JP2680125B2 - Method for forming mesh screen - Google Patents

Description

The present invention relates to a method for forming a mesh screen in a flatbed color scanner or the like, and is particularly obtained by scanning an original consisting of continuous tone color images. 4-color separation halftone gradation of C (cyan), M (magenta), Y (yellow), K (black) that can be reproduced by printing by superimposing an image signal on a halftone screen signal generated electrically. When forming an image, a halftone screen forming method capable of obtaining an arbitrary screen ruling when forming a halftone dot by outputting light spots of a certain size with a recording unit that performs exposure scanning at a certain pitch Regarding Furthermore, the pitch is changed in the number of screen lines where the moire pattern is generated,
The present invention relates to a mesh screen forming method in which a moire pattern is not generated at all screen frequencies.

(Prior Art) In recent years, in the field of printing and plate making, image scanning and reading that electrically processes image information of an original to create a film original for printing in order to rationalize work processes and improve image quality. Recording devices are widely used.

This image scanning reading and recording apparatus basically includes an input unit, a control unit, and an output unit. That is, in the input unit, an image signal is picked up by an illumination optical system, a color separation optical system, and a photometric system, and the image information photoelectrically converted in the input unit is subjected to gradation correction, color correction, Calculation processing such as contour enhancement, conversion of R, G, B → C, M, Y, and K is performed. The image information processed by the control unit is converted again into an optical signal such as a laser beam at the output unit, and the image is recorded on a record carrier made of a photosensitive material. Next, the record carrier is subjected to development processing by a predetermined developing device, and then subjected to printing or the like as a film original.

By the way, when the original document to be printed and reproduced is a continuous tone image such as a photograph or a painting, it is necessary to perform halftone decomposition on the original document in order to express the shade of the image. That is, the continuous tone image is converted into a halftone image which is an aggregate of halftone dots formed in different sizes according to the density of the image. As a method of this halftone decomposition, there is a method of irradiating an optical signal corresponding to the continuous tone image on the record carrier through a contact screen in which the surrounding blurred points are arranged in a mesh shape, The image scanning reading / recording apparatus employs means for electrically forming a mesh screen corresponding to such a contact screen.

Therefore, a method disclosed in Japanese Patent Publication No. 52-49361 will be schematically described as a preferred example of a mesh screen forming method according to the prior art.

In FIG. 12, reference numeral 100 indicates a basic period portion of an electrically formed mesh screen. That is, the mesh screen is formed by repeating the same pattern, and its minimum unit is a basic period portion.
It will be 100. The basic periodic portion 100 is constituted by the scan lines S ₁ through S ₈ of 8 juxtaposed in the Y direction, the scanning lines S ₁ to S ₈ are unique voltage which varies along the respective recording direction X The signals form each part of the basic period part 100. In this case, the voltage values of the scanning lines S ₁ , S ₂ , S ₄ , and S ₅ when passing the points A to D in the halftone dot portion 101 are set to high voltages, respectively, and the voltage of the scanning line S _{3 at} the point E is set to a high voltage. The value is set to low voltage. Then, the voltage value of the scanning lines S ₁ to S ₅ are A to D
Are set so as to gradually decrease from each point to point E. In this case, the voltage signal of each scanning line S _{1 to} S ₈ is, for example, by superimposing a plurality of alternating triangular voltage signals having different periods, and gradually shifting the phase for each scanning line A mesh screen signal can be formed.

Here, when a multicolor image or the like is meshed and copied, it is necessary to generate a plurality of mesh screens and superimpose a halftone image formed by them. Therefore, each mesh screen is formed in a state where it is rotated by a predetermined angle θ with respect to the recording direction X in order to prevent the generation of a moire pattern at the time of superposition.

The fundamental frequency portion 100 formed as described above is
The mesh screen is constructed by periodically generating the scan area of the document at a sufficient frequency. Then, the mesh screen signal constituting the mesh screen is superimposed on the image signal from the original optically read at the input section of the image scanning reading and recording apparatus, and a halftone gradation image is created on the film original. It is.

(Problems to be Solved by the Invention) By the way, the area modulation type halftone for color printing is characterized by the number of screen lines (for example, the number of lines / inch; LPI), the screen angle (m / n), and the halftone pattern.
The screen angle is a rational number defined by m / n in FIG. 12, and is necessary for the four CMYK colors. The screen angle and the halftone pattern are constructed by the method described in Japanese Patent Publication No. 52-49361. In a drum type color scanner, an arbitrary screen ruling can be easily obtained by changing the imaging magnification by optical zoom, but in a flatbed (flat type) color scanner, optical zoom is easy. is not. This is because in a flatbed color scanner, it is necessary to optically perform main scanning of a light spot from the viewpoint of high speed, and it is almost impossible to further add a zoom mechanism thereon. In addition, we change size of light spot,
Changing the pitch has a disadvantage that the control system becomes complicated and large.

The present invention has been made under the above circumstances, and an object of the present invention is to arbitrarily change the screen ruling in a flatbed color scanner or the like without changing the scanning pitch and size of light spots. It is to provide a method for forming a mesh screen. Another object of the present invention is to form a mesh screen in which the pitch is changed only in the screen rulings in which a moire pattern is generated, and the screen rulings can be arbitrarily changed so that the moire pattern is not generated in all screen rulings. To provide a method.

Configuration of the Invention; (Means for Solving the Problems) The present invention relates to a mesh screen forming method,
The above object of the present invention is to provide a multicolor separation halftone scale capable of print reproduction by superimposing an image signal obtained by scanning an original consisting of continuous tone color images with an electrically generated halftone screen signal. When creating a toned image, light dots of a certain size are exposed and scanned at a certain pitch to form halftone dots, and an arbitrary screen ruling can be obtained by changing the number of said pitches. Achieved by

Another object of the present invention is to superimpose an image signal obtained by scanning an original consisting of a continuous tone color image, C, M, by superimposing it on an electrically generated mesh screen signal.
When creating a multi-color separation halftone image that can be printed and reproduced on Y and K plates, the screen angle is a rational number of m / n, and a and γ are integer constants a = (m ² + n ² ) / n - determine the γ becomes relationship, further _{m 0, m 0 (<n} 0), the a ₀ as an integer, in the vicinity of the screen angle 15 ° (m, n, a) = (m 0 .n 0, a 0), Around net angle of 75 ° (m,
n, a) ＝ (n ₀ , m ₀ , a ₀ ), (m, n, a) ＝ at a net angle of 45 °
(1,1, a ₁ ) is obtained, and the scanning pitch is p, and the cycle K of the moire pattern is Then, a ₀ = (n ₀ −m ₀ ) · a ₁ is found under the condition that the cycle of the first-order amore and the cycle of the 45 ° screen are completely equal, and the number of screen lines that can be used with the scanning pitch as a predetermined value. Multicolor separation that can be duplicated by printing by superimposing the image signal obtained by scanning the original consisting of continuous-tone color images with the mesh screen signal generated electrically. When creating a halftone image,
The number of screen lines in which a moire pattern is generated is obtained by exposing and scanning light spots of a certain size at a predetermined pitch to form halftone dots, and by changing the number of pitches to obtain an arbitrary number of screen lines. In (1), the pitch is changed so that a moire pattern does not occur in all screen rulings.

(Function) In the present invention, when creating a CMYK decomposed halftone image, light dots of a fixed size are exposed and scanned at a fixed pitch, and an arbitrary screen ruling is obtained by controlling the number of pitches. Like that. Since the number of screen lines is given by the number of pitches, the present invention can be easily applied to a flatbed color scanner, and the conventional technique can be used as it is for the screen angle and the halftone pattern.

(Example) Select 0 °, 15 °, 45 °, 75 ° as the mesh angle of the CMYK4 plate, assign the Y plate to 0 °, and assign the C, M, K plates to the remaining three angles, respectively. I shall. At this time, it is an empirical fact that the moire by the Y version cannot be visually recognized, and only the moire by the 3rd version of the CMK needs to be considered. Where 15
゜ and 75 、 are exactly 18.4 ゜ and 7 と き when m / n = 1/3 as shown in FIG. 4 if the network generation by rational tangent is used.
1.6 ゜Thus, 15 ° and 75 ° are in a symmetrical relationship with each other across 45 °.

Now consider primary moiré with 15 ゜ and 75 ゜ screens.

When the period of the first screen shown in FIGS. 1 and 2 is d ₁ , the period of the second screen is d ₂ , and the angle between the two screens is α, the angle θ with respect to the horizontal line is shown in FIG. ₁ moiré pattern of the period K ₁ is, in the Figure 2 and moire pattern period K ₂ at an angle theta ₂ is generated with respect to a horizontal line. The xy coordinate axis is considered with reference to the first screen. In Figure ₁ , the coordinates of points P ₀ and P ₁ are And p ₀ = −d ₂ / sin α (2) p ₁ = 2p ₀ + d ₁ · cot α (3). The slope of the straight line l ₀ connecting the points P ₀ and P ₁ are It is. Similarly, the coordinates of points Q ₀ and Q _{1 in} FIG. And q ₀ = −d ₂ / cos α ……… (7) q ₁ = −d ₁ · tan α ……… (8), and the slope of the straight line l ₁ connecting the points Q ₀ and Q ₁ is , It is. If K ₁ and K ₂ are plotted with d ₁ = d ₂ = d,
It looks like the figure. The moiré pattern is acceptable as a fine moiré in a short period, but appears as a prominent pattern in a period of a certain period or more. Therefore, it is found that the angle α formed by the two screens is preferably ± 15 ° with 45 ° as the center, that is, about 30 ° to 60 °.

Next, as a moire generation mechanism, 2nd edition (15mm and 75mm)
I) Consider the relationship between the 45 ° primary moiré pattern generated by the overlay method and the 45 ° screen of the third edition.

The rational tangent parameters shown in Fig. 4 are (m, n,
The angles given by three of a) and corresponding to 15 ° and 75 ° for m <n are tan ^-1 (m / n) and tan ^-1 (n / m), respectively. The minimum unit of the repeating pattern is the four sides of p · a, where p is the scanning pitch and a is an integer constant. m, n, a is an integer, and the method of giving the numerical value is the condition for eliminating the single moire that is disclosed in JP-A-62-188564, that is, γ is an integer. Are satisfied.

Here, 45 ゜ ± (30 ゜ ± Δθ) (15 た だ し 7
The primary moiré formed by the second plate (5 ° is the nominal angle) occurs exactly at 45 °, and the period of this primary moiré and the third plate 45
Matching with the halftone dot interval of ゜ is a sufficient condition that secondary moiré does not occur. Then, when n ₀ , m ₀ (<n ₀ ), a ₀ , a ₁ is an integer, (m, n, a) = (m ₀ , n ₀ , a ₀ ) around 15 °, and around 75 ° At (m, n, a) = (n ₀ , m ₀ , a ₀ ), it becomes a control, and at 45 ° exactly (n, m, a) = (1,1, a ₁ ). Also, the line spacing d _{15 of} 15 ° is And the line spacing d _{45 of} 45 ° is And the real angle θ _{15 of} 15 ° is θ ₁₅ = tan ⁻¹ (m ₀ / n ₀ ) ... (14), and the real angle θ _{75 of} 75 ° is θ ₇₅ = tan ⁻¹ (n ₀ / m ₀ ) ……… (15). Then, if a primary moire is created in the 45 ° direction with a pattern of 15 ° and 75 °, α = θ ₇₅ −θ ₁₅ ……… (16) d ₁ ＝ d ₂ ＝ d ₁₅ ……… (17) Substituting these into the equation (5), the period K of the generated moire pattern is Becomes The condition that the secondary moiré does not occur is that the period of the primary moiré and the period of the 45 ° screen are completely equal, that is, Eqs. (13) and (18) are exactly the same, and K = d ₄₅ ……… (19) At this time Holds, and a ₀ = (n ₀ −m ₀ ) ・ a ₁ ……… (21).

Table 1 shows the number of screen lines that can be used with the scanning pitch p = 11.25 μm based on the above equation (21). * Indicates a relatively long combination of moire periods,
Others are combinations in which moire does not occur. In the case of the mark *, the moire period is long, so that it does not cause a great problem in practical use. However, since a problem arises when strictness is required, in the present invention, the pitch is changed by a predetermined amount in the screen ruling in which the moire pattern is generated. Especially 150 lines and 1
With 20 lines, there is no moire-free combination at a scanning pitch of 11.25μ. As a measure against this, 11.25 μm of 10 /
If 12.5 μm, which is 9 times, is used as the scanning pitch, it is possible to obtain screen lines of 150 lines and 120 lines with no moire.
The screen ruling combinations obtained using the scan pitches of 11.25 μm and 12.5 μm are shown in Table 2.

In Table 2, the coarse screen rulings 65 and 85 use a scanning pitch of 22.5 μm which is twice as large as 11.25 μm. Here, if the scanning pitch P is selected as 2.25 μm, no moiré appears.
Any screen ruling can be selected by color, but realizing a scanning pitch of 2.25 μm has two problems. One is that it is difficult to narrow the light beam (light spot) to 2.25 μm, and the other is that when the scanning pitch is 2.25 μm, the scanning speed is slow and the data capacity is significantly increased. For these two reasons, choosing a scan pitch as small as 2.25 μm is not reasonable.

Next, the light beam scanning device of the present invention will be described with reference to the accompanying drawings.

In FIG. 5, a light beam scanning device 30 is a laser diode for outputting a synchronization laser beam L ₁ under the action of an LD driving unit 31.
32, and a laser diode 34 for outputting a recording laser beam L ₂ under the action of the LD driving unit 33. Synchronizing laser beam L ₁ output from the laser diode 32 is directed to the galvanometer mirror 40 through the collimator 36 and a mirror 38. The recording laser light output from the laser diode 34
L ₂ is guided to the galvanometer mirror 40 via the collimator 42 and the mirror 38 while being deviated from the synchronization laser beam L ₁ by an angle φ. Galvanometer mirror 40 is for reflecting to deflect the synchronizing laser beam L ₁ and the recording laser beam L ₂ by vibrating the mirror at a high speed, the laser beam L ₁ and L reflected and deflected by the galvanometer mirror 40 ₂ is guided to a synchronizing signal generator 50 and an image recorder 52 via a scanning lens 48 composed of an fθ lens. In this case, synchronizing laser beam L ₁ is incident on the scanning lens 48 at an incident angle of an angle φ with respect to the optical axis, is guided to the synchronizing signal generator 50 via the peripheral side of the scanning lens 48. The recording laser light L ₂
Is incident on the scanning lens 48 in a plane including the optical axis, and the scanning lens
The image is guided to the image recording unit 52 through the central portion of 48.

Synchronizing signal generating unit 50 includes a plurality of slits 54 along the scanning direction of the synchronizing laser beam L ₁ are arranged at equal intervals grid
Has 56, synchronizing laser beam L ₁ is guided to the grid 56 via the mirror 58. In this case, a condensing rod 57 is arranged on the back surface of the grid 56, and the laser light L ₁ for synchronization is passed through the condensing rod 57 and the photodetectors 60a and 60b at both ends thereof.
And converted into an electric signal. The electric signals obtained from the photodetectors 60a and 60b are multiplied by a PLL multiplication circuit and supplied to the output control unit 64 as a synchronization signal. Output control unit
Reference numeral 64 controls the LD driving section 33 based on the image signal and the synchronization signal. When the screen ruling and the screen angle are determined as shown in Table 2, a net pattern is designed.
FIG. 6 shows an example of a mesh pattern of 175 lines and 0 °.
For each combination of screen ruling and screen angle shown in Table 2, a halftone pattern (template data) is designed as shown in FIG. 6 and used for halftone screen generation. This template data is usually stored in a floppy disk or ROM of the image output unit, and when the screen ruling and the screen angle are selected, the scanning pitch p shown in Table 2 of the image output unit is selected. The circuit is set to be controlled by the pitch p. Also, the template data stored at the same time is read out to the RAM control. As shown in FIG. 7, halftone data 3 is generated by the read template data 1 and image signal 2.
To generate. In FIG. 7, the template data 1 and the image data 2 are compared, and if the image data 2 is large or equal, “1” is output, and if it is small, “0” is output. Data 3 is obtained, light is modulated by the halftone data 3 to expose the photosensitive material, and a halftone plate is obtained.

Next, a mesh screen forming method applicable to the present invention will be described in detail below with reference to the drawings.

FIG. 8 shows an example of a halftone screen signal, and shows a basic period portion 10 of the halftone screen composed of 100 pieces of halftone dot data. In this case, the basic period part 10 is A to D
The screen angle of the halftone dot portion 12 surrounded by dots is set to θ.

Here, in order for the basic period portion 10 including the dot portion 12 to be the minimum unit of the mesh screen, the screen angle θ is n,
m as an integer It is necessary to set the rational tangent. Also,
Since the basic period part 10 must be composed of an integral number of halftone dot data in the X direction and the Y direction, it is required that the relationship of n · L = α · P (23) holds. It In this case, n · L
Is the length in the X or Y direction of the basic periodic portion 10 when the length of one side of the square constituting the halftone dot portion 12 in the X or Y direction is L, and P is one dot data Is the number of halftone dot data in the X direction or the Y direction that constitute the basic periodic part 10.

On the other hand, each data of the points A to D constituting the dot portion 12 is
In order to prevent a regular pattern from being generated on a reproduced image, it is necessary to form the same halftone data.
That is, between the points A and B constituting the halftone dot portion 12,
An integer number of halftone dot data must be arranged in the X and Y directions. Therefore, assuming that the distance between the points A and B in the Y direction is l, the relationship of l = γP ... (24) is obtained with γ being an integer. Note that a similar relationship is obtained for the X direction. In this case, the distance l can be expressed as l = L · cos ² θ · tan θ (25), and therefore (23), (24) and (2)
5) From formula Is obtained. As a result, when the relationship of the equation (26) is established, the halftone data arranged between the point A and the point B in the Y direction is repeatedly generated, so that the fundamental period part is obtained.
10 can be configured. That is, when the number of halftone dot data forming the basic period portion 10 is set so that an integral number of halftone dot data are arranged between the points A and B, the basic period portion 10 is expressed by the equation (5). It can be represented by halftone dot data of the determined amount of γ / α. For example, in the case of FIG. 8, since tan θ = 1/2 and n = 2, γ / α becomes 1/5, and the basic period part 10 has 20 halftone dot data with a data amount of 1/5. It can be represented by a ₀ and a ₁₉ .

Next, a method of generating a halftone dot image signal from a continuous tone image signal based on the halftone dot data a _{0 to} a ₁₉ forming the basic period portion 10 shown in FIG. 8 will be described.

FIG. 9 shows an example of a circuit for generating a halftone image signal. This halftone image signal generation circuit includes two counters 14 and 16, an address conversion unit 18, and a halftone data memory.
20, a line memory 22, and a binarized signal generator 24. The halftone dot data memory 20 stores the screen angle θ
Also, a desired one of a plurality of halftone dot original data 26 preset according to the halftone resolution level is transferred and stored. Counter 14 counts the clock signal phi _X in the main scanning direction of the continuous tone image and supplies the address conversion section 18 as an address signal X. Further, the counter 16 counts the clock signal φ _Y in the sub-scanning direction of the continuous tone image and supplies it as the address signal Y to the address conversion unit 18. The address conversion unit 18 converts the address signal (X, Y) of the halftone dot data in the basic period portion 10 into the address signal (x, y) of the halftone dot data a ₀ and a ₁₉ stored in the halftone dot data memory 20. It is configured as shown in FIG. That is,
The address conversion unit 18 sends the address signal X via the adder 182.
And a remainder calculation unit 184 to which the address signal Y is supplied. The adder 182 outputs the addition signal F selected by the address signal Y.
(Y) is supplied from the offset table 181. In this case, the offset table 181 is composed of a plurality of data determined by the combination of the screen angle θ and the halftone resolution level, as in the case of the halftone dot original data 26. Further, the remainder calculator 183 calculates the address signal x based on the arithmetic expression of x = MOD (X + F (Y), N _X ) ... (27). N _X represents the number of halftone dot data in the X direction. Remainder calculation unit 184
Then, the address signal y is calculated based on the arithmetic expression of y = MOD (Y, N _y ) ... (28). Incidentally, N _y represents the dot number data in the Y direction.

On the other hand, the line memory 22 is supplied with the continuous tone image signal in the main scanning direction and the clock signal φ _X ,
Outputs of the dot data memory 20 and the dot data memory 20 are supplied to a binarized signal generator 24, respectively. The binarized signal generator 24 compares the halftone data with the image signal and outputs the result as a halftone image signal.

Next, the case of converting a continuous tone image signal into a halftone image signal using the basic period portion 10 shown in FIG. 8 will be described.

The halftone dot original data 26 stores halftone data corresponding to the screen angle θ and the level of halftone resolution. From these halftone data, halftone data a _{0 to} a ₁₉ are selected, and halftone data is selected. The data is loaded into the memory 20 at the address (x, y).
In this case, the address (x, y) is set in a range from (0, 0) to (9, 1). Therefore, when the address signals (X, Y) are input from the counters 14 and 16 to the address conversion unit 18 based on the clock signals φ _x and φ _y , the address conversion unit 18 transmits the address signals (X, Y) to the network. It is converted into the address signals (X, Y) of the point data a _{0 to} a ₁₉ . That is, for example, (X, Y)
= (0,0), the addition signal F (Y) is set to “0” in the offset table 181 shown in FIG. 11, so the output signals x, y from the remainder calculation units 183 and 184 are ( 27)
And (28) result in “0”. Accordingly, the address converter 18 accesses the dot data a ₀ at the address (x, y) = (0, 0) from the dot data memory 20 and supplies this data to the binary signal generator 24. I do. When the address signals (X, Y) from the counters 14 and 16 are (0, 2),
The addition signal F (Y) becomes "4" from Fig. 11, and therefore (2
From (7) and (28), (x, y) becomes (4,0). Accordingly, the address converter 18 selects the halftone data a ₄ from the halftone data a _{0 to} a ₁₉ stored in the halftone data memory 20 and supplies the same to the binarized signal generator 24. Similarly, the halftone data a _{0 to} a ₁₉ forming the basic period part 10 are supplied to the binarized signal generator 24.

On the other hand, the binarized signal generator 24 has halftone data a ₀ through a
Continuous tone image signal stored in the line memory 22 is supplied on the basis of the clock signal phi _x with _19. Therefore, the binarized signal generator 24 compares the dot data a _{0 to} a ₁₉ with the continuous tone image signal, and outputs the result as a dot tone image signal which is an ON / OFF signal. In addition,
The halftone image signal is converted into an optical signal such as a laser beam, and is applied to a film by the apparatus shown in FIG. 5 to form a halftone image.

EFFECTS OF THE INVENTION As described above, according to the halftone screen forming method of the present invention, when creating a multi-color separated halftone image which is all CMYK or a combination of two or more colors, a light of a certain size is used. A desired screen ruling can be obtained by exposing and scanning points at a constant pitch and controlling the pitch. Therefore, the control system is simplified and can be applied to a flatbed color scanner without using a zoom mechanism. In addition, since the pitch is changed by changing a predetermined amount in the number of screen lines where the moire pattern is generated, it is possible to form a stable mesh screen with extremely high accuracy.

[Brief description of the drawings]

1 and 2 are diagrams showing examples of patterns, FIG. 3 is a diagram showing the period of the moire pattern of the patterns shown in FIGS. 1 and 2, and FIG. 4 is an example of halftone dots by rational tangent. FIG. 5, FIG. 5 is a structural diagram showing an example of a light beam scanning device to which the present invention can be applied, FIG. 6 is a diagram showing an example of halftone dot data having a line number of 170 LPI, and FIG. 7 is a diagram showing generation of halftone dot data. FIG. 8 is a diagram showing a state, FIG. 8 is a diagram for explaining a mesh screen signal,
9 is a block diagram of a circuit for generating a halftone image signal, FIG. 10 is a block configuration diagram showing a detailed example of the address conversion unit 18, FIG. 11 is a diagram showing an example of an offset table, FIG.
FIG. 12 is a diagram showing a basic period portion of the mesh screen. 1 ... template data, 2 ... image data, 3 ...
Halftone data, 10: Basic period part, 12: Halftone dot part, 14, 16,… Counter, 18… Address conversion part, 20…
... Halftone dot data memory, 22... Line memory, 24...

Claims (5)

(57) [Claims] 1. A multicolor separation halftone dot image capable of print reproduction by superimposing an image signal obtained by scanning an original composed of continuous tone color images and an electrically generated halftone screen signal. When creating, halftone dots are formed by exposing and scanning light spots of a certain size at a certain pitch.
A mesh screen forming method, wherein an arbitrary screen ruling is obtained by changing the number of pitches. 2. The printing reproduction is carried out with 4 plates of CMYK, a net angle of 0 ° is assigned to the Y plate, and 15 °, 45 ° and 75 ° are C plates and M plates.
The mesh screen forming method according to claim 1, wherein the mesh screen is arbitrarily assigned to the plate and the K plate. 3. A screen angle is a rational number of m / n, a and r are integer constants, and a function of a = (m ² + n ² ) / n · r is provided, and m ₀ , m ₀ (<n ₀ ), a ₀ , a ₁ as integers
In the vicinity of ゜, (m, n, a) ＝ (m ₀ .n ₀ , a ₀ ), and the net angle is 75
In the vicinity of ゜, (m, n, a) ＝ (m ₀ .n ₀ , a ₀ ), and the net angle is 45
At ゜, (m, n, a) = (1,1, a ₁ ) and a ₀ = (n ₀ −m ₀ )
The mesh screen forming method according to claim 2, wherein the mesh screen has a relationship of a ₁ . 4. A C, M, Y, K plate print duplication is possible by superimposing an image signal obtained by scanning an original consisting of continuous tone color images with an electrically generated mesh screen signal. When creating a simple multicolor separation halftone image, the screen angle is a rational number of m / n, and a and r are integer constants.
= (M ² + n ² ) / n · r, and then n ₀ , m ₀ (<
n ₀ ), a ₀ , a ₁ is an integer and (m, n, a) around a net angle of 15 °
= (M ₀ , n ₀ , a ₀ ), (m, n, a) around the net angle of 75 ° = (n ₀ ,
m ₀ , a ₀ ), (m, n, a) = (1,1, a ₁ ) around the halftone angle of 45 ° is obtained, and the scanning pitch is p and the period K of the moire pattern is Then, a ₀ = (n ₀ −m ₀ ) · a ₁ is found under the condition that the cycle of the first-order amore and the cycle of the 45 ° screen are completely equal, and the number of screen lines that can be used with the scanning pitch as a predetermined value. A method for forming a mesh screen, characterized in that it is calculated and determined. 5. A multi-color separated halftone dot image capable of being printed by superimposing an image signal obtained by scanning an original composed of continuous tone color images on an electrically generated halftone screen signal. At the time of creating, the light spots of a certain size are exposed and scanned at a predetermined pitch to form halftone dots.
By obtaining an arbitrary screen ruling by changing the number of pitches, the pitch is changed in the screen rulings in which a moire pattern is generated, and the moire pattern is not generated in all screen rulings. Characteristic mesh screen forming method.