GB2081549A - Halftone picture recording - Google Patents

Abstract

In a method for recording a halftone picture by scanning, when the halftone picture is reproduced on a photosensitive material by a light beam, the brightness and width of the light beam are controlled by a picture signal obtained by scanning an original picture. Each halftone dot area is divided into plurality of divisions and an outline signal is obtained from the divisional signals. Then, a recording signal is produced from the, outline signal and a screen angle signals and then, a width signal and a position signal are obtained from the recording signals thereby recording the desired halftone dot in every division depending on a gradation variation of every division by using the width signal and the position signal.

Description

SPECIFICATION Halftone picture recording The present invention relates to a method and machine for recording a halftone picture by scanning, and more particularly relates to a method and machine for recording a halftone picture, wherein every halftone dot area is divided into a plurality of divisions and the halftone dot is recorded so that every division may have its own halftone dot area rate corresponding to its gradation variation of an original picture to be reproduced in order to increase the resolving power for the halftone picture.

In a conventional picture reproducing machine such as a color scanner and a color facsimile for plate making, a halftone dot signal is electrically produced, and then a halftone dot is reproduced by using the halftone dot signal whose halftone dot area rate is controlled depending on a picture signal picked up from an original picture, instead of using a halftone contact screen, thereby recording a halftone picture.

In the conventional method, the halftone dot area rate of each halftone dot is generally controlled by an average density level of each picture element, which is regarded as a picture signal level and which depends on a width of a scanning line and a sampling pitch when a picture signal is picked up by scanning an original picture photoelectrically. However, in this case, the resolving power for a reproduction picture is low.

In order to improve the resolving power, the halftone dot area is divided into a plurality of divisions and is recorded every division. For example, every division or each picture element is printed or not printed when its input picture signal level or its average density level is larger or smaller than a predetermined threshold. The halftone dot is reproduced by performing the printing of every division in order by a single light beam, or all divisions at the same time by using a plurality of light beams.

In Fig. 1 there is shown a halftone dot pattern of a halftone dot area rate 50%, formed in a conventional manner, every halftone dot area being divided by five in both X and Y directions into 25 divisions, wherein A, B and P denote an outline, a width of a scanning line and a sampling pitch, respectively.

In this conventional method, as shown in Fig. 1, the halftone dot is reproduced in a stair form. Thus, the lay of the printing ink is not very good and the outline of the halftone dot is not always faithfully reproduced.

In this embodiment, as described above, the halftone dot area rate of the divisions of the halftone dot cannot continuously be varied depending on the input picture signal level. Further, when the halftone dot is printed every division, it requires a lot of time, and when all divisions of the halftone dot area are printed at the same time, a plurality of light beams are required, with the result that further acoustooptical element and beam splitter are required.

It is an object of the present invention to provide a method for recording a halftone picture by scanning in which the aforementioned inconveniences and disadvantages are reduced or eliminated, which is simple and stable, which is capable of reproducing a halftone picture accurately, faithfully and quickly, and which increases a resolving power for the halftone picture.

It is another object of the present invention to provide a machine for recording a halftone picture by scanning in which the aforementioned inconveniences and disadvantages are reduced or eliminated, which is simple and stable, which is capable of reproducing a halftone picture accurately, faithfully and quickly, and which increases a resolving power for the halftone picture.

According to the present invention there is provided a method for recording a halftone picture by scanning, wherein, when the halftone picture is reproduced on a photosensitive material by a light beam, a brightness and a width of the light beam are properly controlled by a picture signal obtained by scanning an original picture, characterized in that each halftone dot area is divided into a plurality of divisions, and a halftone dot is recorded in every division depending on a gradation variation of every division.

According to the present invention there is also provided a machine for recording a haiftone picture by scanning, wherein, when the halftone picture is reproduced on a photosensitive material by a light beam, a brightness and a width of the light beam are properly controlled by a picture signal obtained by scanning an original picture, comprising means for producing an outline signal of a halftone dot from a plurality of divisional signals corresponding to divisions obtained by dividing a halftone dot area, means for producing a recording signal from the outline signal and a screen angle signal, means for producing a width of the halftone dot from the recording signal, and means for producing a position signal of the halftone dot from the recording signal.

In order to remove the above described defects and disadvantages, according to the present invention a halftone dot pattern of a halftone dot area rate 50%, wherein every halftone dot area is divided by five in both X ad Y directions into 25 divisions and wherein the outline of the halftone dot is smoothly continuously reproduced, is formed, as shown in Fig. 2, alike Fig. 1.

In order that the present invention may be better understood, preferred embodiments thereof will be described with reference to the accompanying drawings, in which: Figure 1 shows a halftone dot pattern of a halftone dot area rate 50%, each halftone dot area being divided by five in both X and Y directions into 25 divisions according to a conventional method; Figure 2 shows another halftone dot pattern of a halftone dot area rate 50%, alike Fig. 1, according to the present invention; Figure 3 is a schematic perspective view of a scanning means of a conventional scanner for plate making, for recording a halftone dot; Figure 4 shows a relation between picture signal levels and a halftone dot which is divided horizontally into four divisions in a direction of the scanning and is formed every division;; Figure 5 shows a relation between picture signal levels and a halftone dot which is divided vertically into four divisions in a direction perpendicular to the scanning direction and is formed every division; Figure 6 shows another aperture plate having a W-shaped aperture which is used instead of an aperture plate having a V-shaped aperture shown in Fig. 3; Figure 7 shows examples of outline data of the four vertical divisions for recording a halftone dot having a halftone dot area rate 100% with respect to addresses of a memory when a screen angle is 0", 45 or 15 ; Figure 8 is a schematic view of the outline data for recording the upper half of the halftone dot having a halftone dot area rate 100%, stored in a memory when a screen angle is 1 5';; Figure 9 shows a relation between a picture signal level on which the halftone dot area rate of the halftone dot to be formed depends, and an output signal of a dot section counter, by which the address for reading the outline data of the halftone dot out of the memory is determined when a screen angle is 45', - 15" or 0 ; Figure 10 shows address variations of the top of the outline data of the halftone dot in the direction of the scanning when a screen angle is 0', 45 , 15 or 15 ; Figure 11 shows halftone dot areas limited when the screen angles are 0 , 45, and 15 ;; Figure 12 shows halftone dots by hatching, (a) including an unnecessary part, to be recorded in one of the four divisions of the halftone dot area divided in the direction perpendicular to a transverse diagonal line of the halftone dot area; Figure 13 is a block diagram of a control means for performing a method of the present invention by using the scanning means of Fig. 3; Figure 14 shows operating conditions of a dot section counter of Fig. 13; Figure 15 shows data stored in a slope memory when a screen angle is 1 5" or - 1 5"; Figure 16 shows data stored in a limit memory when a screen angle is + 15 , 0" or 45 ; Figure 17 is a block diagram of one embodiment of an address control circuit of Fig. 13;; Figure 18 is a block diagram of one embodiment of a data arithmetic circuitry of Fig. 13; and Figure 19 shows other examples of outline data of the four vertical divisions for recording a halftone dot having a halftone dot area rate 100% when a screen angle is 0 , 45 or 15 .

Referring to the drawings there is shown in Fig. 3 a conventional scanning exposure means for a color scanner for plate making. A light beam emitted by a light source 1 such as a laser tube is passed along its light axis through the first acoustooptical deflector element 2, a Vshaped aperture of an aperture plate 3, the second acoustooptical deflector element 4, and a focusing lens 5 to obtain a minute line image w.

In this embodiment, the first deflector element 2 deflects the light beam vertically, i.e. in the z direction at a desired angle depending on a frequency of an ultrasonic wave supplied thereto so that the height of the light beam projected onto the aperture may be varied in order to vary the width of the light beam therethrough. The second deflector element 4 deflects the light beam horizontally, i.e. in the Y direction at a desired angle depending on a frequency of an ultrasonic wave supplied thereto so that the position of the light beam through the aperture may be shifted in the direction of its width.Thus, the width and the position of the line image w of the light beam can be varied by controlling the frequecies of the ultrasonic waves supplied to the two deflector elements 2 and 4, and by using this line image w the halftone picture can be reproduced onto a photosensitive material mounted to a recording cylinder.

According to the present invention, by using the scanning exposure means of Fig. 3 every halftone dot is recorded so that every division divided of the halftone dot area may have its own halftone dot area rate corresponding to its gradation variation, with the result of the increase of the resolving power.

In Fig. 4 is shown a relation between picture signal levels and a halftone dot whose area is divided horizontally into four divisions in a direction of the scanning, and which is so recorded that every division may have its own halftone dot area rate while the center of the halftone dot is fixed. That is, the time in the scanning direction is divided by the sampling pitch into four periods top,, t,-t2, t2-t3, t3-t4.

In the first, the second, the third or the fourth period t041, t,-t2, t2-t3 or t3-t4, the halftone dot C1, C2, C3 or C4 having a halftone dot area rate 75%, 50%, 25% or 100% is formed partly according to a picture signal level Xt, X2, X3 or X4 corresponding thereto, respectively, while the center of the halftone dot is fixed. Therefore, in this case, every halftone dot is recorded in every division depending on its picture signal level which varies with respect to the time, in other words, the halftone dot area rate can be varied freely in the course of the formation of one halftone dot.

In Fig. 5 is shown a relation between picture signals and a halftone dot whose area is divided vertically into four divisions in the direction perpendicular to the scanning direction, and which is formed that every division may have its own halftone dot area rate while the centre of the halftone dot is fixed, in the same manner as the embodiment shown in Fig. 4 except the dividing direction.

That is, the halftone dot area is first divided into two parts by a centre line or vertical diagonal line which passes the centre of the halftone dot, and then each part is divided into two divisions by a line which is parallel with the center line and is positioned at a distance Lma, or R ma, which substantially equals the scanning pitch or the width of the scanning line, away from the center line, thereby obtaining four divisions LL, L, R and RR, designated from the left hand side.

In the division LL, L, R or RR, the halftone dot Cull, C, CR or CRR having a halftone dot area rate 50%, 25%, 100% or 75% is formed partly according to a picture signal level XLL, X, XR or XRR corresponding to the halftone dot area rate 50%, 25%, 100% or 75%, respectively, while the center of the halftone dot is fixed.

In this embodiment described above, the haltone dot area may equally or unequally be divided. Further, the number of the divisions of the halftone dot area is not restricted to four, and any number may be applied.

When the halftone dot shown in Fig. 5 is recorded, if the central axis of every division is coincident with the center of the line image of the light beam having the same width as that of the division, the recording of the halftone dot by scanning can be performed by the scanning exposure means of Fig. 3 by using the aperture plate 3 having the V-shaped aperture without any trouble.

However, when the center of the light beam is off the central axis of the division, or more than one division are reproduced by one light beam, i.e. the parts separated in the width direction are recorded at the same time such as the divisions LL, L and R of Fig. 5, the scanning light beam should be separated by cutting a certain width of the light beam. In such a case, when the scanning exposure is carried out by using the aperture plate 3 having the V-shaped aperture, unnecessary parts CCR, as shown by a cross-hatching, are recorded.

In order to remove such a problem, the scanning exposure is performed by using an aperture plate 3' having a W-shaped aperture, as shown in Fig. 6, instead of the aperture plate 3 having the U-shaped aperture. The detail of this method is disclosed in Japanese Patent Publication No.

54-21123 (Japanese Patent Application No. 50-73082), and hence its description is omitted for the brevity of the explanation.

Next, a method of forming a halftone dot will be described. A method of producing a halftone dot without divising it into divisions is disclosed in Japanese Patent Laying-Open Specification No. 54-79701 (Japanese Patent Application No. 52-145683).

In this embodiment, an arithmetic circuitry which calculates data for forming an outline of a halftone dot having a halftone dot area rate 100%, is provided. When a halftone dot having an area rate 100% is produced, the entire data of the arithmetic circuitry is utilized. When a halftone dot having less than the area rate of 100% is formed, the outline data for a halftone dot having the desired dot area rate is obtained by controlling addresses and timings for a calculation order and then the center and the width of the desired halftone dot are calculated from the outline data obtained, thereby forming a halftone dot having the desired dot area rate.

In the present invention, the principle concept is the same as this conventional method, that is, instead of the arithmetic circuitry of the conventional method is provided a memory in which the outline data of every division for recording a halftone dot having the dot area rate 100% is stored for each screen angle. The data of each division is read out of the memory by controlling the addressing of the memory to obtain the outline data for recording a halftone dot having the desired dot area rate, and then the center and the width of the desired halftone dot are calculated depending on the outline data obtained in order to record the halftone dot having the desired dot area rate.

In Figs. 7a, 7b and 7c are shown examples of outline data of the four vertical divisions LL, L, R and RR of a halftone dot having a dot area rate 100% when a screen angle 8 is 0 , 45 or 15'.

Fig. 7a shows four outline data of four divisions LL, L, R and RR of the halftone dot having the area rate 100% when the screen angle a is 0'. The upper half and the lower half of the halftone dot having the dot area rate 100% are recorded by selecting the larger outline signals of the divisions RR or R and LL or L.

Fig. 7b shows four outline data of the four divisions LL, L, and RR, in the same manner as Fig. 7a, except that the screen-angle 0 is 45 . When the screen angle 8 is 45 , the width of the scanning line is fixed during recording the halftone dot as shown in Fig. 9A which shows a relation between a picture signal level on which the halftone dot area rate of the halftone dot to be formed depends, and an output signal of a dot section counter, by which the address for reading the outline data of the halftone dot out of the memory is determined when the screen angle is 45 , and therefore these outline data mean the date of the scanning line for recording the halftone dot having the dot area rate 100%.

Fig. 7c shows four outline data of the four divisions LL, L, R, and RR, in the same manner as Fig. 7a, except that the screen angle 8 is 1 5'. In this case, the tops of the data lines for the upper half and the lower half of the halftone dot are somewhat shifted to the left and the right hand sides. The upper half and the lower half of the halftone dot having the dot area rate 100% are recorded by selecting the larger outline signals of the divisions RR or R and LL or L.

When the screen angle H is - 1 5', outline date lines having optical antipode shapes of those of Fig. 7c are obtained and thus are omitted from Fig. 7. The outline data of the four divisions RR, R, L and LL shown in Fig. 7 are stored in memories 21-24 shown in Fig. 13, as hereinafter described Then, a method for forming a halftone dot having a dot area rate less than 100% from the outline data for recording the halftone dot having the dot area rate 100% described above will be described in connection with Fig. 8.

First, the division RR is described. In Fig. 8a, the outline data for recording the halftone dot having the dot area rate 100% is shown by a one-dotted line DFH. The address for reading out the outline data is calculated depending on the picture signal level XRR of the division RR and an output signal T of a dot section counter 31 which is hereinafter described with reference to Fig.

13.

A line passes through an address point (1 OO XRR) in parallel with the output data line DF, and intersections of this parallel line with the line DH and the diagonal FF' are designated as J and K. Then, a line which passes through the point K and an address point (99 + XRR) in parallel with the output data line FH intersects with the line DH at a point L. A line is extended from the point K in a direction perpendicular to the scanning direction and intersects with the transverse diagonal address line at an address point JRR.

When the output signal T of the dot section counter 31 is positioned in a range between zero and (100-XRR), no halftone dot is to be formed and no data is read out of a memory 21 which is hereinafter described.

When the output signal T of the dot section counter 31 is larger than (100 - XRR) and the screen angle is 0 or 45 , the address is always 99, as hereinafter described. But, when the screen angle is + 15 , and the output signal T is positioned in a range between the addresses (100 - XRR) and JRR depending on the picture signal level XRR, the data of the section DE is read out of the memory 21, thereby forming the outline JK of the desired halftone dot.

That is, in detail, in order to form the outline JK of the desired halftone dot, although the output signal T of the dot section counter 31 can directly be used as an address signal, however, according to the present invention for the simplifying the processing, the address T' = [T- OO OO-XRR)] is calculated and then the outline data of the section DE of the outline data DEF, which is determined by the picture signal level XRR, is read out of the memory 21 by the address obtained.

Then, when the output signal T of the data section counter 31 is positioned in a range between the addresses JRR and (99 + XRR), the period EG is skipped over and accordingly the outline data of the section GH is read out of the memory, thereby forming the section KL of the desired halftone dot. That is, the address [T + (100 - X)] is calculated and then the outline data of the section GH of the outline data FGH is read out of the memory 21 by the address obtained.

When the output signal T of the dot section counter 31 is positioned in a range between the addresses (99 + XRR) and 199, no halftone dot is to be formed and therefore no data is read out of the memory 21.

If the desired halftone dot is formed by these data, the upper half part defined by the points (11 O-XRR), J, k, L and (99 + XRR) is produced.

Next, the division R is described. In Fig. 8b, the outline data having a trapezoidal shape for recording the halftone dot having the dot area rate 100% is shown by a broken line MNRS which has the same shape as the trapezoid ODH199 of Fig. 8a. The address for reading out the outline data is calculated depending on the picture signal level XR of the division R and the output signal T of the dot section counter, in the same manner as described above.

A line passes through a point V having an address (100 - XR) in parallel with the output data line MN, and intersections of this parallel line with the line NR and the longitudinal diagonal are designated as W and K'. Then, a line which passes through the point K' and a point Z having an address (99 + XR) in parallel with the output data line RS, intersects with the line NR at a point Y. A line is extended from the point K' in a direction perpendicular to the scanning direction and intersects with the transverse diagonal address line MS at an address point J.

When the output signal T of the dot section counter 31 is positioned in a range between zero and (100 - XR), no halftone dot is to be produced and no data is read out of a memory 22 which is hereinafter described.

When the output signal T of the dot section counter 31 is larger than (100 - XR) and the screen angle is 0 or 45 , the address is always 99, in the same manner as described above.

Then, the screen angle is + 15 , and the output signal T of the dot section counter is positioned in a range between the addresses (100 - XR) and JR depending on the picture signal level XR, the address [T-(1 OO - XR)] is calculated and then the outline data of the section MNP of the outline data MNX, wherein the distance NP equals the distance WP, is read out of the memory 22 by the address obtained, thereby forming the outline VWX of the desired halftone dot.

When the output signal T of the dot section counter 31 is positioned in a range between the addresses JR and (99 + XR), the address T" = [T+ (100 - X)3 is calculated, and then the outline data of the section ORS of the outline data XRS, wherein the distance QR equals the distance XY, is read out of the memory 22 by the address obtained, thereby forming the outline XYZ of the desired halftone dot.

Then, when the output signal T is positioned in a range between the addresses (99 + XR) and 199, no halftone dot is to be formed and thus no data is read out of the memory 22.

If the desired halftone dot is formed by these data, the trapezoid VWYZ is formed.

In this case, the upper half part of the desired halftone dot is made from the outline data of the divisions RR and R by selecting the larger outline data, thereby obtaining the halftone dot defined by the points V, W, J, K, L, Y and Z. The lower half part of the desired halftone dot is formed from the outline data of the divisions L and LL in the same manner as described above.

Although the explanation has been carried out with respect to the screen angle 15 , however, when the screen angle is0' or - 15', the desired halftone dot can be made in the same manner as described above, as readily suggested from Figs. 9b and 9c which show a relation between a picture signal level on which the halftone dot area rate of the halftone dot to be formed depends, and an output signal of a dot section counter, by which the address for reading the outline data of the halftone dot out of the memory is determined when the screen angle is - 15 or 0'.

When the screen angle is 45 , the procedure is simpler than the above description. That is, as shown in Fig. 9, a halftone dot whose dot area rate or width directly depends on the picture signal level X, is to be made, and thus, when the output signal T of the dot section counter 31 satisfies the following formula (100 - X)T(99 + X), the picture signal level X is output as an address signal.

To sum up, when the screen angle 8 is i 1 5 or 0 , in the division RR, the other divisions R, L and LL are carried out in the same manner as the division RR, the address (AD-RR) for the division RR by which the output data is read out of the memory 21, is determined depending on the output signal T of the dot section counter 31 as follows.

(1) O#T < (100X88).. ..(AD-RR)= O (Il) (100 - XRR)TJRR . (AD-RR) = T-(100XRR) (III) JRR < T(99 + XRR (AD-RR) = T + (100 - XRR) (IV) (99 + XRR) < TC1 99 (AD-RR) = O In this embodiment, the position of the point JAR varies depending on the dot area rate of the desired halftone dot to be formed, as described above in connection with Fig. 8, and its examples are shown in Figs. 1 Oa, lOb and 1 Oc when the screen angles are 0 , 45 , 15 and -15".

When the screen angle is 45 , in the division RR, the other divisions R, L and LL are performed in the same manner as the division RR, the address (AD-RR) is determined depending on the output signal T of the dot section counter 31 in the similar manner to the above description as follows.

(I) 0~T < (100XRR).. . ..(AD-RR) = O (Il) (100 XRR)TCJRR ... . .(AD-RR) = XRR (Ill) JRR < T(99 + XRR).... ...(AD-RR) = XRR (IV) (99 + XRR) < T1 99 (AD-RR) = O Now assuming that the outline data of the divisions RR, R, L and LL for the desired halftone dot, read out of the memory by the addresses obtained as described above are designated as (DT-RR), (DT-R), (DT-L) and (DT-LL), the desired halftone dot is an area defined by the lines of the signals U and L obtained by the following formulae (1) and (2).

U = max[(DT-RR),(DT-R)] (1) L = maxC(DT-L),(DT-LL)1 (2) Then, the upper half dot outline signal U and a limit signal (DT-LIMIT) hereinafter mentioned, are compared each other, and the smaller one is designated as a signal U'. The lower half dot outline signal L and the limit signal (DT-LIMIT) are compared each other, and the smaller one is designated as as signal L'.

U' = min(U,(DT-LlMlT)j (3) L' = minL,(lDT-LIMlT)i (4) When the halftone dot area rate is more than 50%, in general, each halftone dot protrudes to the adjacent halftone dot areas, and accordingly the multiple exposure is carried out in the protrudent areas. This is undesirable because of the dispersion of the light on the film, and the like. Further, when the halftone dot area rate is 100%, the entire area should be exposed.

Therefore, according to the present invention, as shown in Fig. 11, the halftone dot area is limited so that each halftone dot exposed having the dot area rate of more than 50% may slightly be overlapped to the adjacent halftone dots. Such a limit control is conducted by the limit signal (DT-LIMIT).

In Figs. 11 a, 1 1 b and 11 c, the limit area is shown by a broken line when the screen angle 8 is 0", 45 and 15 . In Fig. 1 Ic, a changed limit area shown by one-dotted lines extending in the direction perpendicular to the scanning direction, is preferably determined so as to simplify the machine and to minimize the overlapping areas of the halftone dots.

When the outline data (DT-LL), (DT-L) and (DT-R) are nought, the halftone dot surrounded by the lines of the signals U' and L' includes un unnecessary part, as shown by the broken lines in Fig. 1 2a. This is resulted by the fact that the signal L' is assumed to nought. In order to remove such un unnecessary part, the condition is determined in the following equation (5) to obtain a correct halftone dot, as shown in Fig. 1 2b.

L' = Rmax (5) When the outline data (DT-RR), (DT-R) and (DT-L) are nought, the following equation (6) is obtained in the same manner as above.

U' = - Lmax (6) The Lmax and the Rmax indicate the scanning pitch, as shown in Fig. 5.

Then, a shifting amount of the centre of the halftone dot to be formed away from the scanning line in parallel therewith when 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 scanning line when the screen angle is 15 , are determined. Data (DT-SHIFT) and (DT-SLOPE) represent the shifting amount and the slope, respectively. Hence, a distance S from the scanning line to the central axis of the halftone dot is given in the following.

S = (DT-SHIFT) + (DT-SLOPE) (7) Then, the outline data U" and L" for recording the upper half and the lower half parts of the halftone dot whose shifting amount and slope are determined, are exposed as follows.

U" = U' + S (8) L" = L' + S (9) Accordingly, the width and the central position of the halftone dot to be formed are given in the followings.

W = U' + L" In this equation, when the width calculated is smaller than zero, it is set to zero. Thus the following equation is obtained.

W = max[(U" + L"),OJ (10) U" P= (11) 2 In Fig. 1 3 there is shown one embodiment of a control means for performing a method of the present invention by using the scanning means of Fig. 3.

Address control circuits 11-14 calculate addresses for reading the outline data for recording divisions RR, R, L and LL of the halftone dot depending on the picture signal level X, out of the memories 21-24, respectively. In the memories 21-24, the outline data for recording the divisions RR, R, L and LL of the halftone dot having the dot area rate 100% when the screen angles 8 are + 15 , 0" and 45 , are stored, respectively. The read-out data are input to a data arithmetic circuitry 40.

A timing control circuit 30 comprising a halftone dot position calculation circuit outputs a start signal (DF-START) for recording each halftone dot and a shifting amount signal AX which represents a distance of the center of each halftone dot to be recorded away from the position of the recording head in the direction perpendicular to the scanning direction, in synchronization with the rotation of the recording cylinder.

The dot section counter 31 divides the halftone dot area into a plurality of numbers such as 200 in the direction of the scanning direction, and counts the number of clock pulses of the corresponding number 200 to output the signal T for recording the desired halftone dot depending on the picture signal level X, as shown in Fig. 14a. Further, when the halftone dot area is limited in the direction of the scanning direction, the dot section counter 31 can control the output signal T corresponding to the unnecessary parts to zero so that the output data of the memories 21-24 may be zero.

A slope memory 33 stores the slope data (DT-SLOPE for inclining the halftone dot with respect to the scanning line when the screen angle is :::: + 15 . The slope memory 33 is addressed by the output signal T of the dot section counter 31 to output the slope data (DT SLOPE, as shown in Figs. 1 5a and 15b, which are sent to the data arithmetic circuitry 40.

When the screen angle is 0 or 45 , there is no need to incline the halftone dot, and hence the output data of the slope memory 33 is controlled to be always zero.

A limit memory 34 stores the limit data (DT-LIMIT) for limiting the halftone dot area as described above. The limit memory 34 is addressed by the output signal T of the dot section counter 31 to output the limit data (DT-LIMIT), as shown in Figs. 16a, and 1 6b and 16c, when the screen angle 8 is + 15 , 0" and 45 , respectively, thus the read-out data being input to the arithmetic circuitry 40.

A shift memory 35 stores the shift data (DT-SHIFT) which represents the shifting distance of the center of the halftone dot from the scanning line in the direction perpendicular to the scanning line when the screen angle is 0 or 45 . The shift memory 35 is addressed by the shifting amount signal A of the timing control circuit 30 to output the shift data (DT-SHIFT) which is sent to the data arithmetic circuitry 40. The relation between the shift data (DT-SHIFT) and the shifting amount signal AX as the address signal is expressed in the following simple equation, wherein K means a factor of proportionality.

(DT-SHIFT) = K.AX The data arithmetic circuitry 40 selects the larger ones of the outline data (DT-RR) or (DT-R) and (DT-L) or (DT-LL) for recording the upper half and the lower half parts of the desired halftone dot, and then, as occasion demands, it selects the smaller ones of the outline data or the limit signal (DT-LIMIT) and adds the slope data (DT-SLOPE) or the shift data (DT-SHIFT) to the smaller data selected, thereby calculating the central position and the width of the desired halftone dot.

In Fig. 1 7 there is shown one embodiment of the address control circuit 11 for the division RR of Fig. 1 3. The other address control circuits 12-14 have the same contruction and functions as the one 11.

A subtractor 50 subtracts the picture signal level XRR of the division RR from the fixed number 100 to obtain the output signal (100 - XRR) which is sent to a latch 55 and is latched there during the sampling period so as to maintain the picture signal level.

The output signal of the latch 55 is sent to intput terminals A of a comparator 60, a subtractor 65 and an adder 66. The output signal T of the dot section counter 31 is sent to input terminals B of the subtractor 65 and the adder 66. In the subtractor 65 the calculation [T - (100 - XRR)] is carried to obtain an output signal which is to be sent to an input terminal A of a selector 70. In the adder 66, the calculation [T + (1 O0 - XRR) is carried out to obtain an output signal which is to be fed to an input terminal B of the selector 70.In the comparator 60, the signal (100 - XRR) and the output signal T of the dot section counter 31 are compared, and then, when the output signal T is at least the signal (100 - XRR), a high level signal is output to an input terminal A of an AND gate 67.

An adder 51 adds the fixed number 99 and the picture signal level XRR to obtain the output signal (99 + XRR) which is sent to a latch 56 and is latched there during the sampling period so as to maintain the picture signal level.

The output signal of the latch 56 is fed to an input terminal A of a comparator 61, and the output signal T is sent to an input terminal B of the comparator 61. When the signal ,(99 + XRR) is at least the output signal T, the comparator 61 outputs a high level signal to an input terminal B of the AND gate 67.

The output terminal is connected to a control terminal of a gate 71, and, when the output signal T and the picture signal level XRR satisfy the formula [(100 - X)=T'(99 + XRR)], the gate 71 is opened by a control signal of the AND gate 67.

A memory 52 stores the address variation JRR of the top of the desired halftone dot in the scanning direction depending on the dot area rate when the screen angle is i 1 5', as shown in Fig. 10, and the address variation JRR is read out by the pitch signal level XRR and is sent to a latch 57 having the same costruction and functions as the latches 55 and 56. The output signal of the latch 57 is sent to an input terminal A of a comparator 62. The output signal T of the dot section counter 31 is fed to an input terminal B of the comparator 62. The comparator 62 outputs a control signal to a control terminal of the selector 70.

A latch 58 latches the picture signal level XRR fed during the sampling period so as to maintain the picture signal level. The output signal of the latch 58 is sent to an input terminal C of the selector 70. A control signal for the screen angle 45"a is to be supplied to another control terminal of the selector 70. The output signal of the selector 70 is fed to the gate 71.

When the screen angle V is 45 , the control signal for the screen angle 45 is input to the selector 70, and the selector 70 outputs the signal fed to the terminal C. When the screen angle 8 is not 45 , no control signal for the screen angle 45 is input to the selector 70, and the selector 70 compares the data JRR and the output signal T of the dot section counter 31. Then, when the data JRR is at least the output signal T, the selector 70 output the signal fed to the terminal A, and when the data JRR is smaller than the output signal T, it outputs the signal fed to the terminal B.

In Fig. 18 is shown one embodiment of the data arithmetic circuitry of Fig. 1 3. Into a selector 80, the data (DT-RR), (DT-R) and -Lmax are input to its input terminals A, B and C. The selector 80 observes the data (DT-RR]), (DT-R), (DT-L) and (DT-LL) and selects one of the input data to send the selected data U to an input terminal A of a minimum value selector 85, as follows.

(a) when (DT-RR) = (DT-R) = (DT-L) = 0, the selector 80 selects the data -Lmax; (b) when (DT-RR)(DT-R), except the condition (a), it selects the data (DT-RR); or (c) when (DT-RR) < (DT-R), except the condition (a), it selects the data (DT-R).

The data (DT-LIMIT) is fed to an input terminal B of the minimum value selector 85 which selects the smaller data U or (DT-LIMIT) and sends the selected data U' to an input terminal A of an adder 87.

The data (DT-SLOPE) and (DT-SHIFT) are input to input terminals A and B of an adder 81 which adds the two data and outputs the added data S to an input terminal of the adder 87.

Then, the adder 87 adds the data U' and S to obtain the data U" according to the formula (8) described above, and it sends the data U" to input terminals A of an adder 89 and a calculator 90.

The data (DT-LL), (DT-L) and R-max are fed to input terminals A, B and C of a selector 82 which has the same construction and functions as the selector 80, and which observes the data (DT-LL), (DT-L), (DT-R) and (DT-RR), and selects one of the input data to send the selected data L to an input terminal A of a minimum value selector 86, as follows.; (d) when (DT-LL) = (DT-L) = (DT-R) = 0, the selector 82 selects the data -Rmax.

(e) when (DT-LLB(DT-L), except the condition (d), it selects the data (DT-LL); or (f) when (DT-LL) < (DT-L), except the condition (d), it selects the data (DT-L).

The data (DT-LIMIT) is also fed to an input terminal B of the minimum value selector 86 which selects the smaller data L or (DT-LIMT) and sends the selected data L' to an input terminal A of a subtractor 88. The added data S is sent from the adder 81 to an input terminal B of the subtractor 88. Then, the subtractor 88 subtracts the data S from the data L' to obtain the data L" according to the formula (9) described above, and outputs the data L" to input terminals B of the adder 89 and the calculator 90.

The adder 89 adds the data U" and L" to output the added data U" + L" to a gate 91 and a level detector 92. The level detector 92 detects whether the data U" + L" is positive or negative and it controls the gate 91 so as to close it only when the data U" + L" is negative. Thus, the gate 91 outputs the data U" + L" as a width signal representing the width of the halftone dot to be formed when the data U" + L" is positive.

The calculator 90 conducts a calculation U" - 2 and always outputs a position signal representing the central position of the halftone dot to be formed. When the data U" + L" is negative, no width signal is output, and hence no halftone dot is recorded.

In Fig. 1 9 there are shown other examples of outline data of the four vertical divisions when the screen angle 8 is 0 , 45 or 15 , which are used in another method according to the present invention, instead of those shown in Fig. 7.

In this embodiment, the equations (1) and (2) described above are modified to the following equations (1') and (2').

U = (DT-RR) + (DT-R) (1') L = (DT-LL) + (DT-L) (2') The selector 80 selects one of the data input as follows.

(g) when (DT-RR) = (DT-R) = (DT-L) = O, it selects the data -Lmax; or (h) in the other conditions, it selects the data [(DT-RR) + (DT-R)].

The selector 82 selects one of the input data as follows.

(i) when (DT-LL) = (DT-L) = (DT-R) = O, it selects the data -Rmax; or (j) when in other conditions, it selects the data [(DT-LL) + (DT-L).

In the embodiments described above, of course, the screen agnle is not restricted to 0 , + 15 and 45 , any screen angle is applicable.

Although the present invention has been described with reference to preferred embodiments thereof, however, various chages and modifications can be done by those skilled in the art without departing from the scope of the present invention.

For example, since the output signal of the memories and the address signal for them are connected to each other in a primary relation, and hence arithmetic circuits which outputs a signal having a primary relation to an address signal may be used instead of the memories.

Further, instead of the acoustooptical deflector elements of Fig. 3, a pivot mirror or a rotary mirror can be used for reflecting the light beam.

The present invention can be more effectively applied in connection with the invention disclosed in Japanese Patent Laying-Open Spedification No. 56-19056 (Japanese Patent Application No. 54-94275) when an original picture including a picture pattern, a character and a letter is reproduced. In this case, the tint laying of all of the picture pattern, the character and the letter can be carreid out in the same time.

Claims (5)

1. A method for recording a halftone picture by scanning, wherein, when the halftone picture is reproduced on a photosensitive material by a light beam, a brightness and a width of the light beam are properly controlled by a picture signal obtained by scanning an original picture, characterized in that each halftone dot area is divided into a plurality of divisions, and a halftone dot is recorded in every division depending on a gradation variation of every division.

2. A method as defined in claim 1, wherein the halftone dot area is limited so that each halftone dot exposed having the dot area rate of more than 50% may slightly be overlapped to the adjacent halftone dots.

3. A machine for recording a halftone picture by scanning, wherein, when the halftone picture is reproduced on a photosensitive material by a light beam, a brightness and a width of the light beam are properly controlled by a picture signal obtained by scanning an original picture, comprising means for producing an outline signal of a halftone dot from a plurality of divisional signals corresponding to divisions obtained by dividing a halftone dot area, means for producing a recording signal from the outline signal and a screen angle signal, means for producing a width signal of the halftone dot from the recording signal, and means for producing a position signal of the halftone dot from the recording signal.

4. A method according to claim 1 substantially as hereinbefore described with reference to and as illustrated in Figs. 2 to 1 9 of the accompanying drawings.

5. A machine according to claim 3 substantially as hereinbefore described with reference to and as illustrated in Figs. 2 to 1 9 of the accompanying drawings.