Stereoscopic television
United States Patent 2209747

This invention relates to a system of the television type including a transmitter employing scanning means for scanning a picture in strips and converting the varying light intensities into 5' electric impulses by photo electrical devices, amplifying devices and other well known apparatus for...

Paul, Eisler
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Paul, Eisler
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This invention relates to a system of the television type including a transmitter employing scanning means for scanning a picture in strips and converting the varying light intensities into 5' electric impulses by photo electrical devices, amplifying devices and other well known apparatus for the radio or like transmission of the said impulses and receiving apparatus including well known electrical devices for reproducing the electo: tric impulses and scanning means for converting the impulses into strips of varying light intensity which build up the sent picture.

The invention relates more particularly to a television system which aims at producing stereo15' scopic or relief type image pictures. An attempt has been made to utilise the well known stereoscopic system of Dr. Hess in a strip television system. Briefly, in this method, two scanners, -e. g. iconoscopes are spaced about three inches apart and the one scans the odd vertical strips 1, 3, 5, 7, . . ., the other the even vertical strips 2, 4, 6, 8 . . .of the picture, the said strips being produced in their correct sequence by the cathode ray tube of the receiver. The picture is viewed through a vertical grating or adapter so arranged and disposed that one eye observes one set of strips whilst the other observes the other set to produce the Hess stereoscopic effect.

With such a system, it will be observed that each iconoscope scans only one half of the picture, which since the iconoscopes are spaced apart will be slightly different and will therefore be referred to as two sectional pictures. The frequency band required for radio transmission of the electrical impulses will be increased by this system compared with that required for nonstereoscopic work by the square of the number of sectional pictures viewed, as will be clear to those skilled in the art of television. The Hess system is also applicable only if viewed from a limited number of definite positions.

This present invention relates to a system of stereoscopic television utilising a vertical grating system preferably a parallactic stereogram system such as that invented by Clarence Whitney Kanolt of New York, N. Y., U. S. A., and known as the Kanolt system or a grating consisting of cylindrical lenses such as that described in the French Patent No. 745,942.

An object of this invention is to provide an increase in the number of lines or strips as compared with non-stereoscopic television with a minimum in the extension of the width of frequency band required for radio transmission.

A further object is to utilise a system and apparatus which will scan or explore each sectional picture completely without gaps so that the viewer obtains a view of a complete sectional picture.

A further object is to produce a picture which is of the relief image type over a wide viewing angle and so can be seen by a large number of viewers.

Another object is to produce a picture on the screen which is stabilized or is compensated for 1i6 lack of stability without loss of stereoscopic effect.

A still further object is to form on the receiving screen a true picture in relief of moving objects. 15; The novel features considered characteristic of this invention are set out in the appended claims, but same and further objects and advantages will be clearly understood from the following description having reference to the accompanying drawings illustrative of various methods of and apparatus for, carrying the invention into effect.

In the drawings: Figure 1 illustrates the well-known principle of the Kanolt line-grating. Figures 2 to 13 illustrate various apparatus employed in accordance with the invention and diagrams.

Figure 2 illustrates the exploring or scanning of several intermediate films, each of which is 30: taken from a different televising position and which are fed synchronously through the apparatus.

Figure 3 illustrates the analysis of a sectional picture into picture strips. Figure 4 illustrates the exploring of an intermediate film, containing an assembly of several sectional pictures taken simultaneously, and combined on a single film-strip.

Figure 5 shows a detail of a camera designed, 4 in accordance with this invention, for taking views for direct television purposes of one sectional picture.

Figure 6 illustrates a camera for taking a plurality of sectional pictures. Figure 7 is a diagram of the process of taking of objects which are in movement by means of several exploring organs of normal type, such as iconoscopes, or the like.

Figure 8 is a section through the picture screen g5 and grating at the receiver, in diagrammatic form.

Figure 9 illustrates the time characteristics of the horizontally deflecting oscillations of the cathode-ray tube of the receiver. 55I Figures 10 and 12 illustrate these same characteristics when line interlacing process is utilised.

Figure 11 is a front view of a section of the receiver picture screen with a diagram of the positioning of the ray deflecting organs of the cathode ray tube in relation to the direction of the grating (or picture) lines, and Figure 13 illustrates the fitting of a movable grating in front of the receiver picture screen. Figure 14 indicates diagrammatically apparatus constituting a complete system for carrying out the invention.

It is to be understood that the drawings are intended only to illustrate the various parts and circult characteristics diagrammatically in order to enable the invention to be readily understood.

Firstly, Fig. 1 is intended to illustrate the well known Kanolt grating system. In the example illustrated, four sectional pictures have been taken from four different angular positions each being split up into vertical strips. These strips are arranged in groups I, II, III . . . across the picture screen 5 with the strips I, 2, 3, 4, from the first, second, third and fourth sectional picture arranged adjacent and progressively across the screen. That is to say, the strip I of group II is the second strip of the first sectional picture and so on. In practice, there would be more than three groups. In front of the screen 5 is placed a grating 6, which is so gapped that an observer at a suitable distance from the screen will see the strips of one sectional picture with his left eye, and adjacent right hand strips of the next picture with his right eye. Thus an observer can see strips I with the left eye and strips 2 with right eye, or strips 2 with left and strips 3 with right eye or strips 3 with left and strips 4 with right eye. It will be clear that an observer can alter his angular position within an extensive space without losing the stereoscopic effect. The above system is of course well known and needs no further clarification. It is however of importance to realise that if in the line grating system two sectional pictures of square shape are produced, these are built up into a sectional picture of similar proportions necessitating the reduction of the strips into half either by cutting or optically before building up, and a feature of this invention is that the resultant similarly proportioned picture is built up by the dimensioning of the exploring and receiving element area.

The grating referred to above may be replaced by a cylindrical lens grating which also is well known, see for example, French Patent specification No. 745,942. The application of the above stereoscopic method to television gives rise to certain difficulties which are overcome by this present invention. It will however be assumed that the general laws governing grating stereoscopy apply uniformly to the various features of this invention. For convenience the application of the invention more particularly by the Kanolt system is described below, but the variations necessary for its application by other systems on the same principle, e. g. systems employing lens gratings will be apparent to those skilled in the art.

When employing a television system for the reproduction of stereoscopic pictures in accordance with this invention, it is a feature that each sectional picture is explored or scanned completely without gaps between the strips or lines.

With the previously proposed method an example of which is disclosed by British Patent specification No. 413,894, alternate lines of each sectional picture only were scanned. The result of this present invention is achieved by dimensioning the picture exploring element e. g. the light spot area projected through a film by a Nipkow disc or the area of the cathode ray spot on the screen of the iconoscope so that the picture lines scanned are contiguous as shown in Fig. 3. In this figure there is shown a sectional picture A explored by the exploring element 9, which is assumed to be of circular shape, into vertical lines all of which correspond to the picture strips I of the groups in Fig. 1, in that they are reproduced on the receiver picture screen as strips I of the groups.

Assuming for convenience that the sectional pictures and the reproduced pictures are the same size, then calculation shows that the area of a picture element of a sectional picture is n times as large (i. e. n times as wide and of the same length) as the area of a picture element of the reproduced picture. The area of a picture element of the reproduced picture may be defined as the area covered on the reproducer screen by light during the time of transmission of one element of a sectional picture. The reproducing beam of rays has a diameter n times as small as the diameter of the beam exploring the sectional picture on the transmitter. The ratios of the areas of the beams, i. e. of exploring element and the reproducing element is n2:1 if they have the same shape.

The dimensioning of the exploring spot or element as above set out produces a marked advance in the art of stereoscopic television. For example, no picture lines are skipped or omitted and there is consequently no loss of picture content.

The spectator views, not merely a portion of a sectional picture, but the complete sectional picture, within the limits of detail determined by the dimensioning of the exploring picture element.

Secondly, the band of frequencies required for transmission is smaller than in the stereoscopic. television processes hitherto known, operated by skipping of lines in the course of scanning two different pictures, for the same number of lines in the reproduced picture. In the known systems the band increases with the definition and the number of sectional pictures at a rate which is much greater than in the process constituting the subject-matter of this invention, in which the number of sectional pictures does not decrease the dimension of the scanning picture element.

The following numerical example, based on data of a highly simplified character, will serve to illustrate the character of the frequency band required. If it is assumed that only two sectional pictures of square shape, containing each 100 picture lines, are scanned by an exploring element of square shape at the transmitter, and reproduced by a similar element at the receiver, by means of appropriate Nipkow discs, for instance, then in the system of scanning without gaps of each sectional picture in accordance with this invention, we obtain a number of picture elements of 100x100=10,000 per sectional picture, and accordingly a limit of modulation frequency of the television transmitter which is determined by the total number of picture elements of 20,000 (or twice 10,000, n i. e. the number of sectional pictures being 2 in this case). In the known method in which alternate lines are skipped, each picture must be divided into 100 lines and 100 spaces i. e. the exploring element is made one half the normal size and it therefore sustains twice the normal modulation in each line length. Thus each sectional picture affords 100 (lines) x 200 (picture elements in 1 line length)=20,000 picture elements and the two sectional pictures afford 40,000 picture elements. It will be seen therefore that the known method not only omits one half of each picture but involves a four fold (i. e. n2) increase in modulation frequency, whereas the present invention only requires an n fold increase.

In other words for the same modulation frequency, the present invention enables four sectional pictures to be used and this without any omission of lines. Another important advantage is that the present invention gives equal definition vertically and horizontally whereas the known method gives twice as good definition vertically as horizontally.

When the electrical impulses are received assuming that a square shaped screen or a disc adapted to build up a square shaped picture is employed, since the elements of the one picture interlace with those of the other, the composite picture will comprise 200 lines, and consequently the spot or picture element area in relation to the reproduced picture will be one half the area of the exploring element in relation to the explored sectional picture, since the heights of the two screens are equivalent while the line width in the reproduced picture is 1/n relatively to the line width of the explored sectional picture.

The foregoing dimensioning of the picture element sizes in accordance with this invention applies to all the methods and apparatus covered by this invention.

In order that the application of the invention may be more readily understood, reference is here made to Figure 14 which shows in one form a complete television system.

The object is viewed by n (e. g. 4) sets of the apparatus shown in Figure 7. These are arranged in a suitable series of angular positions with respect to the object O. A distributor D in turn connects each of 4 sets of brushes B1, B2, B3, B4 to suitable generators Gv, Gh. of vertical and horizontal deflecting potentials; if the latter are of mechanical type they can be driven from the same motor Mo as the distributor. The brushes Vd, Hd are connected to corresponding brushes Vc, He by an oscillating commutator which changes over the connections to the respective iconoscopes 23, 24 at the same time as the reflectors 21 are rocked so that while any iconoscope of a pair is being scanned the light from lens 20 is being thrown on to the other iconoscope. The change over needs to be intermittent and to do this a Maltese cross mechanism MC is stepped on once per revolution of the distributor D and is arranged to swing each reflector in alternate direction about its axis 22; for instance the reflectors may be biased to one position by springs and swung by cams on the Maltese cross shaft. It will be noted that the segment serving each brush set B only makes contact therewith for a corresponding fraction of each revolution of D; each iconoscope pair is thus actuated in turn and the scanning is done on a line interlacing principle, The Maltese cross mechanisms are timed to reverse the reflectors 21 during the periods the corresponding iconoscope pair is disconnected at D. If deemed desirable the lenses may also be provided with 70' shutters rotated synchronously with D to exclude light during the actual times of reversal of the reflectors.

The commutators and distributor D are also arranged to switch the output of the iconoscopes 75. in proper order to a modulator and amplifier, M, A, respectively, whence signals are radiated by antenna AE.

The receiver is in principle a line interlacing receiver which differs from the known receivers in two respects. The usual interlacing system interlaces two sets of lines only whereas the present receiver requires to interlace n sets of lines. This presents no difficulty being simply a question of ratio of line frequency to frame frequency. The second difference is that in the ordinary interlaced system each successive set of lines only contains 1/n (i. e. 1/2 in practice) of the whole picture whereas in the present invention every set contains the whole of the sectional picture.

But this again presents no difficulty being simply a question of relative horizontal proportions of the scanning and reconstructing elements. In effect the horizontal dimension of the reconstructing element must be 1/n that of the scanning element (ignoring any enlargement or reduction as between the scanned picture and the reproduced picture; if there is such enlargement or reduction, a corresponding factor is involved).

All this means in practice is that the reproducing element must be the same as if the system were one employing n times as many lines for ordinary non-stereoscopic television. As above noted however to avoid losing the stereoscopic effect a certain lateral margin must be provided which can be done in the simplest way by merely abstaining from coordinating the lines closely together or in other words, making the horizontal dimension of the element a little less than the value first mentioned. This will result in spaces between the lines themselves and between the 5: groups as in Figure 8.

The minimum complete receiver will include an antenna, AE, an amplifier Am, a detector Det, a generator Gv of vertical deflecting oscillations, a generator Gh of horizontal deflecting oscillations, and a cathode ray tube 48 and grating 50 as in Figure 13. This receiver operates on well known lines except for the two differences above noted which however require no additional or novel apparatus. In practice synchronizing must also be provided for, but the invention involves no features which prevent the use of the usual system in which the return parts of the saw tooth deflecting potentials are employed for this purpose, and filters provided in the receiver to filter out the synchronizing pulses and direct them to the respective oscillation generators.

Reference will now be made to Figs. 2 and 4 of the drawings which illustrate the transmission of scenes by the intermediate film process. In this process according to the invention, n sectional pictures are taken simultaneously by n filming cameras from different angular filming positions, or by one camera capable of taking n views of the same scene as seen from suitable different angular positions.

In Figure 2 four films are shown being scanned; a is an intermediate film containing all sectional pictures A derived from the first filming position, b is an intermediate film containing all sectional pictures B derived from the second filming position; similarly for films c and d. Films a, b, c and d are fed synchronously and continuously past respective Nipkow discs 8a, 8b, 8c and 8d, each with a series of apertures, which explore separately each of the films. Behind each of the films is fitted a photo-cell, and in front of each of the discs there is a source of light with a suitable optical system in the usual manner. All photocells or first amplifiers, which may be fitted independently for each photo-cell, act upon the joint main amplifier from which the signals are conveyed to the transmitter. The output terminals of all photo-cells or first amplifiers are, for this purpose, connected directly with the input terminals of the joint main amplifier, for instance. This result can also be obtained by coupling the outputs of all first amplifiers with the input of the main amplifier across trans10: formers. In this specification I have not illustrated usual transmitting and receiving circuits and apparatus, including provision for synchronizing if necessary, since such follow conventional lines, for example, circuits and apparatus such as are set out in the well known text book "Television Reception," M. von Ardene, translated by O. S. Puckle, London, 1936, may readily be employed.

The apertures in the discs are so displaced in relation to each other that only one disc scans at a given moment. The number of apertures with which each of these discs is provided is only one quarter of the number of the apertures made in a disc of ordinary type operated at the same number of revolutions for exploring completely a picture in an ordinary television process of non-stereoscopic type. As a consequence of this arrangement, the first picture line which is transmitted is derived from the sectional picture A, the second from the sectional picture B, the third from the sectional picture C, the fourth from the sectional picture D, the fifth again from A, the sixth again from B and so forth. The diameter of the apertures made in the discs, and con35: sequently of the picture elements obtained in the course of scanning is such that the picture lines of each sectional picture which are scanned are closely adjacent, as is shown by Figure 3.

Referring now to Fig. 4 the four different films 410 each bearing one sectional picture have been combined on one strip. The said strip is fed intermittently past a Nipkow disc 10 of usual form, which revolves at four times the normal speed, the speed of the film 10 also being four ,1; times normal.

One frame of sectional picture A is scanned first, then sectional picture B, then sectional picture E, then sectional picture D and the impulses are passed to the amplifiers of the transmitting apparatus. The signals are received by a receiver in which the time bases are so arranged to produce the correct interlacing of the picture lines in the order A, B, C, D on the receiver screen to conform with the form of picture in Fig. 1. The principle of this interlacing is of course well known in non-stereoscopic television c. f. British Patent specifications Nos. 381,898 and 423,101 and by suitably arranging the circuit of the time base controlling the picture 00 frequency at the receiver, the picture can be built up to the form disclosed in Fig. 1. The horizontally deflecting oscillation required to achieve this is of the type illustrated in Figs. 10 and 12 later described.

05 It is well known in ordinary film stereoscopy that if an attempt is made to produce a stereoscopic effect of moving objects by taking the sectional pictures at different instants a false or pseudo-stereoscopic effect results. This can be readily overcome according to this invention by making use of the intermediate film process but certain difficulties are present if the picture is televised directly especially when employing an interlaced line process.

Figures 5, 6 and 7 show a method of direct televising by iconoscopes or like devices. Fig. 5 shows an optical system for a television camera and it is assumed that four such cameras are employed. Each camera is designed to decompose optically the sectional picture which it takes 5, into strips representing the whole contents of the picture, and not merely 1/n of the total strips of the sectional picture. Suitable optical devices such as cylindrical lenses, concave mirrors or the like are provided to reduce the vertical dimension of the picture to the fraction of its original corresponding to the number of sectional pictures. Thus, if four cameras are employed the light of the picture will be reduced to one quarter. 12 and 13 illustrate optical con- 16 trivances for producing parallel rays and 14 illustrates a system of vertical cylindrical lenses for concentrating the sectional picture into picture lines on to a screen 15. The picture from each of the four devices I is then projected by a mirror system 16, 7I onto the photo-sensitive layer of an iconoscope or the like so that the first line of the first camera is followed by the first line of the second, third and fourth cameras and so on. Fig. 6 shows in diagrammatic form a composite camera for resolving four sectional pictures on to one iconoscope. The line pictures on the four screens 15a, 15b, 15c and 15d of the cameras I a, lb, lic and iId are projected by conven- "0 tional lens systems within the camera and omitted for clarity, the arrangement being such that the mosaic plate 18 of the iconoscope 19 receives the strips as above set out with reference to Fig. 5. The picture on the plate 18 will be s5 essentially the same as that appearing on the receiving picture screen, although it is, of course, reduced to one quarter (or to the nth fraction) of the height of the picture at the receiving end.

If the object taken is stationary, the mosaic plate 18 of the iconoscope 19 may be explored by any of the processes employed for this purpose, e. g. a cathode ray controlled by the usual time base. In the case of moving objects, the stereoscopic error which is due to the fact that the parts of the picture on the left of the picture, are, in between the scanning moments, illuminated for a period of time which differs from the period of illumination of the parts which are on the right, will be comparatively small if no interlaced line process is employed. If, on the other hand, such interlaced line process is employed, this error assumes proportions which are such that the device shown diagrammatically in Figure 7 must be employed for the camera described. If the camera is employed for the production of a television intermediate film, which is intended to contain the same strip-shaped pictures as the mosaic plate 18 of the iconoscope 19 of Figure 6, then the photo-sensitive coating of the television intermediate film takes the place of the mosaic plate 18 of Figure 6, and the iconoscope 19 is dispensed with.

Figure 7 is a diagrammatic illustration of a device allowing of the taking of stereoscopic television views of moving objects even if use is made of a line interlacing system. The televising appliance illustrated applies to one single sectional picture.

Part 20 is an optical system, and 21 is a mirror, which occupies, for the duration of one period, the position shown by full lines, and occupies, for the next duration of one period the position shown by lines of dashes, by pivotal movement of the axis 22. This may be done by means of a Maltese cross coupled to a shutter rotating in front of. the lens. Parts 23 and 24 are ordinary iconoscopes or devices of a like nature. With the axis 22 is also connected a commutator of suitable type, which will, during all or part of the time in which the mirror 21 is in the position indicated by full lines, connect the tube 24 with its sources of potential, or with a part of the same, and connect up the tube 23 during the period of time in which the mirror occupies the position indicated by lines of dashes. The result is obtained in this manner that each of the tubes is illuminated during a period of exposure, without being explored during this period, and that the exploring of each tube takes place during the period following its period of illumination, during which it receives no illumination. It will be clear that the inherent retentivity of the plate enables exploration to be accomplished in the manner.

A rotary deflecting oscillation generator (potentiometer, inductor, or the like), of wellknown type in itself, may be connected with one of the continuously operated parts, such as the 2Maltese cross, as may also be a distributor, combined with the commutator, which will not only connect up the tubes 23 and 24, which take only one sectional picture, such as A, but also the remaining six tubes, which take the sectional pictures B, C, and D, at a definite rhythm and at definite times.

The size of picture element employed in the course of exploring of the mosaic plates of the iconoscopes 23 and 24 is such that the whole picture is explored without gaps, and that the conditions illustrated on and in connection with Figure 3 apply. The exploring is carried out, either by the method shown in Figure 2, or in Figure 4, if use is made of a line interlacing process. The place of the iconoscope 23 or 24 can also be taken by the television camera shown by Figure 5.

Referring now to the receiver screen, it will be appreciated that the deflecting saw tooth oscillations producing the vertical lines and frames by deflecting the cathode ray should theoretically be linear, but since with apparatus at present employed it is impossible to produce such oscillations, means are provided, in accordance 50. with this invention to prevent slight deviations and like instability from spoiling the stereoscopic effect. Figure 8 is a diagrammatic section through the picture screen 5, and grating 6 fitted in front of same. The figure is similar to that illustrated in Fig. 1, except that between the groups, intermediate blank strips 25 are located.

There are also located between the strips themselves, blank spaces.

A sideways movement of the picture up to the width of the strip 25 can occur without the stereoscopic effect being lost, the effect to a viewer being merely that of a slight sideways movement of the picture. Without such strips the movement aforesaid would result in adjacent C0 strips of the groups becoming visible through the same grating aperture, or if the deviation occurs in a strip without the gaps between the strips there would be an overlapping of the strips.

The ratio of grating strip width to grating aperture width is also increased and the picture strips I and 4, located at the ends of the groups I, II, III etc. are visible through a wider angle. The use of such strips is particularly advantageous with a cylindrical lens grating of the type set 7.R forth in French specification No. 745,942 since otherwise the marginal picture strips I and 4 are located at or on the boundary of two adjacent cylindrical lens grating elements, which leads to difficulties from an optical point of view. This defect is now eliminated through the provision of strips without picture contents, and it becomes unnecessary to shut off these marginal strips by means of special devices.

Strips without picture contents may also be provided between the various vertical picture strips 1, 2, 3, and 4, simply by abstaining from co-ordinating the same very closely to each other, and a further sub-division of the margin of allowance of the horizontally deflecting oscillations is thereby provided. The stability of the horizontally deflecting oscillations is alone material from the point of view of stereoscopic effect.

Strips without picture contents are, according to this invention, produced on the receiving picture screen by means of a special formation of the deflecting oscillations, without requiring any extension of the frequency band of transmission.

These deflecting oscillations are illustrated by Figures 9 and 10, the amplitudes being shown as ordinates, and the time as abscissa.

Figure 9 shows a horizontally deflecting oscillation 26, consisting of a combination of a normal saw-tooth deflecting oscillation 27 and of a stepped oscillation 28 with straight steps. The amplitude of this deflecting oscillation corresponds to the whole width of the picture, and the height of each of the straight steps 30 corresponds to the width of a strip without picture contents on the picture screen. The duration 31 of the deflecting oscillation is that of the reconstruction of the whole picture. The width of step 32 represents the duration of the picture reconstruction of one of the groups of picture strips I, II, etc. The time-value 31 is equal to the product of the time-value 32 and of the number of grating elements. The diagram has the same appearance if strips without picture contents are provided in between the picture-lines.

The rule applying to each grating element or 4 groups of picture-strips also applies to each picture-line. If strips without picture contents are made to alternate with picture-lines, whilst strips without picture contents, of different width, are also inserted between the groups of picture lines, the deflecting oscillation constitutes a combination of a normal saw-tooth deflecting oscillation and of two stepped deflecting oscillations.

The deflecting oscillation illustrated may be generated in any manner well-known in itself, as by means of suitably dimensioned rotary potentiometers, rotary generators, valve-circuits in accordance with the overlapping principle, etc.

The diagrams shown are, of course, only of a 60o theoretical character. They will not, in practice, have vertical flanks or the like.

Horizontal deflection of the cathode-ray of the receiver tube by the deflecting oscillation illustrated by Figure 9 can be employed in a mode of transmission in accordance with Figure 2. The cathode-ray is deflected once from the left to the right during the duration of a picture.

A line-interlacing receiving process is employed in the case of a transmission in accordance with Figure 4. During each period of scanning of a sectional picture, the cathode-ray of the receiver tube is taken once from the left to the right, and therefore n times in the duration of a picture. Care must be taken, however, that the picture lines 2 are reproduced adjacent to the picture lines 1, and so forth.

This result is obtained, according to this invention, by means of a horizontally deflecting oscillation of the type illustrated by Figures 10 and 12. The ordinate is again the amplitude of the oscillation, and the abscissa is the time.

In Figure 10, the value 33 corresponds to the total width of the picture, 34 to the horizontal 11 distance between the picture lines of the first and of the last group of picture strips bearing the same numbers at the receiver picture screen, and consequently to the horizontal distance between the picture strip 1 of the group of picturestrips I and the picture strip I of the last group of picture-strips, 35 is the total duration of the picture, 36 the duration of a sectional picture, and 37 corresponds to the distance between two adjacent picture lines of one and the same group of picture strips, and consequently between the picture lines I and 2 of the group of picture lines I.

The deflecting oscillation shown by Figure 10 constitutes a combination of two normal sawtooth deflecting oscillations, which are not displaced in phase in relation to each other, and the frequency of which stands in the ratio of 1:n.

It will be observed that in Figure 10, n-=3 whereas in the other examples n=4. But it will be readily understood what is necessary for any required value of n. A strip without picture contents in between the various picture lines is determined by the choice of the amplitude 38 (38=n times 37), and a strip without picture 35: contents between groups of picture lines is determined by the choice of the amplitude 34. There are various known ways in which such a deflecting oscillation can be generated.

Figure 11 is a diagrammatic illustration of the 4' receiver picture screen, on which is shown the path of the cathode-ray, with indication of the positioning of the ray deflecting plates, assuming that use is made of deflecting oscillations of the type illustrated by Figure 10 but for a value of n=4. The dimensions are greatly exaggerated.

To the pair of plates 39 is conveyed the vertically deflecting oscillation, and to the pair of plates 40 the horizontally deflecting oscillation.

The cathode-ray then follows on the picture screen the path indicated by 41. Its return stroke is indicated by lines of dashes. As is shown by this drawing, the vertical picture line forms, with the pair of condenser plates 40, an acute angle 42, which must be present if an interlaced line process with deflecting oscillations in accordance with Figure 10 is employed. It is in this instance larger than in a case of use of other processes, because, in this instance, without the omission of a saw-tooth, n minus one picture-lines are always skipped in any one horizontal traverse, and strips without picture contents may also be skipped. As the direction of the grating must correspond to that of the picture lines, the design of the receiver tube must be such that the direction of intersection of the axes of the deflecting device is inclined by a small angle 42 in relation to the direction of the grating, and consequently in relation to the vertical. The references I, 2. 3, , 5, 25, ., II. and III apply to the same elements as in Figure 8.

Figure 12 illustrates, in the same manner as Figures 9 and 10, a horizontally deflecting oscillation allowing of the use of the interlaced line process already described, without causing the picture to sustain any distortion. This oscillation consists of an additive combination of two deflecting oscillations having stepped characteristics in time, with straight steps Figure 9 shows a combination of a stepped and of a saw-tooth oscillation, whilst Figure 10 shows a combination of two saw-tooth oscillations and Figure 12 a combination of two stepped oscillations.

In Figure 12, 43 is the duration of the collective picture, 44 that of a sectional picture, and 45 that of the reconstruction of a vertical picture line, whilst 46 corresponds to the horizontal distance between two picture lines bearing the same numbers in two adjacent groups of picture-lines, such as the horizontal distance between the picture line I of the group of pictures lines I and the picture line I of the group of picture lines II on the receiver picture screen, and 47 corresponds to the distance between adjacent picture lines within one and the same group of picturelines, such as the distance between I and 2 within each of the groups of picture-lines. The oscillation constitutes a combination of the stepped oscillation with the height of step 47, and of the stepped oscillation with the height of step 46, and allows of reproduction of pictures transmitted in accordance with Figure 4. No indication of synchronisation has been given for the lines or frames. The synchronisation arrangements made in connection with the process covered by this invention are not in any way different from the usual and well-known processes.

In the event of the amount of deviation exceeding, in the course of picture reconstruction on the receiver picture screen, the limits specified above as permissible, and in those cases in which the margins of allowance for which provision is made under this invention is not fully utilised, a provision is made of a device allowing of the grating fitted in front of the receiver picture screen to following the deviations of the picture.

The grating 50 in Fig. 13 is fitted outside the cathode ray tube 48, in front of the picture screen 49, or is adjustable in relation to the picture screen by means of a micrometric screw. The grating can also be mounted so as to drop clear of the picture screen so that for the purposes of ordinary television, the picture screen may be viewed without the interposition of a grating. Another mode of execution would consist of fitting, inside the tube, a glass plate provided with the fluorescent coating on one of its sides, whilst its other side is provided with the grating, which is formed as vertical cylindrical lenses of small radius as in the usual cylindrical lens gratings.

The stability of the picture, in so far as it is of particular importance for the purposes of the stereoscopic effect, is a function of the constant of the deflecting oscillation which deflects the cathode-ray horizontally in the receiver. The collective picture will be displaced horizontally if the said deflecting oscillation is not uniform.

According to this invention any variations from the uniform oscillation are conveyed by suitable relays to an electro magnet which displaces the grating horizontally in accordance with the variations. The directions of displacement in Fig. 13 are perpendicular to the plane of the drawing and are indicated by the two reference figures 51 and 52 which are marked below it. If the grating is rigidly connected with the picture-screen, and forms a solid unit with it, then the picture screen may be displaced jointly with the picture-screen.

As the displacements of the picture are compensated by the displacements imparted in this manner to the grating, so that picture and the grating remain reciprocally in stable positions, the deviations of the collective picture are compensated. These deviations amount, at the maximum, to the frequency of the change of pictures.

The damping of the displacements of the grating must comply with this requirement.

I claim: 1. In a television system wherein stereoscopic television pictures are produced by the parallactic stereogram method, means for exploring in parallel lines completely that is without interlinear gaps, each of a plurality of sectional pictures derived from a like plurality of different televising positions, by means of a picture exploring element whose dimension at right angles to the direction of the length of the exploring lines is substantially equal to the dimension of said sectional picture in said former direction divided by the number of lines in said sectional picture, and means for reproducing a collective picture built up of a number of reconstructed lines equal to the total number of lines in all said sectional pictures by positioning said reconstructed lines in correspondence with the sectional pictures to which they are appropriate and substantially without overlap, the said reconstructed lines being relatively narrowed so that the collective picture is substantially the same shape as each of. said sectional pictures.

2. In a television system the combination of means for exploring by adjacent vertical strips each of a plurality of sectional pictures derived from a like plurality of different televising positions, means for transmitting impulses obtained by the exploration to a receiving position, a cathode ray tube and a fluorescent screen receiving the cathode rays, at said receiving position, vertical and horizontal ray deflecting means in said tube, means for applying the picture impulses to the ray generated in said tube, means for actuating said vertical ray deflecting means and said horizontal deflecting means to effect line interlaced reproduction so that corresponding lines from each sectional picture are reproduced as a group within a width corresponding with the width of one line of the sectional picture, and a receiving grating having one line for each said group placed in parallel relation to said fluorescent screen with its lines parallel to said groups of lines. PAUL EISLER.