Title:
Television scanning
United States Patent 2274366


Abstract:
My invention relates to the art of television and particularly to the scanning of the screen of a cathode ray tube employed therein. A television system well known at the present time employs double interlaced scanning and has a frame frequency of 30 per second. Such a frame frequency is much...



Inventors:
Siegfried, Hansen
Application Number:
US25919439A
Publication Date:
02/24/1942
Filing Date:
03/01/1939
Assignee:
GEN ELECTRIC
Primary Class:
Other Classes:
348/E3.053
International Classes:
H04N3/34
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Description:

My invention relates to the art of television and particularly to the scanning of the screen of a cathode ray tube employed therein.

A television system well known at the present time employs double interlaced scanning and has a frame frequency of 30 per second. Such a frame frequency is much higher than is necessary to preserve continuity of motion in the reproduced picture, hence the system is wasteful of band width. Efforts have been made in the past to reduce the frame frequency, namely, the number of pictures per second, without introducing flicker or impairing continuity of the reproduced picture by the use of interlace higher than double. Such higher interlacing however, introduces an objectionable amount of that phenomenon called "crawl," namely, the crawling effect of the picture lines, which becomes noticeable when the observer moves his eyes at a certain speed up or down the picture such as when following a moving object shown thereon.

It is the object of my invention to provide an improved method of scanning in a cathode ray tube and an improved apparatus for carrying out that method whereby the excessive band width may be materially reduced without the addition of an objectionable amount of crawl.

In accordance with my invention, I move the electron beam of the cathode ray tube or tubes in a television system in a manner to cause the beam to scan the screen thereof successively in a plurality of spaced parallel lines and thereafter to scan the screen intermediate said lines in a plurality of interlaced lines. As a result I have found that the frame frequency may be greatly reduced without producing an objectionable flicker or lack of continuity of motion. The reduction of the frame frequency permits a corresponding reduction in the band width of frequencies required for the transmission of the picture. Because of the interlaced interlace scanning which I employ the amount of crawl produced is not objectionable.

My invention will be better understood from the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

Referring to the drawing, Fig. 1 is a circuit diagram illustrating by way of example, one form of apparatus embodying my invention; Figs. 2, A and B, shows the path traced by the electron beam in two simplified arrangements of that form of my invention illustrated by Fig. 1 and Fig. 3 is a diagram similar in part to Fig. 1 illustrating a modification. Because of the great difficulty, if not the impossibility of constructing a patent drawing with which one could trace the movements of the beam in a cathode ray tube in scanning a frame or picture comprising several hundred lines, I have chosen to describe my invention first as applied to an extremely simple form embodying only a few lines which are widely spaced apart. Having explained the principle by means of this simple example its application to a commercial form will be readily apparent.

As is well known to those skilled in the art the electron beam of a cathode ray television tube is made to scan the tube screen or target whether the tube is of the transmitting type or the receiving type by causing the beam to move simultaneously in two directions substantially at right angles to each other, one being in the direction of the scanning lines, usually horizontal, and the other substantially at right angles thereto, hence, usually vertical. In accordance with one form of my invention, I cause the beam first to scan successively every fifth line, that is, it successively scans lines 1, 6, 11, 16, etc. to the end of the picture and then to scan the intermediate lines in an interlaced manner. This system of scanning I have termed, interlaced quintuple interlace.

This may be more readily understood by referring to Fig. 2A where the scanning lines 1, 6, 11 and 16 are shown by a full black line, the horizontal fly backs being shown by lighter full lines. Since lines 1, 6, 11 and 16 divide the total scanning lines into groups of five it is convenient to consider every fifth line as having the same number, such being shown in Fig. 2A by the second column of numbers. In this figure it will be seen that the number of lines called 1, shown by a solid line, is 3%, the first line 1 beginning at the point 1 and the last line 1 terminating at the point 2, its length being 3/% the length of a full line. Vertical fly back then occurs taking the line to the point 3 at the top of the picture where a new line starts which is line 3, represented by dashes. The last portion of line 3 terminates at the point 4 whence fly back takes it to the point 5 at the top of the picture. Line represented by a dash and two dots, now begins, terminating at the point 6. Fly back carries the line to the point 7 where line 2, represented by dots, begins. Line 2 terminates at 8, fly back carries it to 9 where line 4, represented by a dot and a dash, begins. Line 4 terminates at 10. At this point the scanning is complete and the line returns to the starting point 1. Thus the picture is scanned with a quintuple scanning and the lines comprising each group of five are scanned with an interlaced scanning, hence I have applied the term "interlaced quintuple interlace." The advantage of the above-described system of interlacing is that the number of frames or pictures per second may be very materially reduced without sacrificing continuity of motion or producing flicker and without objectionable crawl. I have found, for example, that whereas the number of frames or pictures per second common heretofore has been 30, by employing my invention, I can reduce that number by the factor, 2.5, .namely, to 12 frames per second and still obtain equally good results. The important result of such a material reduction in the frame frequency required is that it obviously permits a corresponding reduction in the band width of frequencies necessary to transmit the pictures with the same degree of definition. For example, where a band width of approximately 4 megacycles was necessary for a 441 line picture with a frame frequency of 30, a band width of approximately 1.6 megacycles is sufficient for substantially the same number of lines with a frame frequency of 12. If, however, one is more interested in obtaining greater detail he may retain the 4 megacycle band width but increase the number of lines.

The interlaced quintuple interlace system of scanning which I employ is obtained by supplying the proper frequencies to the beam deflecting means of a cathode ray tube of a well known form employed in television. In the case of the simplified form illustrated by Fig. 2A where the picture comprises only 18 lines, the line or horizontal frequency may be 216 cycles -per second and the field or vertical frequency may be 60 cycles per second. A 216 cycle frequency represented at 12 will therefore be applied to the horizontal deflecting means of the tube and a 60 cycle frequency represented at 13 will be applied to the vertical deflecting means thereof. The combined effect of the two electric fields resulting from these two frequencies operating at right angles to each other is to cause the cathode beam to make a trace on the screen approximately of the form shown by Fig. ZA. For convenience in making the drawing I have not attempted to show the various lines, particularly the fly backs, exactly as they would actually appear since an approximate showing is ample. for the purpose of disclosing my invention. It will be noted that the ratio of the line frequency, 216 cycles, to the vertical frequency 60 cycles, is 3%, namely an integer plus %. This corresponds with the total number of each of lines 1, 2, 3, 4 and 5 in Fig. 2A as pointed out above which was 3%. The number of complete pictures per second is equal to 60 divided by 5 namely 12, there being 5 fields to each frame or picture.

Having described the simplified form of my invention, I shall now refer to the more practicable form illustrated by Fig. 1 and applied to a system having 448 scanning lines, approximately the present standard number of lines. In this figure the cathode ray tube 15 is shown as a television camera or transmitting tube having the mosaic screen 16 and the optical system I1 by which pictures may be projected on the screen from the film 18 which may be a motion picture film moved intermittently in the well known manner. The tube is also provided with the usual electrodes connected in the usual manner but not shown in the drawing. For produting the horizontal and the vertical deflections of the beam the tube is shown provided with the deflecting windings 20 and 19 respectively which may be of any suitable and well known form. The frequencies for controlling the scanning movements of the beam originate with the master oscillator 25 which, in the form of my invention represented by Fig. 1, produces a frequency of 26,880 cycles per second. This frequency is supplied to the multivibrator 26 which, having a ratio of 5, reduces the frequency to 5376 cycles per second. It is also supplied to the chain of multivibrators 21, 28 and 29 which, having ratios respectively of 8, 8 and 7, reduce the frequency respectively to 3360 cycles, 420 cycles and 60 cycles per second. The deflecting windings 20 and 19 are supplied with saw tooth waves having frequencies respectively of 5376 cycles and 60 cycles per second from the saw tooth generators 30 and 31 which may be of any common and well known construction. The generator 30 is controlled in a well known manner by the 5376 cycle frequency supplied to it from the multivibrator 26 and likewise the generator 31 is controlled by the 60 cycle frequency supplied to it from the multivibrator 29. The ratio of the line .frequency, 5376 cycles, to the vertical frequency, 60 cycles, in this case is 89%; thus, as in the previously described example, this ratio is an integer plus %. The frame frequency or number of complete pictures per second is equal to 60 divided by 5, namely 12, rather than 30, the number common at present.

For radio transmission of the output of the cathode ray tube and the synchronizing signals I have shown the radio transmitter 34 connected to`-receive the output of the tube 15 and to receive the output of the supersynchronizing pulse generator 35 which may be of any suitable and well known form, the generator being controlled by connections with the multivibrators 26 and 29 whereby the line and framing synchronizing pulses may be transmitted to the receiver.

Referring back to Fig. 2A it will be remembered that lines 1, 2, 3, 4 and 5 of each group were interlaced so that scanning took place in the order 1, 3, 5, 2, 4, this order being the result of there being 3% lines of each number or, what is the same thing, of choosing a line frequency and a'vertical frequency having the ratio of 3%.

My invention is not limited to this particular form of interlacing of the lines in each group but applied equally well if they are interlaced such that scanning occurs in the order 1, 4, 2, 5, 3. For that order of scanning there will be 3%/ lines of each number or, what is the same thing, the ratio of the line frequency to the vertical frequency will be 3%. Such an arrangement is represented by Fig. 2B where the lines are represented in the same manner as in Fig. 2A, the line frequency is 204 cycles per second, and the vertical frequency is 60 cycles as before. Obviously, 3 plus % equals 4 minus %. Since in Fig. 2A the ratio is 3 plus % and in Fig. 2B it is 4 C5 minus %, it will be seen that in accordance with my invention the ratio of the line frequency to the vertical frequency may be expressed broadly as differing from an integer by /%.

If the system of interlace disclosed in Fig. 2B beemployed in the more practicable system illustrated by Fg. 1 in which the number of lines is approximately standard the master oscillator will have a frequency of 25920 cycles per second, the multivibrator 26 will have a frequency of 5184 cycles per second and the chain of multivibrators 27, 28 and 29 will have frequencies respectively of 4320, 540 and 60 cycles per second.

The saw tooth generator 30 in that case will have a frequency of 5184 cycles per second. Thus if the above-mentioned frequencies be employed in the circuit shown by Fig. 1, the number of scanning lines will be 4S2 and the ratio of the line frequency to the vertical frequency will be 86 plus % which is the same as 87 minus %; in other words, the ratio is a number which differs from an integer by %.

The interlaced quintuple interlace system which I have devised and described above is not limited to the frequency numbers mentioned above, but may be employed for the production of pictures having a number of lines equal to any number which ends in 2, 3, 7 or 8. Inasmuch as multivibrators are at present found necessary for the reduction of the master oscillator frequency to that desired for the sweep circuits and since multivibrators having ratios greater than .10 are at present not practicable, these elements or the possible combinations thereof constitute a limitation on the line numbers of the pictures which may be transmitted in accordance with my invention. By way of example I have shown by the following table a number of pictures whose lines vary approximately from 300 to 1200 with the multivibrator ratios necessary for each, assuming a vertical frequency of 60 and employing my interlaced quintuple interlace scanning system.

1.---.....--. 2.------3....------. 5._ 6 ..--..-79 ------8 9--- 11-----12---1314 .-... 15.--. No. of lines of picture 343 378 392 432 448 512 567 588 648 672 768 882 972 1,008 1,152 Multivibrator ratios 7,7,7 6,7,9 7,7,8 6,8,9 7,8,8 .8,8,8 7,9,9 3,4,7,7 8,9,9 4,4,6, 7 4,4,6,8 3,6,7,7 3,6,6,9 4,6,6,7 3,6,8,8 In the above table, rows 1, 2, 5, 7, 8, 10 and 13 apply where the ratio of the line frequency to the vertical frequency is an integer plus %; the other rows apply where that ratio is an integer plus 2%.

That part of the above description describing what is shown in Fig. 1 is an example of a picture having 448 lines and the modified form of that figure employing different frequencies is an example of a picture having 432 lines.

In Fig. 3 I have illustrated a complete system involving my invention including both the transmitting and the receiving apparatus and employing my interlaced quintuple interlace scanning for a 1152 line picture.

The transmitter comprises the cathode ray tube 15' similar to that shown in Fig. 1 and provided with the screen 16' and the optical system 17' which in this case is represented as being arranged to project a view on the screen. The tube is also provided with the horizontal and vertical deflecting windings 20' and 19' respectively as in Fig. 1. The master oscillator 38 in this case produces a frequency of 69120 cycles per second. This frequency is supplied to the multivibrator 39 which having a ratio of 5 reduces the frequency to 13824 cycles per second.

It is also supplied to the chain of multivibrators 40, 41, 42 and 43 which, having ratios respectively of 3, 6, 8 and 8, reduce the master oscillator frequency respectively to 23040, 3840, 480 and 60 cycles per second. The deflecting windings 20' and 19' are supplied with saw tooth waves having frequencies respectively of 13824 cycles and 60 cycles per second from the saw tooth generators 44 and 45. The generator 44 is controlled by the 13824 cycle frequency supplied to it from the multivibrator 39 and likewise the generator 45 is controlled by the 60 cycle frequency supplied to it by the multivibrator 43. As in Fig. 1 the output of the tube and the synchronizing signals are shown supplied to the radio transmitter 34', the latter through the super synchronizing pulse generator 35'.

The ratio of the line frequency, 13824 cycles in this case, to the vertical frequency, 60 cycles, is 230%; thus as in the previously described examples this ratio is an integer plus %. As before the frame frequency, being 60 divided by 5, is 12. Since the ratio is an integer plus the fraction 2 the lines are scanned in the order 1, 4, 2, 5, 3, just as in Fig. 2B.

Inasmuch as my invention is applicab'e not only to television transmitting apparatus but to television receiving apparatus I have included in Fig. 3 a diagrammatic representation of such'apparatus including a cathode ray receiver of well known form. In this figure the radio signals transmitted by the transmitter 34' and picked up by the antenna 50 are amplified by the radio frequency amplifier 51 and then passed to the converter 52 to which is also connected the oscillator 53 as in well known superheterodyne radio receiving apparatus. The output of the converter is supplied to the video intermediate frequency amplifier 54 and, assuming that sound is being transmitted as well as pictures, is also supplied to the sound intermediate frequency amplifier 55. This amplifier connects through the detector 56 and the audio frequency amplifier 57 with the loud speaker 58 in the usual manner. The output of the video intermediate frequency amplifier 54 is supplied through the detector 59 and the video amplifier 60 to the cathode of the cathode ray receiving tube 61. The horizontal beam deflecting winding 64 of the tube is supplied from the horizontal sweep frequency generator 63 which produces 13824 cycles per second or approximately that frequency and the vertical beam deflecting winding 62 is supplied from the vertical sweep frequency generator 65 which produces 60 cycles per second. The two synchronizing frequencies" taken from the detector 59 are separated from each other by the separator 66 and supplied to the proper generators 63 and 65 to keep the pulses produced thereby in synchronism with the received pulses.

That form of my invention illustrated by Fig. 3 and producing 1152 lines, it will be noted, is well 00 adapted for use in connection with television receivers constructed to produce the present standard 441 line pictures having double interlace inasmuch as the horizontal or line frequency, namely 13824, of my transmitter is so close to the hori05 zontal line frequency, 13230, of those receivers that their horizontal sweep frequency generators are readily pulled in step at the end of each line.

Hence such a receiver may be used to receive a 0 picture transmitted in accordance with my invention and comprising 1152 lines without alteration therein or change in adjustment.

With the modification shown by Fig. 3 one obtains the same economy in band width as with 7. the form shown by Fig. 1. For example, instead of requiring a band width of approximately 26 megacycles for the 1152 line. picture using the standard double interlace and-with 30 pictures per second I can, by employing iy invention, reduce the number of pictures to 12 and thus reduce the band width by the factor 2.5 to approximately 10.4 megacycles.

For the purpose of assisting the reader in obtaining a clear understanding of my invention the above detailed description has been confined to what I have termed an interlaced quintuple interlace system.' My invention, however, is not limited to that particular system although for various reasons I prefer it to the modifications which I shall now describe. Inasmuch as the systems comprising these other modifications differ from that already illustrated only in the frequencies empSloyed, it would seem to encumber the drawing unnecessarily to illustrate each in. addition to the illustration already provided. ' Instead of employing line and vertical frequencies whose ratio is an integer plus % or 3/, I may employ frequencies- whose ratio is an integer plus various other fractions such for ex-ample as 2/7, 3/7, 4/7, 5/7, 3/8, 5/8, 2/9, 4/9, 5/9, 7/9, 3/10, 7/10, 2/11, 3/11, 4/11, 5/11, 6/11, 7/11, 8/11, 9/11, 5/12, 7/12, 2/13, 3/13, 4/13, 5/13, 6/13, .7/13, 8/13, 9/13, 10/13, 11/13, 3/14, 5/14, 9/14, 11/14, 2/15, 4/15, 7/15, 8/15, 11/15 and 13/15. Moreover, I may, if desired, employ fre- 3( quencies having a ratio which iicludes a fraction whose denominator is a still higher number.' In the. quintuple, arrangement illustrated by the drawing, it will be noted that in no case did the fraction added to the integer to express the ratio of the two frequencies comprise either 1/5' or 4/5. The reason is that a ratio including such fractions would not produce the desired interlacing. A broad statement of my invention therefore is that the ratio of the line and vertical frequencies is equal to an integer plus a fraction which, expressed in its lowest terms hence is prime, has a numerator that is more than one and is less than the denominator minus one.

Inasmuch as the rate of crawl upward and down-- 4 ward becomes more nearly the same as the fraction approaches 1/2, Iprefer in those cases where one may choose between several fractions and particularly where the fractions have small denominators to employ those . frequencies whose c ratio is an integer plus a fraction which is close to 1/2: Thus, for example, in the case of fractions having 7 for the denominator I prefer 3/7 or 4/7 to 2/7 or 5/7.

I have chosen the particular embodiments described above as illustrative of my invention and it will be apparent that various other modifications may be made without departing from the spirit and. scope of my invention which modifications I am to cover by the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is: 1. In television the method of scanning lines in a cathode ray tube which comprises moving. the electron beam of the tube in one direction at a certain frequency, and simultaneously moving it in a direction substantially at right angles thereto at a frequency having a ratio to said certain frequency equal to an integer plus a fraction which in its lowest terms has a numerator that is more than one and is less than the denominator minus one.

2. In television the method of scanning lines in -a cathode ray tibe which comprises moving the electron beam of the tube in one direction at a certain single frequency and simultaneously moving it in a direction substantially at right angles thereto at a single frequency having a ratio to said certain frequency equal to an integer plus a fraction whose denominator is an odd number and whose numerator differs by onehalf from being equal to one-half of the denominator.

3. In television the method of scanning lines in a cathode ray tube which comprises moving the electron beam of the tube in one direction at a certain frequency and moving it simultaneously in a direction substantially at right angles thereto at A frequency which differs from an exact multiple of said frequency by /s%.

4. In television the method of scanning lines in a cathode ray tube which comprises moving the electron beam of the tube in one direction at a certain frequency and moving it simultaneously in a direction substantially-at right angles thereto at a frequency having a ratio to said certain frequency equal to an integer plus %.

5. In television the method of scanning lines i in a cathode ray .tube which comprises moving the electron beam of t the tube in one direction at a certain frequency and moving it simultaneously in a direction substantially at right angles thereto at a frequency'having a ratio to said certain o frequency equal to an integer plus 2/.

S6. Television apparatus comprising a cathode ray tube having a screen, beam deflecting means and energizing means connected therewith for causing the beam to scan the screen successively in a plurality of spaced parallel lines, said means Including means for causing the beam to scan the screen intermediate said lines in a plurality of interlaced lines.

7. Television apparatus comprising a cathode 0 ray tube having a screen arranged to be scanned by the'beam thereof in a plurality of lines and means for causing the beam to move in the. direction of said lines and in a direction substantially at right angles thereto, said means includ5ing means for causing the ratio of the frequency of movement of the beam in the direction of the lines to the frequency of its movement in the other direction to equal an integer plus a fraction which, in its lowest terms, has a numerator that e0 is more than one and is less than the denominator minus one.

8. Television apparatus comprising a cathode ray tube having a screen arranged to be scanned 'by the beam thereof in a plurality of lines and i5 means for causing the beam to move in the direction of said lines .and in a direction substantially at right angles thereto, said means including means for causing the ratio of the frequency of movement of the beam in the direction of..the Slines to the frequency of its movement in the other direction to equal an integer plus a frac* tion whose' denominator is an odd number and whose numerator differs by one-half from being equal to one-half of the denominator.

5 . 9. Television apparatus comprising a cathode ray tube having a screen arranged to be scanned by the beam thereof in a plurality of lines and means for causing the beam to move in the direction of said lines and in a direction substantially 70 at right angles thereto, said means including means for causing the ratio of the frequency of movement of the beam in the direction- of the lines to the frequency of its movement in the other direction to differ from an integer by /.

10. Television apparatus comprising a cathode ray tube having a screen arranged to be scanned by the beam thereof in a plurality of lines and means for causing the beam to move in the direction of said lines and in a direction substantially at right angles thereto, said means including means for causing the ratio of the frequency of movement of the ray in the direction of the lines to the frequency of its movement in the other direction to equal an integer plus %.

11. Television apparatus comprising a cathode ray tube having a screen arranged to be scanned by the beam thereof in a plurality of lines and means for causing the ray to move in the direction of said lines and in a direction substantially at right angles thereto, said means including means for causing the ratio of the frequency of movement of the ray in the direction of the lines to the frequency of its movement in the other direction to equal an integer plus 2/%.

12. Television apparatus comprising a cathode ,ray tube having a screen arranged to be scanned by the beam thereof in a plurality of lines, means for deflecting the beam in the direction of the lines, means for deflecting the beam in a direction substantially at right angles thereto, means 28 for producing a plurality of deflection frequencies whose ratio differs from an integer by % and means for supplying said frequencies each to one of said deflecting means.

13. Television apparatus comprising a cathode ray tube having a screen, and means for causing the beam of said tube to scan said screen In a plurality of spaced lines comprising a plurality of groups of five lines each, said means including means for causing the beam to scan successively corresponding lines of said groups and including means for causing the beam to scan successively lines 1, 4, 2, 5 and 3 of said groups in the order named.

14. Television apparatus comprising a cathode ray tube having a screen and means for causing the beam of said tube to scan said screen in a plurality of spaced lines comprising a plurality of groups of five lines each, said means including means for causing the beam to scan successively corresponding lines of said groups and including means for causing the ray to scan successively lines 1, 3, 5, 2 and 4 of said groups in the order named.

SIEGFRIED HANSEN.

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