US2216264A - Means and method of image analysis - Google Patents

Description

i- 1, P T'. FARNswoRTH 2,216,254

BEANS AND METHOD OF IMAGE ANALYSIS Filed July 6, 1955 1 LIGHT LIGHT -e- INVENTORT PH/LO 7: FAPNS O h.

Patented Oct. 1,

2,216,264 MEANS METHOD or MAGE ANALYSIS Application July 6, 1935, Serial No. 30,119

6 Claims.

My invention relates to a means and method of image analysis, and more particularly to a photoelectric tube and system adapted for electron beam analysis for use in television or in allied arts where such analysis is desirable.

This application embodies the broad method disclosed and claimed by me in my copending application Serial No. 29,242, filed July 1, 1935, for an electron image amplifier, and this applica- 19 tion discloses and claims an alternate means and method by which the insulated grid structure described and claimed in my companion application, Serial No. 30.118, filed July 6, 1935, for a Charge storage dissector, now United States Patent No. 2,140,695, issued Dec. 20, 1938, may be utilized for electron beam analysis.

The broad method is applicable to both transmitting and receiving cathode ray tubes and systems employing them, the specific embodiment 20 described herein as utilizing my broad method being a transmission device.

Among the objects of my invention are: to

provide a method of electron image amplification adapted for use in a transmitting dissector tube or in a cathode ray receiving tube; to provide a method of increasing the sensitivity of television transmission cells; to permit the production of television signals by reflected light of ordinary intensity; to increase the electrical output of a photoelectric cell; to increase the electrical output of a television cell in order to provide satisfactory television signals without the use of complicated and sensitive amplifiers; to provide a television system wherein amplification of an electron image or any portion thereof may be accomplished without dissecting said image into picture elements; to provide a method of amplification for photoelectric purposes, particularly 40 in television wherein the degree of amplification is limited by the extremely high frequencies which must be handled where the image is dissected before amplification; to provide a means and method whereby relatively large currents may be secured from a television transmitting cell; to provide an image amplifying structure which is simple and practical to fabricate; to provide an amplifier of photoelectric currents wherein extremely high amplifications may be obtained within the photoelectric cell itself; to provide a means and method for modulating an electron stream to produce an electron image; to provide a means and method for modulating a. 5g uniform electron stream by photoelectrons cre- I therefore to be understood that my method is applicable to other apparatus, and that I do not limit myself, in any way, to the apparatus of the present application, as I may adopt various other apparatus embodiments, utilizing the method, within the scope of the appended claims.

In my previous patents, as follows:

Patent No. Issued Aug. 26, 1930. Feb. 16, 1932. Dec. 26, 1933. July 20, 1937.

and others, I have described television transmitting apparatus and systems wherein an optical image of the object or picture field is thrown upon a photosensitive cathode and the emitted electrons are accelerated and focused to form an electron image. By electron image" I mean a plane through which the electron stream passes, the electron density of which varies spatially across the stream in the same manner as the illumination density varies across the optical image. In other words, the electron density values represent spatially the illumination of the picture field.

The electron stream forming this image may be deflected by means well known in the art, but preferably by magnetic means, to pass over an aperture in such a manner as to efiect the dissection of the image. Selected portions of the electron stream passing through the aperture are collected to form a picture current or train of picture signals which may be amplified and modulated upona radio wave, or transmitted by wire. This method of television transmission offers the advantage of having no moving parts and of being suitable for the electrical transmission of pictures having any desired fineness of detail.

The principal weakness of this method lies in the fact that only a relatively small portion of the electrons emitted from the total photoelectric area is used at any given instant and at the present time photoelectric emission is relatively small in intrinsic value. Therefore, the highest tory picture currents may be obtained. With small output currents, attempts to amplify the signals above a certain level bring in background noise, shot effect and other ordinarily negligible factors which tend to make the amplified picture currents unsatisfactory and distorted, and the received picture lacking in the detail which it would have if such interference were not present.

In the present invention the fundamental principles of my prior inventions are retained and other desirable features added. In my Patent No. 2,140,695 for a Charge storage dissector, mentioned above, I utilize a specific embodiment of my broad method by forming a charge image on an insulating medium and then passing a stream of electrons having uniform cross-sectional density through the charge image to produce an electron image corresponding to the charge image and to the optical image responsible for the charge image. In that patent the charge image released electrons from a space charge in the uniform stream to form the electron image, which thus became more powerful than any image which could be created electrically by direct action of light or photoelectric means. The present --application differs from the patent referred to in that the electron image is not scanned in the present application.

The broad method described and claimed in my application Ser. No. 29,242 for an Electron image amplifier, mentioned above, is that of forming a charge image in space and passing a uniform electron stream through this charge image to create an electron image which is then scanned to produce a train of television signals.

The broad method of the present case utilizes the same broad principles as outlined above, but modified in that I form a charge image in space corresponding to an optical image as far as spatial distribution is concerned, and then pass a defined beam of electrons through elementary areas of the charge image to produce modification of the electron beam, this modification then being collected to form the trainof television signals. In other words, the charge image is scanned by a moving beam of electrons, and the amount of modification by the charge image of this beam is the television signal.

Broadly, in terms of apparatus, my present invention comprises the use of means for forming a charge image bound on an insulator, this image being formed by the action of an optical image on aphotoelectric surface closely adjacent thereto. The charge image is then scanned by an electron beam emitted from an electron gun in two directions so that successive elementary areas of the insulating surface carrying the charges infiuence the electron beam and modify it. The electrons remaining in the beam after modification are collected upon an anode and utilized in an output circuit to form the train of television signals desired.

The means by which the charge image is formed in this particular invention is the same as that described in my copending application, Serial No. 39,604, filed September '7, 1935, and now United States Patent No. 2,141,836, issued Dec. 27, 1938, for a Charge storage dissector tube, and the method by which the charge image is formed is fully described and claimed in my Patent 2,140,695 for a Charge storage dissector,

mentioned above. In these two patents the charge storage electrode serves both as a source of photoelectrons for charging an insulating surface, and also embodies the insulating surface itself; the photoelectric material being preferably on one side of the electrode and the insulating material on which the charges are fixed being.

preferably on the opposite side of the electrode.

I am fully aware that devices operating somewhat along the lines of the device herein to be described have been utilized before, but these prior devices have all utilized a photoelectric mosaic surface comprising a multitude of discrete islands of photoelectric material. Inasmuch as the formation of such a photoelectric mosaic is a difiicult'procedure and one which is liable to many accidents during the course of formation, and would, for that reason, be hard to duplicate in commercial quantities for praoparticular photoelectric surface may be, under the teachings of my various inventions referred to, continuously conductive.

Various other modifications and applications of my invention will be apparent to those skilled in the art, and for other broad objects of my invention I prefer to refer to a detailed description of a preferred embodiment of my invention as shown in the drawing, in which:

Figure 1 is a. longitudinal sectional view of a preferred type of dissector tube embodying my invention and provided with charge storage electrodes formed as indicated in Figures 3 and 4.

Figure 2 is a conventionalized diagram showing one circuit in which the tube of Figure 1 may be connected for operation.

Figures 3 and 4 are cross-sectional views,

greatly enlarged, of the individual wires of two forms of charge storage structures.

Describing my apparatus in detail, an envelope I is provided at one end with a transparent window.2 throughwhich an optical image of an object may be projected upon a charge storage electrode 5 by means of any convenient lens system, not shown. 7

An electron gun assembly is provided closely adjacent the window 2.' This gun assembly comprises a heater 1 and emitter 8 and an apertured anode 9, the assembly being cooperative to project a narrow defined beam of electrons on the charge storage electrode 5. In practice the gun assembly is made sufficiently small so that it does not obstruct an appreciable amount of light, nor

does it distort the optical image to any great film l6 extending along the walls of the tube and connecting to the edges ofthe charge storage electrode 5. Exterior connection I! is provided for the collecting anode i2, and an anode shield connection I8 is provided for the anode shield. The combined action of the films 3 and [0 creates an electrostatic lens, as described and claimed in my prior application, Serial No. 56,976, filed Dec. 31, 1935, and now United States Patent No. 2,153,918, issued April 21, 1939.

Among others, there are two structural embodiments which may be used in the charge storage electrode 5, both of which, however, accomplish the same function. Figure 3 shows one way in which the grid structure may be made. Here, a foundation wire I9 is provided with a uniform coating of insulating material 20 over the complete surface thereof, and the insulating material on the side of the structure facing the window 2 is provided with a layer of photo-electric material 2l.

In the other embodiment shown in Figure 4, the foundation wire 22 itself is preferably of silver having a sensitized photoelectric surface 26 thereon, and the side of the charge storage electrode away from the window 2 is provided with a coating of insulating material 20. Thus, either modification will have a photoelectric surface facing the window 2 and an insulating surface facing the collecting anode l2.

In forming the charge storage electrode shown in Figure 3, I prefer to utilize a nickel wire screen for the foundation wire I9 and to form the insulating layer 20 thereon by completely smoking the screen with the fumes of burning magnesium to deposit a continuous layer of magnesium oxide. I then evaporate on this one side of the electrode a thin layer of metallic silver. This deposition may be accomplished by evaporation under vacuum, as is well known in the art. Oxidation of the silver film is then carried out by using a high-voltage glow discharge in oxygen, and the oxidized surface is then sensitized with caesium, preferably with care being taken not to leave an excess of caesium. An excess of caesium can be prevented by baking the tube at sixty degrees on the pump after the photoelectric surface is formed, or by other means well known in the art, thus leaving a sensitive photoelectric surface 2| facing the window 2, this surface being continuously conductive and not a mosaic.

In the second method of forming the charge storage electrode the foundation screen of the electrode is preferably of solid silver; in other words, the screen is woven of silver wire. The screen is then smoked on one side only with magnesium oxide until it can be seen by examination that the silver wires on the side of the screen facing the collecting anode l2 are fully covered with magnesium oxide, with bare silver wire facing the window 2. The screen is then subjected to the glow discharge in oxygen, the exposed silver portion oxidized, and caesium deposited on this oxidized surface so that a continuously conductive photoelectric surface 24 is formed facing the window 2.

Thus it will be seen that in both embodiments a charge storage electrode is formed with a photoelectric surface facing the clear window 2 in a position to receive an optical image thereon, whereas the opposite face of the screen directed toward the anode I2 is provided with an insulating surface.

In operation the tube is hooked up in one preferred circuit as shown in Figure 2. Here the heater 7 is energized by heater'source 25 heatii the cathode 8, the front face of which faces t-l anode opening and is preferably coated with z electromemitting material. Electrons are th' emitted and the gun anode 9 is connected to ti cathode through a gun source 26 with a positi potentiol on the anode 9 so that an electron bea of relatively small cross-section is projected in space in the direction of the'charge storage elel trode 5.

In order that the cross-section of the beam cor tacting the charge storage electrode 5 be of air mentary size I prefer to focus the electrons i the beam in the plane of the charge storage elel trode 5, following the method disclosed an claimed in my Patent No. 1,986,330, issued Jam ary 1, 1935, utilizing for this purpose a focusin coil 21, the magnetic field thereof being produce by current from focusing source 28 under the cor trol of a variable resistor 28'.

I also prefer to be able to move the electro beam in two directions in order that the entir picture area of the charge storage electrode 5 is scanned in successive elementary areas thereo and I utilize for that purpose preferably mag netic means comprising scanning coils 29 and 3 supplied with current from scanning oscillator 30' and 3|, respectively.

The charge storage electrode 5, together witl the collecting anode shield I5, is maintained a a potential somewhat'positive with respect to th electron gun by attachment to an acceleratinl source 32, and the collecting anode I2 is main tained still more positive by battery 33, the posi tive end of which is connected directly to th collecting anode I2 and the negative end to a! output resistor 34 across which output leads 3i are connected.

The device is now ready for operation.

An object or picture .field is illuminated, am the light therefrom is focused by means of E lens system, not shown, onto the photoelectril face of the charge storage electrode 5. The photoelectric emission therefore will take place ovei the entire illuminated surface in accordance with the illumination intensity of the various elementary areas thereof.

I offer the following explanation of operation as based on observed results, the experimentation being by no means complete, as the obscurity and complexity of the problem renders my theory liable to reformation in view of additional facts, when obtained. Therefore, I do not wish to be bound by all points of my present explanation, although I believe it to be fundamentally correct.

During operation I prefer to operate the charge storage electrode at a positive potential. Let us assume, for a specific example, that the grid foundation is operated at a potential greater than the point of unitary secondary-emission ratio for the insulator. Under these conditions the photoelectrons emitted from the front face of the charge storage electrode under the influence of light will be pulled through the grid meshes and some portion of them, at each elementary area, will be trapped on the insulator immediately behind the illuminated area, and thus a negative charge will be formed on the insulator which will represent in value the illumination intensity failing on the photoelectric surface emitting these electrons. Thus, there will be formed on the insulating surface facing the collecting anode if a charge image representing spatially the illumination intensity of the optical image. The charge storage electrode is then scanned by means of the beam from the gun under the control of the scanning oscillators and coils, and as it passes over the screen, certain of the electrons in the lower velocities in the scanning beam will tend to pass through the grid meshes to reach the collecting anode l2. A portion of the scanning beam may also impact the surfaces 2| of the charge storage electrode 5 and release therefrom a cloud of secondary electrons which tend to be attracted through the apertures of the electrode 5, by the potential on the collecting anode 12, as elemental streams of electrons.

Certain of the electrons in the scanning beam, however, will have higher velocities than others, and certain of these electrons will strike portions of the insulating surface with a suilicient velocity to create secondary electrons, thus creating a positlve charge thereon, the amount of which will be dependentupon the amount of negative charge already on that elementary area of the insulator and the number of such impacting electrons.

As the fixed charges vary in successive elementary areas in accordance with the optical image,.the potential of the insulator at the point of scansion will also vary, and more or less lowvelocity electrons from the beam and from the secondary electron cloud produced by the impact of the scanning beam on the surfaces 2| will pass through the charge storage electrode meshes, as determined by the combined charges on the insulator. Those electrons which do pass through the screen are collected upon the collecting electrode I2 and passed as a current through the output resistor 34, thus giving rise to a train of television signals, the amplitude values of which will represent the optical illumination of the points under scansion. At the same time, the action of the high-velocity component of the scanning beam, by producing secondary electrons, leaves a positive charge upon the insulator which tends to return to an equilibrium value due to the leakage through the insulator to the foundation. Equilibrium being accompllshed, with the next optical shift there is a new charge built up on theinsulator from the photoelectric emission which again modifies the beam on its next passage over that particular area. a

The charge storage electrode 5 may also be operated in such a manner that no secondary electrons are produced by the action of the scanning beam, the scanning beam in this instance having either a relatively very low or a relatively very high velocity in the plane of the charge storage electrode 5, and in this case the modulation is downward, the scanning beam simply being modulated by the charges fixed on the insulator; and equilibrium is also obtained in this case by leakage which, of course, is to be regulated so that equilibrium is obtained between optical image shifts.

There will be other methods of operating the device apparent to those skilled in the art whereby combinations of charges, either positive or negative, in accordance with the velocity of photoelectrons and scanning electrons reaching the insulator, can be utilized to modulate the electron beam as it sweeps over the charge storage electrode.

'My invention, as outlined in the instant case, utilizes therefore the cross-section of the scanning beam as an effective scanning aperture and no apertured anode is needed, collecting anode l2 being positioned so that it will receive electrons passing through the screen at any eleformed in space, asin the other embodiments referred to in my previous applications and patents listed above, although there is of course an electron image formed in the plane of the charge storage electrode while the photoelectrons are passing through the meshes of the electrode to charge the insulated surface.

I have therefore succeeded in forming a charge image on an insulating surface without the use of a photoelectric mosaic, and with very simple apparatus. Amplifications better than one thousand have been obtained without the use of excessively high voltages or complicated apparatus, thus eliminating the use of high-gain amplifiers with their accompanying noise factors.

I claim:

1. Means for producing television signals comprising a unitary apertured control electrode having a conductive foundation, a photoelectric face on one side thereof and an insulating face on the other side thereof, means for scanning said photoelectric face with an electron beam of relatively high velocity and of elemental dimensions, means for creating photoemission of relatively low velocity from said photoelectric face, means for drawing the produced photoelectrons through the apertures in said control electrode onto said insulating face, and means for collecting electrons passing therethrough.

2. In combination, an envelope containing a unitary apertured control electrode having a photoelectric face on one side thereof and an insulating face on the other side, means for causing photoemission from said photoelectric face, means for drawing photoelectrons through said apertures to charge said insulating face, and means for directing a stream of electrons of elementary cross-section through said apertures in the same direction as the movement of said photoelectrons, and means for collecting electrons from said latter stream passing through said control electrode.

3. The method of controlling an electron stream by an apertured grid, which comprises initiating photoelectron emission from one side of said grid, drawing said photoelectrons through the apertures in said grid, trapping said photoelectrons on the other side of said grid to produce a charge pattern thereon corresponding to said photoelectron emission, scanning said grid by an electron stream of elemental cross-section, and collecting electrons from said latter stream after modification thereof by said trapped charge.

4. The method in accordance with claim 3, wherein said photoemission is initiated by an optical image, and wherein the charge pattern produced spatially corresponds to the spatial elemental intensities of the optical image.

'5. An, arrangement for producing television picture signals comprising an apertured control electrode having a photoemissive face, means for creating on said electrode by photoemission from said face a charge image corresponding to an optical image to be transmitted, means for scanning said electrode with an electron beam of, elemental cross-section to produce by impact on said electrode a cloud of secondary electrons, means tending to cause a portion of the secondary electrons constituting said cloud to flow away from said electrode, the magnitude of said portion being controlled in accordance with the charge of elemental areas of said charge image, and means for producing from electrons flowing through the apertures in said electrode picture signals.

6. An arrangement for producing television picture signals comprising an apertured control electrode having a conductive foundation, a photoelectric face on one side thereof and an insulating face on the other side thereof, means for scanning said photoelectric face with an electron beam of elemental cross-section for causing elemental streams of electrons to flow through the apertures in said control electrode, means for projecting onto said photoelectric face an optical image to be transmitted to create photoemission from said photoelectric face, means for drawing the produced photoelectrons through the apertures in said control electrode onto said insulating face to produce on said insulating face a charge image corresponding to the image to be transmitted, elemental areas of said charge image modulating said elemental streams of electrons flowing through said electrode apertures, and means for collecting electrons passing through said apertured electrode to television picture signals.

PHILO T. FARNSWOR'I'H.

produce 10

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