 60a has eight halftone dot cells 62 corresponding to the eight halftone dot threshold cells 32 shown in FIG.
In each halftone dot cell 62, a halftone dot 50a of the same shape composed of 3 × 3 black pixels is formed.

Further, the value of the image data G is 50% in halftone dot%.
Halftone dot pattern data H appearing on the output side of the comparison unit 22 when the gradation value (G = 199) corresponding to [%]
Is the halftone dot pattern data Hb, the threshold matrix 3
4, the pixels corresponding to the threshold value T of T = 199 or less are blackened, so that the pixel corresponding to this halftone dot pattern data Hb in FIG.
The halftone dot pattern 60b shown in is created.

This halftone dot pattern 60b has a structure in which eight halftone dot cells 62 each have a halftone dot 50b of the same shape consisting of 5 × 5 black pixels.

Further, the value of the image data G is about 82 in halftone dot%.
Halftone dot pattern data H appearing on the output side of the comparison unit 22 when the gradation value (G = 327) corresponding to [%]
Is the halftone dot pattern data Hc, the threshold matrix 3
4, the pixels corresponding to the threshold value T of T = 327 or less are blackened, and therefore, the pixel corresponding to the halftone dot pattern data Hc shown in FIG.
The halftone dot pattern 60c shown in FIG.

This halftone dot pattern 60c has halftone dots 50c of 41 black pixels of the same shape in each of the eight halftone dot cells 62, in other words, 3 × 3 = 9 white pixels. The halftone dots 50c having the same shape are formed.

Further, the value of the image data G is about 98 in halftone dot%.
Halftone dot pattern data H appearing on the output side of the comparison unit 22 when the gradation value (G = 391) corresponding to [%]
Is the halftone dot pattern data Hd, the threshold matrix 3
4, the pixels corresponding to the threshold value T of T = 391 or less are blackened, and therefore the pixel corresponding to this halftone dot pattern data Hd is shown in FIG.
The halftone dot pattern 60d shown in FIG.

In this halftone dot pattern 60d, halftone dots 50d having the same shape each consisting of 49 black pixels in each of the eight halftone dot cells 62, in other words, a halftone dot 50d having one white pixel are formed. It is configured to be formed.

Thus, the threshold T of the threshold matrix 34 is
The halftone dot 50 (50a, 50b, 50c, 50d) created by each of the eight halftone dot threshold cells 32 is
However, it is created so that the input image data G grows in substantially the same shape as the gradation of the input image data G increases.

Here, in the halftone dot pattern 60d having the eight halftone dots 50d of the same shape shown in FIG. 6, the gradation of the image data G is increased and the value thereof is the image data G = 39.
Image data from 1 to the next gradation (higher gradation) G = 392
Therefore, as shown in FIG. 7, the corresponding threshold value T = 392
Let us consider a halftone dot pattern 60e having a halftone dot 50e in which the pixel 64 in which is arranged becomes a black pixel and the number of black pixels is increased by one.

The halftone dot pattern 60e shown in FIG. 7 is composed of eight halftone dots (halftone dots 5 of the same shape in which only one pixel is blank).
7 dots 0d and halftone dots 5 of different shapes with all pixels blackened
One halftone dot 50e out of eight halftone dots (0e is one)
However, the shape and growth of the remaining halftone dot 50d for one pixel are different.

It has been described in the section of the prior art that undesired periodicity (moiré) is easily generated on a halftone dot pattern in which a plurality of halftone dot patterns 60e are arranged vertically and horizontally.

Therefore, in the present invention, the threshold value matrix correction unit 14 corrects the threshold value T so that the halftone dot pattern 60e shown in FIG. 7 does not occur.

The halftone dot pattern 60f shown in FIG. 8 shows the halftone dot pattern 60f of the input image data G = 392 created after the threshold value T of the halftone dot pattern 60e shown in FIG. 7 is corrected. In the threshold matrix 34 forming this halftone dot pattern 60f, the threshold T (T = 393) of the pixel 64 is corrected to the threshold T (T = 392).

By correcting the value of the threshold value T in this way, the image data G in which the gradation of the input image data G is the same for all the halftone dots 50d forming the halftone dot cell 62
= 391 (see FIG. 6), and when the image data G = 392 increases by one gradation, the halftone dot pattern 60 shown in FIG.
d is retained.

Then, when the gradation of the input image data G becomes the next gradation (higher gradation) image data G = 393, at least two halftone dots 5 as shown in FIG.
0e is a halftone dot pattern 60 in which the number of blackened pixels is increased by one pixel.
f. Therefore, it is possible to eliminate or alleviate the occurrence of undesirable periodicity (moiré) that is easily visible on a halftone dot pattern in which a plurality of halftone dot patterns 60f are arranged vertically and horizontally.

Similarly, from the state shown in FIG.
When the image data G becomes the next gradation (lower gradation) image data G = 390, the corresponding threshold value T = 390 is arranged as shown in FIG. Let us consider a halftone dot pattern 60g having halftone dots 50g in a state where a certain pixel 66 becomes a white pixel and one black pixel decreases (one white pixel increases).

The halftone dot pattern 60g shown in FIG.
Among the halftone dots (7 halftone dots 50d having the same shape and one halftone dot 50g having a different shape, a total of 8 halftone dots), only one halftone dot 50g is a halftone dot for the remaining one pixel. The shape (growth) of the point 50d is different. For this reason, it has been described in the section of the prior art that undesired periodicity (moiré) occurs on a halftone dot pattern in which a plurality of halftone dot patterns 60g are arranged vertically and horizontally.

Therefore, according to the present invention, the threshold value T is corrected by the threshold value matrix correction section 14 in this case as well.

The halftone dot pattern 60h shown in FIG.
Halftone dot pattern 60 after correction of halftone dot pattern 60g shown in FIG.
It shows h. In the threshold matrix 34 forming this halftone dot pattern 60h, the threshold value T of the pixel 68 (T = 390)
Is corrected to a threshold value T (T = 391).

By correcting the value of the threshold value T in this manner, image data G = in which the gradation of the input image data G is the same for all the halftone dots 50d forming the halftone dot cell 62.
391 (see FIG. 6), the image data G is reduced by one gradation.
= 390, as shown in FIG. 10, at least two halftone dots 50g become a halftone dot pattern 60h in which the number of white pixels is increased by two pixels.
On a halftone dot pattern in which a plurality of h are arranged vertically and horizontally, it is possible to eliminate or alleviate the occurrence of the above-mentioned undesirable periodicity (moiré).

Thus, for example, as shown in FIG. 6, the halftone dot threshold cells 32 forming the threshold matrix 34 (see FIG. 2) for the input image data G (G = 391) of a certain gradation are used. When the halftone dots 50d to be created are halftone dots having the same shape, each halftone dot threshold value is applied to the image data G (G = 392, 390) of the next grayscale (previous grayscale) of the certain grayscale. The shape of each halftone dot 50 created by the cell 32 either keeps the same shape or continues, or
0, not one but two halftone dots 50e (see FIG. 8), 5
The shape of 0 g (see FIG. 10) is the same as the halftone dot 50d.
The shape of halftone dot 50e increased by 1 pixel with respect to
If the halftone dot patterns 60f (see FIG. 8) and 60h (see FIG. 10) are formed so as to have the shape of the halftone dot 50g with reduced pixels, the occurrence of undesirable periodicity (moire) can be reduced or eliminated. You can

Here, the threshold value T for all gradations of values 0 to 399
Considering that undesired periodicity (moiré) is easily observed in halftone dot gradations of 50% or more, especially in shadow areas of 90% or more, so-called tone jump is 50%. Consider that it is likely to occur in the vicinity.

From these two points, when the gradation is 50% or more in halftone dot%, the halftone dot 50 of each halftone dot created by each halftone dot threshold cell 32 is applied to the input image data G having the gradation of 50% or more. Be sure to use halftone dot patterns (for example, halftone dot patterns 60b, 60c, 60d) that all have the same shape, and all halftone dots in the halftone dot cell 62 have the same halftone. Each halftone dot threshold cell 32 for the image data G of the tones (both or both of the tones before and after a certain tone)
The halftone dot 50 created by the above method holds all the halftone dots 50 having the same shape as a certain gradation, or the two halftone dots 50 have the same shape.
It is not possible to use halftone dot patterns 60g and 60h having a halftone dot shape with one pixel increased or one pixel decreased with respect to
By arranging the threshold value matrix 34 in which the threshold values T are arranged so as to have a gradation of not less than%, it is possible to eliminate or alleviate the periodicity (moiré) in the halftone dot pattern 60, and in the vicinity of 50%. The tone jump that tends to occur can be suppressed.

11 and 12, the screen angle is 45 degrees, and the threshold value T corresponding to 50% or more of the gradation with respect to the uncorrected threshold value matrix 34 is halftone dot (FIGS. 11 and 12).
The middle and upper thresholds are pre-correction thresholds, which match the gradation of the input image data G. ) And the threshold value T corresponding to the corrected threshold value Matrices 34 having a gradation of 50% or more.
(The lower threshold value in FIGS. 11 and 12 is the post-correction threshold value.).

When the halftone dot% is 50% or less, the upper threshold value T before correction (0 to 199) and the lower threshold value after correction T are set.
Since (0 to 199) is matched, it is omitted.

Since the threshold value matrix 34 in the example of FIG. 2 is composed of eight halftone dot threshold cells 32, eight halftone dots 50 of the same shape are obtained for every eight gradations.

Therefore, the input image data G marked with a circle
Then, the upper threshold T is corrected to the lower threshold T so that the halftone dots 50d have the same shape.

Further, in the gradation corresponding to the halftone dot percentage of 90% or more and 100% or less, the input image data G marked with X is
Of the eight halftone dots 50, only one halftone dot 50 corresponds to one pixel, and the upper threshold value T is set to the lower threshold value T so that the blackened pixels do not increase or decrease.
Has been fixed.

For gradations corresponding to halftone dots of 50% or more and 90% or less, 1 in the input image data G marked with Δ.
Even if only one halftone dot 50 has one pixel of blackened pixels, the periodicity of the halftone dot pattern is not conspicuous.
There are places where the threshold value T is corrected and places where it is left uncorrected.

Note that, in FIGS. 11 and 12, the threshold value T in the blank portion in the lower row is the same as the threshold value T in the upper row, and is therefore omitted.

Further, in FIGS. 11 and 12, with the hatched threshold value T, all the halftone dots 50 formed in each of the eight halftone dot cells 62 have the same halftone dot shape.

In FIG. 12, at the threshold value T which is cross-hatched, at least two halftone dots among the halftone dots 50 formed in each of the eight halftone dot cells 62 have one black pixel. It has a halftone dot shape. That is, since only one halftone dot 50 among the eight halftone dot cells 62 does not have a halftone dot shape having a large number of black pixels for one pixel, the occurrence of undesirable periodicity (moiré) is eliminated or reduced. Can be made.

Next, another modification example of the threshold value T in the case where the halftone dot percentage is around 50% will be described.

As described above, in FIG. 4, the halftone dot pattern 60 corresponding to the input image data G = 199 with the halftone% of 50%.
b.

In the case of the threshold value matrix 34 before the correction of the threshold value T, the value of the input image data G for which all the halftone dot shapes should be the same is G = 207, but at the previous gradation level. When certain input image data G = 206, as shown in FIG. 13, only one halftone dot 50i is different in shape from the other halftone dots by one pixel, which is not preferable.

Therefore, in this case, as shown in FIG. 14, the threshold value T = 207 of the pixel 70 is modified to the threshold value T = 206 (see the corresponding threshold value in FIG. 11).

With such correction, the input image data G
= 206 and 207, the halftone dot pattern 60j shown in FIG. 14 is composed of halftone dots 50j having the same shape.
Is obtained.

As shown in FIG. 15, when the input image data G = 208, one halftone dot 50k is allowed to be different from the shapes of other halftone dots, giving priority to the fact that no tone jump occurs. ing.

16 and 17 show the corrected threshold value T to be assigned to the threshold value matrix 34 in the lower stage, assuming that the gradation of the input image data G changes from 0 to 399 to 0 to 1021. There is. The idea of modifying the threshold T is
Since it is similar to FIGS. 30 and 31, description thereof will be omitted.

18 and 19 show the corrected threshold value T to be assigned to the threshold value matrix 34 in the lower stage, assuming that the gradation of the input image data G changes from 0 to 399 to 0 to 255. There is. Even in this case, the threshold value T
The concept of the correction is the same as that of FIGS.

[0109]

As described above, according to the present invention, the next gradation of a certain gradation in which the shape of each halftone dot becomes a halftone dot of the same shape {the higher and lower gradations of a certain gradation are obtained. Both gradations (front and rear gradations), or either one of the gradations. } Among the shapes of the respective halftone dots created by the respective halftone dot threshold cells for the image data of {1}, a halftone dot is increased or decreased by one pixel with respect to the halftone dots having the same shape. Since there is no dot shape, it is possible to eliminate or alleviate the periodicity (moiré) in the halftone dot pattern.

That is, in the multi-halftone dot cell, only one halftone dot cell can eliminate or alleviate the periodicity (moiré) that occurs in the halftone dot pattern by having the halftone dots different in growth by one pixel. it can.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a plate making system according to an embodiment of the present invention.

FIG. 2 is a schematic diagram of a threshold matrix.

FIG. 3 is a halftone dot pattern (45
18%).

FIG. 4 is a halftone dot pattern (45
50%).

FIG. 5: Halftone dot pattern (45
82%).

FIG. 6 is a halftone dot pattern (45
And 98%).

FIG. 7 is a halftone dot pattern (45 degrees, 9 degrees) where moire is visually recognized.
It is a figure of 8.25%).

FIG. 8: Halftone dot pattern (45
98.5%).

9 is a halftone dot pattern (45 degrees, 9
7.75%).

FIG. 10: Halftone dot pattern (45
97.5%).

FIG. 11 is an explanatory diagram (1/2) of threshold values before and after correction with 400 constituent pixels.

FIG. 12 is an explanatory diagram (2/2) of threshold values before and after correction with 400 constituent pixels.

FIG. 13 is a halftone dot pattern in which only one halftone dot among eight halftone dots has one pixel less than one pixel (45 degrees, 51.75%).
FIG.

FIG. 14 is a diagram of a halftone dot pattern (45 degrees, 52%) in which moire is no longer visually recognized by correcting the threshold value.

FIG. 15: Halftone dot pattern (45 degrees, 52.25%) created by giving priority to avoiding tone jump over visual recognition of moire
FIG.

FIG. 16 is an explanatory diagram (1/2) of threshold values before and after correction with the number of constituent pixels of 1022.

FIG. 17 is an explanatory diagram (2/2) of threshold values before and after correction with the number of constituent pixels of 1022.

FIG. 18 is an explanatory diagram (1/2) of threshold values before and after correction when the number of constituent pixels is 200.

FIG. 19 is an explanatory diagram (2/2) of threshold values before and after correction with 200 constituent pixels.

FIG. 20 shows a halftone dot pattern (0
The degree is 93.75%).

21 is a diagram of a halftone dot pattern in which four halftone dot patterns of FIG. 20 are arranged vertically and horizontally.

FIG. 22 is a halftone dot pattern (45
It is a figure of (degree).

23 is a diagram of a halftone dot pattern (45 degrees) in which four halftone dot patterns of FIG. 22 are arranged.

FIG. 24 is a diagram of a halftone dot pattern in which moire is visually recognized.

FIG. 25 is a diagram of a halftone dot pattern in which moire is visually recognized.

FIG. 26 is a diagram of a halftone dot pattern in which moire is visually recognized.

FIG. 27 is a diagram of a halftone dot pattern in which moire is visually recognized.

FIG. 28 is a diagram of a halftone dot pattern in which moire is visually recognized.

FIG. 29 is a diagram of a halftone dot pattern in which moire is visually recognized.

FIG. 30 is a diagram of a halftone dot pattern in which moire is visually recognized.

FIG. 31 is a diagram of a halftone dot pattern in which moire is visually recognized.

FIG. 32 is a conceptual diagram of threshold value correction.

FIG. 33 is a diagram of a halftone dot pattern in which a threshold value is corrected and moire is no longer visually recognized.

FIG. 34 is a diagram of a halftone dot pattern in which a threshold value is corrected and moire is no longer visually recognized.

[Explanation of symbols]

2, 2a to 2d, 62 ... Halftone dot cells 3, 3a to 3d, 50, 50a to 50k ... Halftone dots 4, 4a to 4f, 6, 6a to 6d, 60, 60a to 60
j ... Halftone dot pattern 10 ... Plate making system 11 ... Input terminal 12 ... Halftone dot pattern data creating unit 14 ... Threshold matrix correction unit 16 ... Display unit 18 ... Image output machine 22 ... Comparison unit 24 ... Address calculation unit 26 ... Threshold matrix storage Part 28 ... Halftone attribute input unit 32 ... Halftone dot threshold cell 34, TM ... Threshold matrix 64, 66 ... Pixel G ... Input image data H, Ha to Hd ... Halftone dot pattern data T ... Threshold

Continued front page    F term (reference) 2C262 AA24 AB01 BB06 BB22 BB25                       BB27                 2H084 AA25 AE06 BB13 CC12                 5B057 AA11 BA30 CA02 CA08 CA12                       CA16 CB02 CB07 CB12 CB16                       CE13                 5C077 LL03 MP02 NN05 PP45 RR06                       RR16 TT08

Claims (9)

[Claims] 1. A gradation pattern of input image data and a threshold value matrix of at least four halftone dot threshold cells are compared to create a halftone dot pattern having the same number of halftone dots as the halftone dot threshold cells. In the halftone dot pattern creating method, the threshold matrix is created so that each halftone dot created by the at least four halftone dot threshold cells grows in substantially the same shape in accordance with an increase in gradation of input image data. The shape of each halftone dot created by each halftone dot threshold cell with respect to the image data of the next gradation of a certain gradation in which the shape of each halftone dot is the same shape as the halftone dot is The same shape as the halftone dot shape of a certain gradation is maintained, or the shape of two halftone dots in the shape of each halftone dot is increased or decreased by one pixel with respect to the halftone dot of the same shape. Characterized by having a halftone dot shape Point pattern creation method. 2. The halftone dot pattern creating method according to claim 1, wherein the certain gradation is a gradation of 50% or more in halftone dot,
Halftone dot pattern creation characterized by always using a halftone dot pattern in which all halftone dot shapes created by each halftone dot threshold cell are the same for input image data with a gradation of 50% or more Method. 3. The halftone dot pattern creating method according to claim 1, wherein the shape of each halftone dot created by each of the halftone dot threshold cells for the image data of the next gradation of the certain gradation is said. Keep the same shape as the halftone dot shape, or 2
The use of a halftone dot pattern in which the shape of each halftone dot is one dot increased or decreased by one pixel with respect to the same-shaped halftone dot is characterized by a gradation of 90% or more. Halftone dot pattern creation method. 4. The halftone dot pattern creating method according to claim 1, wherein when the certain gradation is a gradation of 50% or more in halftone dot,
Be sure to use a halftone dot pattern in which all the halftone dot shapes created by each halftone dot threshold cell are the same for input image data with a gray scale of 50% or more. The shape of each halftone dot created by each halftone dot threshold cell with respect to the gradation image data holds the same shape as the halftone dot shape of the certain gradation, or the shape of two halftone dots is The use of a halftone dot pattern in which the halftone dot shape is increased or decreased by one pixel with respect to the halftone dot having the same shape has a gradation of 90% or more. Method. 5. The halftone dot pattern creating method according to claim 1, wherein the maximum number of threshold values stored in one halftone dot threshold value cell is 10.
A method for creating a halftone dot pattern, characterized in that the number is zero. 6. The halftone dot pattern creating method according to claim 1, wherein the halftone dot output resolution is 2000 [pixels / inch] or less. 7. A gradation pattern of input image data and a threshold value matrix of at least four halftone dot threshold cells are compared to create a halftone dot pattern having the same number of halftone dots as the halftone dot threshold cells. In the correction method of the threshold value matrix used at this time, each halftone dot created by the at least four halftone dot threshold cells grows in substantially the same shape according to the increase of the gradation of the input image data. When the threshold matrix is created in, each halftone dot created by each halftone dot threshold cell with respect to image data of a next gradation of a certain gradation in which the shape of each halftone dot is a halftone dot of the same shape. The shape of the dot maintains the same shape as the halftone dot shape of a certain gradation, or the shape of two halftone dots in the shape of each halftone dot is one pixel for the halftone dot of the same shape. Halftone dot shape that increases or decreases by 1 pixel Threshold matrix correction method characterized by correcting the threshold value constituting a sea urchin the threshold matrix. 8. A data structure of a threshold matrix composed of a plurality of halftone dot threshold cells each comprising a plurality of thresholds, wherein each threshold value of the halftone dot threshold cells corresponds to an increase in gradation.
When halftone dots are arranged so that they have substantially the same shape and are large, and the shape of each halftone dot created by each halftone dot threshold cell for input image data of a certain gradation is the same halftone dot, The shape of each halftone dot created by each halftone dot threshold cell with respect to the image data of the next gradation of a certain gradation holds the same shape as the halftone dot shape of the certain gradation, or The threshold value is characterized in that the threshold value is arranged so that the shape of two halftone dots in the shape of the dot becomes a halftone dot shape in which one dot is increased or decreased by one pixel with respect to the halftone dots having the same shape. Matrix data structure. 9. A recording medium for recording a data structure of a threshold matrix composed of a plurality of halftone dot threshold cells each having a plurality of threshold values, wherein the data structure of the threshold matrix is each of the halftone dot threshold cells. The threshold value is arranged so that the halftone dots become larger in a substantially uniform shape in response to an increase in the grayscale, and the halftone dots of each halftone dot created by each halftone dot threshold cell for input image data of a certain gray scale are set. When the shapes are halftone dots of the same shape, the shape of each halftone dot created by each halftone dot threshold cell for the image data of the next gradation of the certain gradation is the halftone dot shape of the certain gradation. So that the shape of two halftone dots in the shape of each halftone dot becomes a halftone dot shape that is increased or decreased by one pixel with respect to the halftone dot of the same shape. A recording medium having a threshold value.