JPS6235303B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for recording a reproduced image as a halftone dot image in an image scanning recording device such as a color scanner for plate making or a facsimile machine, and particularly relates to a method and apparatus for recording a reproduced image as a halftone dot image. The present invention relates to a method and apparatus for improving the resolution of a reproduced halftone image by dividing it into a plurality of sections and recording halftone dots with an area corresponding to the gradation change of the original image to be reproduced in each section.

In an image scanning recording device such as a color scanner for plate making, a halftone dot signal is created electrically, the area ratio of the halftone dot is controlled according to the image signal level from the original picture, and a halftone dot image corresponding to the original picture is recorded. Various methods have already been proposed to do this.

However, conventional means generally regard the average level of one pixel, which is determined by the scanning line width and sampling pitch when picking up image signals by photoelectrically scanning an original image, as the image signal level, and treat each halftone dot as a unit. Generally, the dot area ratio is controlled as follows, but the disadvantage is that the resolution of the reproduced image is low.

Therefore, in order to improve resolution, a method has already been disclosed in which one halftone dot is divided into a plurality of parts (for example, Japanese Patent Application No.
No. 54195 (Japanese Unexamined Patent Publication No. 138445) and patent application No. 138445
-Refer to No. 14282 (Special Publication No. 52-33523)).

In these conventional methods, one halftone dot is divided into a plurality of parts, and each pixel is burned or burned depending on whether the input image signal level corresponding to that division is larger or smaller than a predetermined threshold. In the case of printing, those pixels are printed in multiple steps or simultaneously using multiple light beams.

With these conventional methods, for example, one halftone dot is divided into 5 parts in one direction for a total of 25 parts, the left side of the contour line has a halftone dot area ratio of 50%, and the right side has a halftone dot area ratio of 0.
When a halftone image is formed using an image signal obtained by scanning an image corresponding to %, the result is as shown in FIG. 1a. In the figure, D is the contour line, B is the scanning line width, and P
is the sampling pitch.

As can be seen from Figure 1a, the conventional method for forming halftone dots has the disadvantage that the formed halftone dots become step-like, making it difficult for printing ink to adhere to them, and that outlines cannot always be faithfully reproduced. There is.

As described above, in the conventional method, the reason why the halftone dots become stepwise and the outline part cannot necessarily be faithfully reproduced is that in the conventional method, each divided pixel is set to a predetermined input image signal level corresponding to that section. The reason is that the area ratio of the divided halftone dots cannot be changed continuously in response to the input image signal level. Conceivable.

Furthermore, in conventional methods, printing one halftone dot in multiple batches requires a lot of printing time, and printing one halftone dot at once requires multiple light beams. Accordingly, there are drawbacks such as the need for an acousto-optic element, a beam splitter, etc., resulting in an increase in cost.

The present invention provides a method and apparatus for recording a halftone dot image that solves these conventional drawbacks and inconveniences. When a halftone dot image is formed from the obtained image signal, it becomes as shown in FIG. 1b. The difference from the conventional example shown in FIG. 1a is that the formed halftone dot outline is smooth. The outline part is drawn the same as in Figure 1a for convenience, but in reality, one pixel area obtained by dividing one halftone area (the area surrounded by the dotted line in Figure 1) into 25 is divided into 25 parts of the input image. A halftone dot with an area ratio corresponding to the average image signal level in one pixel determined from the proportion occupied by the outline part and the density of the outline part of the input image is formed for one pixel of each image outline part.
Finer gradation can be obtained than in the conventional example.

A first object of the present invention is to provide a halftone dot image scanning and recording method and an apparatus thereof, in which the outline shape of halftone dots is smooth and the outline portion and other parts of the original image can be faithfully reproduced.

A second object of the present invention is to provide a halftone dot in which one halftone dot is divided into a plurality of parts, and the halftone dot area ratio is continuously varied according to the input image signal level in each divided section. An object of the present invention is to provide an image scanning recording method and apparatus.

A third object of the present invention is to
An object of the present invention is to provide a halftone image scanning and recording method and an apparatus thereof, which can print two halftone dots at once using one light beam.

A fourth object of the present invention is to provide a halftone image scanning and recording method that allows the number of divisions of one halftone dot to be easily increased compared to conventional methods, and thus provides higher resolution than conventional methods. The goal is to provide equipment.

A fifth object of the present invention is to provide a halftone image scanning and recording method and apparatus that enable tone reproduction without jumps.

Other objects and advantages of the present invention will become apparent from the detailed description below.

Various methods have already been proposed for recording halftone images using scanners such as plate-making scanners. The proposed device is shown in Figure 2.

Since the device is explained in detail in the specification of the above-mentioned application, only the main points thereof will be described here.

A light beam from a light source 1 such as a laser is deflected by changing the frequency of ultrasonic waves supplied to the first acoustic element 2. This deflection angle change occurs in the Z-axis direction shown in the lower left of the figure, and the position where the light beam passes through the V-shaped slit 3 moves in the Z-axis direction.
The width of the light beam changes after passing through it.

Moreover, when the frequency of the ultrasonic waves supplied to the second acoustic element 4 is changed, the light beam is deflected in the Y-axis direction, so that the line image W can be moved in the line direction.

As described above, by changing the frequency of the ultrasonic waves supplied to the two acousto-optic elements 2 and 4, the length and position of the line image W can be appropriately changed, and the traveling photosensitive material is exposed to the light to form a halftone image. Record.

The present invention, when scanning and recording halftone dot images using such a device, divides each halftone dot into a plurality of sections, and calculates the difference based on the gradation change of the original image to be reproduced corresponding to each section. By recording halftone dots, the resolution of the duplicate halftone dot image is improved. First, a method for increasing the resolution in the scan direction will be explained based on FIG. 3.

In FIG. 3, in the conventional general method, the average signal level X of the image signal from time t ₀ to t ₄ is
In contrast, in the present invention, halftone dots were recorded using
The period from time t ₀ to _{t 4} is divided into a plurality of sections, and the center of the halftone dot remains fixed, and the halftone dots are recorded at the average image signal level during the divided period. Here, for ease of understanding, a simple example in which the area is divided into four sections will be explained.

In the example shown in the third figure, the original image signal level X ₁ in the first period t ₀ to _{t 1} corresponds to the signal level for forming 75% halftone dots, so 75% halftone dots are formed in the second period t _{1 .} ~ _t2
The original image signal level X ₂ corresponds to the signal level for forming 50% halftone dots, so
The original image signal level _X3 in the period _t2 to _t3 corresponds to the signal level for forming 25% halftone dots, so the 25% halftone dot is set to the original image signal level X3 in the fourth period _t3 to _t4 . ₄ is
This corresponds to the signal level that forms 100% halftone dots, so each halftone dot is cut perpendicular to the scan direction at the sampling pitch and recorded while keeping the center of the halftone dot fixed. The purpose of this method is to freely change the size of halftone dots even while they are being formed, depending on the temporally changing original image signal level.

FIG. 4 shows a method for increasing the resolution in the direction perpendicular to the scan direction.

In Fig. 4, in the conventional general method, the average signal level of the image signal is recorded in this direction as well, but in the present invention, it is divided into multiple sections and the center of the halftone dot is fixed. The purpose is to record halftone dots at each average image signal level in each divided section while keeping the image level unchanged. Here, for ease of understanding, a simple example in which the area is divided into four sections will be explained.

In the same figure, first divide the halftone dot into two along the center line,
Further divide from the center line to the left (Lmax) and right (Rmax), and divide from the left.
shall be referred to as LL, L, R and RR.

In the example shown in the figure, the original image signal level of section _LL
Since corresponds to the signal level that forms a 50% halftone dot, the original image signal level _X of the section L corresponds to the signal level that forms a 25% halftone dot. In section L, the original image signal level X R corresponds to the signal level that forms a 25% halftone dot, and in section R, the original image signal level X _R corresponds to a signal level that forms a 100% halftone dot.
The original image signal level of the section _RR is 75.
It corresponds to the signal level that forms halftone dots of %, so
In section RR, 75% of halftone dots are recorded by cutting the halftone dots in the scan direction at the boundaries of each section, keeping the center of the halftone dot fixed.

Note that the slit used in the device shown in the second figure is V-shaped, and this V-shaped slit 3
When forming halftone dots using It may be smaller than. In such a case, when attempting to form halftone dots faithfully to the input image, it is necessary to form halftone dots in the shape shown in the shaded area in Figure 4. It is necessary to block the light beam by a predetermined width at a predetermined position near the left end. However, when using one light beam, it is impossible to create two divided light beams at the same time with the structure of the V-shaped slit 3.
Halftone dots are also formed at the same time in the crosshatch area in FIG. Although this halftone dot formation method does not pose any practical problems in many cases, if more faithful halftone dot formation is desired, the following method may be used.

That is, in the second illustrated device, instead of the V-shaped slit 3,
The W-shaped slit shown in Fig. 18 disclosed in Japanese Patent No. 21123) may be used. If a slit with such a shape is used, if the horizontal linear light beam that enters the slit moves above the center of the slit, the width of the linear light beam will change and it will move below the center of the slit. When the linear beam is moved, the linear beam is divided into two parts, and the width of the two parts changes, as well as the distance between them, so that the desired halftone dots can be formed in the sections LL, L, and R in FIG.

Next, a specific method for forming halftone dots will be explained.

Regarding the method of forming halftone dots without dividing them one by one, the present applicant previously filed a patent application as Japanese Patent Application No. 145683-1983 (Japanese Patent Application No. 79701-1983).

This invention is explained in detail in the specification, so I will only briefly summarize the main points here. Place, area
When forming a 100% halftone dot, all calculation data is used; when forming a halftone dot with a smaller area, the required address and timing of the calculation command are manipulated. The halftone dot is formed by obtaining the contour signal of the halftone dot of the area and calculating the center position and width of the halftone dot from the contour signal.

In the present invention, the basic idea is the same, and for simplicity, a memory device is used instead of the above-mentioned arithmetic circuit, and the area is divided into multiple pieces in advance.
The outline data of the halftone dots in each section necessary to form a 100% halftone dot is stored for each halftone dot angle, and the data for each section is read by manipulating the address to create the required halftone dot. The halftone dot is formed by obtaining the contour signal of the halftone dot of the area and calculating the center position and width of the halftone dot from the contour signal.

The data on the outline of the halftone dot mentioned above is, for example, the fifth halftone dot.
This is shown in the figure.

Figure 5 a shows the area 100 when the halftone dot angle is 0°.
It is a halftone dot outer signal obtained by dividing the halftone dot of % into four, and the division
By selecting the signal with the larger halftone dot outline signal level between RR and section R, or between the halftone dot outer signal level between section LL and section L, whichever is larger, a network with an area of 100% is created. The upper and lower halves of the points can be contoured.

Figure 5b shows the case where the halftone dot angle is 45 degrees, and as is clear from Figure 7a, the difference from the other halftone dot angles is that the halftone dots are recorded with a size determined by the original image signal level. When forming one halftone dot without dividing it, it is sufficient to keep the width of the light beam constant for one halftone dot during the halftone dot formation period. Therefore, in this case, the data is for determining the width of the light beam at the start of halftone dot formation, which is determined by the signal level of the original image.

Figure 5c shows the area when the halftone dot angle is +15°.
It is a halftone dot outer signal obtained by dividing a 100% halftone dot into four,
The difference from the 0° case is that when forming halftone dots at an angle to the scan line, the inclination angle is 45°.
Since the angle does not have a unique feature as in the case of ゜, the positions of the vertices of the upper and lower halves of the halftone dot are shifted from the center. In this case as well, the area 100 % halftone dots can be formed. Note that the case of −15° is not shown because it has a mirror image relationship with the data of +15°. Note that the contour data of each halftone dot angle section RR, R, L, and LL shown in FIG. 5 are stored in the memories 21, 22, 23, and 23 of FIG.
It is stored in 24.

Next, a case will be described in which a halftone dot having an area smaller than 100% is formed from the contour data of the above-mentioned halftone dot having an area of 100%.

First, I will explain the section RR part.

In FIG. 6a, the contour data of halftone dots with an area of 100% are D to F to H. The address for reading this data is calculated from the original image signal level _XRR and the output T of the dot section counter 31, which will be described later. During a period in which the output T of the dot section counter 31 is greater than 0 and less than (100-X _RR ), halftone dots are not formed, so data in the memory 21, which will be described later, is not read out.

When the output T of the dot section counter 31 is larger than (100 _-
In the case of ±15°, during a period smaller than the value of _JRR , which is uniquely determined by the value of _the original image signal level Form.

To be more specific, in order to form the outlines J to K of the halftone dots, it is possible to directly use the output T of the dot section counter 31 as an address. -X _RR )'' _, and using T' = [T-( _100- .

During a period in which the value of the output T of the dot section counter 31 is larger than J _RR and smaller than (99+X _RR ), it jumps from point E to point G and is stored in the memory 21.
Read out the G to H sections of the data, and read out the halftone dots K to H.
Form L section. That is, "199-(99+X-T)"
Then, using [T+(100-X)] as an address, the section G to H determined by the original image signal level _XRR is read out of the data between F and H.

During the period when the value of the output T of the dot section counter 31 is from (99+X _RR ) to 199, there is no need to form halftone dots, so the contents of the memory 21 are not read out. If halftone dots are formed using this much data, the points (100-X _RR ), J, K, L, and (99
+X _RR ) is formed as a halftone dot.

Next, regarding section R section, Fig. 6b
The outline data of 100% halftone dots is M~N~R
This is the part indicated by ~S. The output T of the dot section counter 31 is greater than 0 (100-X
During the period smaller than _R ), there is no need to form halftone dots, so data in the memory 22 is not read out. The output T of the dot section counter 31 is (100-
_{X _}
In the case of ゜, for a period smaller than J _R that is uniquely determined by the value of the original image signal level X _R corresponding to the section R section, "T-(100-X _R )" is calculated,
( _{100 -}
Form W to X.

The output T of the dot section counter 31 is J
A period greater than _R and less than (99+X _R ) is defined as "T
+(100-X)", T"=[T+(100
-X)'' as an address, read out the Q to R to S sections determined by the original image signal level X _R from the data X to R to S in the memory 22, and
~ form Z. Dot section counter 31
During the period from (99+X _R ) to 199, there is no need for the output T to form halftone dots, so data in the memory 22 is not read out.

If halftone dots are formed using this much data,
The area surrounded by points V, W, Y, and Z will be formed as a halftone dot.

In order to form one halftone dot from the outer data of the divided halftone dots, considering the upper half of the halftone dot, by selecting the maximum value from the data of sections RR and R, the sixth Halftone dots can be formed in the area surrounded by points V, W, J, K, L, Y and Z in figures a and b. A similar operation is performed for the lower half of the halftone dot, and one halftone dot contour signal is obtained from the data of the L and LL sections.

Above, we have explained the case where the halftone dot angle is +15°, but it can be inferred from Figure 7 b and c that the same idea can be applied to the case where the halftone dot angle is -15°, which is a mirror image of 0° and +15°. Dew.

When the halftone dot angle is 45°, it is easier than the former, and as can be deduced from FIG. When the output T of the dot section counter 31 is (100-X)≦T≦(99+X), the original image signal level X is output as an address.

To summarize, the halftone dot sections RR, R, L and LL
Since we can have a common way of thinking about the
Considering RR, when the halftone dot angle is ±15° and 0°, the address of the memory device 21 can be determined as follows based on the value of the output T of the dot section counter 31.

() When 0≦T<100−X _RR AD−RR=0 () When 100−X _RR ≦T≦J _RR
AD-RR=T-(100-X _RR ) () When J _RR <T≦99+X _RR
AD-RR=T+(100-X _RR ) () 99+X _RR <T≦199 AD-RR=0 However, J _RR is the locus drawn by the apex of the halftone dot when the size of the halftone dot changes ( The changes in the horizontal coordinates of the line segment F-F' in FIG. 6a take values as shown in FIG. 8a, b, and c.

Also, when the halftone dot angle is 45°, the same idea can be applied to each section, so if we consider the section RR () 0≦T<100-X _RR , AD-RR=0 () 100-X _RR When ≦T≦J _RR
AD-RR=X _RR () J _RR <T≦99+X _RR AD-RR=X _RR () 99+X _RR <T≦199 AD-RR=0.

The outline data of the halftone dots read from the address obtained in this way is stored in the sections RR, R, L and LL.
For (DT-RR), (DT-R), respectively
When (DT-L) and (DT-LL), the area surrounded by U and L expressed by the following equation becomes a halftone dot.

U = max (DT-RR, DT-R) (1) L = max (DT-L, DT-LL) (2) Next, the upper half halftone dot outline signal U and the limit signal (DT-LIMIT) Compare them, select the smaller value, and set that value as U'. Further, the lower half halftone dot outline signal L and the limit signal (DT-LIMIT) are compared, and the smaller value is selected and that value is set as L'.

U″=min(U, DT-LIMIT) (3) L′=min(L, DT-LIMIT) (4) By the way, limit (halftone area restriction) generally means that if the halftone area exceeds 50%, If there are adjacent halftone dots that protrude into the area of adjacent halftone dots, they overlap.
Multiple exposure is unfavorable in terms of resolution due to scattering within the film. But 100%
In the case of halftone dots, it is undesirable to have areas where halftone dots do not fit, so as shown in Figure 9, a small overlapping area is left at the boundary between adjacent halftone dots to create a restricted area for halftone dots. This is intended to prevent multiple exposure.

In addition, Fig. 9c shows the case where the halftone dot angle is +15°, and in this case, it is also possible to make the limit (the dotted line area in the figure) in the same shape as when the halftone dot angle is 0° and 45°. However, in order to simplify the apparatus, the area in the direction perpendicular to the scan direction is indicated by a dashed line.

If such a limit switch is provided, even when a large number of halftone dots are formed adjacent to each other, the portion that is exposed multiple times will be limited to a small portion of the boundary, and the image quality will not be impaired.

Next, (DT-LL), (DT-L) and (DT-
When R) is all 0, when halftone dots are formed in the area surrounded by U' and L', halftone dots are formed in the area shown by the hatched area in Figure 10a, and unnecessary parts (dotted line area) are formed.
Halftone dots are formed up to This is because "L'=0", and in order to remove unnecessary portions, the following equation is set and halftone dots are formed as shown in FIG. 10b.

L'=-Rmax (5) Similarly, (DT-RR), (DT-R) and (DT
-L) are all 0, U'=-Lmax (6) Here, (Lmax) and (Rmax) are the distances from the center line to the line that divides the halftone dots in the scan direction, as shown in Figure 4. It is.

As described above, the formed halftone dots are translated or tilted relative to the scan line to form actual halftone dots. That is, the halftone dot angle is 0.
In the case of angles of 45° and 45°, the amount of deviation at which halftone dots are formed parallel to the scan line is defined as "DT-SHIFT". Also, the halftone dot angle is ±15
When the dot angle is 0° and 45°, the halftone dot is tilted with respect to the scan line. Although this is not necessary when the halftone dot angle is 0° and 45°, the signal amount is defined as "DT-SLOPE".

S=DT−SHIFT+SLOPE (7) Therefore, U″=U′+S (8) L″=L′−S (9) Therefore, the halftone dot width W and The position P is given by the following equation.

W=U″+L″ However, if the calculation result W<0, W=0.

Therefore, W=max(U″+L″, 0) (10) P=U″−L″/2 (11) FIG. 1 shows a block diagram of an example of a control circuit for improving the resolution of an image.

In Fig. 11, 11 to 14 are halftone dot sections.
In order to record halftone dots of a size corresponding to the original image signal level X corresponding to RR, R, L and LL,
This is an address control circuit that calculates an address for reading data from the memories 21 to 24 that store data on the outline of necessary halftone dots.

21 to 24 are memories, partitions RR, R, L
For LL and LL, data on the outline of halftone dots with halftone dot angles of ±15°, 0°, and 45° with an area of 100% are stored, and the read data is input to the data calculation circuit 40, respectively. .

Reference numeral 30 denotes a timing control circuit, which includes a halftone dot position calculation circuit, etc., and sends a halftone dot formation start signal (DF-) to each halftone dot in synchronization with the rotation of the storage cylinder.
START), and the amount of deviation (△
Output.

Reference numeral 31 denotes a dot section counter, which is used as a clock pulse when one halftone dot is divided into, for example, 200 in the scan direction to form halftone dots of a size corresponding to the original image signal level. is as shown in FIG. 12a.

Further, when it is necessary to apply a limit in the scan direction, the output T of the dot section counter 31 corresponding to the unnecessary portion is set to 0, as shown in FIG. 12b, and the output data of the memories 21 to 24 are set to 0.
It can also be used to

33 is a memory that outputs the (SLOPE) signal,
This is for tilting the halftone dots with respect to the scan line when the halftone dot angle is ±15°. memory 3
Addressing No. 3 uses the output T of the dot section counter 31 to obtain output signals as shown in FIGS.

Note that when the halftone dot angle is 0° and 45°, there is no need to tilt the dot with respect to the scan line, so operations such as setting all data in the memory 33 to 0 are performed.

34 is a memory used when it is necessary to apply a limit as described above. Addressing of the memory 34 is performed using the output T of the dot section counter 31, and the outputs are as shown in FIGS. 14a, b, and c.
Enter 0.

35 stores a value (DT-SHIFT) that indicates how far the center of the halftone dot deviates from the scan line in the direction perpendicular to the scan line when the halftone dot angle is 0° and 45°. This is the memory that exists. Addressing of the memory 35 uses the output (ΔX) of the timing control circuit 30. Output of memory 35 (DT-SHIFT) and address (△
The relationship with X) is a linear relationship as shown in the following equation.

That is, DT-SHIFT=K・△X However, K is a proportional constant 40 is a data calculation circuit which selects the larger value from (DT-RR) and (DT-R) which are the outputs of memories 21-22. , and selects the larger value from (DT-L) and (DT-LL), which are the outputs of the memories 23 to 24, to obtain signals that form the outline of the upper and lower halves of the halftone dots, and if necessary, The outer signal of the halftone dot and the limit signal (DT-LIMIT) are compared, the smaller value is selected, and the slope signal (DT-LIMIT) is selected.
The center position of the halftone dot and the width of the halftone dot, which are the final signals forming the halftone dot, are calculated from the addition of the shift signal (DT-SHIFT) or the shift signal (DT-SHIFT).

FIG. 15 shows address control circuits 11 to 14, one of which is the same for each section.
Of these, address control circuit 1 of section RR
1 shows an example of the configuration of No. 1.

In FIG. 15, 50 is a subtracter that subtracts the original image signal level _XRR of the section RR from a constant (100).The output signal, which is the quotient, is input to the latch 55, and the level does not change during the sampling cycle. to retain data.

The output signal of latch 55 is input to input terminal A of comparator 60 and subtractor 65.

The subtracter 65 performs the calculation "T-(100-X _RR )" and inputs its output to the input terminal A of the selector 70 .

The adder 66 performs the calculation "T+(100-X _RR )" and inputs the output to the input terminal B of the selector 70 .

The comparator 60 compares the (100-X _RR ) signal with the output T of the dot section counter 31, and outputs T.
When the two are equal or larger, a high level output signal is input to the input terminal A of the AND gate 67.

Reference numeral 51 denotes an adder that adds a constant (99) and the original image signal level X _RR , inputs the result to a latch 56, and holds the data so that the level does not fluctuate during the sampling period.

The output of latch 56 is the input terminal A of comparator 61.
input.

The output T of the dot section counter 31 is input to the input terminal B of the comparator 61, and (T≦99+
X), AND the high level signal as the output
It is input to terminal B of gate 67.

Since the output of the AND gate 67 is connected to the control terminal of the gate 71, the output T of the dot section counter 31 and the original image signal level
When the relationship with _RR is (100−X≦T≦99+X),
Gate 71 is opened.

52 is a memory in which the above-mentioned halftone dot angle is ±
In the case of 15 degrees, this is data on the change in horizontal coordinates of the locus of the apex of the halftone dot when the halftone dot area changes, and data as shown in FIG. 8 is shown.

Reference numeral 57 denotes a latch similar to the aforementioned latches 55 and 56, and its output is inputted to input terminal A of comparator 62.

The output T of the dot section counter 31 is connected to the other input terminal B, and this output is connected to the control terminal of the selector 70.

A latch 58 holds the original image signal level X _RR so that it does not change during the sampling period, and its output is connected to the input terminal C of the selector 70 . The other control terminal of the selector 70 is connected to a signal for a dot angle of 45°, and the output of the selector 70 is connected to the input terminal of the gate 71.

In the case of a halftone dot angle of 45°, a control signal for a halftone dot angle of 45° is input. Selector 70 outputs the C input. When the halftone dot angle is other than 45°, the control signal for the halftone dot angle of 45° is not input, and the data J _RR at the apex of the halftone dot is compared with the output T of the dot section counter 31, and if J _RR ≧T. outputs the A input. Furthermore, if J _RR <T, the B input is output.

FIG. 16 is a block diagram showing an example of the configuration of a data calculation circuit.

80 is a selector that inputs the input signal (DT-RR),
(DT-R), (DT-L) and (DT-LL) are monitored. (a) When (DT-RR) = (DT-R) = (DT-L) = 0, ( −Lmax) signal.

(b) In cases other than (a), when (DT-RR)≧(DT-R), select the (DT-RR) signal.

(c) In cases other than (a), when (DT-RR) < (DT-R), select the (DT-R) signal.

As described above, three input signals are appropriately selected and output depending on the three cases.

The output of the selector 80 is connected to the input terminal A of the minimum value selection circuit 85, and (DT-LIMIT)
Compare the signals and select the one with the smaller value to obtain the U′ signal. The U' signal is connected to input terminal A of adder 87, and the other terminal B has (DT-SLOPE)
Adder 8 that adds the signal and (DF-SHIFT) signal
1 is connected to perform the calculation of equation (8).

Letting the output signal of the adder 87 be U'', U'' is connected to the input terminal A of the adder 89 and the input terminal A of the arithmetic unit 90.

82 is a selector that operates in the same way as 80, and monitors the input signals (DT-LL), (DT-L), (DT-R), and (DT-RR). )=(DT-L)=(DT-R)=0, select (-Rmax).

(E) When (DT-LL)≧(DT-L) other than in (E), select (DT-LL).

(f) If (DT-LL) < (DT-L) other than in (d), select (DT-L).

As described above, three input signals are appropriately selected and output depending on the three cases.

When the output signal of the selector 82 is L, L is connected to the input terminal A of the minimum value selection circuit 86 (DT
−LIMIT) signal and select the smaller value.
Obtain L′ signal. The L' signal is connected to the input terminal A of the subtracter 88, and the output of the adder 81 is connected to the input terminal B, and the calculation of equation (9) is performed.

When the output of the subtracter 88 is an L'' signal, the L'' signal is connected to an input terminal B of an adder 89 and an input terminal B of an arithmetic unit 90.

The adder 89 performs “U″+L″, and its output signal is sent to the gate 91 and level detector 92.
connected to each input terminal.

The level detector 92 detects the positive and negative levels of the (U″+L″) signal, and operates to close the gate 91 only when this indicates a negative value. Therefore, when the (U″+L″) signal is a positive value, the gate 91 outputs it as a “W” signal.

The arithmetic circuit 90 is composed of a subtractor and a divider that performs "U"-L"/2.

The output (U″-L″/2) signal of the arithmetic circuit 90 is always output as the (POSITION) signal, but
When the (U″+L″) signal becomes a negative value,
Since the (WIDTH) signal is not output, nothing is recorded as a result.

It is also possible to consider a method that is partially modified from the method described above.

That is, instead of the halftone dot outline data shown in FIGS. 5a, b, and c, the data shown in FIGS. 17a, b, and c are used. In this case, it is necessary to change the operation of the data calculation circuit shown in FIG. 16 as follows.

Using equations (1) and (2) above, U = DT-RR + DT-R (1') L = DT-LL + DT-L (2') Also, the operation of the selector 80 is (ki) DT-RR = DT-R = When DT-L=0,
(-Lmax) is output.

(h) In cases other than item (g), output (DT-RR+DT-R).

Furthermore, the operation of the selector 82 is as follows: (i) When DT-LL=DT-L=DT-R=0, (-Rmax) is output.

(e) In cases other than (e), (DT-LL+DT-
L) is output.

You can change it like this. Other than this, various other changes are possible.

Although memory is used in various places in the present invention, since the output has a linear relationship with respect to the address, a linear equation is used for the input signal instead of the memory and address designation circuit, etc. Of course, it is also possible to use an arithmetic circuit that calculates an output having the following relationship.

As described in detail above, by applying the present invention, when scanning and recording a halftone dot image, one halftone dot can be divided into a plurality of parts and recorded, and changes in the input image signal can be recorded with high fidelity. This makes it possible to reproduce high-quality duplicate images.

In particular, by using it in conjunction with the method disclosed in the earlier patent application No. 54-94275 in which halftone dots are cut out and recorded along the image outline, the original image containing pictures and characters can be printed with halftone dots. When recording as a point image,
It has the effect of being able to shade the text and the pattern at the same time.

Furthermore, the present invention has the following advantages over the conventional method described with reference to FIG. 1a.

(b) In the conventional method, one halftone dot is divided into a plurality of parts, and each pixel is printed depending on whether the input image signal level corresponding to that division is higher or lower than a predetermined threshold. Either it is not baked in (discontinuous tone reproduction),
In the method of the present invention, one halftone dot is divided into a plurality of parts, each pixel calculates the outline signal of the halftone dot according to the input image signal level corresponding to that division, and then calculates the width and center of the light beam. By calculating the position, printing can be performed by continuously changing the halftone dot area ratio according to the input image signal level (continuous tone reproduction).

(b) In the conventional method, one halftone dot is printed in multiple batches, which requires a lot of printing time.
In the method of the present invention, the halftone dot signals divided into a plurality of parts are combined into one and printed at once, so that the printing time can be shortened. In other words, this is the same as printing one halftone dot without dividing it.

(c) In the case of the conventional method, if one halftone dot is to be divided into multiple parts and printed at the same time, multiple light beams are required, and at the same time, multiple acousto-optic elements, beam splitters, etc. However, according to the method of the present invention, the light beam is 1
A book may be sufficient, and only two acousto-optic elements are required.

(d) In the conventional method, increasing the number of halftone dot divisions in the scan direction requires the addition of a memory device, but the method of the present invention allows multi-division (examples) without modifying the control circuit. (200 divisions) and can handle even minute image changes.

(E) In the conventional method, as shown in Figure 1a, even when scanning an image with a constant signal level other than the outline of the image, the outline shape of each halftone dot becomes step-like, and the ink in the printing process is However, in the method of the present invention, the outline of each halftone dot is smooth as shown in FIG. 1b, and the ink spreads well in the printing process, making it easy to work.

(F) As mentioned above, in the conventional method, the outline shape of the halftone dots is stepped as shown in Figure 1a, making it difficult to estimate the halftone dot area ratio visually during the plate-making process. In the method of the invention, the outline shape of each halftone dot is smooth as shown in FIG. 1b, and the halftone dot area ratio can be estimated by visual observation.

Furthermore, in the case of a method of removing halftone dots along the outline of the image, as in Japanese Patent Application No. 54-94275, it is necessary to determine how to remove halftone dots from the image information around the area to be removed. Although the technology equivalent to recognition is required and the device becomes relatively complicated, the method of the present invention allows one halftone dot to be finely divided, and can be applied relatively inexpensively along the image contour. It is now possible to form halftone dots, and even when recording an original picture containing a picture and text as a halftone image, the text and picture parts can be shaded at the same time, and almost the same effect as in the case of this prior application can be achieved.

Although the present invention has been described above based on the illustrated embodiments, the present invention does not stop there.
Various modifications and changes are possible.

For example, in the above embodiment, the present invention is implemented with an apparatus that records a halftone image by deflecting a light beam using an acousto-optic element, but a swinging mirror is used. It can also be applied to a case where the light beam is deflected by.

Also, regarding the halftone dot angle, the above-mentioned 0°, ±15
The present invention is not limited to 45° or 45°, but can also be applied to halftone images at any other arbitrary angle.

[Brief explanation of the drawing]

Figure 1a shows a case where one halftone dot is divided into five in one direction using the conventional method to form a halftone dot with a halftone dot area ratio of 50%, and Figure 1b shows a halftone dot formed using the method of the present invention. FIG. 2 is a perspective view showing an example of an apparatus for recording halftone dot images using a scanner such as a conventional plate-making scanner, and FIG. FIG. 4 is a diagram showing the relationship between the image signal level and the halftone image when halftone dots are formed by dividing the image into halftone dots. FIG. 5 is a diagram showing the relationship between the image signal level and the halftone dot image. FIG. The figure shows how the upper half of the halftone dot is formed when the halftone dot angle is +15°, and FIG. 7 shows the memory address for forming the halftone dot of a size corresponding to the original image signal level X. Figure 8, a diagram showing the specification method, shows the movement of the vertex in the horizontal direction when the size of the halftone dot changes.When the halftone dot angle is 0° and 45°, it is constant (unchanged) and ±15 Figure 9 is a diagram showing an example where a limit is set for halftone dots, and Figure 10 is a diagram showing that the halftone dots are divided into four sections perpendicular to the scan direction. Even when the input image signal of the middle 3 sections is 0,
FIG. 11 is a diagram showing an example of a halftone image to show that halftone dot formation faithful to the original image signal level X can be performed. FIG. 12 is a block diagram showing an example of the apparatus of the present invention in FIG. FIG. 14 is a diagram showing data stored in the limit memory, FIG. 15 is a block diagram showing an example of the address control circuit, FIG. 16 is a block diagram showing an example of the data calculation circuit, and FIG. FIG. 18 is a diagram showing halftone dot outline data different from the data shown in FIG. 5, and FIG. 18 is a diagram showing a slit having a shape different from the V-shaped slit 3 shown in FIG. 1... Light source, 2... First acousto-optic element, 3...
V-shaped slit, 4... second acousto-optic element, 5...
Imaging lens, 11-14... Address control circuit, 21-24... Memory, 30... Timing control circuit, 31... Dot section counter, 33-35... Memory, 40... Data calculation circuit, 50 ...Subtractor, 51...Adder, 52...Memory, 55-58...Latch, 6
0 to 62...Comparator, 65...Subtractor, 66...
Adder, 67...AND gate, 70...Selector, 71...Gate, 80, 82...Selector,
81... Adder, 85, 86... Minimum value selection circuit, 87... Adder, 88... Subtractor, 89...
Adder, 90...Arithmetic unit, 91...Gate, 92
...Level detector.

Claims (1)

[Scope of Claims] 1. When scanning and exposing a photosensitive material with a light spot, the width dimension of the light spot intersecting the scanning direction is set in synchronization with the halftone information of the required halftone image and the scanning of the photosensitive material. In a method of scanning and recording a reproduced halftone dot image of the original picture by controlling based on an image signal of the original picture to be outputted, each halftone dot area in the halftone dot information is divided into a plurality of sections, and the divided A halftone image scanning and recording method characterized by obtaining a halftone dot contour signal based on the gradation change of the original image to be reproduced corresponding to each section, and controlling the width dimension of a light spot using the halftone dot contour signal. . 2. The halftone image scanning and recording method according to claim 1, wherein the maximum value of the width dimension of the light spot is limited so as to slightly overlap at the boundary between mutually adjacent halftone dot recording areas. 3. In an apparatus that scans and exposes a photosensitive material with a light spot whose width dimension intersecting the scanning direction changes based on an image signal obtained by photoelectrically scanning an original image, and records a reproduced halftone dot image of the original image. means for dividing the halftone dot into a plurality of sections; means for synthesizing a halftone dot contour signal from the image signals of the plurality of sections corresponding to the respective sections; and a halftone dot slope signal or a halftone dot slope signal or means for synthesizing deviation signals, means for calculating a width signal of the outer halftone dot, means for calculating the position of the halftone dot, and changing the width and position of the light spot based on the calculated value. 1. A halftone image scanning and recording device comprising: means.