US2280572A - Scanning means and method - Google Patents

Scanning means and method Download PDF

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Publication number
US2280572A
US2280572A US751449A US75144934A US2280572A US 2280572 A US2280572 A US 2280572A US 751449 A US751449 A US 751449A US 75144934 A US75144934 A US 75144934A US 2280572 A US2280572 A US 2280572A
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United States
Prior art keywords
scanning
frequency
lines
picture
oscillator
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Expired - Lifetime
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US751449A
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English (en)
Inventor
Philo T Farnsworth
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Farnsworth Television and Radio Corp
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Farnsworth Television and Radio Corp
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Publication date
Priority to BE412107D priority Critical patent/BE412107A/xx
Application filed by Farnsworth Television and Radio Corp filed Critical Farnsworth Television and Radio Corp
Priority to US751449A priority patent/US2280572A/en
Priority to GB30344/35A priority patent/GB459400A/en
Priority to FR797332D priority patent/FR797332A/fr
Application granted granted Critical
Publication of US2280572A publication Critical patent/US2280572A/en
Anticipated expiration legal-status Critical
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N3/00—Scanning details of television systems; Combination thereof with generation of supply voltages
    • H04N3/10—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical
    • H04N3/30—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical otherwise than with constant velocity or otherwise than in pattern formed by unidirectional, straight, substantially horizontal or vertical lines
    • H04N3/34—Elemental scanning area oscillated rapidly in direction transverse to main scanning direction

Definitions

  • Figure 1 is a diagram illustrating a preferred apparatus for scanning motion picture film and transmitting the signals derived therefrom.
  • FIG. 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.
  • FIG. 4 is a diagram of another method of displacement, I
  • FIG. 5 is a diagram wherein the same picture field is scanned three times.
  • Such a rate 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 necessaryy to change the television system if a higher television picture rate is desired.
  • 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.
  • the motion picture frame may be scanned three times if desired, or-a combination of three and two as will be described later.
  • 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.
  • 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.
  • 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.
  • My invention is directed toward overcoming the disadvantages enumerated above, meanwhile keeping all the advantages of interlacing.
  • 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.
  • the broad aspect of myapparatus comprises the preferred use of a cathode ray tube for scansion either as a transmitter or a receiver,
  • 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.
  • 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.
  • this oscillator may supply a square wave formor a slope wave form.
  • 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 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.
  • 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.
  • 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 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.
  • the displacement wave is indicated by the numeral 89 in Figure 3.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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,
  • 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.
  • succeeding patterns are dissimilar, one having a half line at top and bottom, the next having full lines in the same positions.
  • 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-.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Oscillators With Electromechanical Resonators (AREA)
  • Ultra Sonic Daignosis Equipment (AREA)
  • Transforming Electric Information Into Light Information (AREA)
US751449A 1934-11-05 1934-11-05 Scanning means and method Expired - Lifetime US2280572A (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
BE412107D BE412107A (id) 1934-11-05
US751449A US2280572A (en) 1934-11-05 1934-11-05 Scanning means and method
GB30344/35A GB459400A (en) 1934-11-05 1935-11-02 Scanning means and method
FR797332D FR797332A (fr) 1934-11-05 1935-11-05 Procédé d'exploration par lignes décalées, en particulier pour la télévision

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US751449A US2280572A (en) 1934-11-05 1934-11-05 Scanning means and method

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US2280572A true US2280572A (en) 1942-04-21

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FR (1) FR797332A (id)
GB (1) GB459400A (id)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2458771A (en) * 1943-03-15 1949-01-11 Univ Michigan Supersonic reflectoscope
US2472774A (en) * 1945-10-17 1949-06-07 Farnsworth Res Corp Irregular interlace scanning system
US2524349A (en) * 1939-11-28 1950-10-03 John H Homrighous Television system

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR819883A (fr) * 1936-07-04 1937-10-28 Perfectionnements aux appareils de télévision notamment à leurs systèmes de balayage
US2435962A (en) * 1940-11-20 1948-02-17 Columbia Broadcasting Syst Inc Color television
FR2502873B1 (fr) * 1981-03-27 1986-01-17 Thomson Csf Dispositif pour la production d'images televisees, a matrice a transfert de charges

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2524349A (en) * 1939-11-28 1950-10-03 John H Homrighous Television system
US2458771A (en) * 1943-03-15 1949-01-11 Univ Michigan Supersonic reflectoscope
US2472774A (en) * 1945-10-17 1949-06-07 Farnsworth Res Corp Irregular interlace scanning system

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Publication number Publication date
FR797332A (fr) 1936-04-24
BE412107A (id)
GB459400A (en) 1937-01-07

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