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Title:
Color television
United States Patent 2330172
Abstract:
The present invention relates to systems for the production of television pictures in natural colors. There have been many proposals for utilizing the so-called additive method of color reproduction in television systems. In this system the final colored picture is obtained by superimposing...


Inventors:
Henry, Rosenthal Adolph
Application Number:
US26687639A
Publication Date:
09/21/1943
Filing Date:
04/08/1939
Assignee:
SCOPHONY CORP OF AMERICA
Primary Class:
Other Classes:
313/2.1, 313/465, 348/E9.025
International Classes:
H01J31/20; H04N9/31
View Patent Images:
Description:

The present invention relates to systems for the production of television pictures in natural colors.

There have been many proposals for utilizing the so-called additive method of color reproduction in television systems. In this system the final colored picture is obtained by superimposing a plurality of partial images, the color of each partial, image being one of the so-called primary colors of the particular color process employed. This process is usually a three color process employing certain red, green and blue colors as the primary colors, but other color processes such as a two color process have been proposed. The superposition of the partial images can be effected simultaneously or successively, and they can be projected one on top of the other, or the corresponding elements or lines of the partial images can be placed side by side or interleaved respectively.

The use of additive methods possesses the serious disadvantage that the light efficiency is poor. In the average only a small part of the incident white light is utilized in forming the color picture; for example in a three color system only one-third of the incident light is utilized.

In color photography an alternative method, known as the subtractive method, is used. In this system the color values are derived from the incident white light by the successive subtraction of certain portions thereof, by passing the light in succession through transparencies, each of which contains a record of one partial image in the form of a deposit having a color which is complementary to the primary color of, and a transparency proportional to the intensity of the partial image in question. Thus if a three color process based on red, green and blue as the primary colors is employed, the complementary color deposits in the three respective transparencies would be bluish green (minus red), magenta (minus green) and yellow (minus blue) respectively. At points corresponding to white in the final color picture each transparency is free from any color deposit so that the whole of the white light incident at this point passes through all the transparencies without substantial loss.

To produce a color picture by the subtractive method having the same brightness as a picture produced by the additive method only a fraction of the illuminating light is necessary, for example one third in the case of a three color system.

According to the present invention there is provided a color television system which employs the subtractivemethod. This is achieved by deriving from a transmitter by any known or suitable color separation method sets of modulated signals each representative of the intensity of one of the primary colors of the object to be transmitted, utilizing each of these sets at the receiver to produce a corresponding fugitive color deposit in a transparent screen, the color of the deposit in each screen being complementary to the primary color represented by the corresponding set of signals, and the density of the deposit in each screen being inversely proportional to the intensity of the primary color in the object, and passing white light through all the screens in succession on to a reproduction surface.

The transparent screens are preferable image screens of the ionic crystal material type described in co-pending application No. 253,182. If certain crystals, which are normally transparent to visible light, are struck by a beam of cathode rays, X-rays, radium rays, or by light of a suitable wave length, a deposit of opaque material, which is constituted by what will hereinafter be referred to as "opacity centres," is created in this crystal,.the degree of opacity depending on the intensity of the incident radiation. Examples of such crystals are many of the alkali and alkaline earth halides, such as the chlorides, bromides and iodides of sodium and potassium, lithium bromide, calcium fluoride, and strontium fluoride and chloride; and also certain silver salts such as silver bromide. In the case of the alkali halide crystals research has indicated that the opacity centres probably consist of neutral alkali atoms which are loosely bound in the interior of the crystals in some manner or bther, and which are similar to the deposit of metallic silver in a latent photographic image. The deposit of metal in the crystal lattice can also be created by heating an alkali halide crystal in an atmosphere of the vapor of its alkali metal, which diffuses into the crystal.

Once formed, the opaque deposit can also be destroyed by the above mentioned rays, the amount of destruction in a given time interval depending on the intensity of the rays and on the density of the deposit already formed. Thus the gross effect of any given intensity of the incident radiation, being the result of an equilibrium between the formation and destruction of the deposit, may be an increase of the deposit for low intensities and a decrease for the high intensities, in a manner similar to the well known "solarisation" of the latent photographic image. Thus, over a range of low intensities of the incident raSdiation, increase in intensity wvill result in an increase of the deposit, whilst over a range of high intensities an increase in intensity will result in a decrease of the deposit. The materials exhibiting this property may be defined as ionic crystals in which the injection of electrons Into the crystal lattice can produce an opaque deposit which can be moved within the crystal lattice by application of electric fields and heat.

In the co-pending application referred to above there is contemplated the use of a transparent crystalline material of the type defined in the image screen of a television receiver. The material may be in the form of a single flat crystal, a mosaic of small crystals, or a micro-crystalline structure. A composite crystal or a mixture of the two or more of such crystalline materials may be used. In most cases, and particularly when the material is in the form of a single crystal, a disappearance of the opaque deposit can be produced by maintaining the crystal in an electric field and at a suitable temperature, in which case the deposit is drawn through the crystal towards the positive pole producing the electric field. When it reaches the positive pole it disappears, leaving the crystal substantially transparent. The speed of movement of the deposit depends upon the strength of the field and upon the temperature, and can be varied within wide limits by varying either magnitude. For a given field strength this speed of movement increases with the temperature of the crystal. The spectral transmission of these colored deposits is different for different materials, and can also be varied by changing the temperature.

Thus for a given alkali'halide crystal the spectral absorption curves get broader and the region of maximum absorption is shifted towards the longer wave-lengths with increase of temperature. Thus by a suitable choice of material and/or operating temperature screens having deposits of the colors necessary for any color process can be obtained. For example in a three color process based on red, green and blue as the primary colors, suitable materials for the three screens are the following alkali. halide crystals: KBr, KI, RbCl, RbBr, for the minus red deposit, KC1, NaBr for the minus green deposit and NaC1, LiAC, KF for the minus blue deposit.

A preferred embodiment of the invention as applied to a television receiver intended to reproduce colored pictures according to a three color process will now be described by way of example with reference to the ,accompanying drawings in which Figs. 1 and 2 show diagrammatically two alternative arrangements according to the present invention.

Referring to Fig. 1, three cathode ray tubes I, 2 and 3 are provided, each comprising a transparent image screen indicated at 4, 5 and 6 respectively. Each screen is situated in an electric field provided by pair of transparent electrodes 7, 8 and 9, across which is maintained a potential difference by means of a source of potential 10. The screens are also maintained at a suitable temperature by means, of a thermostatic control of suitable form, which in the example shown consists of a source of current 11 for each tube which passes a current through one of the electrodes 7, 8 and 9 of each screen, the amount of the current and hence the temperature for each screen being controlled by a thermo-couple 12 in each screen. The details of the various forms of the tubes shown in the drawings and thermostatic control means therefor are fully disclosed in co-pending application Serial No. 253,182 and being fully described therein, are only shown diagrammatically in the present application. Means indicated at 13, 14, 15 are associated with the tubes for producing a scanning cathode ray beam, and amplifying arrangement 16 by signals representative of one of the primary colors of the object being transmitted. The sense of the modulations applied to the beam is such that the density of the deposit produced is inversely proportional to the intensity of the corresponding primary color. The three beams are caused to traverse the three screens 4, 5 and 6 in synchronism by means of scanning coils 13a, 14a, and 15a.

The material and/or temperature of the screens are chosen so that the colored deposits produced therein have the required complementary colors. White light from a suitable source 17 is projected successively through the three screens 4, 6 and 6 in such a way that the screen images are superimposed in register on a reproduction surface 18. This can be done by fully illuminating the first screen with a condenser system 19 which also forms an image of the light source II on a first projection lens 20 situated between 'the first two screens 4 and 5.

This projection lens 20 forms an image of the first screen 4 on the second screen 5 in register, and the light is focussed by means of a field lens 21 on to a second projection lens 22 which forms an image of the second screen 5 on the third screen 6 in register.. A field lens 23 focusses the light passing through the screen. 6 into a final projection lens 24 which forms an image of the third screen 6 on the reproduction surface 18, forming thereon the final col6r picture.

It will be noted that with the inverting optical system shown the image on the screen 4 must be inverted, that on screen 5 upright and that on screen 6 inverted, so that the projection lens 24 forms an upright image of the screen 18.

This can be arranged by applying the deflecting currents to the coils 13a, 14a and 16a in a suitable sense.

An alternative arrangement is shown in Fig. 2, In which parts similar to those of Fig. 1 are given the same reference numerals. The first screen 4 in the tube I is the same as that shown In Fig. 1. In place of the two tubes 2 and 3 of Fig. 1 there is used in the arrangement of Fig. 2 a single tube 25 having two cathode ray guns 14 and 15, and a double screen which is composed of two screens 26 and 27 separated by a common transparent positive electrode 28 and having on their outer surfaces transparent negative electrodes 29 and 30 respectively. Thus electrical fields are maintained in the screens in such a way that the color deposits in the two screens will move towards each other and disappear at the common electrode. The beam from the gun 14 produces in the screen 26 an image corresponding to the image on the screen of Fig. 1, and the beam from the gun 15 produces in the screen 27 an image corresponding to the image on the screen 6 of Fig. 1. A lens 31 forms an image of the screen 4 on the composite screen 26, 27, and the projection lens 24 acting in conjunction with a collecting lens 32 forms the final image on the projection screen 18. In a three color process the tube 25 would be used in conjunction with a single tube containing another screen, as shown in Fig. 2, whilst for a two-color process it could be used alone. : As pointed out in the co-pending application referredif - ~ e6 the i-e'fea iaiii@ g ci~ en ture- pert3na 'ccurs;"it Is"rnecessry to transmit more than 50 partial images per second in order to avoid flickering at high intensities.

In the present system in which complete storage of the partial images over the picture period are possible a picture repetition frequency of 17-20 per second is completely satisfactory, and hence the total width of the frequency band necessary to transmit the signals is no greater than that required to transmit the signals representing a black-and-white picture by methods in which no storage of the received picture takes place.

I claim: 1. Television receiving apparatus for the reproduction of colored objects, said apparatus comprising means for receiving N sets of transmitted signals each representative of one of the N color components of the object to be transmitted, N transparent screens each corresponding to one of said sets of signals and each screen including a layer of an alkali halide, means for scanning each of said N screens with a cathode ray beam, means for modulating the N cathode ray beams each with the corresponding set of received signals, said alkali halides being of such nature and being held at such a temperature that as a result of said scanning there is produced in each screen an image in a color which is complementary to the color of the corresponding transmitted color component, the density of said image being inversely proportional to the intensity of said color component, means for rendering said image fugitive within the frame scanning period and optical means for projecting a light beam through said screens to form a composite color image of the transmitted object.

2. Television receiving apparatus for reproduction of colored pictures comprising a plurality of cathode ray tubes, each tube being controlled by a transmitted color component of the original picture, a screen surface on each of said cathode ray tubes adapted to be scanned by an electron beam produced in each of said cathode ray tubes, 6 said screen being composed of a material which when subjected to electronic bombardment has a color complementary to the color of the corresponding component of the original picture, said material being normally transparent when not subjected to electronic bombardment, the intensity of the color of any elemental area of said surface being proportionate to the intensity of electronic bombardment, means for modulat- 7 ing said cathode ray beam inversely proportionate to the color intensity of said component of the original picture, a source of light and means for viewing a complete image, said cathode ray tubes being. positioned between said source of 7 light and said viewing means in such a manner that light will pass in series through said tubes ~:tand the various color components of the ligiht will be successively subtracted therefrom in proortion c --rresVondiw g efsaft1 reondingi-idlrk BleĆ½n8ft Pa 6siof' 3 ` screens d 3 3'vAteevisilo eceiving-appraitu&d ti7 (fyi described cli al wiaime.~r'in sain  screi'ed atin' teadl coaatesatiaanjpaĆ½fift atkalihalidjier -a tblivlifoneeivinig'apaatusPety tentai across said layer. - 'i.a. i.. 6. A television receiving apparatus of the type described in claim 2 wherein said screen com20 prises a transparent alkali halide layer between a pair of transparent electrodes adapted to create a potential difference across the alkali halide layer.

7. A television receiving apparatus of. the type 25 described in claim 2 wherein said screen comprises a transparent alkali halide layer between a pair of transparent electrodes adapted to create a potential difference across the alkali halide layer, and a means for controlling the tempera30 ture of said alkali halide layer.

8. A television receiving apparatus of the type described in claim 2 wherein said screen comprises a transparent alkali halide layer between a pair of transparent electrodes adapted to create ;5 a potential difference across the alkali halide layer, and a means for controlling the temperature of said alkali halide layer, said means comprising a source of current in circuit with one of said transparent electrodes and a thermostat 0 controlled by the temperature of said alkali halide layer controlling the amount of current flowing through said electrode from said source of current in accordance with the temperature of said alkali halide layer.

.5 9. A television receiving apparatus of the type described in claim 2 having three screens and said screen material comprising a transparent alkali halide layer, wherein one of said screens is formed of an alkali halide from the group 0 consisting of potassium bromide, potassium iodide, and rubidium chloride, and another of said screens is formed of an alkali halide from the group consisting of potassium chloride and sodium bromide, and the third screen is formed of an alkali halide from the group consisting of sodium chloride, lithium chloride and potassium fluoride.

10. Television receiving apparatus for the reproduction of colored objects, said apparatus 0 comprising means for receiving N sets of transmitted signals each representative of one of the N colored components of the object to be transmitted, N screens each corresponding to one of said sets of signals and each screen including 5 a layer of an ionic crystal material, means for scanning each of said N screens with a radiant beam, means for modulating the 1 radiant beams each with the corresponding set of received signals, said crystal materials respectively being of ) such nature that said scanning will produce in each screen an image in a color which is complementary to the color of the corresponding transmitted color component, the density of said image being inversely proportional to the intenSsity of said color component, means for renderIng said image fugitive within the frame scanning period, and optical means for projecting light through said screens to form a composite colored image of the transmitted object.

11. The combination in an apparatus to form an image of an object, of a plurality of normally transparent layers of Ionic crystal material each provided with two opposite faces, each of said layers being of a different ionic crystal material, all of .the materials being such that colored areas movable between said faces may be created therein by a radiant beam, but said materials respectively being such that the colored areas created in each will be complementary to a different primary color, a scanning means for each layer, means to control each scanning *means in accordance with the intensity of a primary color in the object and to modulate said scanning means to an intensity inversely proportional to the intensity of that primary color in the object to thereby create colored areas in the complementary color in successive elemental portions of the layers, and means to restore said layers to their normal light transmitting characteristics within a predetermined time period.

ADOLPH HENRY ROSENTHAL.