US2168047A - Electro-optical system - Google Patents

Description

Aug'. 1, ,1939. A. M. sKELLEr-r 2,158,047

' ELEcTRo-OPNCAL' SYSTEM I Filed Dec. 24, 193s :s shets-sne-et 1 /NMENTOR AMS/ELMU- M? A77' RNEV AUS 1 1939- A. M. SKELLETT 2.158.047

ELECTRO-OPTICAL SYSTEM Filed Dec. 24, 1936 3 Sheets-Shreet 2 QQ um INVENTOR AM. SKELLETT @M NQ ma it* bl|| Q @SEQ mbt Q .W E .3.11 Qzxmf @S u JQ ...usm .QOQHQ @MASK uur@ Q56 Y QQ SQSSQNQQ.

ArroR/VEY Aug. l, 1939. A. M SKELLETT ELECTROPTICAL SYSTEM 3 Sheets-Sheet 3 Filed Dec'. 24, 1936 /A/VE/VTOR AMS/ELLEN 5J A 7` TURA/EV hanna Aug. `1, 19394 PATENT OFFICE ELECTRO-OPTICAL SYSTEM Albert M. Skellett, Madison,

Bell Telephone Laboratories,

New York, N.

N. J., Y assigner to Incorporated,

Y., a corporation of New York Application December 24, 1936, Serial No. 117,521

22 Claims.

This invention relates to electro-optical systems and more particularly to the electrographic on of images 'or facsimiles.

It is an object of this invention to provide a.

novel electro-apical system resembling a television system in which a comparatively narrow frequency band is required for transmission.

It is a feature of this invention that a pictorial or graphic representation is traced rather than scanned.

At the .present time, so far as known, the trend ln lthe development of television transmission systems in which scanning is used appears to be toward the use oi' higher'and higher frequency band widths in order to have satisfactory entertainment value. Some known systems require band widths of a million cycles and upward and band widths of such magnitude require carriers of ultrahigh frequency. A feature of the present `invention is that, inasmuch as the subject is traced rather than scanned, the required frequency transmission band is so narrow that one 0r two channels in th may be used as the carriers. Some subjects, such as cartoons and sketches may be satisfactorily transmitted in this manner and still have much entertainment value. In one embodiment oi' this invention shown by vway of example for purposes of illustration, a

3o graphic or pictorial representation such as a.

mapa

wrling, drawing, diagram, painting, picture.

printing, sketch, cartoon or the like, is traced 'by a stylus arranged so as to continuously vary two resistances at right angles to each other in such a manner that as the stylus moves over the lines or boundaries of areas of distinctive tone values of said representation varying voltages arev produced at the resistances corresponding tothe X and Y coordinates oi' the stylus n pdnt as it progresses with respect to a pair of coordinate axes. The areas of distinctive tone` value maybe no more than lines in some cases.

These voltages are recorded-as tracks on a suitsuch as a lm, and the tracks are used .to generate, signal currents Y. ablerecord membe which are transmitted to a receiving station and there used to deilect the cathode ray beam in a cathode ray'tube in accordance with the successive values of the coordinate voltages. A conwftlct mechanism, may be l, cut-of signal on thevlm wheneverl the stylus is lifted from the subject'and this cutoif signal may be transmitted to the receiver and there applied to a control electrode Ain the cathode ray tubetocutothebeamduringthisperiod. .A

radio broadcast range l Y from the record member;

provided. for recording sound track may also be applied to the ilm and transmission made from this track by well-known means to a loud-speaker at the receiving station.

In order to produce a continuous image on the screen of the cathode ray tube, transmission 5 is made from the record over and over again in order to take advantage of the phenomenon of v, persistence of vision. The drawings or cartoons may be animated by changing slightly the Voltages in any appropriate way for each successive tracing of the stylus as by tracing consecutively sketches which differ slightly from eacb other. In the case of animated subjects image currents Yare generated only once from the tracks of each sketch, but image currents generated from twenty such sketches are transmitted every second in order to make the image animated. The time allowed for transmission does not in any way limit the time allowed for tracing a representation with the stylus as the record may be made in advance of the transmission time. As a modiiication the tracks may be 1recorded on a circular member and this record lplaced on a shaft rotating twenty times per second but this modication is not so suitable for animated subjects. The invention will be more readily understood by referring to the following description, taken in connection with the accompanying drawings forming a part thereof in which: y Fig. 1 is a schematic diagram' oi' the transcriber oi' this invention;

Fig. 2 is. a detail view oi apparatus for forming the coordinate voltages;

Fig. 3 shows the`apparatus for reproducing Fig. 4 shows'the receiving system;V Fig. 5 shows a method of tracing the subject with a stylus;

Fig. 6 is a representation of the X and Y coordinate voltages produced by tracing the subject of Fig. 5; Fig. 'I is an stylus: and

Fig- 8 shows a modified transmitter. Referring more particularly to the drawings,v Fig. 1 shows a schematic diagram of apparatus for converting the movements of a stylus into a record oi' coordinate voltage`s `which apparatus will-be designated a transcriber. Inv general the transcriber comprises means such as a stylus Ilxfor tracing the lines or boundaries of 'distinctive areas of a subject O, means for translating the movement of the stylus into X and Y coordinate voltages, and' suitable means for recording vthese coordinate voltages on al suitable record 5'5 enlarged cross-sectional view of a member, such as, for example, a photographic For producing the two coordinate voltages, a device similar to a telautograph 'may be used. Stylus I may be connected to two resistances lI and I2 arranged at right angles to each other so that as the stylus is moved over the representation O, which is mounted on a suitable supcomplete description of the resistances and their control means, reference will now be made to y Fig. 2 which shows a detail view of the apparatus. involved. `The stylus I0 is placed in the .intersection I5 of the slots l5 and I1, respectively,

of the control bars I8 and I9 which are made of insulating material. As the stylus I0 is caused to move over the surface of the subject or representation O, sliders and 2| of conducting material attached to the control bars I8 and I9 vary the resistances II and I2 in theinput circuits of amplifiers 22' and 23 which may be, for example, of the multi-stage type. In some casca-the amplifiers 22 and 23 may not be necesy sary. The control bars I 3 and I9 are guided in their paths by means of rails 24, 25, 25 and 21.

The speed at which the stylus is moved over certain portions of the representation will de-v termine the brightness of vthat portion at 'the lreceiving station. For example, if a line is quickly traced the image of the line will be very faint.

After amplification by the ampliers 22. and

23, the' imagecurrents in channels `I and 2 arecaused to vary the illumination of light from suitable sources and 31 through light valves'29 and 29, respectively.- The optical system for the light valve 28 comprises a light source 30, a lens 3| `for focussing the lightupon the light valve 28, moving ribbon 32 of the light valve 28, lens 33 and a prism 34 for directing the light passing through the light valve 28 upon a moving film 35 to form a track 35 thereon corresponding at -all vtimes to the X position ofthe stylus. The track 36, and also the other tracks, on the nlm 35V have been shown as of the variable density type, but it is obvious that the optical system may be so arranged as to form variable area tracks instead. Themethod of forming the tracks on the moving film- 35 is similar tothe well-known sound track recording technique. The optical system4 for the light valve 29 comprises the lightl source 31, lens -38 for focussing the light from the source- 31 upon the aperture of the light valve 29, ribbon 39 for controlling thepassage of light through the light valve, lens 40 and prism 4I for directing the light upon the illm 35 to form a variable density track 42 thereon. The use of the prisms 34 and 4I makes it possible to displace the light valves 28 and 29 from each other more than would otherwise be possible.

The film 35 may also have a track 43 to record the sound accompaniment. The schematically 'shown system for this sound accompaniment comprises a microphone 44 for generating currents corresponding. to the desired sound accompaniment, and an amplifier 45 for amplifying these currents which are then used t0 Qontrol the movement of the ribbon 46 of a light valve 41. The optical system for the light valve 41 comprises a light source 48 and lenses 49 and 50 on opposite sides of the light valve.

While the drawings illustrate the sound ac- 5 l companiment being recorded at the same time as the other tracks, it may be desirable in some instances to record it. at a diierent time. For example, if the coordinate tracks are made on the film at a speed different from the speed of the 10 film during transmission from these tracks to a receiving station, it is Vadvisable to have a sound track made on a film moving at the same speed as that used in transmitting the sound. The

sound track may be made on a separate film and 15 this illm developed and a positive made. A positive is also made of the developed lm containing the tracks corresponding to the coordinate positions of the stylus and the two films are combined,

both picture tracks and sound tracks being 2Q .printed to give the master negative.

If desired, the sound track may be displaced with respect to the corresponding image track on the iilm asin the usual sound motionpicture practice.

-The moving film 35 may also contain a fourth 25 track. Since each drawing transmitted must be resolved into a single line it is obvious that for some drawings this line must not be continuous if all details are included. For example, if it is.

desired to transmit twocircles, one inside the 30 other, theremust be .a break in the lineat the completion of one circle as the spot goes over to the other circle. This maybe done either by a modulating voltage which cuts off the electron beam of the receiving cathode ray tube as it n traverses the unwanted path, or by moving the spot over the unwanted path so quickly that the' line is too faint to be seen. The track 5I on the film 35 is representative of the time the stylus I0 is lifted from the surface of the object O and is, 4G

thus used to control the electron beam at the` receiver. In order to better understand the control means for producing this track, reference will now be made to Fig. 'I which shows a detail view of the stylus I0.

The stylus I0 comprises a casing 52 of any suitable material, such as for example, black micarta, at the butt end of which is secured an inner sleeve member 53 of conducting material.

A tracing member 55 of any suitable material, w such as for example, steel, is adapted to be moved in an axial direction within the casing 52 when the stencil is pressed down against the surface of the subject O. As the tracing member 55 is attached by means of a micarta spacing member 55 55 to a rod 51, the rod 51 also moves in an axial direction with respect to the casing member 52. The micarta spacing member 56 is prevented from moving in a downward direction bya shoulder 53 on the casing member 52, it being caused to rest 00 against this shoulder because of the action ofthe spring 59 surrounding the rod 51 and pressing against the sleeve 53. The top end of the rod 51 has a contact point 60 of contact metal which is adapted to contact a second contact point 5I which is held in a stationary position within the conducting sleeve 53 by means of the spacing member 62, which isof insulating material. Fas.- tened to the contact member 6I is an electrical lead connection 63 and fastened to the sleeve I3 70 is a lead connection 54. When the stylus I0 is tracing the outline of the subject O, the spacer 5B is raised from the shoulder 58 againstthe-action of the spring 59 thereby causing contact member 60 to come into electrical contact with 75 the member 6| and close Va circuit comprising battery 34 and electromagnets 65 and 36 connected in parallel (see Fig. 1). The electromagnets 65 and 66l are adapted to control an apparatus for recording the track 5| representing the cut-o5 signal on the moving lm 35.

This recording apparatus comprises a light source 61, a lens 63, an opaque mask 63 having an aperture therein, a lens 1| and means repr'esented generally by the plate 12 having an aperture 13 therein for preventing light from the light source 61 from reaching theaperture 10. 'I'he apertures 13 and 10 are so arranged with respect to each other that when there is no flow of current through the electromagnets 65 and 66 (as when the stylus I0 is raised from the surface of the subject O), light from the source 61 will pass through both of them and generate a track 5| on the lm' 35. When the circuit through the electromagnets 65 and 66 is closed, however, (as by the stylus resting on the subjectO) the plate 12 is drawn down against the action of the springs 14 and 15 so as to cover up the aperture 10 in the plate 69, thus producing no track on the film 35. The track 5| thus represents the period or periods of time when the stylus I0 has been lifted from the outline of the subject O, and may be use d to control the generation of a signal which may be used to modulate the beam of a cathode ray tube used at the receiver in such a manner as to cut off the beam during the period of time that the stylus is lifted from the outline of the subject O being traced at the transmitter. It should be, of course, understood that any other suitable means for producing a cut-oli signal may be used instead of the one described above which is merely for the purpose of illustration.

vAfter the film has been developed, fixed and dried in accordance with well-known photographic technique, the tracks on the film are used to control the generation of signal currents for transmission to a receiving station. Fig. 3 is a schematic representation of apparatus for transmitting from the film 35. Light from an elony gated light source |40 is focussed upon the illm by means of a suitable optical system represented generally by lens |4|` and is projected through apertures |43, |44, and |46 of amask |42 to illuminate respectively the tracks 36, 5|, 42 and 43 of the film 35. It is to be understood that the lens I4I may comprise four different lens-systems, if desired. The light passing through thev film 35 falls upon photoelectric cells 11, 13, 13 and 30 located directly behind the film and as close thereto as is practical. (For convenience of illustration these cells are shown at a considerable distance from the fm.) These cells generate signal currents respectively proportional to the density" of the particular portions of the tracks 36, 5|, 42 and 43 respectively opposite the apertures |43, |44, |45 and |46. If desired, the photo-cells 11, 13, 13. and 30 may be spaced farther apart than shown, any suitable optical arrangement being used to separate the rays fromv the respective tracks.

The signal currents generated by the photoelectric cells 11, 13,'13 and 30 are then used to modulate carrier waves generated by means such as, for example, oscillators`3l, 32, 33 and 34, the modulators 05. 36, 31 or 33 being used to perform this modulation. Band- pass filters 33, 30, 3| vand 92 are preferably used to exclude all frequencies except those of the desired band width. The currents in channels A. B, C and D are then amplified by the amplier 33, which may comprise a number of stages, and transmitted over suitable wire or radio lines 34 to the receiving system shown inv Fig.' 4. If desired, the amplifier 93 may comprise four separate units.

The receiving system shown in Fig. 4 comprises a suitable amplifier 95, four band- pass filters 96, 31, 33 and 33 for selecting the appropriate channels, and demodulators |00, |0|, |02 and |03 for demodulating the received signals in the various channels. The signals in channels A and C are then applied to two pairs of deflecting plates |04 and |05 of a cathode ray receiving tube |06 those in channel B are used to cut off the beam in the tube at times when the stylus |0 is lifted from the subject; and those in channel D are used to produce sound effects.

The cathode ray tube |06 comprises a means such as a cathode |01 and an anode |33 for producing a beam of electrons and a second anode |09 for accelerating this beam toward a fluorescent screen ||0. 'I'he voltages from the channels A and C create electrostatic fields between the defiecting plates |04 and |05,'respectively, which deflect the beam to positions corresponding to the successively traced positions of the stylus at the transmitting station. The voltages across the defiecting pates are balanced with respect to thev steady image may be formed on the fluorescent screen l0 of the cathode ray receiving device |06 which corresponds to the subject O at the transmitting station. The length of the continuous belt corresponds to one complete tracing of the subject. I

The drawings or cartoons may be animated by changing slightly the voltages in any appropriate way for each succeeding tracing. This introduces no added requirements of any kind in the transmission. Drawings differing slightly from each other may be successively traced by the stylus and in this manner an animated motion picture may be produced `on the fluorescent screen ||0. It is thus possible to transmit by this method animated cartoons.

'111e signals in channel B (cut-olf signal) are applied to a control or modulating electrode member III. The negative voltage applied between the cathode |01 and the modulating member I|| causes the cathode ray beam to be cut off, thus producing no line or trace on the screen I I0 when the stylus |0 is lifted from the subject O.

The signals in channel D may be conducted to any suitable loud-speaker arrangement ||2 through any appropriate amplifying means ||3. The observer thus sees a moving picture and hears the sound accompaniment.

In order to fully understand the operation of the image or facsimile transmission system shown in Figs. l, 3 and 4, some of the theory of this system will now be considered. It is inherent in well-known systems in television that high denition must at all times be realized no matter how simple the transmitted image may be. Many useful and entertaining images, however. do not contain a great amount of detail and in transmitting them large blank areas on the available field are wastefully transmitted. The animated cartoon is an example of such a simple image. By making it possible to transmit the figure and line background without the blank areas a great simplification can be brought about. The system of this invention was designed to take advantage of this fact.

By the application receiving plates |04 and |05 of the cathode ray tube |06, the cathode ray beamof the tube may be made to traverse any path desired. Furthermore, if the spot is made to follow a certain path, such as that shown in Fig. 5, over and over, approximately twenty times a second, this tra-ce will appear on the end of the tube as a stationary image.

Two potentials, each varying in intensity with time, are needed to properly actuate the spot. They are applied, one across the horizontal set and one across the vertical set of defiecting plates of the cathode ray tube |06. They are directly proportional, respectively, to the X and Y coordinates of the points of the figure, that is, points I, 2, 3, 4, etc. of Fig. 5, taken along the path of the spot in the direction in which it moves. These potentials for the image of Fig. 5 are shown in graph form in Fig. 6.

Any method of recording the X and Y potentials may be used as, for example, photographic film. The film of Fig. 1 is an example of this method of recording. They may be recorded or plotted, as a modification, as a circular track either of the variable area or variable density type, the former being illustrated in Fig.'8. Each of the image tracks, that is, the area between each curve and its base circle is made contrasting with the background and the disc |22 containing the curved image tracks |20 and I2| is mounted on the shaft of a motor |23 which is adjusted to run at a speed of, for example, twenty revolutions per second. The disc is brightly illuminated by light from a source |24 which is reflected by a curved mirror |25. oriented slit |21 are arranged in such a manner that a portion of the image of the track |20 falls across'the slit |21. Behind the slit |21 is a photoelectric cell |28 which receives the illumination passing through the slit to generate therefrom signals which may be used to modulate a carrier such as that of channel A of Fig. 3. Thus the output of the photoelectric cell |28 is directly proportional to the X coordinate of the stylus position at any instant of time. The apparatus to the left of the line X-X in Fig. 8 may be the same as the apparatus to the right of the line X-X for channel A in Fig. 3 with the possible addition or subtraction of one amplifying stage in the case where the area between each coordinate curve and its base circle is made white and the background black.

A similar set-up comprising a lens |29, a radially oriented slit |30, and a photoelectric cell |3| may be used to produce potentials which are proportional to the Y coordinates of the successively traced points of the subject O. Auxiliary apparatus for channel C which may be connected on the left of the line Y-Y in Fig. 8 may be similar to that shown to the right of the line Y-Y in Fig. 3 with the addition or subtraction of one amplifying stage if the image track is white rather than black as shown in Fig. 3.

For the simplest type of image in which the drawing may be resolved into a single unbroken line, e. g., the object in Fig. 5, the total frequency spectrum of band width needed for accurate reproduction of the sketch will consist of the sum of the band widths needed to transmit accurately the X and Y potentials. These may be assumed to be equal. The band widths may then be determined by the analysis of the X (or Y) potential of proper potentials to the A lens |26'and a radially y is analyzed harmonically.

variations of a single trace by means of harmonic analysis.

The magnitude of this potential E may be expressed as a function of time by a Fourier equation with an infinite number of terms.

where ,f is the fundamental or trace frequency -(about twenty per second) and An and 4m are the amplitude andphase angle of the nth harmonic.

However, an infinite number of terms is of no value here because of the limitations of the eye and of the cathode ray tube |06. All components above a certain value of n would add so little to the reproduced image that it would be impossible to distinguish the difference due to their absence. For any subject, therefore, the problem becomes that of determining the highest value of n needed for satisfactory reproduction. The band width will be that included between ,fr and the frequency' of this nth component.

In general, the threekinds of detail which will suffer most by the elimination of high order terms are straight portions, sharp kinks, and small bends, i. e. bends of small (approximate) radius of curvature. This is true for the straight portions simply because it is easier for the eye to distinguish a small deviation from a straight line than to detect the difference between two curvatures which are slightly different. A steep fron such as often arises in wave analysis and which requires relatively high order terms will not appear in the problem considered here, because of the assumption that the spot moves with uniform speed.

A certain degree of departure from the linearity of the straight portions and from the exact form of the various curvatures and also a certain amount of waviness may be tolerated. These are the defects in the image which will be occasioned by the elimination of the terms of the series above the nth. Furthermore, such defects will be more detrimental the smaller the detail, since enough terms will always be transmitted to give a good overall shape and good form to the larger details. Now it is much more important to reproduce correctly the general overall form of the image than the smaller details. Thus the band width is largely determined by the fidelity of small detail desired.

Suppose therefore that the smallest detail, in

E: f LmEdt-l-A. sin (6.4...) n-l the form of a small bend or kink in the curve of a potential function, is picked out and a small portion of the curve in which this detail occurs For the purpose at handonly a small number of terms or harmonics need be considered. The results of the analysis may be written in the form of an equation of the usual Fourier type and the term having the largest coefficient will, in general, be the most important one in contributing to the shape of the desired detail. In any'case this most importan term may be determined by graphically synthesizing the terms. A little experience in harmonic analysis will enable one to determine it, in most cases, by inspection alone.

If the band width extends up to and includes the frequency of this term, the detail in the image which gave rise to that in the potential curve will in general be reproduced in approximate form. The band width determined in this manner may therefore be taken as that necessary for satisfactory reproduction. A

ligure was two thousandl cycles.

lli

y the base line roughv check was obtained on the adequacy of this approximate method by equivalently shortening the band width of the apparatus used in the reproduction of the gure shown in 5. The total band width determined as above for this The bands passed by the ampliiiers 'were equivalently reduced toV 1300 cycles each and no marked change in the image occurred.

The rst term. of the series of Equation l for each component curve is of importance for centering the image in the eld. It is i/f- FL Edf. 2) This is simply the total area between the voltage curve and the line representing zero voltage over one cycle of period f divided by the length of It thus represents the mean distance of the curve from the zero axis. If this mean distance, which can be considered a direct current component, is eliminated from the image signal current, the shape of the component curve and hence also of the image would not be altered but the centering of the image would vary as the figures move around in the field. As an example of the effect of this', suppose that the image consists of a central human figure and a very simple background. As the ligure starts to Walk from the center to the side of the field, the absence of the transmission of this centering component holds the figure near the center and the'background slides away in the opposite direction, an effect which is sometimes desired. This component would be eliminated by ordinary alternating cur- .rent ampliiiers or other apparatus incapable of passing direct or low frequency currents but if the/image frequencies are used to modulate a carrier or carriers, the frequency band may be made to extend to zero on the low frequency end and this component will then be included in the transmission even when ampliiiers or other appa- Vratus like that just mentioned is employed. If

a carrier is 'not used the problem is similar to that encountered in ordinary television when the components representative of average bright.

. With most modern broadcasting stations definitely transmitting an audio band 7500 cycles wide and attempting to transmit one up to 10,000jcycles (a total transmitted band width ot20,000. cycles) in the interest of high quality music, it is apparent that by proper engineering, animated cartoons ot a degree of complexity. of dennite entertainment value plus a sound accompaniment of at least 3000 cycles may be transmitted from a modern radio broadcasting station. This may be accomplished as follows: Let it be assumed that the band width for each component image potential is 5000 cycles and for the sound band is 3000 cycles. Each of these will be used to modu- .Which, 'in general, have decreasingly lower amlate a separate carrier as in Fig. 3 and by proper iilters one side-band of each will be discarded. There will be left for transmission three carriers and their single side-bands (if a cut-ofi` signal is transmitted there will be an additional carrier). 5 The carriers will have been chosen so that the sound channel falls in the center of the transmitted band of the broadcast transmitter with the image channels on either side of it and with a spacing between channels of several hundred cycles. The carriers for the image channels will be placed near the sound band so that the higher frequencies will be at the edges of the transmitted band (one channel has the upper and the other the lower side-band) Thus the total transmitted band will be somewhat less than 14,000 cycles wide, which is equivalent to transmitting au audio range of 7000 cycles by the usual method (transmitting both side-bands). It is possible therefore to transmit images of even greater complexity than that of Fig. 5 from a modern radio broadcasting station having iilter circuits, etc., arranged for high fidelity sound broadcasting. -By this arrangement the higher frequencies,

plitudes, are placed at the outside of the band and interference between stations will not be materially greater than it is now with high ndelity radio transmission.

It will. thus be observed that this system will produce visual programs of high entertainment value without requiring band widths any larger than those of the ordinary high fidelity radio transmitting stations of today.

Various modiiications may be made in the'invention as above disclosed, the scope of which is4 indicated bythe appended claims. The expression along the boundaries of distinctive areas" used in the claims is intended tocbe inclusive of the case where a distinctive area is a line. The 140 two parallel boundaries of a line area are for practical purposes coincident so that a stylus tracing the line is in effect tracing each boundary of the line area; that is, tracing both boundaries of the line area simultaneously. This term, along the boundaries of distinctive areas, is also intended to be inclusive of the case where the areas are distinguishable by differences in elevation as, for example, a gure cut from cardboard and placed or mounted upon a flat support having 50.

the same or different tone value or an element of Wax forming a eld in which a line drawing, figure or design of any kind is produced by indentations in the wa thus forming depressed line areas. Y

What is claimed is:

1. A method oi image production comprising the steps of tracing the boundaries of distinctive areas of a subject lying substantially in a plane, simultaneously generating by said tracing two` potentials the values of which at each instant are respectively proportional to the distances from the boundary element then being traced to two coordinate axes, making two records-corresponding respectively to the variations of said two poa5 tentials, transmitting within the period of persistence of vision from said records potentials corresponding to a complete tracing of said subject, and immediately repeating said last step.

2. In combination a support for a subject, a stylus for tracing the boundaries of distinctive areas of said subject, means for generating potentials representative of the changing location'of said stylus with respect to coordinate axes, means :for recording said potentials, and means for reu peatedly transmitting from said recording sets of signals each set representative of a complete tracing of said subject and each in a time interval within the period of persistence of vision.

3. A transcriber comprising a.c stylus for tracing boundaries `oi distinctive areas or a subject, means controlled by the raising of said stylus from said subject for generating a signaLmeans for recording said signal, and means for utilizing said recording to control the intensity of a cathode ray beam.

4. In combination, a stylus for tracing the outline of a subject at a transmitting station, a. record member at said station, means for directing a beam'ofl light to said record member, and means operable upon the lifting of said stylus from said representation for controlling the intensity of said light beam.

5. In combination, means for generating signals varying with the location of successively traced points on the boundaries of distinctive areas of acomplete subject, means for transmitting said signals to a receiving station, a cathode ray tube at said receiving station, said cathode ray tube having means for generating a beam of electrons, two sets or electrostatic deilecting plates, and a uorescent screen, means for applying to the sweep plates of said cathode ray tube potentials which continuously vary in accordance with the signals received at the receiving station so that said beam traces on said screen-an image of said object, and means for retransmitting at predetermined intervals within the period of persistency of vision signals similar toV said iirst signals representing a completely traced subject so that an apparentiy steady and continuousimage is formed on the screen of said cathode ray tube.

6. In combination, means for converting the motion of a stylus along the boundaries of distinctive areas of a subject into two potentials continuously varying in accordance with successive positions of the stylus, a circular disc for recording said potential variations corresponding to a complete subject in polar coordinates along the complete circumference of two coaxial circles Von said disc, means for rotating said disc so that a complete revolution is made within the period of persistency of vision, and meansfor transmitting these potential variations from saidrecord member to a receiving station.

7. A method of producing variations in density of the received image in the cathode ray tube oi.'

an electrograph system in which the boundaries of distinctive areas of a subject at a transmitting station are traced by a stylus comprising tracing lines of the subject at the transmitting station ci less density with greater speed than lines of greater density.

8. -A method of imagev productiong comprising the steps of tracing the boundaries of distinctive areas of a 'series of successive representations of a subject, each representation in the series dif- Iering from its preceding representation by an extent corresponding vto a difference in time within the period oi persistence of vision, simultaneously generating by said tracing two potentials varying in accordance with the positions of the successively traced elements of said jboundaries with respect to a coordinate system, recording the 'potential variations, and transmitting signals from said recording at such a rate that the signals corresponding to a complete tracing of one of the representations oisaid subject occurs within the period of persistence of vision.

9. A method of image production comprising the steps of tracing the boundaries of distinctive areas oi' a subject, simultaneously generating by said tracing two potentials varying in accordance ordinate system, recording these potential variations as two tracks coaxially arranged on a circular disc, turning said circular disc at such a speed with respect to a pick-up device that signals corresponding toa complete tracing of said subject are generated within the period of persistence of vision, and retransmtting from said disc signals corresponding to complete tracings of said subject at intevals within the period of persistence of vision.

10. A method of image production comprising the steps of tracing the boundaries of distinctive areas of a subject, simultaneously generating by said tracing two potentials varying in accordance with the positions of the successively traced elements of said boundaries with respect to a coordinate system, photographing these potential variations as parallel tracks on a sensitive film, developing, fixing and drying said lm, transmitting from the tracks on said lm within the period of persistence of vision signals corresponding to a complete tracing of said subject, and repeatedly transmitting from said iilm signals from the tracks thereon corresponding to complete tracings of said subject, each within the period of persistence of vision.

11. A method of image production comprising the steps of tracing the'boundaries of distinctive areas of successive representations of a subject, each representation in the series differing from its preceding representation by an extent corresponding to a difference in time within the period `of persistence of vision, simultaneously generating by said tracing two potentials varying in accordance with the positions oi successively traced elements of said boundaries with respect to coordinate axes, photographing these potential ordinate system, recording these potential variations, generating from said recording two signals varying in accordance with the positions of ,the

successively traced points of the subject at such a rate that the signal corresponding to a complete tracing of said subject is generated within a time interval within the period of persistence of vision, modulating separate carrier waves with said signals, and ltransmitting said modulated carriers to a receiving station.

13. .A method of image production comprising the steps of tracing the boundaries of distinctive areas of 'a subject, simultaneously generating by said tracing two potentials varying in accordance with the positions ofthe successively traced elements of said vboundaries with respect to .a coordinate system, recording these potential variations, generating from said recording two signals varying in accordance with the positions ofthe successively traced points of the subject at such a. time interval within the period of persistence oi' vision, modulating separate carrier waves with said signals, transmitting said modulated carriers to a receiving station, demodulating said modulated carriersat, said receiving'station, and

1 applying the signals resulting from said demoduf lation to a receiving member to form thereby an image of said subject.

14. lA'method of image production comprising the steps ot tracing the boundaries of distinctive areas of a subject, simultaneously generating by said tracing two potentials varying in accordance with the positions of the successively traced elements of said boundaries with rpect to a coordinate system, recording these potential variations, generating irom said recording two signals varying in accordance with the, positions oi the successively traced points oi the subject at such a rate that the signals corresponding to a complete tracing of said subject are generated within a time interval within the period of persistence oi vision; modulating separate carrier waves with said signals, filtering said modulated carrier waves to remove one side-band of each, transmitting the remaining side-bands to a receiving station, illtering the received side-bands to divide them into their respective channels, demodulating the resulting signals in the respective channels, and applying the signals resulting from said demodulation to Va receiving member to form thereby an image of said subject.

15. A method of transmitting signals for the production at a receiving station of an image of a subject at a transmitting station comprising the steps of tracing the boundaries of distinctive 'areas of said subject, simultaneously generating by said tracing two potentials'varylng in accordance with the positions of the successively traced elements o1' said boundaries with respect to a coordinate system. generating a third potential variation whenever the tracing member is lifted from the boundaries oi' said subject, recording all three oi' these potentials, generating from said recording two signals varying in accordance with the positions of the successively traced points of the subject at such a rate that the signals cor.

'- responding toa complete tracing oi said subject are generated within a time interval within the period of persistence of vision and a third signal corresponding to the period o! time the tracing member is lifted from the surface of said subject, and transmitting 'all three oi' said signals to a receiving station where they cooperate to form an image of said subject.

16.l A method o! controlling from a transmitting station a cathode ray beam in a receiving de vice, said device being used to produce an image o! a subject the boundaries of distinctive areas of which are traced at said transmitting station which comprises the steps oi' generating potentials when the tracing member at the transmit` tingstation is moved from the plane o! the subject, recording saidpotentials, reproducing po- .tcntials i'rom said. recording, transmitting said reproduced potentials to said receiving station,

and applying said received potentials to the control means for said cathode ray beam in such a manner that said beam is substantially extinguished when the tracing member is moved from the plane of the subject.

17. A method of transmitting signals for producing at a receiving station an. image of a subject at the transmitting station with sound ac-.

companiment comprising the steps of tracing the boundaries of distinctive areas of'rsaid subject, the complete subject being traced within a period of time much greater than the period oi' persistence of vision,'simultaneously generating by said tracing two potentials continuously varying in accordance with the positions of the successively traced elements of said boundaries with respect to coordinate axes, recording these po-y thereon, printing a master negative from said master positive, and moving said master negative with respect to pick-up apparatus at the speed at which said sound accompaniment was recorded, said speed being such that the tracks 'corresponding to a complete tracing of said subject pass the pick-up apparatus within the period of persistence of vision.

' 18. Means for making a record member for controlling the production of an image of a subject comprising means for generating two potentials continuously varying in accordance with the positions of the successively traced. elements of theboundaries of said subject with respect to coordinate axes, a ilm, means for moving said lm, a pair of light valves, a light source associated with each iight valve, means including said light valves for modulating the light from said sources in accordance with the changes in said Y two varying potentials, and means for projecti'or moving said iilm member, a pair of light valves, a light source associated with each light valve, means-for modulating the light from each of said sources in accordance with the changes in the two varying potentials, means for projecting said modulated light 'beamsupon said moving iilm to form thereon two parallel tracks, a third light valve, a source of light associated with said third light valve, means tor controlling said third light valve in accordance with the lifting of the tracing member from the surface of said subject, and means for projecting the lightv through said third light valve as a third track onsaid iilm parallel to said ilrst two tracks.

20. A cathode ray device comprising means for generating a beam of electrons, two pairs of clectrostatic d etiecting plates for giving the beam a motion having Vcomponents at right angles to each other, a iiuorescent screen-on which said beam impinges, said screen beinrrof such material that it emits light only a-relatively short time after being impulsively energized -by said beam, such period of time beingmuch shorter than the period oi' persistence oivisionand means for impressing upon said pairs of deecting plates, respectively, varying trains of potentials representative, of successively tracedv positions, with respect to coordinate axes, along the boundaries of distinctive areas of a subject thev image of which is to be produced, the varying trains of potentials correspondingto a complete tracing of said subject being impressed upon said plates within the period of persistence of vision, and means for repeatedly impressing upon said pairs of deiiecting plates varying` trains of potentials each train representative of complete successive representations of said subject.

21. A cathode ray device comprising means for generating a beam of electrons, two pairs of electrostatic defiecting plates for giving the beam a motion having components at right angles to each other, a iiuorescent screen on which said beam impinges, said screen being o! such mate- I rial that it emits light only a relatively short time after being impulsively energized by said beam, such period of time being much shorter than the period of persistence of vision, and

means for impressing upon said pairs of deflecting plates, respectively, varying trains of potentials representative of successively traced positions, with respect to coordinate axes, along the boundaries of distinctive areas of a subject the image of which is to be produced, the varying trains of potentials corresponding to a complete tracing of said subject being impressed upon said plates within the period of persistence of vision, and means for suppressing the beam for a period after each of the boundaries corresponding to a

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