DE3131390A1 - METHOD AND DEVICE FOR RECORDING A HALFTONE IMAGE BY SCANNING - Google Patents

Description

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DESCRIPTION

The invention relates to a method and an apparatus for recording a halftone image by scanning and is particularly directed to a method and apparatus for recording a halftone image dividing each halftone dot area into a number of sub-areas and recording the halftone dot so that that each sub-area has its own halftone dot area ratio can have according to the associated gradation variation of the original image to be reproduced in order to improve the resolution for the Increase halftone image.

With conventional picture reproduction machines such as color scanners or platemaking color facimiles, instead of using a halftone contact screen, a halftone dot signal is electrically generated and then using the Halftone dot signal recorded a halftone dot whose

Halftone dot area ratio depending on one of one c

Original image picked up image signal is controlled, and so '"* · ■

recorded a halftone image.

In the conventional method, the halftone dot area ratio is used of each halftone dot is essentially controlled by the average density value of the individual picture elements, the is regarded as an image signal and is the width of a scan line and depends on the scanning step when an image signal is photoelectrically picked up by scanning an original image. That However, the resolving power for the reproduction image is low in this case.

To improve the resolution, the halftone dot area is divided into a number of partial areas and recorded in partial areas. For example, each sub-area or each picture element is printed or not printed, depending on whether its image signal value or its mean density value is above or below a specific threshold. The halftone dot is recorded by 'dividing the individual sub- ^ * -

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are printed sequentially using a single light beam or simultaneously using multiple light beams or copied.

Fig. 1 shows a conventionally produced halftone dot pattern having a halftone dot area ratio of 50%, dividing each halftone dot area by fifth is divided into 25 sub-areas in both the X and Y directions and A, B and P outline, width of a scan line and Designate sampling step.

In this conventional method, as shown in Fig. 1, the halftone dot is recorded in the form of a step. Laying out the printing ink is therefore not very good, so that the outline of the halftone dot is not always faithfully reproduced.

In this embodiment, as set out above, the Halftone dot area ratio of the partial area of the halftone dot cannot be continuously changed with the input image signal value. Further, when the halftone dot is partial area for partial area is written, considerable time is required, while on the other hand, if all partial areas of the halftone point are written simultaneously, several light beams are required, which has the consequence that more acousto-optical Elements and beamsplitters are required.

To circumvent and eliminate the disadvantages and inconveniences described above, according to the invention, a half creates tone patterns with a halftone dot area ratio of 50%, in which, as in Fig. T, each halftone dot area passes through Fifth division in both the X and Y directions into 25 sub-areas, in which, however, the outline of the halftone point is smoothly and continuously reduced.

The object of the invention is to provide a method of recording a halftone image by scanning, the above Does not have disadvantages and inconsistencies, simple and stable as well as being able to produce a halftone image accurately, faithfully and reproduce quickly, and moreover the resolving power increased for the halftone image.

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Another object of the invention is to provide an apparatus for recording a halftone image by scanning which is free from the aforementioned inconveniences and Disadvantages is simple and stable as well as being able to reproduce a halftone image accurately, faithfully and quickly, and this also has the ability to resolve the halftone image elevated.

In a method in which when the halftone image is reproduced on photosensitive material by means of a light beam is suitable, brightness and width of the light beam by an image signal obtained by scanning an original image are controlled, it is proposed according to the invention that each halftone dot area is divided into a number of sub-areas divided and recorded in each sub-area a halftone dot depending on the gradation variation in the respective sub-area will.

The device for recording a halftone image by scanning, at what if the halftone image is sensitive to light Material is reproduced by means of a light beam, brightness and width of the light beam by means of a scanning an image original, obtained image signals are suitably controlled, according to the invention comprises a device for generating an outline signal from a number of partial area signals, which correspond to partial areas obtained by dividing a halftone dot area, a device for generating a Recording signal from the outline signal and a screen angle signal, means for generating a width signal of the halftone dot from the recording signal, and means for generating a position signal of the halftone dot from the recording signal.

Preferred embodiments of the invention are described below in conjunction with the accompanying drawings. On this shows:
1 is a halftone dot pattern obtained by a conventional method and has a halftone dot area ratio of 50%, each halftone dot

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point area is divided into 25 sub-areas by dividing it into five in both the X and Y directions,

Fig. 2, a further halftone dot pattern of a halftone dot area of 50% as shown in FIG. \ According to the invention,

3 is a schematic perspective view of the scanning device a conventional plate-making scanner for recording a halftone dot,

Fig. 4 shows the relationship between image signal values and a halftone dot divided horizontally into 4 sub-areas in Scanning direction is divided and section by section is formed,

Fig. 5 shows the relationship between image signal values and a halftone dot divided vertically into 4 sub-areas is subdivided to the scanning direction and is formed part by part,

6 shows a further diaphragm plate with a W-shaped diaphragm opening, which instead of a diaphragm plate with a V-shaped Aperture as shown in Fig. 3 is used,

Fig. 7 shows examples of outline data of the 4 vertical divisions for recording a halftone dot with a halftone dot area ratio of 100% in relation to addresses of a memory if the screen angle is 0 °, 45 or Is 15 °,

Fig. 8 is a schematic view of the outline data for recording the upper half of the halftone dot with a halftone dot area ratio of 100% as shown in are stored in a memory if the screen angle is 15 °,

Fig. 9 shows the relationship between an image signal value from which the halftone dot area ratio of the to be generated Halftone dot, and an output of a dot sub-area counter by which the address for

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the readout of the outline data of the halftone dot from the memory is determined for a screen angle of 45, -15 ° or 0 °,

Fig. 10 address dependent variations of the top of the outline data of the halftone dot in the direction of the scan if

the screen angle is 0 °, 45 °, 15 ° or -15 °, 11 clipped halftone dot areas for screen angles of

0 °, 45 ° or 15 °,

Fig. 12 hatches halftone dots - where (a) is an unnecessary one Part contains - that is in one of the four parts

enough to record the halftone dot area divided perpendicularly to a transverse diagonal line of the halftone dot area are.

13 shows a block diagram of a control device for implementation of the method according to the invention using

application of the scanning device of FIG. 3,

14 shows the operating conditions of the dot subrange counter from FIG. 13,

Fig. 15 data stored in a slope memory for a Screen angles of 15 or -15,

16 shows data stored in a limiting or trimming memory for a screen angle of + _15,

0 ° or 45 °,
FIG. 17 is a block diagram of an embodiment of an address control circuit of FIG. 13;

Figure 18 is a block diagram of an embodiment of the data computing circuit of Fig. 13, and

Fig. 19 shows further examples of outline data of 4 vertical divisions for recording a halftone dot with a halftone dot area ratio of 100% for one Screen angles of 0 °, 45 ° or 15 °.

Fig. 3 of the drawings shows a conventional scanning exposure device for a plate-making color scanner. One emanating from a light source 1, which can be a laser

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Light beam passes through a first acousto-optical along its axis Deflection element 2, a V-shaped aperture of a diaphragm plate 3, a second acousto-optical deflection element and an imaging lens 5 with a fine image line w results.

In this embodiment, the first deflecting element directs the light beam vertically, i.e. in the Z direction, with a desired one Angle, depending on the frequency of a supplied to the deflection element Ultrasonic wave from, so that the height of the beam of light irradiated on the diaphragm can be varied to thus to vary the width of the light beam passing through it. The second deflecting element 4 directs the light beam horizontally, tal, i.e. in the Y-direction, with a desired angle depending on the frequency of an ultrasonic wave guided by the deflecting element from so. that the position of the through the aperture passing light beam can be shifted in the direction of its width. The width and position of the image line w control the light beam by controlling the frequencies of the ■ ultrasonic waves supplied to the two deflecting elements 2 and 4, and using this image line w, the halftone image can be made on a photosensitive image mounted on a recording cylinder Material can be reproduced.

According to the invention, using the scanning exposure device 3 each halftone dot is recorded in such a way that each partial area of the halftone dot is its own Halftone dot area ratio according to its gradation variation may have, with the result of an increased resolving power.

In Fig. 4, there is shown the relationship between image signal values and a halftone dot, the area of which is horizontally divided into 4 divisions in the scanning direction and which is recorded so that each division can have its own halftone dot area ratio while the center of the halftone dot is fixed. That is, the time in the scanning direction is t _Q -t ₁ , tj-t ₂ ,

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^t 2 ~ ^t 3 ' ^t 3 ~ ^t 4 ^divided

In the first, second, third or fourth time range

tg-t .., t ₁ ~ t ₂ , t ₂ -t ₃ or t ₃ ~ t ₄ becomes the halftone point C ^, C ~, C-. or C. with a halftone dot area ratio of 75%, 50%, 25% or 100% corresponding to the associated image signal value X ₁ ^ X ₂ , X ₃ or X ₄ , the center of the halftone dot being fixed. Therefore, in this case, each halftone dot is recorded in each partial area depending on its image signal value which changes as a function of time, in other words, the halftone dot area ratio can be freely changed in the course of forming a single halftone dot.

Fig. 5 shows the relationship between image signals and a halftone dot whose area is vertically divided into four divisions in the direction perpendicular to the scanning direction. and which, apart from the partial direction, is designed in the same way as in the embodiment of FIG. 4 becomes that each sub-area can have its own halftone dot area ratio while the center of the halftone dot is fixed.

In detail, the halftone dot area is first through a center line or one through the middle of the halftone dot running vertical diagonal line divided into two parts, after which each part by a line parallel to the center line at a distance L or R, which is essentially is equal to the scanning step or the scanning width of the scanning line, from this center line, into two sub-areas is subdivided, which means, from left to right, the four sub-areas LL, L, R and RR are obtained.

In the sub-areas LL, L, R and RR, the half-tori point C ₁ ^, C _L , C _R or c _RR with a halftone dot area ratio of 50%, 25%, 100% and 75% corresponding to an image signal value Xtt / Xt ι ^x _r or X _RR / which corresponds to a halftone dot area ratio of 50%, 25%, 100%, or 75%, partially formed, while the center of the halftone dot is fixed.

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In the embodiment described above, the Halftone dot area can be divided equally or unequally. Furthermore, the number of partial areas of the halftone dot area is limited not on four, but can be anything. When the halftone dot shown in Fig. 5 is recorded is, if the central axes of the individual sub-areas with the center of the image line of the light beam with the same Width as the sub-areas coincide, recording the halftone dot by scanning by means of the scanning exposure device 3 using the diaphragm plate 3 with a V-shaped diaphragm opening without difficulty be performed.

However, if the center of the light beam lies outside the central axis of the partial area or if more than one partial area is reproduced by a single light beam, that is, when the parts separated in the width direction, such as the partial areas LL, L and R of FIG. 5, are recorded at the same time , the scanning light beam should be divided by cutting out a certain width of the light beam. In such a case, when the scanning exposure is performed using the diaphragm plate 3 having a V-shaped diaphragm aperture, unnecessary parts C _{0n become} as shown by

LK

Cross-hatching are recorded.

In order to eliminate this problem, the scanning exposure is carried out using a ^{diaphragm plate 3 1} having a W-shaped diaphragm opening shown in FIG. 6 in place of the diaphragm plate 3 having a V-shaped diaphragm opening. Details of this method are described in Japanese Patent Application Publication No. 54-21123, so its description is omitted here for the sake of brevity.

Next is a method of forming a semi-. tone point described. A method of producing a Halftone dot without division into partial areas is disclosed in Japanese Patent Application Publication No. 54-79701

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described.

In that embodiment, an arithmetic circuit is provided which receives data for forming the outline of a halftone dot calculated with a halftone dot area ratio of 100%. If a halftone dot is to be created with a dot area ratio of less than 100%, this is obtained Outline data for a halftone dot with the desired dot area ratio by controlling addresses and times for a calculation sequence, according to which the center and width of the

desired halftone point is calculated from the obtained outline data which is a halftone dot with the desired dot area ratio is trained.

In the present invention, the basic concept is that
same as in this conventional method, that is, instead of the arithmetic circuit of the conventional method, is a

Memory is provided in which the outline data of each sub-area for recording a halftone dot with a dot area ratio of 100% are stored for each screen angle. The data of each sub-area is carried out from memory

Control of the addressing of the memory to obtain the

Outline data for recording a halftone dot with the
desired point area ratio read out, after which center
and width of the desired halftone dot depending on the
sequentially obtained outline data for recording the

Halftone dot with the desired dot area ratio
be calculated.

7a, 7b and 7c are examples of outline data of the four vertical divisional areas LL, L, R and RR of a halftone dot a point area ratio of 100% for a

Screen angles θ of 0 °, 45 ° and 15 ° are shown.

Fig. 7a shows four outline data of four divisional areas LL, L, R and RR of a halftone dot with a dot area ratio of 100% when the screen angle θ is 0 °.
The top half and bottom half of the halftone dot
with the point area ratio of 100%

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choice of the larger outline signals of the sub-areas RR or R and LL or L selected.

Fig. 7b shows four outline data of the four partial areas LL, L, R and RR in the same manner as in Fig. 7a except that the screen angle θ is 45 °. When the screen angle θ is 45 °, the width of the scanning line is during recording of the halftone dot, as shown in Fig. 9a, which shows a relationship between an image signal value, of which the point area ratio of the halftone point to be formed depends, and an output signal of a dot subrange counter, by which the address for reading out the outline data of the halftone dot from the memory is determined, for a screen angle of 45 ° represents why this outline data is the scan line for recording the halftone dot mean with the point area ratio of 100%.

Fig. 7c shows four outline data for the four sub-areas LL, L, R and RR- in the same way as Fig. 7a except that the screen angle θ is 15 °. In such a case, the peaks of the data lines are for the top half and the bottom Half of the halftone dot shifted slightly to the left or right. The top half and bottom half of the halftone dot with the dot area ratio of 100%, by selecting the larger outline signals of the sub-areas RR or R or LL or L recorded.

If the screen angle θ is -15 °, outline data lines are obtained, which are mirror-inverted to those of FIG. 7c, which is why they are omitted in FIG. The in Fig. 7 The outline data of the four partial areas RR, R, L and LL shown in FIG. 13 are stored in memories 21 to 24 shown in FIG. as will be described below.

A method of forming a halftone dot with a dot area ratio less than 100% is now disclosed from the outline data to record the above-described halftone dot with the dot area ratio of 100% in Connection with Fig. 8 described.

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First, the sub-area RR will be described. In Fig. 8a

the outline data for recording the halftone dot with dot area ratio of 100% are shown by a dot-dash line DFH. The address for reading out the outline data is dependent on the image signal value X _n - of the sub-area RR

KK

and an output signal T of a dot subrange counter 31, which is described below with reference to FIG. 13, calculated.

A line runs parallel to the output data line DF through an address point (100-X _R ), intersections of this parallel line with the line DH and the diagonal FF 'being denoted by J and K. Furthermore, a line through the point K and an address point (99 + X _Dt) ) intersects in parallel

KK

runs to the output data line FH, the line DH at a point Li A line extends from point K in a direction perpendicular to the scanning direction and intersects the transverse diagonal address line at an address point ^J RR

When the output signal T of the dot subrange counter 31 is in a range between 0 and (100-X _nD ), should

KK

no halftone dot will be formed and no data will be made read out from a memory 21 to be described below.

When the output signal T of the dot sub-area counter 31 is greater than (100-X _n ^) and the screen angle is 0 or 45 °

KK

the address is always 99, as described below. If, however, the screen angle is -15 ° and the output signal T, depending on the image signal value X _._, lies in a range between the addresses (100-X__) and J _{or (} ,

KK KK

the data of the sub-area DE are read out from the memory 21 and thus the outline JK of the desired halftone point educated.

That means in detail that for the formation of the outline JK of the desired halftone dot, although the output signal T of the dot subrange counter 31 is directly used as an address signal

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can be used, according to the invention to simplify the method, the address T ¹ = / Τ- (100-X ) J is calculated and then the outline data of the sub-area DE of the outline data DEF, which are determined by the image signal value X, from the memory 21

KK

can be read out by the address obtained.

Further, when the output T of the data sub-area counter 31 is in an area between addresses J _._ and

KK

(99 + X _OT J, section EG is skipped

KK

and accordingly, the outline data of the partial area becomes GH read out from the memory, with which the sub-area KL of the desired halftone dot is formed. That means that the Address / τ + (100-Χ) _7 is calculated and then the outline data of the sub-area GH of the outline data FGH can be read from the memory 21 by the address obtained. When the output signal T of the dot sub-area counter 31 is in a range between the addresses (99 + X) and 199

KK

no halftone dot is to be formed, which is why none Data are read out from the memory 21.

When the desired halftone dot is formed by this data, the upper half defined by dots (110-X ₀₁₅ ), J, K, L, and (99 + X_ _D ) is created.

KK KK

Next, the portion R will be described. In Fig. 8b, the trapezoidal outline data is for recording a Halftone dot with a dot area ratio of 100% represented by a dashed line MNRS, which is the same Has a shape like the trapezoid ODH199 of FIG. 8a. The address for the readout of the outline data is carried out in accordance with the image signal value X of the sub-area R and the output signal T of the point

subrange counter is calculated in the manner described above. Passes through a point V with an address (100-X_.)

a line parallel to the outline data line MN, the points of intersection of this parallel line with the line MR and the longitudinal diagonal being denoted by W and K ¹ . Further, a line passing through the point K ¹ and a point Z having an address (99 + X ₀ ) parallel to the outline data line RS intersects the

«Eg

■ · ν

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Line NR at a point Y. ^{A line extends from point K 1} perpendicular to the scanning direction and intersects the transverse diagonal address line MS at an address point J _n .

If the output signal T of the dot subrange counter is in a range between 0 and (100-X _{n), no half-}

to generate tone point and there will be no data from one of the following read out memory 22 still to be written to.

If the output signal T of the dot subrange counter is greater than (100-X _R ) and the screen angle is 0 ° or 45 °, the address is always 99 in the same way as described above Output signal T of the dot sub-area counter in the area between addresses (100-X ₀ ) and J_. depending on the image signal value

X, the address / T- (IOO-X ) J is calculated, after which the κ κ

Outline data of the section MNP of the outline data MNX, where the Distance NP is equal to distance WX due to the address obtained are read out from the memory 22 and thus the outline VWX of the desired halftone point is formed.

If the output signal T of the dot subrange counter is in a range between the addresses J _n and (99 + X _D ),

κ κ

the address-Τ "= / τ + (100-X) J is calculated, whereafter the outline data of the section QRS of the outline data XRS, where the distance QR is equal to the distance XY, read by the address obtained from the memory 22 and thus the outline XYZ of the desired halftone dot is formed.

If the output signal T then lies in a range between the addresses (99 + X _R ) and 199, no halftone dot is to be formed, which is why no data are read out from the memory 22 «

When the desired halftone dot is formed by this data the trapezoid VWYZ is generated.

In the present case, the upper half of the desired Halftone dot from the outline data of the sub-areas RR and R and by selecting the larger outline data, where one gets the halftone dot defined by the points V, W, J, K, L

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Y and Z is defined. The lower half of the desired halftone point becomes from the outline data of the sub-areas L and LL in formed in the same way as described above.

The explanation referred to the case of a screen angle of 15, for a screen angle of 0 or -15 however, the halftone dot can be produced in the same way as described above, as can be easily seen from FIGS. 9b and 9c, which gives the relationship between an image signal value of which the halftone dot area ratio of the to be formed Halftone dot depends, and the output signal of the dot subrange counter, through which the address for reading the outline data of the halftone dot is determined from the memory for a screen angle of -15 ° or 0 °.

For a screen angle of 45 ° the procedure is simpler than described above. That is, as shown in Fig. 9a, to produce a halftone dot whose dot area ratio or width depends directly on the image signal value X, so if the output T of the dot subrange counter 31 of the relationship (100-X) = T- (99 + X) is sufficient, the image signal value X as the address signal is issued.

In summary, the following can be said. If the. Screen angle θ is -15 or 0, in the sub-area RR ~ the other sub-areas R, L and LL are executed in the same way as the sub-area RR - the address (AD-RR) for the sub-area RR, through which the outline data are read from the memory 21, depending on the output signal T des Pump subrange counter 31 is determined as follows:

(I) 0 → T <(100-X _RR ) (AD ^ RR) = O

(II) (100-X ^) ^ T ₌ J _RR (AD-RR) = T- (100-X ^)

(III) Jpj ^ TS (^ + Xrr) (AD-RR) = T +

(IV) (99 + X _OD ) <T = 199 ... (AD-RR) = O

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In this embodiment, the position of point J ₁ ,,, as described in connection with FIG. 8, changes from

KK

depending on the dot area ratio of the desired halftone dot to be formed, with associated examples in 10a, 10b and 10c for screen angles of 0 °, 45 °, 15 ° and -15 are shown.

For a screen angle of 45 in sub-area RR the other sub-areas R, L and LL are in the same In the same way as the sub-area RR - the address (AD-RR) as a function of the output signal T of the dot sub-area counter 31 determined in a manner similar to that described above as follows:

(I) 0 = T <(100-X _D _) (AD-RR) = O

(ID ( ¹⁰⁰ ^ RR * = ^T = ^J RR (AD-RR) = X _RR

(III) J _RR <T <(99 + X _RR ): .. (AD-RR) = X _RR

(IV) (99 + X ^ X T ^ l 9 9 (AD-RR) = O

It is now assumed that the outline data of the sub-areas RR, R, L and LL for the desired halftone dot, the as described above, can be read from the memory by the addresses obtained with (DT-RR), (DT-R), (DT-L), and (DT-LL), then the desired halftone dot is located in an area that is defined by the lines of the signals U and L obtained by the following formulas (1) and (2).

U = max / "(DT-RR), (DT-R) ^ (D

L = max / (DT-L), (DT-LL) 7. (2)

Then the upper halftone dot outline signal U and a limit signal (DT-LIMIT) mentioned below are compared with one another, and the smaller signal is designated ^{as signal U 1.} The lower halftone dot outline signal L and the limit signal

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(DT-LIMIT) are also compared with one another and the smaller is referred to as signal L ¹ .

U ¹ = min / rev, (DT-LIMIT) 7 (3)

L ¹ = min / L, (DT-LIMIT) 7 (4)

When the halftone dot area ratio is more than 50%, In general, a halftone dot protrudes into adjacent halftone dot areas, which is why in the overlapping areas a multiple exposure would be performed. This is because of the light scattering in the film and the like. Undesirable. Further if the halftone dot area ratio is 100%, the entire area should be exposed. Therefore, according to the invention, as shown in Fig. 11, delimits the halftone dot area so that that each exposed halftone dot with a dot area ratio of more than 50% adjoining halftone dots only slightly overlaps. Such a limit control is carried out by the limit signal (DT-LIMIT).

In Figs. 11a, 11b and 11c is the boundary area for screen angles of 0, 45 or 15 ° shown in dashed lines. According to FIG. 11c, a dash-dotted line is preferably used Modified boundary area represented by lines extending in a direction perpendicular to the scanning direction, designed to simplify the machine and minimize the overlap areas of the halftone dots.

When the outline data (DT-LL), (DT-L) and (DT-R) are zero, the ^{halftone dot surrounded by the lines of the signals U 1} and L ^{1 contains} an unnecessary part as shown by the broken lines in Fig 12a is shown. This arises. from the fact that the signal L ^f is assumed to be zero.

In order to eliminate such an unnecessary part, a correct halftone dot is obtained as shown in FIG. is shown, the condition is determined according to the following equation (5).

L ¹ = -Rmax (5)

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When the outline data (DT-RR), (DT-R) and (DT-L) are zero, the following equation (6) is obtained in the same manner as above:

U '= -Lmax (6)

- - ■. ■

Lmax and Rmax give the sampling step as shown in FIG is on.

Then, the displacement of the center of the halftone dot to be formed from the scanning line will be parallel to it if the screen angle is 0 ° or 45 °, and a slope of the central axis of the halftone dot to be formed with respect to the scan line, if the screen angle is -15 °, determined. Data (DT-SHIFT) and (DT-SLOPE) represent shift or slope This results in the distance S of the scanning line from the central axis of the halftone dot according to the following equation: S = (DT-SHIFT) + (DT-SLOPE) (7)

Then, the outline data U "and L" are used for recording the the upper half and lower half of the halftone dot, whose shift and slope are determined, exposed as follows:

U "= U ¹ + S (8)

L "= L ¹ + S -. (9)

Accordingly, the width and center position of the halftone dot to be formed are given by the following equation:. W = U ¹ + L "

In this equation, if the calculated width is less than zero, it is set to zero. You get so the following equations;

W = max / U "+ L ¹¹ ), 0 / .. (10)

P =

»Β

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13 shows an embodiment of a control device for carrying out the method according to the invention using the scanning device of FIG. 3.

Address control circuits 11 to 14 calculate addresses for reading out the outline data for recording partial areas RR, R, L and LL of the halftone dot depending on the image signal value X from the memories 21 to 24. In the memories 21 to 24 are the outline data for recording the partial areas ER, R, L and LL of a halftone dot with dot area ratio 100% for screen angles θ -15 °, 0 ° and 45 ° are saved. The data read out are input to a data computing circuit 40.

A timing control circuit 30 which is a halftone dot position calculating circuit contains a start signal (DF-START) for the recording of the individual halftone dots and a shift signal X, which represents the distance of the center of each halftone dots to be recorded from the position of the recording head perpendicular to the scanning direction, in synchronization with the Rotation of the recording cylinder off.

The dot sub-area counter 31 divides the halftone dot area into numbers such as 200 in the scanning direction and counts the number of clock pulses of the corresponding number 200 for the output of the signal T for recording the desired Halftone dot depending on the image signal value X, as shown in Fig. "14a. Further, when the halftone area in Direction of the scanning direction is limited, the dot sub-area counter 31 can correspondingly not need the output signal T Control parts to zero so that the output data of the memories 21 to 24 are then zero.

A slope memory 33 stores the slope data (DT-SLOPE) for the inclination of the halftone dot with respect to the scanning direction, if the screen angle is -15 °. The slope memory 33 is determined by the output signal T of the dot sub-range counter 31 addresses and outputs slope data (DT-SLOPE) as shown in FIGS. 15a and 15b,

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which are given to the data computation circuit 40. For screen angles from 0 ° or 45 ° there is no need to incline the semitone point, which is why the output data of the slope memory 33 can then always be controlled to zero.

A limit memory 34 stores the limit data (DT-LIMIT) to limit the halftone dot area in the above described way. The limit memory 34 is addressed by the output signal T of the dot sub-area counter 31 and outputs limit data (DT-LIMIT) as shown in Fig. 16a, 16b and 16c are shown off when the screen angle is -15 °, 0 ° or 45 °, and the data read out in this way are transferred to the computing circuit 40 entered.

A shift memory 35 stores the shift data (DT SHIFT) which represent the shift of the center of the halftone dot with respect to the scanning line perpendicular to the scanning line for a screen angle of 0 ° or 45 °. The shift memory 45 is addressed by the shift signal X of the timing control circuit 30 and outputs shift data (DT SHIFT), which are given to the data calculation circuit 40. The relationship between the shift data (DT-SHIFT) and the shift amount signal ^ x as an address signal is expressed by the following simple equation, in which K denotes a proportionality factor:
(DT-SHIFT) = Κ.ΔΧ

The data calculating circuit 40 selects the larger one of the outline data (DT-RR) or (DT-R) and (DT-L) or (DT-LL) for recording the upper and lower halves of the desired halftone point and then select the smaller one if necessary from outline data and limit signal (DT-LIMIT) and adds the slope data (DT-SLOPE) 'or the displacement data (DT-SHIFT) to the selected smaller data and thus calculates the central position and the width of the desired Halftone dot.

Fig. 17 shows an embodiment of the address control

■ "m · ♦

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circuit 11 for the sub-area RR of FIG. 13. The other address control circuits 12 to 14 have the same structure and operate in the same manner as the address control circuit 11.
A subtracter 50 subtracts the image signal value X _._

of the sub-area RR from the fixed number 100, whereby the output signal (100-X) is obtained, which is applied to a latch memory 55 and held there during the sampling period in order to maintain the image signal value. The output signal of the latch memory 55 is applied to the inputs A of a comparator 60, a subtracter 65 and an adder 66. The output signal T of the partial dot range counter 31 is applied to the inputs B of the subtracter 65 and the adder 66. _{In the subtracter 65, the calculation / t + (100-X n} ) J is carried out in order to obtain an output signal to be sent to an input A of a selector 70. _{In the adder 66, the calculation / τ + (100-X 0n} ) ] is carried out in order to obtain an output signal to be sent to an input B of the selector 70. _{In the comparator 60, the signal (100-X) and the output signal · T of the dot subrange counter} 31 are compared, after which, if the output signal T is at least the signal (100-X 0n), a signal with high

KK

hem value is given to an input A of an AND gate 67. An adder 51 adds the fixed number 99 and the image signal value X to obtain the output signal (99 + X _RR ), which is applied to a latch memory 56 and held there during the sampling period to maintain the image signal value.

The output signal of the latch memory 56 is applied to an input A of a comparator 61, the output signal T to an input B of the comparator 61. When the signal (99 + X _RR ) is at least the output signal · T, the comparator 61 outputs a signal · with a high value to an input B of the AND gate 67. The output is connected to a control terminal of a gate 71, where if the output signal T and the image signal -

♦ · ft P.

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. value X _RR the relation ^ (100-X) = T = (99 + X _RR ) 7, the gate 71 is opened by a control signal of the AND gate 67. A memory 52 stores the address _{variation J RR of} the tip of the desired halftone dot in the scanning direction depending on the dot area ratio when the screen angle is -15 ° as shown in Fig. 10, the address variation J _RR being read out and recorded by the step _{signal value X RR} a latch memory 57 is given, the structure and function of which corresponds to the latch memories 55 and 56. The output signal of the latch 57 is applied to an input A of a comparator 62. The output signal T of the partial dot range counter 31 is applied to an input B of the comparator 62. The comparator 62 outputs a control signal to a control terminal of the selector 70. A latch memory 58 holds the image signal value X _n supplied during the scanning period in order to maintain the image signal value.

■ KK

to obtain. The output signal of the latch memory 58 is applied to an input G of the selector 70. A control signal for a screen angle of 45 is to be given to a further control connection of the selector 70. The output of the selector 70 is put on gate 71.

When the screen angle θ is 45 °, the control signal for a screen angle of 45 ° is input to the selector 70, and the selector 70 outputs the signal given to the terminal C. If the screen angle θ is not 45 °, no control signal for a screen angle of 45 is input to the selector 70, and the selector 70 compares the data J _R and the output T of the dot sub-area counter 31. Then, if J _DO , the selector 70 outputs at least that Starting

KK

signal T is / the signal given to terminal A, while if J__, it is smaller than the output signal T, the

KK

the terminal B applied signal outputs.

Fig. 18 shows an embodiment of the data calculation circuit of FIG. 13. The data (DT-RR), (DT-R) and -Lmax at its inputs A, B and C are input to a selector 80.

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The selector 80 observes the data (DT-RR), (DT-R), (DT-L). and DT-LL) and selects one of the input data and outputs the selected data U to an input A of a minimum value selector 85 according to the following scheme:
5

(a) if (DT-RR) = (DT-R) = (DT-L) = 0, the selector 80 selects -Lmax;

(b) if (DT-RR) - (DT-R), except condition (a) holds, it selects (DT-RR); and

(c) if (DT-RR) <(DT-R), unless condition (a) applies, he selects (DT-R).

(DT-LIMIT) is applied to an input B of the minimum value selector 85, which is the smaller of the two data U or

Selects Ί5 (DT-LIMIT) and applies the selected data U ¹ to an input A of an adder 87.

The data (DT-SLOPE) and (DT-SHIFT) are sent to the inputs A and B of an adder 81 are given, which adds the two data and the addition data S to an input of the adder 87 there. The adder 87 then adds the data U 'and S to obtain U "according to the above formula (8) and outputs U" the inputs A of an adder 89 and a calculator 90.

The data (DT-LL), (DT-L) and -Rmax are given to inputs A, B and C of a selector 82 which is tion matches the selector 80 and the data (DT-LL), (DT-L), (DT-R) and (DT-RR) are observed and one of these data and sends the selected date L to an input A of a minimum value selector 86 according to the following scheme:

(d) if (DT-LL) = (DT-L) = (DT-R) = 0, the selector 82 selects -Rmax;

(e) if (DT-LL) ^ (DT-L), unless condition Cd) applies, he selects (DT-LL); and

(f) if (DT-LL) <(DT-L), unless condition (d) applies, he selects (DT-L).

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(DT-LIMIT) is also applied to an input B of the minimum value selector 86, which selects the smaller of the data L and (DT-LIMIT) and ^{outputs the selected data item L 1} to an input A of a subtracter 88. The addition size S becomes
from the adder 81 to an input B of the subtracter 88. The subtracter 88 subtracts S from L ¹ to obtain L ″ according to the above formula (9) and applies L ″ to the inputs B ′ of the adder 89 and the calculator 90.

The adder 89 adds U "and L" and outputs the addition data U "+ L" to a gate 91 and a level detector 92. The level detector 92 determines whether U "+ L" is positive or negative and controls the gate 91 so that it only closes if ü "+ L" is negative. The gate 91 thus gives U "+ L" as the width
of the width signal representing the halftone dot to be formed

off when U "+ L" is positive.

U "-L"

The calculator 90 performs a calculation -5- and always outputs a position signal that represents the center position of the halftone dot to be formed. If U "+ L" is negative, becomes no width signal output and therefore no halftone dot recorded.

Fig. 19 shows other examples of outline data of the four
vertical subregions for a screen angle θ of 0 °, 45 ° or 15, which are used in a further method according to the invention instead of that shown in FIG.
In this embodiment, the above-mentioned

Equations (1) and (2) modified ^{to the following equations (1 1} ) and (2 ^1).

U = (DT-RR) + (DT-R) (T)

L = (DT-LL) + (DT-L) (2 ')

The selector 80 selects one of the input data according to the following scheme:

(g) if (DT-RR) = (DT-R) = (DT-L) = 0,

he chooses -Lmax; and

(h) for other conditions he chooses /(DT-RR).+ (DT-R) /
the end. .

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The selector 82 selects one of the input data according to the following scheme:

(i) if (DT-LL) = (DT-L) = (DT-R) = 0, selects -Rmax; and
(j) in the case of other conditions, he chooses

ΛDT-LL) + (DT-L) 7.

In the embodiments described above, the screen angle is of course not limited to the values 0 °, -15 ° and 45 °, every screen angle can be used.

The invention has been made with reference to preferred embodiments but modifications are available to those skilled in the art.

Since, for example, the output signal of the memory and the associated address signals are connected to one another in a basic relationship, arithmetic circuits that output a signal can be which is fundamentally related to an address signal, can be used in place of memories. Furthermore, instead of the acousto-optic deflector of Fig. 3 pivot or Rotating mirrors can be used to reflect the light beam. The present invention can be used in connection with the in Japanese Patent Application Publication No. 56-19056 disclosed invention can be applied more effectively when an original image with an image pattern, a character and a Letters is reproduced. In this case, the hue of the entire picture pattern, the character and the letter in the . run at the same time.

Be on your toes

Claims (3)

PATENT CLAIMS fi \. A method of recording a halftone image by scanning, in which, when the halftone image is reproduced on a photosensitive material by means of a light beam, brightness and width of the light beam are appropriately controlled by an image signal obtained by scanning an original image, characterized in that each halftone dot area is divided into a number is divided by sub-areas and a halftone dot is recorded in each sub-area depending on a gradation variation in that sub-area. Dainippon Screen .. .., ^{PH / HP} , J 3 ¹ f ⁵ 3 ⁹ 1390 2. The method according to claim 1, characterized in that the halftone dot area is so limited so that each exposed halftone dot has a dot area ratio slightly overlaps adjacent halftone dots by more than 50%. 3. Device for recording a halftone dot by scanning, in which when the halftone image is recorded on a photosensitive material by means of a light beam , brightness and width of the light beam by means of an image signal obtained by scanning an original image is suitably controlled, characterized by means for generating an outline signal of a halftone dot from a number of partial signals which correspond to partial areas obtained by dividing the halftone dot area are, a device for generating a recording signal from the outline signal and a screen angle signal, a device for generating a width signal of the halftone point from the recording signal, and means for generating a position signal of the halftone point from the Recording signal.