GB2129650A - A method and machine for scanning and recording a picture - Google Patents

Abstract

Where a linearly moving reading or recording head, describes a spiral path over the rotating drum carrying the original or recording sheet, skew distortion (Fig. 1b) can occur. Such distortion is removed by moving the head in a line (C) lying in a plane parallel to the cylinder axis and at an angle ( theta ) to said axis. <IMAGE>

Description

SPECIFICATION A method and machine for recording a halftone picture by scanning This invention relates two a cylindrical picture scanning or recording method suitable for practice in a picture scanning and reproducing machine such as color scanner or the like as well as a machine adapted to practice the scanning or recording method.

First of all, the recording method will be described.

The rotating-cylinderscanning method is generally adopted as a picture recording method suitable for practice in a picture reproducing machine such as color scanner orthe like.

The rotating-cylinderscanning method requires a recording machine which is composed of a cylinder rotating art a high speed, a recording head movable relative to the cylinder in a subscanning direction or in the direction of the cylinder axis, and drive means.

The above rotating-cylinder scanning method is accompanied by two problems, firstly in the time required for scanning and secondly in the resolution.

Longertime is required for scanning if the number of scanning lines is increased in order to improve the resolution. The term "the number of scanning lines" as used herein means a value which indicates how many scanning lines are contained per unit length in thesubscanning direction or axial direction ofthe cylinder. Fine details of an original picture may be reproduced better as the number of scanning lines increases. However, it is necessary to spend longer time for scanning as the number of scanning lines increases.

Accordingly, it has been proposed to shorten the time required for scanning by arranging a plurality of recording light beams in the axial direction of the cylinder.

Fig. 1 (a } illustrates a cylinder 1 having a radius R and a recording surface of a width B, which cylinder 1 is rotated at a constant speed. Fig. 1 (b) is a development of a recording film 2.

The recording film 2 is placed on the cylinder 1 by an adhesive tape orthe like, while using punched aperturesformed along the leading edge of the recording film 2. A desired picture can be recorded on the entire surface of the recording film by causing a recording head, which is equipped with a unillustrated, for example, four light sources or light guides (hereinafter called "light sources") so asto radiate independently-modulated four light beams from the four light sources respectively, to subscan at a constant speed in a direction indicated by the arrow b while rotating the cylinder 1 at a constant speed in a direction indicated by the arrow a.

Assuming now that the width of the unit scanning line of a single light beam from the recording head and the number of beams are respectively P (the width of each picture element) and m (four beams in Fig. 1), scanning lines extend oblique and, when each scanning line has run once all over the circumference of the cylinder 1, its lead angle 0 is expressed by the following equation on the basisofthe distance MP advanced in the axial direction.

e = tan 12zP - 6 (mP 2FR) Therefore,the lead angle 6 becomesgreaterand the recorded picture is hence more distorted asthe number of beams m increases.

In a picture reproducing machine ofthe above sort, picture signals are, however, fed to the recording head by mounting an original picture on an original picture cylinder and reading the original picture while moving the reading head in the subscanning direction. Therefore, the obliqueness of the picture, which obliqueness occurs due to the presence of the aforementioned lead angle 6, can be automatically compensated.

When feeding orthogonal picture signals and obtaining a reproduced picture with a good geometrical accuracy at a recording unit ofthe cylindrical scanning machine, the X-Y orthogonal picture sing als must first all be converted to X'-Y' oblique coordinate system data (oblique angle: 6). However, itis noteasyto carryoutthe coordinatetransformation by electrical means.

The so-called intermittent pitch shifting method has been observed to effect such a coordinate transformation. However, the intermittent pitch shifting method is costly to practice and is not suited for effecting such a coordinate transformation art a high speed.

Here, it may be contemplated to obtain a reproduced picture as if the X-axis on the surface ofthe recording film 2 has been made equal to the oblique angle 6 occurred with respect to the Y-axis as shown in Fig. 2(a), by shifting the feed timing ofthe picture signals ahead by one picture element along the main scanning linewheneverthe recording head is moved by a certain specific distance in the subscanning direction so that the distorsion ofthe reproduced picture, which distorsionwould otherwise occur due to the lead angle 6may be corrected.

In such a conventional stepwise coordinate correction method in which distorsion in data of an oblique coordinate system is corrected by shifting the feed timing of picture signals, the number m of light beams from the recording head becomes unavoidably greater and the oblique angle 6 increases as the scanning width mP per each single rotation of the cylinder becomes wider.

The above described stepwise coordinate correc tion method is thus accompanied by such a draw back that, as the oblique angle 8 increases, distorsion of a linear picture takes place frequently along the sub scanning line and the extent of such distorsion is as much as exactly one picture element, namely, is considerably great.

The above drawback may be improved to a certain extent, for example, by correcting the timing of picture signals along the main scanning line either from one picture element to another orfrom a few picture elements to the nextfew picture elements in the subscanning direction; or by correcting the timing of such picture signals eitherfrom one rotation ofthe cylinder to another orfrom a few rotations of the cylinderto the next few rotations of the cylinder as illustrated in Fig. 2(b) or Fig. 2(c) respectively.

However, a clock required for effecting such timing correction must have an extremely high level of resolution relative to the frequency of each single rotation ofthe cylinder. Therefore, it is impossible to practice the above correction method in a current high-speed picture reproducing system.

The present applicantsfiled on October2, 1982a Japanese patent application on a method entitled "Method for Correcting Distorsion of Picture Recorded in Picture Scanning and Recording Machine".

This method however requires somewhat complex circuitry.

With the foregoing in view, the present invention has as its principal object the provision of a cylindrical picture recording method which can reproduce a picture without distorsion from picture information input as orthogonal data, orwhich at least offers improvements in this respect.

Another principal object of this invention is to provide a system adapted to practice the above cylindrical picture recording method.

In one aspect ofthis invention, there is thus provided a methodforscanning and recording a picture, which method comprises moving a reading or recording head over a read-in scanning or recording cylinderwhich is driven and rotated, in a plane parallel to the axis ofthe cylinder, and in a direction extending at an angle 6 with the axis of the cylinder.

In another aspect of this invention, there is also provided a system for scanning and recording a picture, which system comprises means adapted to move a reading or recording head over a read-in scanning or recording cylinder which is driven and rotated, in a plane parallel to the axis of the cylinder, and in a direction extending at an angle with the axis ofthe cylinder.

An embodiment ofthe invention will now be described by way of example with reference to the accompanying drawings in which: Fig. 1 (a) and 1 (b) are respectively a perspective view and development illustrating a previous cylinder-type recording system; Fig. 2(a) through Fig. 2(c) show reproduced pictures obtained respectively in accordance with previous methods, Fig. 3(a) through Fig. 3(c) are a perspective view, cross-sectional view and development of a cylinder in a cylinder-type recording system, which perspective view, cross-sectional viewand developmentwill be referred to explain the method ofthis invention; Fig. 4 is a view showing a reproduced picture obtained in accordance with the method ofthis invention;; Fig. 5(a) is a schematic view of an input scanning unit and Fig. 5(b) is a development of an original picture applied overthe circumferential surface of a cylinder; and Fig. 6 is a simplified block diagram of a picture scanning and recording machine equipped with a cylinder-type input scanning unit and another picture signal input unit.

Figs. 3(a) through 3(c) illustrates one example of a cylir -' i useful in the practice ofthe method accord ing to this invention. A recording film 12 is mounted as a photo-sensitive material over a cylinder 11, which has a radius Rand a recording surface of a width B, Making use of register apertures 1 2b the upper extremities of which are aligned along a line extending in parallel with the upper edge 1 2a of the film.

In an unillustrated recording machine, a recording head equipped with exposing light sources for radiating for example m streams of fine light beams in such a way that it is movable in a plane parallel to the axis ofthe cylinder 11 and along a straight line c which extends at an oblique angle 6 with the axis of the cylinder 11.

Here, it is preferred to arrange the m pieces of exposing light sources in the same direction as the moving direction of the recording head, namely, in a direction which extends atthe angle 6 with the axis of the cylinder 11. However, the above manner of arrangement of the exposing light sources is not essential, because no significant distorsion occurs when the cylinder has rotated only once or so.

The cylinder 11 is rotated for example at a constant speed in a direction indicated bythe arrow a. The recording head adapted to radiate m streams of exposing light beams in parallel to one another is moved in a plane parallel with the axis of rotation of the cylinder 11 ,with a lead angle equal to the oblique angle 6 relative to a straight line which extends in parallel with the axis of rotation of the cylinder 11.

Accordingly, the entire surface of a recording film 12 shown in Fig. 3(c) isscanned oblique atthe oblique angle 6 with a side edge 1 2c of the film (here, the side edge 1 2c has been assumed that it is aligned exactly in the circumferential direction ofthe circumferential surface ofthe cylinder 11). thus, them lines of the scanning lines draw multiple helices and are capable of recording and reproducing the desired picture.

Let's now assume thatthe lead angle ofthe multiple helices and the width to be exposed by a single exposing light beam bee and P respectively, the lead angle 6 may be represented bythefollowing equation on the basis of a distance mP over which the recording head capable of radiating m beams moves in the X-axis direction wheneverthe cylinder 11 is rotated once.

8=tan-l (1) Inthe above case,the reproduced picture is recorded on the recording film 12 and the X- and Y-a,xes ofthe orthogonal system have respectively been turned by the angle 6 relative to the upper edge 1i2a and side edge 12cofthe recordingfilm 12 if picture signals fed to the recording machine are orthogonal data.

Winen making for example a printing plate by applying the recording film 12 firmly to a printing plate material and then exposing the printing plate material to lightthrough the recording film 12, the obliqueness ofthe picture can be corrected if the recording film 12 is arranged oblique at the angle Oso asto compensate the obliqueness. Alternatively, the recording film 12 may be applied around the circumferential surface of the cylinder 11 by making the recording film 12 oblique bythe lead angle 6 in advance.

The recording head is generally able to output light beameforexamplefrom laser sources, LEDsorthe like arranged in multiplicity and in parallel with one another and modulated independently so thatthe recording film 12 is exposed to the light beams to reproduce a picture on the recording film 12. It is moved in a plane parallel to the axis of rotation ofthe cylinder 11 and in a direction oblique at the angle 6 with the axis so thatthe locus of movement of the recording head indicates, strictly speaking, such a helical motion as extending around the cylinder 11.

By approximating the above helical motion by such a linear motion C as shown in Fig. 3(a), the structure of the drive meansforthe recording head may be simplified here.

Accordingly, a discussion will hereinafter be made on the deviation which occurs in the distance from the circumferential surface ofthe cylinder when the locus of movement of the recording head is approximately bythe linear motion C.

Supposing that the recording head has assumed the right position at the widthwise center of the cylinder 11 and, when the recording head has come to either one of both ends ofthe cylinder 11,the upward or downward deviation ofthe optical axis is express ed by H, H may be represented by the following equation.

B H = 2 tan o (2) where B means the maximum subscanning length.

Here, the recording head produced a deviation 5, which is represented by the following equation, with respect to its distance from the circumferential surface ofthe cylinder 12.

6 = R(1-cos o() (3) whereocmeansthecentral angle shown in Fig. 3(b).

On the other hand, with respect to each point of exposure on the surface ofthe recording film 12, the deviation A caused byS in the Y-axis direction is expressed by the following equation.

A = - H (4) Itwill hereinafter be made clearthatthe deviations 5, A represented respectively by the equations (2) and (3) may be ignored when the oblique angle 6 is not so large.

The deviation A which occurs in the Y-axis direction on the surface of the recording film 12 is represented by the following equation.

where m = 10, 2nR = 500 mm (20 inches), P = 0.025 mm (10-3 inch) and B = 400 mm (16 inches} for example, the maximum value of cx, namely ocmax is about4nx 10A radian. On the other hand, a,,, is 3xr2 x l0~9mm', b 0.03,am.

Accordingly, the deviation A may be ignored without raising any problem.

The deviation a in equation (3) relates to the depth error of the focus point of the recording head. Since smax = R(1 - cost ) i R. d max 2 the maximum value omaxoftheabove deviation is 2n x 10-5 mm = 0.06 pm where the above exemplary figures are used again. Accordingly, the deviation 8 may be ignored without encountering problems.

As has been described, the present embodiment can provide a cylindrical picture recording method which permits to obtain reproduced pictures with ease because orthogonal picture signals can be reproduced free of distorsion without need for shifting electrically the feed timing of the signals by making the moving direction of a recording head slightly oblique to the axis of a cylinder.

Bythe way, the plurality of exposing beams was employed intheabove embodiment. Need less to say, the above method can be practiced even when only one beam (of a large diameter) is used.

In the above description, the present invention was applied to the picture recording side. The present invention may be applied to the reading side of pictures, in other words, to the scanning side.

Next, a description will be made applying the present invention to the reading side.

In an inputscanning unitwherean original picture is placed around a rotary cylinder and picture signals are read in, it is also possible to obtain picture signals at the same time, the number which picture signals is equal to the number of photo detectors, by arranging the photo detectors in a reading head along the subscanning direction so as to focus images of the original picture on the light receiving surfaces of these photo detectors by means of an imaging lense and moving the reading head in the axial direction of the cylinder at a speed predetermined relative to the rotation ofthe cylinder.

As examples ofthe plurality of photo detectors provided in the reading head, there are array-type solid-state pickup devices. Besides, separate-type sensors may be arranged or an optical path may be divided by means of mirrors or prisms into a plurality of optical paths which are then respectively led to separate photomultipliertubes or the like.

Here again, it is preferable to arrange such photo detectors in the same direction as the moving direction of the reading head similar to the aforementioned exposing light sources.

By arranging the photo detectors in the above manner, it is possible to shorten the time required for scanning without lowering the resolution.

Fig. 5(a) is a schematic illustration of the entirety of an input scanning unit in which four photo detectors 17 are provided. Fig. 5(b) is a development of an original picture applied on the circumferential sur face of a cylinder. In fig. 5(a), numerals 13 and 14 indicate an input scanning cylinder and an original picture or a manuscript respectively. Designated at numeral 15 is a reading head, whereas numerals 16 and 17 indicate a lens and the photo detectors respectively.

Here again, the co-ordinates are not orthogonal upon reading the original picture if the moving direction ofthe reading head 15 is coincided with the axial direction ofthe cylinder.

Accordingly, the reading coordinates can be made orthogonal by inclining the moving direction ofthe reading head 15 at the lead angle 6 with the axis of the cylinder as described above.

The above arrangement ofthe reading head 15 has brought about a valuable merit that the problem of picture distorsion does not occur even if a picture signal obtained at first in the above-described input scanning u nit is synthesized with another picture signal ofthe orthogonal coordinates system obtained from another unit and the resulting synthetic picture signal is then output.

Generallyspeaking,pattem signals and picture signals produced utilizing computers orthe like as if obtained from function generators or picture signals supplied from character generators, halftone pattern generator orthe like are fed as signals of the strict orthogonal coordinates system.

When overlapping these picture signals with picture signals from a cylindrical input scanning unit to reproduce a picture, an extremely severe value is required forthe tolerance to picture distorsion.

An application of the method of this invention to an input scanning unit permits direct reading of picture signals ofthe orthogonal coordinates system even if the input scanning unit is ofthe cylinder-type, thereby exhibiting an important merit that no serious problem occurs when the resultant picture signals are overlapped with picture signals of another orthogon al coordinates system.

Fig. 6 illustrates one embodiment ofthe structure in which the method according to this invention has been applied to the input scanning unit.

An input scanning unit 21 scans and reads an original picture 14 applied around a cylinder 13 by means of a reading head 15 so as to obtain picture signals, which arethen supplied to a signal processing circuit22sothattheymaybe converted to output signals of desired forms.

On the other hand, picture signals obtained from a picture signals input circuit 23 of a picture input unit (for example, digitizer), character generator or the like which generates picture signals of another orthogonal coordinate system ofthe input scanning unit 21 are inputtogetherwith picture signals from the above-described signal processing circuit 22 to a discrimination circuit 24 for synthesizing a picture.

Based on signals from the discrimination circuit 24 which outputs operation results on either one ofthe input picture signals or both of the input picture signals in accordance with designated synthesis conditions, a picture is recorded at a picture recording unit 25.

It is desirous that the picture recording unit 25 provides a picture of the orthogonal coordinates system. As one way for obtaining such a picture at the pict - recording unit 25, it may be contemplated to adoptthe method ofthis invention which method was described as the first embodiment of thins invention in the above.

In the above case, the lead angles 6 ofthe picture recording unit25and input scanning unit 21 are determined respectively by the number of light beams from the recording head, the number of photo detectors provided in the reading head and the number of scanning lines as well as the diameters of the recording cylinder and original picture-mounting cylinder. However, it is not essential to make, for example, the number of light beams from the recording head equal with that of photo detectors provided in the reading head so long as the lead angles 6 ofthe picture recording unit 25 and input scanning unit 21 satisfy conditions required to obtain picture signals of orthogonal coordinates systems.

As simple multiplier means, it is extensively practiced to make the diameter of the original picture-mounting cylinder different from that ofthe recording drum. Besides,the numbers of light beams, photo detectors or scanning lines atthe recording side may be rendered differentfrom that at the scanning side.

If the latter multiplier means is employed,the method ofthis invention proposes to give a suitable lead angle 8 whenever such a change has been made.

This may however be effected by merely adjusting the angle (i.e., 6) of the subscanning axis because the locus ofthesubscanning motion ofthis invention is not a helix buta straight line. This is one of very important advantages ofthe embodiment of this invention.

Since it is desirousthatthe subscanning axis takes its correct position at a point as close as possible to the widthwise center of the cylinderwhen adjusting the angle ofthe subscanning axis, it is desired to shift both ends ofthe subscanning axis by a same distance in opposite directions while holding the subscanning axis at the widthwise center ofthe cylinder when changing the lead angle 6. However, the lead angle 6 may be satisfactorily adjusted even if the subscanning axis is shifted only at one end thereof. When adjusting the subscanning axis in the latter manner, it is preferred to effect the shifting ofthe subscanning axis in such a mannerthatthe subscanning axis comes to its correct position at the widthwise center of the cylinderwhen the average of a variety of necessary lead angles has been taken.

Certain preferred embodiments of the method according to this invention have been described above. Fromtheforegoing description, itis believed thatthe machine ofthis invention has also been understood.

Although the present invention has been shown and described with reference to the preferred embodiments illustrated in the accompanying draw ings,verious changes and modifications can be made thereto by those skilled in the art without departing from the scope of the present invention.

Claims (20)

1. A method for scanning and recording a picture, which method comprises moving a reading or recording head over a read-in scanning or recording cylinderwhich is driven and rotated, in a plane parallel to the axis ofthe cylinder, and in a direction extending at an angle 6 with the axis ofthe cylinder.

2. A method as defined in Claim 1, wherein a plurality of exposing light beams are radiated in parallel to one another from the recording head.

3. A method as defined in Claim 2, wherein a plurality of exposing light sources are arranged in a direction which extends at the angle 6 with the axis of the cylinder.

4. A method as defined in Claim 1, wherein a plurality of photo detectors are arranged substantially in parallel to one another in the reading head.

5. A method as defined in Claim 4, wherein the plurality of photo detectors are arranged in a direction which extends at the angle 6 with the axis of the cylinder.

6. A method as defined in Claim 1, wherein the method is carried out by additionally using a separate orthogonal input unit.

7. A method as defined in Claim 1, wherein the reading or recording head is most spaced from the cylinder at both ends of the cylinder and the distances between the reading or recording head and both ends ofthe cylinder as equal to each other.

8. A machine for scanning and recording a picture, which machine comprises means adapted to move a reading or recording head over a read-in scanning or recording cylinder which is driven and rotated, in a plane parallel to the axis of the cylinder, and in a direction extending at an angle û with the axis of the cylinder.

9. A machine as defined in Claim 8, wherein a plurality of exposing light beams are radiated in parallel to one anotherfrom the recording head.

10. A machine as defined in Claim 9, wherein a plurality of exposing lightsources are arranged in a direction which extends at the angle 6 with the axis of the cylinder.

11. A machine as defined in Claim 8, wherein a plurality of photo detectors are arranged substantially in parallel to one another in the reading head.

12. A machine as defined in Claim 11, wherein the plurality of photo detectors are arranged in a direction which extends atthe angle 6 with the axis of the cylinder.

13. A machine as defined in Claim 8, wherein a separate orthogonal input unit is additionally provided with machine.

14. A machine as defined in Claim 8, wherein the reading or recording head is most spacedofrom the cylinder at both ends ofthe cylinder and the distances between the reading or recording head and both ends of the cylinder are equal to each other.

15. A method according to claim 1 substantially as described herein with reference to Figs 3to 6 ofthe accompanying drawings.

16. A method according to claims 8 substantially as described herein with reference to Figs 3 to 6 of the accompanying drawings.

17. Amethodfprscanning and recording a picture substantially as described herein with refer enceto Figs 3 to 6 ofthe accompanying drawings.

18. A machine for scanning and recording a picture substantially as described herein with reference to Figs 3 to 6 of the accompanying drawings.

19. Amethodforscanning and recording a picture comprising any novel feature or combination offeatures disclosed in this application.

20. A machine for scanning and recording a picture comprising any novel feature or combination of features disclosed in this application.