US2280572A - Scanning means and method - Google Patents

Description

April 21, 1942. P. 'r. FARNSWORTH SCANNING MEANS AND METHOD Fiied Nov. 5,1934

- 2 Sheets-Sheet 2 YINVENTOR, PHILO 7. FARNSWORTH.

qg 7 rrol gzys Patented Apr. 21, 1942 SCANNING MEANS AND METHOD Phllo T. Farnsworth, San Francisco,.0alif., as-

signor, by mesne assignments, to Farnsworth Television & Radio Corporation, Dover, Del., a corporation of Delaware Application November 5, 1934, Serial No. 751,449

9 Claims.

vide a simple means and method for interlacing scansion lines in image dissection or reconstruction.

Other objects of my invention are: to provide a means and method for covering a picture field by the use of a succession of displaced scanned areas; to provide a means and method of interlacing scansion lines in television; to provide a means and method of interlacing the scanning lines of a scanned field when using commensurable scanning frequencies; to provide an improved means and method of transmitting and receiving television images; toprovide a means and method of increasing the detail of a picture field; to provide a means and method of obtaining a succession of television pictures at a rate differing from a succession of originating images; to provide a new and novel method of scanning motion picture film for television; to provide a means and method of scanning motion picture film when intermittentlyprogressed; to provide such a means and method when the film is intermittently progressed at a standard rate and scanned at a different rate; to provide a scanning system for the transmission of television images from motion picture film wherein the scanning frequencies are coordinated with the rate of advance of said film; to provide a television system wherein the scanned field in a receiver is the same regardless of synchronizing pulse from a transmitter; to provide an interlaced scanning system in television having interlocked commensurable scanning frequencies; to provide a means and method for shifting successive scanned areas to cover a picture field in a suc-.

invention herein described, as various forms may be adopted within the scope of the claims:

The drawings which accompany and form a part of this specification are all diagrammatic in nature and have been, in order to more easily illustrate the subject matter, reduced to 1QWt terms. While I have chosen, for purposes of illustration, a cathode ray transmitter and receiver, it will be obvious from that which follows that the method can be applied not only to other apparatus of like character but also to apparatus wherein mechanical scansion is employed.

Figure 1 is a diagram illustrating a preferred apparatus for scanning motion picture film and transmitting the signals derived therefrom.

Figure 2 is a diagram of a cathode ray receiver embodying my invention.

Figure 3 is a diagram illustrating one method of obtaining a displacement of the scanned area.

Figure 4 is a diagram of another method of displacement, I

- Figure 5 is a diagram wherein the same picture field is scanned three times.

It appears desirable, in modern television, to scan a picture field several times with a plurality of parallel scanning lines and then to interlace the scanning lines in successive pictures. 'Several advantages are acquired by this procedure, not the least important of which is the improved scansion of motion picture films. It is well known in the art that at the present time the motion picture industry has standardized upon a film speed of ninety feet per minute, using an intermittent movement for the optical transmission of still pictures at a rate of twenty four pictures per second. Before the days of sound tracks synchronized with or actually on the film, such pictures could be run at a speed which varied somewhat from the standard without great harm. The action would be merely speeded up or slowed down and the flicker reduced or increased. The synchronization of the sound record with the film, however, changed the situation and there is now no leeway whatsoever in the speed, it must be ninety feet per minute and twenty-four pictures per second.

Such a rate, however, is not necessarily the proper one for a succession of television images. and as' it is not practical, in view of the extent of the motion picture industry, to change the number of pictures per second on the film, it is necesary to change the television system if a higher television picture rate is desired.

This has been done by the use of interlaced scanning lines. Each stationary motion picture frame is scanned twice, for example, and the area scanned displaced by the width of half the distance between the lines in succeeding pictures. We then have at the television receiver forty eight scansions per second each with half the number of lines in one picture and the other half offset in the next picture, the two combining because of persistence of vision to give to the eye the complete picture with a full number of lines. The motion picture frame may be scanned three times if desired, or-a combination of three and two as will be described later.

One verydistinct advantage which can be obtained by the use of a higher rate of picture transmission is that when there are sixty complete scansions per second, sixty cycle alternating current pick-up is not seen in the receiver. Under ordinary circumstances it is very difficult to keep out of the picture interference due to induction of sixty cycle current, and when such induction is present it can be seen in the picture as a rolling change of intensity. This gives rise to that phenomenon known as "flag waving" as the changes of light and shade appear and disappear in the picture. This interference appears to greatly increase the flicker.

If the images succeed each other at a rate of sixty per second flag waving does not occur and the image is steady and flicker is greatly reduced. A

The general idea of interlaced scanning is not new per se. It has been used before but has been produced by an entirely difierent means and method than that here disclosed.

One particular prior method is accomplished by making the vertical scanning frequency, which hereafter I prefer to call the low scanning frequency, and the horizontal scanning frequency, which I will hereafter refer to as the high scanning frequency, These incommensurable frequencies working simultaneously will cause a phase shift of the area scanned between scansions, thus producing the interlaced effect. A concrete example in explanation of this is where the motion picture film is projected at a rate of twenty four per second. The low scanning frequency can be made sixty per second and the high scanning frequency such that it will give two hundred and forty seven lines for the complete picture field of one hundred twenty three and one half lines per scansion. The frames of the motion picture film are projectedin such a way that one frame is held stationary for a sufficient length of time for two scansions to occur and the next frame is held stationary for a sufficiently long time for three scansions to occur. termittent motion of the projector to hold every other frame half again as long as the preceding, sixty complete scansions may be made per second, each having a uniform time.

The interlacing is accomplished because of the fact that the number of lines in a complete scansion is fractional. For example, in the first scansion the first line will begin at the upper left hand corner of the( field and slant somewhat downwardly across the picture. Parallel lines will succeed each other as the scansion progresses until the arrival at the bottom when the scansion will end in the middle of the bottomv line. The low frequency will then bring the incoinmensurable.

Thus by changing the intem, in order to give sixty scansions per sec-.

and. that it is necessary to scan one picture three times and that the identical area of the picture is scanned the third time as is scanned the first time, thus in the scansion of two frames of a motion picture five times, the same detail is produced as if the same two frames were to be scanned twice. 7

It will be apparent, however, that with a low scanning frequency of sixty per second and a high scanning frequency of seven thousand, four hundred and ten per second, that there will be harmonics of the low scanning frequency which will come exceedingly close. to the fundamental and harmonics of the high frequency even though the fundamentals are incommensurable. It should also be noted that in case a cathode ray tube is used either at the transmitter or the receiver, that the field of the low frequency scanning element and the field of the high frequency scanning element must be positioned to affect the cathode ray beam simultaneously, usually at or near the same locality on the beam. It is therefore-very difficult if not impossible to prevent these fields from intermingling with a consequent persistent tendency-of the two frequencies to lock into synchronism, thus'destroying their incommensurability.'

Even though both of the frequencies are stabilized with a crystal, certain of their harmonics may be so close that they will tend to interlock in spite of the stabilization. Immediately interlocking occurs all interlacing is lost. The scansion lines of each succeeding picture will overlie each other, and the image as seen drops back he one having only half the proper number of nes.

A further disadvantage in the use of the scan: ning frequencies which are incommensurable with each other is that the required incommensurability can be maintained only when the synchronizing pulse is present. Consequently the receiver will always show the simpler scanning I surable scanning frequencies, that the method aperture back to the top line where, beginning in the middle, it will start the first line of the next scansion which will also slant downwardly with the same angle as before, so that succeeding scansion lines will be inbetween those of pattern when the set is not tuned to a station.

The interlocks which occur and destroy the interlacing may occur at any time in the middle of a program, for example, necessitating a shutdown and a new start in order to reestablish incommensurability and consequent proper number of lines.

From the above it can therefore be seen that while it is possible, under carefully supervised laboratory conditions, to maintain incommenis not what might .properly be said a commercial way to produce a higher scanning rate with interlaced scanning lines.

My invention is directed toward overcoming the disadvantages enumerated above, meanwhile keeping all the advantages of interlacing.

In broad terms, my method comprises scanning an area of a picture field smaller than the field, and displacing the areas scanned in succeeding scansions by a distance sufficient to cover the field in a given number of scansions. I prefer to use high and low scanning frequencies which are commensurablefand positively interlocked, although frequencies which the first scansion. The end of this scansion will be at. the lower right hand corner, and when scansion again begins at the top it will start at the upper left hand corner and the cycle will be repeated. It is to be noted that with this sysare commens'urable normally will remain interlocked.

The broad aspect of myapparatus comprises the preferred use of a cathode ray tube for scansion either as a transmitter or a receiver,

or both, and means for deflecting the cathode.

ray beam in two directionswith interlocked ire quencies and additional means for cyclically shifting the course of the beam between successive scansions by a distance smaller than the distance between scansion lines.

My invention can be more completely understood both as to means and method by reference to the drawings, the preferred system shown being used for purposes of illustration only.

In Figure l, which is a simplified diagram of a television transmitter, light from a source H is passed through a condensing lens l2 and then passes through a motion picture film it which is under the control of an intermittent sprocket l5 operated in any convenient manner well known in the art. The image formed by the passage of light through a single frame 16 of the film passes into a cathode ray dissector tube H to fall on a photoelectric cathode Hi there-- of. .The optical system shown is purely diagrammatic, and any standard motion picture machine will do for the combination of the light source, lens, sprocket and film combination shown. The cathode ray dissector tube shown is similar in its fundamentals to that described and claimed by me in my Patent No. 1,773,980, issued August 26, 1930.

An electrical image is formed in space by the electrons emitted'under the influence of the optical image falling on the photoelectric cathode l8, and this image is oscillated, by means of the low frequency scanning coil [9 and the high frequency scanning coil 20 supplied by their respective oscillators 2i and 22, past an aperture 2% in the anode assembly 25, selected portions passing through the aperture to fall on a collecting anode 26 to form a train of television signals in accordance with the original optical image.

The television signal thus produced is passed into an amplifier and tr nsmitter 2i, therefrom to be radiated or otherwise transmitted. I prefer to make the high and low frequencies commensurable, as for example using a two-one interlace, a low frequency of forty-eight cycles per second and a high frequency of five thousand, seven hundred and sixty cycles per second. I then prefer to positively interlock these two frequencies by means of an interlocking device 28 which may be a crystal operating on a common harmonic of the two oscillators. The low frequency oscillator 22 is then provided with a fraction oscillator 29 which, in the hypothetical case above referred to, will be one-half of the low frequency.

This latter oscillator can be synchronized from the low frequency oscillator and can feed back into it so that energy therefrom will pass into the low frequency scanning coil 20. As will be later described, this oscillator may supply a square wave formor a slope wave form.

I then prefer to transmit the synchronizing pulses from these oscillators through a line 80 into the amplifier and transmitter to be transmitted along with the accordance with any standard practice.

In the above transmitting arrangement, I prefer to utilize slope waves for scanning and to scan in straight parallel lines.

At the receiver the signals and synchronizing pulses are picked up and passed into a combined receiver and amplifier 3!. From here the signals pass to the grid 32 of a cathode ray tube 35, the tube being provided with the usual cathode 35 and perforated anode 36 as well as with a fiuorescent'screen 31 at the opposite end of television signal train, in

.the tube. The synchronizing pulses pass through a synchronizing line 39 to-the low frequency receiving oscillator 40, operating the low frequency scanning coil M, and the high frequency receiving oscillator 62 operating the high frequency receiving scanning coil 44. These two oscillators are, as in the transmitter, preferably provided with a positive receiving oscillator interlock and the lowfrequency oscillator is provided with a fractional receiving oscillator 46 synchronized from and feeding the low'frequency receiving oscillator 40 exactly asin the transmitter. In other words, both the transmitter and the receiver are provided with one low and high frequency scanning oscillator which will interlock, the frequency oscillator, in both cases, being supplied with an additional oscillator in step therewith, which, in the case of two-one interlacing operates at one-half the low frequency rate.

Figures 3 and 4 illustrate what happens when each motion picture frame is scanned twice to give a two-one interlace. between the two figures is that in Figure 3 a slope wave displacement oscillator is used and in Figure 4 a square wave displacement oscillator is used.

Let us suppose that, as is customary, the motion picture film I4 is being intermittently moved at a rate of twenty four frames per second. One frame constitutes the picture field. I then may scan each frame twice, utilizing a low frequency of forty-eight and a high frequency of five thousand, seven hundred and sixty to give two hundred andforty lines in the complete picture field. Each scansion, however, will have only one hundred and twenty lines therein and will cover only a portion of the field. This low scanning frequency is diagrammatically indicated by the slope wave curve QB in Figure 3, the curve representing the output of the low frequency oscillator alone. I then adjust my displacement oscillators to a frequency of twentyfour per second, also a slope wave in this in stance. The displacement wave is indicated by the numeral 89 in Figure 3. I prefer to make this a negative wave and have it subtract from the curve 48, but this is arbitrary. As the output of both of these oscillators is passed into the low frequency scanning coil, the combined output can be represented by the curve indicated by, the numeral 50 in Figure 3. By the use of the slope wave 49 added to slope wave 48, the area traversed by successive low frequency scansions is displaced. The first scansion will scan an area having one hundred and twenty lines which may be diagrammatically indicated by the area 5| in Figure 3. The next scansion will have the same number of lines but will be displaced as shown by the area 52 in Figure 3. As those two scansions succeed each ,other they, when superimposed, will cover the entire picture field 54 with a total of two hundred and forty lines. The cycle will repeat and the end result will be a succession of scansions each with one hundred and twenty lines, each one being displaced by half a line from the, succeeding one. The impression given to the eye is an entire picture field having two hundred and forty lines. The only care that must be taken with this combination of oscillators is that the amplitude of the wave 49 should be just sufficient to displace the area by half a line. This, however, has not been found at all difficult to do in practice.

In Figure 4 the low scanning frequency 48 has The only difference p been modified by the use of a positive square wave 55 which produces a combined wave 50 which is identical in its ability to produce the shift as the slope wave 49 in Figure 3. The combination of the scansions 5| and 52 will cover the field 54 in exactly the same way as in Figure 3. A negative pulse may also be used if desired.

In Figure 5 I have shown a combination of frequencies whereby I am able to scan each picture field three times, each time with onethird the number of lines desired in the complete field and shifting the area scanned by a distance of one-third the distance for three scansions and then starting anew. This I do by modifying the low frequency output 48 by a slope wave impulse 56 extending over three of the low frequency cycles. This gives me a progressive downward shift of the area scanned and the combined field is shown by the numeral 51, the two additional fields being indicated by the numerals 58 and 59.

It should be noted that if the displacement wave is straight during the scansion no disturbance of pattern is caused by its addition to the low scanning frequency, and if slope waves are used having uniform increments, as many scansions as desired may be made in order .to cover a single picture field.

My method may be expressed mathematically by saying that if I scan a complete picture field X times, each time covering an area having a length L with a frequency F in the direction of L, with a concurrent frequency of NF transverse thereto, N being an integer, then I should displace the area scanned in the direction of L b an amount equal to L v XN between scansions until the entire field is covered. In case I wish to add the factor which is brought into the method by the rate of progression of the individual pictures of the motion picture film, and if these frames appear at the rate of I per second with uniform exposure, then if I scan each frame X times, each time covering an area having a length L with a frequency of IX in the direction of L and a concurrent frequency of N X IX transverse thereto, N being an integer, I displace the area scanned by an amount equal to between scansions until theentire field is coverezh Should I desire to produce sixty scansions per second from a motion'picture intermittently v moved at a rate of twenty-fourframes per 'sec- 0nd, I provide an intermittent mechanism which will hold every other frame stationary for onehalf longer than the preceding frame and scan one frame twice, the next three times. I will then use sixty cycles for my low scanning frequency and as I desire two hundred and forty theproper apparatus, mechanical methods will lines in my complete picture field, with two-one interlacing, I use one hundred and twenty lines in each separate scansion thus developing a high scanning frequency of seven thousand two hundred, which of"course is commensurable with sixty. The displacement frequency will 7 be thirty cycles per second'to give the desired interlace.

I may, however, use a low frequency of sixty, a high frequency of seven thousand, two hundred, and a displacement frequency of twenty; This will give eighty lines to the scansion and a threeone interlace,

It should be here noted that the successive scanning patterns as produced in my'system as described are identical; that is, there are the same number of lines in each, no fractional lines, and no change in pattern between successive scansions. In systems depending on incommensurability for interlacing the succeeding patterns are dissimilar, one having a half line at top and bottom, the next having full lines in the same positions.

There are several variations in the means to accomplish the method desired. For example, instead of having a special displacement oscillator at both receiver and transmitter, Imay prefer to generate a non-uniform low frequency pulse at the transmitter.

Several features of my invention merit special comment:

As the high and low scanning frequencies are always interlocked, it is not possible for a simple field to appear in the receiver either during the reception of a picture or whenno transmitted impulses are being received. It is therefore never necessary to stop the operation of the device in order for the proper interlaced field to be maintained.

The general control of my invention is simple. It is well known in the art that it is easier to control the amplitude of a device than it is to con trol the frequency, especially when there is a constant tendency for incommensurable frequencies to interlock. The only requirement for a faithful interlace, using my system as described above, is

that the amplitude of the displacement oscillator output be definite and unvarying. I have found that it is possible to maintain a constant amplitude without the necessity for continual hand adjustment, the variation in amplitude be-.

ing so small that the eye cannot detect any variation in the position of the interlaced lines, which would occur, of course, if the amplitude was too large or too small.

The frequencies being all commensurable remain in step, and I use a crystal interlock for safety rather than of necessity, the crystal electrical variations pf' the-optical paths. Such apparatus presents nov unusual difficulties and will be obvious to thoseskilled in the, art. It is to be understood; therefore, that I- do not wish to be limited in the interpretation of the appended claims to electrical methods of scanned area displacement, as it will be. obvious that with be-equally satisfactory to produce the desired result. v

Neither ,do I desire to be be obvious that; there are many combinations of waves or pulses which can be made additive or subtractive so that theproper displacement increment will be available at the proper time and by the proper amount; Many such other combito mechanical systems as limited to any particular wave form; either in the scanning oscilla-1 tor or in the displacement. oscillator, as it will nations will undoubtedly suggest themselves to those skilled in the art.

I claim:

1. In combination with a cathode ray tube having a cathode ray beam adapted to scan a picture field, means for deflecting said beam, comprising a pair of deflecting elements positioned to deflect said beam in two directions, a high frequency oscillator supplying one of said elements, a low frequency oscillator supplying the other of said elements, said oscillators having commensurable frequencies, means for interlocking said frequencies, and an additional oscillator operating at a frequency lower than said low frequency oscillator connected to the output of said low frequency oscillator.

2. In combination with a cathode ray tube having a cathode ray beam adapted to scan a picture field, means for deflecting said beam, comprising a pair of deflecting elements positioned to deflect said beam in two directions, a high frequency oscilaltor suplying one of said elements, a low frequency oscillator supplying the other of said elements, said oscillators having commensurable frequencies, means for interlocking said frequencies, and an additional oscillator operating at a frequency lower than said low frequency oscillator connected to the output of said low frequency oscillator and synchronized in common with said low frequency osciliator.

3. In combination with a cathode ray tube,

having a cathode ray beam adapted to scan a picture field, means for deflecting said beam, comprising a pair of deflecting elements positioned to deflect said beam in two directions, a high frequency oscillator supplying one of said elements, a low frequency oscillator supplying the other of said elements, said oscillators having commensurable frequencies, means for interlocking said frequencies, and an additional oscillator operating at a frequency lower than said low frequency oscillator connected to the output of said low frequency oscillator and synchronized by said low frequency oscillator.

4. The method of producing intercolated scanning of a surface by means of an electron beam which comprises deflecting the beam in one direction at a constant periodicity and deflecting the beam at right angles to the first direction at a periodicity which is different for successive pictures and which varies according to a predetermined law.

5. The method of producing interlaced scanning in a cathode ray tube which comprises generating saw-tooth electric waves at a certain frequency and deflecting the cathode ray horizontally in accordance with said waves, generating saw-tooth electric waves at a comparatively low frequency which are characterized in that each saw-tooth differs from the preceding sawtooth by a predetermined amplitude, and simultaneously deflecting the cathode ray vertically in accordance with the second mentioned,sawtooth waves.

6. The method of producing interlaced scanning in a cathode ray tube which comprises generating saw-tooth, electric waves at a certain frequency and deflecting the cathode ray horizontally in accordance with said waves, generating saw-tooth electric waves at a comparatively low frequency which goes into said certain frequency a whole number of times and which contain a saw-tooth component lower in frequency than said low frequency, and simultaneously deflecting the cathode ray vertically in accordance with the second-mentioned saw-tooth waves.

7. The method of producing interlaced scanning in a cathode ray tube which comprises generating saw-tooth electric waves at a certain frequency and deflecting the cathode ray horizontally in accordance with said waves, generating saw-tooth electric waves at a comparatively low frequency which goes into said certain frequency a whole number of times and which are characterized in that each saw-tooth differs from the preceding saw-tooth by a predetermined amplitude, and simultaneously deflecting the oathode ray vertically in accordance with the second mentioned saw-tooth waves.

8. In a television system, a cathode ray tube, means for producing saw-tooth waves occurring at a certain frequency and for deflecting the cathode ray horizontally in accordance with said waves, means for producing saw-tooth waves occurring at a comparatively low frequency which contain a saw-tooth component comprising sawtooth waves occurring at a sub-multiple frequency of said low frequency, and means for'simultaneously deflecting said cathode ray vertically in accordance with said second-mentioned waves, the magnitude of said sub-multiple component being such as to cause interlacing of successive scannings.

9. The invention according to claim 8 characterized in that said sub-multiple frequency is one-half of said low. frequency.

PHILO '1. FARNSWORTH.

c 1 CERTIFICATE OF CORRECTION. Patent No. 80,57 April 1, 19h

PHILO T. FARNSWORTH.

.It is hereby ertified.'that error appears in the printed specification of the above mmbered patent rreqyziring correction asfollowa: Page first column, line 1 for field of read "field or"; and second column, line 1," for give re ad "get-E; page 5, Second 9 line 16, before "fre- 'quency" insert lowand that the said Letters Patent should be read with this correction thereinthat the same may conform to the. record of the case in the Patent Office. Q Signed and sealed tluie 1st day of September, A. D.. 1914.3.

7 Henry van Arsdale-, (Seal) v Acting Commissioner of Patehts.-

- CERTIFICATE OF conmaenou. Patent No. 80,57 April 1, 1918-.

PHILO T. FARNSWORTH- It is hereby certified "that error appears the printed sfiecification of theabove numbered patent requiring correction asfo-llowsz Page first column, line M4, for field, of" read ---field or---; ahd second column, -line 1, for give re ad "get-F; page 5, Second fi l r line 16,' before- "frequency" insert lowand thet the said Lettere Patent should be read with this correction therein that the same may conform to the. record of the case in the Patent; Office. Signed and sealed thie lat day of September, A. D. 1914.

Henry Ven Arsdale-Q (s al) Y Acting Commissioner of Patehts.-

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