US2568448A

US2568448A - Parallax correction in color television

Info

Publication number: US2568448A
Application number: US775731A
Authority: US
Inventors: Hansen Siegfried
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1947-09-23
Filing date: 1947-09-23
Publication date: 1951-09-18
Anticipated expiration: 1968-09-18
Also published as: FR983016A; GB656207A

Description

Sept. 18, 1951 s. HANSEN 2,568,448

PARALLAX CORRECTION 1N COLOR TELEVISION Filed sept. 2s. 1947 Hi A Attorney `Patented Sept. 18, 1951 UNITED STATES PATENT OFFICEv PARALLAX CORRECTION IN COLOR TELEVISION Siegfried Hansen, Los Angeles, Calif., assignor to General Electric Company, a corporation of New York 4 Claims. l

This invention relates to improvements in television tubes of the type comprising a plurality of alternate primary color strips on either the screen of a receiving tube or the color filtering screen of a transmitting tube and a plurality of grid wires arranged to direct an electron beam alternately and selectively to the color strips. It has for its general object the provision of a screen construction which avoids parallax errors in tubes of that type.

The invention itself together with further objects and advantages thereof will best be understood by reference to the following specification when taken in connection with accompanying drawings in which the Fig. l represents schematically a prior art tube construction o i the aforementioned type which illustrates the parallax errors which it is the object of the present invention to correct; Fig. 2 represents schematically television tubes have a grid and color strip arrangements improved in accordance with the invention to avoid parallax errors, while the Figs. 3 through 8 illustrate various steps in one process or method for constructing the improved color strip arrangement of the Fig. 2.

The Fig, 1 represents in schematic cross section a typical receiving tube of the type now known in the art (cf. British Pat. No. 443,896-

General Electric Co., Ltd. and Leslie Connock Jesty) and may comprise generally, an electron gun I, a conventional vertical-horizontal deflection plate system IA, a grid 2 and a picture screen 3 comprised of a plurality of threads or strips 4 of fluorescent material of` different colors arranged in parallel configuration (i. e. normal to the plane of the ngure) on a glass plate 5. These fluorescent strips may comprise any suitable fluorescent material capable of fiuorescing under impact of electrons in suitable colors (preferably'the primary colors green, red and blue) and distributed in the order indicated by the initials G, R and B in the Fig. l. The grid 2 may comprise a series of parallel wires arranged in a configuration generally parallel to the screen 3, each of the individual wires being parallel to the colored strips of the screen. As will be noted from the gure, all of the green strips of the screen are aligned with the gaps between the individual grid wires; all of the red strips are aligned with the alternate grid wires G which are electrically common by virtue of the common lead 1; while all of the blue strips are aligned with the intermediate grid wires 8 which are similarly electrically common by virtue of their connection to the lead 8.

In the operation of devices of the type shown in the Fig. 1, it has heretofore been assumed that an electron beam which is adapted to excite the picture screen 3 approaches that screen normally, i. e. as though the distance from gun I to screen 3 were great enough to cause the beam to strike the screen at a substantially angle at all portions of the screens surface. In that event, if there be no potential diierence between the grid wires E and the grid wires 8, all electrons of the stream will pass in substantially straight lines centrally through the interstices between the grid wires and impinge only upon the green strips I. If the alternate grid wires 6 have a positive potential imposed upon them with respect to the intermediate wires 8, then the electron beam will be focused to impinge only upon the red strips. Similarly, if that potential relation be reversed and the wires 8 made more positive than the wires 6, then the electron beam will be caused to focus on the blue strips. In a manner readily understood by those skilled in the art, the entire screen may be scanned by an electron beam by appropriately varying the potential difference between wires 6 and wires 8, the beam may be caused to scan in repeating cycles first the red series of strips, then the green series and then the blue. The latter effect may be accomplished by imposing a suitable potential wave upon the wires 6 and 8 by a suitable voltage source Ill which may be a relaxation oscillator or similar device producing a block or square shaped wave of the type shown graphically within the block.

It has been found that the assumption of normal approach of al1 electron particles of beam to the color screen is not suiliciently accurate in practice and will give rise to undesirably large parallax errors when the beam is emanating from point source such as point Il representing the center of deflection of the conventional beam deflection system employed and positioned at the usual finite distance from the grid-screen structure. The error thus introduced may in practice be sufficient to cause considerable distortion in the proper color relationships of the picture and may be viewed as being caused in the following manner. Assuming that there is no potential difference between the grid wires 6 and 8 and thattherefore the beam is intended to strike only the green strip, it will be noted that for the outer peripheral portions of the screen 3, the beam in traversing the interstices between any two grid members may be directed at the blue or red strips rather than the green because of the angular relations involved, This is illustrated for example by the dotted line I2 repre .3 senting one illustrative position of the beam. It will be noted that because of the angular relationL caused by the proximity of the point II to the screen structure, the beam has been directed.

, of deflection will usually be the same regardless of the direction of the beam path across the screen.

It will be understood that the arrangements of the Figures 1 and 2 will be enclosed in any of the suitable envelopes known for cathode-ray devices y of this nature in the art. The screen 3 may comployed in practice this parallax effect may be y enough to introduce substantial distortion.

In order to avoid the mentioned parallax effects, there is provided the arrangement shown in Fig. 2 wherein the color strips of screen 3 are positioned in more widely spaced relation than the Wires of grid 2 in order,to.compensate for the divergence of the beam especially in these outer portions. It will be noted that in this case the red strips 4 are aligned with the wires 6 of the grid but not by way of parallel lines as before. In this case, they are all aligned along radii (illustrated by dotted line I3) emanating from the point source of the electrons at the point II and each passing through one of the grid wires 6 and the corresponding red strips 4. Substantially, the same arrangement is employed for the green strips 4 which are similarly aligned with the interstices between the grid wires along radii (illustrated by dotted line I4) extending from the point II and through those interstices. The same arrangement is made with the blue strips 4 which in this case are aligned along radii (illustrated by dotted line I5) through the grid wires 8 and converging at the point II. The effect is, therefore, to increase the pitch of the screen (the spacing between the centers of adjacent color strips) with respect to the pitch of .the grid wires (spacing between centers of adjacent wires) by a factor determined by the relative spacings of point Il, grid 2 and screen 3. The relation between the pitch of the grid wires and that of the screen color strips may be represented in general form by the following formula representing the situation -for a parallel grid plane configuration andv a parallel color screen:

Where: l

Ps=the pitch of the screen color strips Pg=the pitch of the grid wires A=spacing between grid and screen B=spacing between center of deection and screen the case of the conventional electrostatic deilecl tion plate systems, the center of deflection of that set of plates which sweeps the beam in the direction normal to the length of the color strips and grid wires is the one of importance to the invention. For magnetic deflection systems, the center prise either lthe end face of such a tuoe or it may comprise a separate glass plate mounted therewithin. The grid 2 may be mounted in any suitable manner within the tube in parallel relation f to the screen.

'Ihe following described process will be found to be one particularly suitable to the construction of parallax corrected color strip screens of the type of Fig. 2. A principal advantage lies in the fact that it obviates difficulties inherent in conventional methods of measuring and controlling the very small differences in pitches required by expression (1). As a rst step, there may be manufactured a set of printing plates for printing in three steps each of the three series of color strips upon plate 5. The printing'plates may be fabricated by a method similar to that used in photo-engraving, and which may be illustrated by the Figs. 3 and 4. For the first printing plate which is to be used for printing the green strips 4 of Fig. 2, a glass plate I9 provided with a series of fine parallel lines 20 having the same relative position and spacing as the interstices of the wires of grid 2 (e.g. 0.005 lines with 0.005 spacing) is positioned between a point source of light 2I and a photographic plate 22 which may be of glass or similar material provided with a coatingV 23 of any suitable photosensitive emulsion. By point source of light is of course, meant any source having as little dimension as practicable except along the direction parallel to the color strips or grid wires, i. e. a point or line source. The lined glass plate I9 will be positioned with respect to thelight source 2I in a position corresponding to that which the grid structure 2 would have with respect to the point II in the Fig. 2 with lines 20 corresponding in position to the grid wire interstices. Similarly, the photographic plate,22 will be in a position corresponding to that of the screen in Fig. 2. The spacings are not necessarily identical with those in the final tube structure, but must be in the same relative proportion after taking into account all contributing factors such as index of refraction in the glass, etc. It will be apparent, therefore, that if the light from the light source 2I be allowed to illuminate the photographic plate, there will be formed thereon a negative having translucent lines (unexposed portions) corresponding to the desired distribution of the green color lines on the screen 3 of Fig. 2. The positions of the latter will be precisely those desired for the correction of the parallax error. After exposure and development the glass photographic plate 22 with its negative may, as indicated in Fig. 4, be imposed upon a copper printing plate 24 which is provided with a photo-sensitive emulsion lm 25 which renders plate 24 acid resistant at any points which have been exposed to light and yet capable of being acid etched at unexposed points. Plate 24 may thus be of the type common in the photo-engraving art and the etching process there employed may be used. If a print of the negative on plate 22 be made upon the film 25 by exposure to light there will be formed on the lm 25 print of a series of lines (exposed portions) corresponding in position to the desired position of the green color strips 4 in the screen of Fig. 2. By appropriate acid treatment the intermediate unexposed portions may be etched away in the usual manner and there will remain at the exposed portions of the copper plate 24 a series of elevations or ridges 2B in the coniiguration of parallel lines corresponding to the desired position of the green color strips 4. The copper plate in this form is indicated in the Fig. 5. the ridges 26 being positioned in the green strip configuration and intervening grooves being in positions corresponding to the positions of the red and blue color strips 4 of screen Blof Fig. 2.

The copper plate 24 may be employed to print the color strips of green fluorescent material upon the plate 5 of the Figs. 2 and 6 in the following manner. The ridges 26 may be thinly coated with a suitable adhesive material to which a phosphor powder will adhere and the plate 24 lmay be pressed against the glass plate 5 thereby leaving thereon a series of lines of the adhesive material in proper positions. Thereafter the plate 5 may be dusted with the appropriate phosphor material which will adhere to the adhesive material as a binder. Excess phosphor material may then be removed by use of a iine brush or by blowing with an air stream.

The width of the ridges 26 may be readily controlled during the etching process in order to insure that they are neither too narrow nor too wide to form a color strip print of the desired width. If the acid etching action be of short time duration, the grooves between ridges 26 will be small and consequently the ridges will be wide. Conversely, if the action be of long time duration, the grooves will be large and the ridges of correspondingly narrow width. The manner of control of etching time to this end is well known in the art.

The same method may be employed for printing the red and blue lines upon the plate 5. For those cases, there may be prepared one or more printing plates similar to plate 24 but having a series of elevations or ridges corresponding in position to the position of the red and blue strips of the screen 3 in Fig. 2. A separate plate may be prepared for each of the red series and the blue series of lines if desired but as will be indicated below a single reversible plate may be made to serve the purpose of both. Such a plate is shown in the Figs. 6 and '1 as plate 21 having ridges 28. In the Fig. 6 it is shown as being employed to print the blue lines; while in the Fig. 'Z it is shown as being employed in a position inverted with respect to that of Fig. '1 to print the red lines. As will be observed from a study of the color strip coniiguration of the preceding figures, a plate of this nature must be capable of printing a blue line in each of one series of alternate gaps between the uniformly spaced green lines; while for the red lines the plates must be capable of printing a red line in each of the remaining series of alternate gaps not occupied by the blue lines.

Thus, the plate 21 will obviously have a spacing between ridges 28 which is exactly twice the spacing of the ridges 26 on plate 24 of the Fig. 5 employed to print the green lines. The Fig. 6 indicates the plate as in the proper position to print the blue lines in vone series of alternate spaces between the green lines in the pattern corresponding to that of Fig. 2. In the Fig. 7, the plate has simply been inverted with respect to its Fig. 6 position whereby the order of the ridges 28 of the plate 21 is transposed to correspond to the other series of alternate spaces between the green lines thus corresponding in position to the position of the red lines in the Fig. 2.

The manner oi' preparing the plate 21 employed in the Figs. 6 and '1 is substantially the same as that employed to prepare the plate 24 for the printing of the green lines and the iirst step is indicated schematically in the Fig.' 8 which corresponds to that of Fig. 3. In this case, however, a lined plate 29 corresponds to the plate I9 of the Fig. 3 but has a series of ne parallel lines 30 with three times the spacing between them as was the case with the plate I9 (e. g. 0.005 inch lines with 0.015 inch spacing). The lined glass plate 29 may be positioned with respect to the light sourcp 2l in a position corresponding to that which the grid structure 2 would have with respect to the point i l in Fig. 2 with the lines 30 corresponding in position to the grid wires 8. Similarly the photographic plate 3l having emulsion iilm 32 will be in a position corresponding to that of the screen in Fig. 2. It will be apparent therefore that if light from the source 2l now be allowed to illuminate the photographic plate, there will be formed thereon a negative having translucent lines (unexposed portions) corresponding to the desired distribution of the blue lines of the colored screen 3 of Fig. 2. The position of the negative lines will be precisely those desired for the correction of parallax error. From` already described in connection with the printing of the green lines. y

The red lines may be printed upon the plate 5 in substantially the same manner. If desired a separate printing plate 21 could be prepared for the red lines simply by inverting the lined plate 29 of Fig. 8 and preparing a negative which would then have lines corresponding to the red color strips. However, it will be observed that the preparation of a separate plate for the red lines is rendered unnecessary by virtue of the fact that the plate 21 used to print the blue lines may simply be inverted and used as the printing plate for the red lines because the inversion will bring the ridges 28 into the proper order or configuration corresponding to the proper position of the red lines.

The method of imprinting color strips on,

out departing from the invention in its broader aspects, and therefore, the appended claims are intended to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electrical beam deflection device for color television comprising a color screen having a plurality of intermeshed sets of different color strips. the strips within each set being of the same color, a source of an electrical particle beam adapted to be deflected about a center of deilection to scan said screen and a control member positioned between said screen and said center of deflection including a plurality of elongated control members positioned between said screen and said center of deflection fordetermining the set of color strips on which the beam impinges when scanning the screen, the elongated conductors corresponding in number to one set of strips of said screen and supported in spaced apart relation, the space'between adjacent conductors bearing the same ratio to the spacing between adjacent color strips of one set as the distance between the center of defiection of the beam and the control member bears to the distance between the center of deilection of the beam and the surface of the screen whereby parallax errors in the impingement of the beam on a selected set of color strips is substantially eliminated.

2. An electrical beam deilection device for color television comprising a color screen having three intermeshed sets of different color strips, the

strips within each set being of the same color,

a source of an electriealparticle beam adapted to be deflected about -a center of deflection to scan said screen, a control member positioned between said screen and said center of deflection comprising two sets of elongated conductors with each set insulated from the other, the conductors of one set being supported on radii extending from the center of deflection to one set of color strips, the conductors of the other set lying on radii extending from the center of deflection to a second set of color strips and the third set of color strips lying on radii passing from the center of deflection and through the spaces between the two sets of conductors.

3. An electrical beam deflection device for color television comprising a color screen having a plurality of inter-meshed sets of different color elements, the elements within each set being of the same color, a source of an electrical particle beam adapted to be deflected about a center of deilection to scan said screen and a control member positioned between said screen and said center of deflection including a plurality of electrostatic control portions positioned between said screen and said center of deflection for determining the set of color elements on which the beam impinges when scanning the screen,

the electrostatic control portions corresponding in number to one set of elements of said screen and supported in spaced apart relation, the space between adjacent control portions bearing the vsame ratio to the spacing between adjacent color elements of one set as the distance between the center of deflection of the beam and the control member bears to the distance between the center of deflection of the beam and the surface of the screen whereby parallax errors in the impingement of the beam on a selected set of color elements is substantially eliminated.

4. An electrical beam deflection device for color television comprising a color screen having three inter-meshed sets of different color elements, the elements within each set being of the same color, a source of an electrical particle beam adapted to be deflected about a center of deflection to scan said screen, a control member positioned between said screen and said center of deilection comprising two sets of conductors with the conductors of each set connected together and insulated from the other, the conductors of one set being supported on radii extending from the center of deflection to one set of color elements, the conductors of the other set lying on radii extending from the center of deilection to a second set of color elements and the third set of color elements lying on radii passing from the center of deilection and the spaces between the two sets of conductors.

SIEGFRIED HANSEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Great Britain Nov. 5, 1935