BE667504A - - Google Patents

Description

  

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  The invention relates to a television system and more particularly to a time-bandwidth compression system and a method of television transmission,
The prior art television systems, due to their high scanning speeds required for high definition transmission of moving pictures, have a transmission rate. medium with an extraordinarily wide band.

   However, there are numerous cases where it is not necessary to transfer a moving image, but instead it is desired to quickly transfer a still image,

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 such as, for example, a photo or a "snap-shot" from a moving scene or a printed document in two colors. It is also highly desirable that a television system for transmitting such still pictures can explore common tone frequency telephone lines, even when it comes to transmission over long distances.



   However, in the prior art closed-chain television systems, broadband media such as a coaxial cable or an mi are used for the broadcast of still pictures. microwave channel. The known facsimile systems have also been used for transferring still images; however, transferring a single image takes a considerable time in such systems, usually from three to three minutes.



   For the transmission of still images over narrow band media, television systems and methods have already been proposed using low scan rates, as for example in Belgian Patent No. 641584. The system of this patent uses three scan speeds to provide final transfer times of ten, twenty or forty seconds per frame, according to the desired final transfer times; the slowest scan speed is used for an image that contains the greatest amount of fine detail.

   However, it is further desirable that in such a narrow band television transmission system the video signals be transmitted in the minimum time without affecting the final. It is further desirable that the system with reduced transmission time on

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 can be adapted in a simple and easy manner to existing low scan rate television transmission systems, the procedure as described in the above and to conventional television systems.

   Most of the printed documents, such as typewriter pages and many half-tone images, contain a considerable amount of redundant information, such as the background or white, on which the contracting or black image information occurs. It will be appreciated that the time required to transfer the still image of a printed document or of a half-tone image can be shortened by compressing the redundant information, i.e. by compressing the information into a frame in less than the normal transmission time by suppressing the redundant to some extent.

   Belgian patent 654812 describes and illustrates a time-bandwidth compression scheme in which a clock pulse is used to sample the scanned video signal. However, that system is not limited only to transferring two-color still images, but generates horizontal quantization in addition to the vertical quantization caused by the discrete scan lines; In the system described in the aforementioned Belgian patent 641584, vertical scan lines are used as opposed to the horizontal scan lines used in prior art television systems.

   Experience with television broadcasts has shown that about 75% of the picture elements in the vertical direction are individually reproduced by the scan lines, while the remainder merges. When horizontal crossed out 2 words.

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 If sampling is used, there will be a similar reduction in horizontal final and thus in order to achieve the same image definition in a time-bandwidth compression system, where clock pulses are used to sample a scanned video signal, the bandwidth must be increased.

   Thus, when the loss of horizontal definition due to the horizontal sampling is 25%, the time-bandwidth compression must become 1.33 times to obtain the same definition.



   It is therefore for ',! This is intended to indicate a time-bandwidth compression scheme in which there is no degradation in picture definition, as is the case with the above-described scheme, where clock pulses are used to obtain the horizontal sample of the scanned video signal, and that further not until transmission of multiple color images is limited.



   The bandwidth and / or transmission time in a television system is limited by the smallest information element in the picture to be transmitted. The known television systems use both fast scan and slow scan types, for line and field, uniform scan rates.

   It is now believed that a black-and-white image is exposed to the camera tube of a television system, where the image consists of a single black letter I on a white background, and that this image is scanned in a straight line in order to generate a time-based video signal. to gain. When it is further assumed that the scanning of the image is a position video signal and

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 produces a negative black video signal from the camera tube,

   it will be found that scanning the single black letter I on the image through a single scan line will produce a white video output signal from the white background in the image for a period of time much longer than the black video output signal which only occurs when the black letter I is scanned and transfers the useful information, i.e., the white video output carries redundant information before and after the occurrence of the black video output.

   It will now be appreciated that as the scan rate of the camera tube in the transmitting station and of the picture tube @ the receiving station of long series of redundant information being transmitted, for example, is increased at the same time, thus effectively compressing the redundant information. in a single coded pulse, the time required to transmit the image can be significantly reduced. Assuming a television system must be able to transmit information written with the typewriter with good definition,

   will show that a full typed page has the greatest concentration of black! contains information and therefore provides the least opportunity to reduce airtime; the pica font is about 0.1 inch high and 0.06 inch wide, with the thickness of each letter being about 0.01 inch. About eighty percent of an area completely typewritten is white, and counting the edges of a page makes this number even greater.

   In addition, approx. for two percent of a typed page a series of single-

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 fold white elements present in the center of certain letters (now defined as white or black elements with a width of 0.01 inch in the scan direction).



  On a typed page, single black elements are more frequent due to the thickness of the letters and how much so the scanning speed can be increased to encode white or black information on a typed page, a greater reduction in transmission time is possible when redundant energy is used. encrypted. With a fully typed page, when each sequence of two white elements is broadcast as one video pulse with a duration corresponding to the duration of a single element, the total transmission time can be reduced by about 1.6; and a completely clean page would give a 2: 1 reduction in airtime.

   When every re @@ s of five white elements is sent as one pulse u @, the transmission time can be reduced by a factor of 2.5.



   In accordance with the time bandwidth compression system of the invention, as in conventional television systems, consecutive scan lines are used. When scanning in the image to be transmitted, when information of a particular nature, such as vit information, is encountered, the scanning speed is increased and this information is transmitted with a first video signal level.

   However, when this video signal information lasts less than a predetermined time, or the information is of a different nature, for example black information, the alt-load rate is reduced to a lower normal value and the information is transmitted with a second level from the black information. and with a third intermediate level when it concerns white information

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 affects. Thus, according to the system and method of the present invention, the video signal is transmitted at three levels, black level to be fat, normal scan speed white level, and fast scan white level.

   The receiver can detect these three video signal levels, and can therefore provide the picture tube with a fast scan when it is a first video signal, i.e. fast scan vit information and a ± tasting at the normal speed of the second level, i.e. black signal, or a third level, normal scan rate white signal, the first and third level of the video signals being displayed through the picture tube as a white image.

   Although the term "black" was used with regard to the second level video signal, it will be appreciated that a gray area between the third level, i.e. the white signal at normal scanning speed, and the second level, i.e. black signal, is also possible.



   It is an object of the invention to provide an improved time-bandwidth compression system for television transmission.



   It is another object of the invention to provide an improved method of time bandwidth compression for television transmission.



   It is a further object of the invention to provide an improved time-bandwidth compression scheme and an improved television transmission method which is not limited to transmitting two-tone information, respectively.

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   It is yet another object of the invention to provide an improved time-bandwidth coapression system and an improved television transmission method that can be easily incorporated into existing television systems.



   It is yet another object of the invention to provide an improved time-bandwidth compression system and an improved television transmission method, wherein the definition is improved over prior art time-bandwidth compression systems, without a corresponding increase in the bandwidth needed.



   The invention will now be explained in more detail with reference to the figures.



   Figure 1 is a block diagram of the transmitting station system according to the invention;
Figure 2 is a block diagram of the receiving station system according to the invention;
Figure 3 is a block diagram of an example embodiment of the video sample and video change circuits of the system of Figure 1;
Figure 4 is a diagram of importance in explaining the mode of operation of the system according to the invention;
Figures 5 and 6 are diagrams illustrating the functioning of the video sample and video change circuits of Figure 3;
Figure 7 is a diagram of the signals supplied in the embodiment of Figure 3 during a particular scan line;

   

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Figure 8 is a diagram of the signals supplied in the receiving equipment of Figure 2 during the same scan line as in Figure 7.



   Figure 9 is a diagram indicating the deflection voltages supplied in the camera tube and in the picture tube during a particular scan line, respectively.



   Figure 10 is a schematic depicting the fast deflection switch used in the transmitting and receiving station;
Figure 11 is a diagram showing the coding of the synchronizing signals in three levels;
Figure 12 is a schematic of the sync signal encoder for outputting the encoded sync signals of Figure 11;
Figure 13 is a block diagram. of a sync signal decoder for decoding the encoded sync signals of FIG. 11;

   
Figure 14 is a block diagram of a modified embodiment of a video change circuit;
Figure 15 is a diagram depicting the signals occurring in the system of Figure 14;
Figure 16 is a block diagram of another modified embodiment of a video change circuit to provide 3: 1 compression;
Figure 17 is a diagram indicating the signals that occur in the system of Figure 16.



   The transmitting system of the invention shown in Figure 1, generally designated 20, includes a suitable camera tube 21, which may be a vidicon tube such as the VL-7290,

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 or any other conventional camera tube such as an image orthicone, an image analyzer or a flying spot scanner. at each of these tubes, the optical image to be transmitted is converted into a corresponding electrical characteristic pattern and an electron beam is generated which scans a target in the case of all the aforementioned tubes except the image decomposition tube, thereby producing a video signal in time. base is raised;

     at the image decomposition tube, the beam is generated by an optocathode onto which the optical image is projected and is thus space-modulated in accordance with this image, which beam is moved over a hole to generate the video signal.

     In the case of the vidicon tube used in the slow scan television system according to the aforementioned Belgian Patent No. 641-4, a shutter mechanism exposes the target for a short time to the optical image which discharges the target, and the subsequent scanning during a frame recharges the target, generating the video signal on a time basis.



   A normal deflection excitation circuit, to say a constant current source 12, is across the deflection stop switch
23 with the time chains for fast and normal deflection
24, 25, which are themselves connected by the switch 26 to circuit 31 and to the deflection elements of the camera tube 21.



   Connected to deflection circuit 22 is a conventional sync and blank signal generator 28 for resetting the line and field deflections, which generator is also connected to camera tube 21 to block it during line and field flyback.

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   A video sampling circuit 29 to be described in more detail below is connected to the video signal output circuit 30 of the camera tube 21, to the deflection stop switch 23 and to the fast deflection switch 26. A video signal change circuit 32 is connected to the video signal output circuit 30 of the camera tube 21 and to the video sample circuit 29.

   The original video signals appearing at the output circuit 30 of the camera tube 21 are sampled by the sampling circuit 29, as will be further described below, and when black information is detected, the sampling circuit 29 causes the switch to for the fast deflection 26 1 connects the normal deflection timing circuit 25 to the a2 deflection element 27 of the camera tube 21 so that the image is scanned at the normal speed, i.e., the slow speed. When a white information video signal is detected, the sampling circuit 29 causes switch 26 to connect the fast deflection timing circuit 24 to the deflection elements 27 of the camera tube 21, so that the image is now quickly scanned.



   According to the invention, when the white information video signal has a duration which is shorter than a predetermined minimum. time, the sampling circuit 29 causes switch 23 to stop scanning for a period of time which, when added to the duration of the short white information video signal, shows a similar relationship to this short signal as the relationship between the high and low scanning rates. exists.

   Thus, when the relationship between the high and low scanning speed is 2: 1, the deflection stop switch 23 will be operated so long that the deflection is activated.

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 interrupted for a time equal to the duration of the short vitinlormation signal. whereas, when the relationship between the high and low scan speed is 3: 1, the scan is interrupted for a time equal to twice the duration of the short white information signal.



   When such a white information item having a duration shorter than a predetermined time is discovered, and thus the deflection is interrupted in the above-described manner, the video change circuit 32 generates a white information video signal having a third level interposed between the white information video signal levels. fast scan and the black information signal level in slow scan, this white information signal then having a duration equal to the duration of the short white information signal plus the duration of the interruption of the scan,

     that is, the scanning signal has a duration that is the same as the duration it would have had if this white information had been initially scanned at a low speed.



   For example, if it is assumed that the minimum video signal that can be transmitted is 100 microseconds in duration and that the ratio of the major to the minor scan rate is 2: 1, in order to provide a compression ratio of 2: 1, If the white information video signal has a duration longer than 100 microseconds, this signal will be transmitted immediately with a first "whiter than white" level.

   However, when scanning at high speed, if the duration of the flash signal is less than 100 microseconds, for example 75 microseconds, the scan will

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 be interrupted for the same amount of time, namely 75 microseconds, and the video change circuit will generate a video signal of 150 microseconds duration at the normal vit level, that is, the intermediate level between the fast scan vit level and the smart level.



   It will be appreciated that two contrasting characteristics in the image viewed through the camera tube, such as white and black, will initially produce video signals with two extreme levels, such as vit positive and black negative where the vit positive signal is is fast scan, while the normal scan white signal level is supplied by the video change circuit 32 under control of an original shorter white video signal having a level intermediate between the fast scan white signal level and the black video signal level.

   It will also be appreciated that under control of all shades of gray in the image, video signals are produced with levels intermediate between the black level and the vitlevel at normal scan.



   As will be described in more detail, a sync signal encoding circuit 33 connects the sync and quench signal generator 28 to the output circuit 34 of the video change circuit 32 to provide an encoded three-level sync signal for the broadcast. The output chain 34 of the video change chain is connected to the usual transmission equipment, which may be of the type described in the above-mentioned Belgian patent.
No. 641584.



   The receiving station which is generally 35 in FIG

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 includes a suitable synchronization signal decoder 36, to be described in more detail, having an input circuit 37 connected to conventional reception and detection equipment. Circuit 36 includes a first output circuit 38 in which the individual sync signals occur and a second output circuit 39 in which the individual video signals occur. A picture tube 40 is provided, the grid of which is connected via a video pulse generator 42 to the output chain 39 of circuit 36.

   The video pulse generator 42 generates signal pulses which, applied to the control grid of the picture tube 40, output when the received video signals exceed a predetermined threshold level indicated by the dashed line 43, the first level for high-speed video signals. scan and the intermediate level for normal scan video signals. first and second level white signals produce a white image on the picture tube 40 and black signals produce a black image.



   The deflection circuit 44 may be the same as the deflection circuit 22 of the transmitting station, and is connected by switch 45 to the fast and normal scan timing circuits 46, 47 which may also be the same as circuits 24, 25 and the switch.
26 from the broadcasting station. Switch 45 selectively connects the fast and normal scan timing chains to a deflection circuit 41 connected to the albending elements 48 of picture tube 40.



   The level detector circuit 49 connects the output circuit 39 of circuit 36 to the switch 45. The detector 49 detects video signals from which the level exceeds the

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 EMI15.1
 6c <'iippe? .1iJn 3 &l¯I!;;! 7: gi2'fe:! 1 level, ie the Géastü i,:. . or '1!.; 'fit tdgndlen with fast scan and operate the sc81t; lielaaz 45 03:

   in response to these signals, the raQ3.le a ± tube time * n 46 with the deflection elements 48 of the picture tube 40 \: 0 7ez "b: i.1.1.dn, whereby the electron beam in the picture tube is deflected at the same speed as this in de ¯r: .4 21 gsz: .h.edtf However, when a signal cet 22n t0cd i78. a ".: 's:' 'Tld'L'OSiCzia2tl, or a 3.'. c. noc ee: 2 ': 18!' dc: 1 If a white video signal with normal sensing is received, switch 45 is affected so that the deflection timer circuit 47 is connected to the albending element 48 hours so that the beam in the picture tube &; '0 [1.at ce: Jc:! Et5. ::: 7, the speed is deflected when this occurs in the GeubDi3 3i.

   It will be clear that the ¯4? Lv ¯w ± -JI'lle1ITcnisation! Lalen which occur in dM output chain 33 '7th. I: o:! / 2 l:' 3rd <& 3C before the well-known return. bunch 7ili? qui = ",", "0. i": i are supplied to the a..bj.a3.g circuit 44. In fligo3 i Gn 'exemplary embodiments of the video vtcp ok tce 29 and the video verifying circuit 32 of FIG. <I # Taarin o72: r-eell'tc!: L ± .ticrë; 1;:; * # ten with the same rate \ .Tij5in9'9 "GGJWn ::, ij1 Jt: 112'eduh !. Da; it : iveat, detector circuit 52, which it Ge ::? bQ2 ': Ge si!) 1'laJ.2: .l! cut :: 0tn can exist, is with the titg;' 2g ± b \; (; m 30 of the canera tube 21 are connected, where i; 1 <; güE; üsitoten 53 and due switch 26 is connected. The sitting level that emerged in the output chain 30 of the caera tube 21 ;.

   Connected to the output circuit 53 of the detector 52 is a known signal inverter 54, which

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 also connected to an input 55 of a known "and" gate 56, which cell. is indicated by "and" port no.3. Also associated with the output 53 of detector 52 is a known differencing and bypass circuit 57. The output 58 of circuit 57 is provided with a monestable multivibrator 59, which does not generate a pulse of a predetermined duration T, in response to the signal supplied by the differential circuit 57 by the occurrence of the leading edge. The pulse T gives the above-mentioned minimum transmission time.

   The output 60 of the monostable multivibrator 59 is connected to the other input of the "and" port 56. The output of "and" gate 56 is just connected to a differentiating circuit 61. The output of the differentiating circuit 61 is connected to the clipping circuits 62 and 63. The output of circuit 62 is connected to the adjustment circuit of the bistable multivibrator 64.



   The output 53 of the white level detector circuit 52 is also connected to a pulse shaping circuit 65, which itself is connected to a timing circuit 66 which includes a charging capacitor which, upon charging, measures the length of the pulse supplied by the pulse shaping circuit 65. The output 58 of circuit 57 is connected to a timing circuit 66 so that the signal supplied by the differential circuit 57 as a result of the leading edge, which will coincide with the start of the pulse applied by the pulse shaping circuit 65 to the timing circuit 66, will initiate a rapid discharge of the time capacitor, causing the voltage across the capacitor to drop to zero. The signal appearing at the output 67 of the timer 66 is

   will have a duration equal to twice the duration of the control signal applied to the output 53 of the vit-level detector.

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 tor 52 occurs, for a ratio of the fast scan speed to the slow scan speed of 2: 1.



   The output 67 of the timer 66 is connected to a threshold detector 68, which itself is connected to another differentiation and clipping circuit 69.



   The food 69 connected sees the reset circuit of the multistable multivibrator 64 for resetting it in response to the signal supplied by the differentiating circuit 69 due to the trailing edge. The output 70 of the bistable multivibrator 64 is connected to the deflection stop switch 23 and also to one of the inputs of "and" port 72. The other input 73 of "and" port 72 is connected to a source 74. providing a fixed DC voltage corresponding to the third or intermediate white signal level with normal scan. The output 75 of the "and" port 72 is connected to the output of the buffer amplifier 81.



  The baffle amplifier 81 prevents signals appearing at the output 75 from affecting the output circuit 30 of the camera tube 21. When a signal appears at output 70 of the bistable multivibrator, output 75 will be held at source 74 voltage.



   A delay line 76, where the delay has the same duration as the duration T of the pulse supplied by the monostable multivibrator 59, is connected between output 75 of buffer amplifier 81 and "and" port 72, and output 34.



  The output 77 of the cut-off circuit 63 is connected to the adjustment circuit of the bistable multivibrator 78, which is connected by the trailing edge through the differentiating circuit.

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   61 and the signal supplied to the clipping circuit 63 is set.



  Another delay line 79, having a delay time of the duration equal to the duration of the pulse T generated by the monostable multivibrator 59, is connected to output 80 of the pulse shaping circuit 65. The delay line 79 is connected to a differential and cut-off circuit 82, which is connected to the reset circuit of the bistable multivibrator 78, thereby resetting it by the signal supplied by the differential circuit 82 as a result of the trailing edge. Output 83 of the bistable multivibrator 78 is connected to one of the inputs of "and" port 84.

   The other input 85 of "and" port 84 is connected to a source 86, which provides a fixed DC voltage of the same level as source 74, to make up the intermediate or third level of the normal scan white video signal, and the output 87 of "and" port 84 is connected to output 34. Thus, when a signal occurs at output 83 of the bistable multivibrator 78, output becomes
34 held at source 86 level.



   Fig. 4A shows a part of a specific line scanned in the camera tube 21. In this figure where the distance is the ordinate and the scan is in the direction indicated by the arrow 88, the parts 89-1, 89-2, 89-3 and 89-4 of the scanned line are white information in the scanned image, and parts 90-1, 90-2, 90-3 and 90-4 black information.



   As will be described in more detail, the electron beam of the camera tube 21 will be controlled such that it scans the blanks 89-1, 89-2, 89-3, 89-4 at the fast deflection speed, for example with twice the normal speed and

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 the black parts 90-1,90-2,90-3 and 90-4 with the normal small deflection speed.



   Figure 48 shows an original video signal appearing at the output 30 of the camera tube 21, the time now being ordinate, and the scanning of the viewed line on the target of the camera tube 21 is initiated by the sync signal 92, shown here as a signal having a fourth blacker-than-black level that is lower than the black level. In Fig. 4C, the pulses 93-1, 93-2, 93-3 and 93-4 are depicted which are supplied by the monostable multivibrator 59, each of duration T and each initiated by the appearance of a respective video signal with a white level at the output circuit 30 of the camera tube 21.

   Thus, the white portion 89-1 in the scanned line on the pull electrode of the camera tube 21 results in an original video signal with a white level 94-1, which produces a corresponding control signal at the output 53 of the white level detector 52, which itself initiates pulse 93-1 with a duration T longer than the duration of a white level video signal at fast scan 94-1. As will be further described, the deflection is interrupted during the interval 95-1 with the same duration as the original white level video signal 94-1.

   At the end of the a ± bend stop interval 95-1, the deflection is resumed and as the black portion 90-1 is then scanned, the scan will be at the normal or slow speed, causing the video signal with black level 96- 1 is resurrected.



  When the next white portion 89-2 of the scanned line is next, the a ± probe speed is increased to produce an original video signal with white level at fast a ± -

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 tasting 94-2 results, which itself initiates the pulse 93-2 of the monostable multivibrator. Pulse 93-2 will have a duration longer than the duration of the original white level video signal 94-2, which will result in an interruption of the deflection during interval 95-2, which has the same duration as the original white level video signal 94-2.

   At the end of interval 95-2, the scan resumes at the normal or slow speed because it is now the turn of the black portion 90-2 of the scanned line, providing an original black level video signal 96-2. Upon reaching @@ a of the healthy portion 89-3 of the scanned line, an original vit-level fast scan video signal 94-3 is generated, thereby generating the monostable multivibrator pulse 93-3.

   However, the white fast scan video signal 94-3 has a longer duration than the multivibrator pulse 93-3. so that the scan is not interrupted, but instead continues at high speed until the black portion 90-3 of the scanned line is next, at which point the scan speed is reduced to the normal low speed and a black level video signal 96-3 is resurrected.

   Likewise, the white portion 89-4 of the scanned line is scanned at the high speed, generating an original white fast a ± tasting video signal 94-4, thereby generating the monostable multivibrator pulse 93-4, which produces a has longer duration than the white fast scan video signal 94-4, interrupting the scan for the interval 95-3, which has the same duration as the white video signal 94-4.

   The interrupt of the scan during the interval 95-3 is followed by the for

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 scan the black portion 90-4 of the scanned line at the normal low speed, providing the video signal with black level 96-4.



   From a comparison of Figures 4A and 4B, showing only a small portion of a scanned line on the target of the camera tube 21 and the resulting original video signal in the output circuit 30 of the camera tube, it will be seen that the video signal has been time period i is generated which is less than would be required if the respective line on the target is continuous with the normal; male slow speed would be scanned.



   5 and 3, the operation of the video sample and video change chains will now be described.
29,32 on the appearance of an original white video signal at fast scan 94-3 with a longer duration than the respective monostable multivibrator pulse 93-3. The control signal at the output 53 of the vit-level detector
52 has the same duration as the original vit-level video signal 94-3, as indicated at 94-3C in FIG. 5B, and the inverted signal supplied by inverter 54 is indicated at 97 in FIG. 5D.

   The signals 98 and 99 generated by the differentiating and cutting circuit 57 due to the leading edge and the trailing edge of the control signal 94-3C are shown in FIG. SE. It will be seen that the inverted signal 97 and the monostable multivibrator pulse
93-3 are applied to "and" gate 56, and that is where the pulse
93-3 ends before the termination of the control signal
94-3C, no output signal at the output 62 of the "and" gate 56 will occur.

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   The shaped control signal 94-3C appearing at the output 80 of the pulse shaping circuit 65 is indicated at 94-3S in FIG. 5G and the time signal 100 supplied by the timing circuit 66 is shown in FIG. 5H;

   the charging capacitor of the timing circuit 66 charges when the pulse 94-3S is applied, when the signal at output 80 of the pulse form circuit 65 is zero, the charging capacitor discharges to provide the signal 100, which has a duration twice as long as the duration of the control signal 94-3C. The signal 102 supplied by the threshold detector 68 and shown in Figure 51 thus has the same duration as the time signal 100 and after differentiation in circuit 69 produces the signals 103 and 104. The positive peak 103 is cut off and the negative peak 104 becomes let through.



   The leading and trailing edges of the output signal from the "and" gate 56 are differentiated in circuit 61.



    The bistable multivibrator 64 is toggled by an output signal at the output of circuit 62 and since under the conditions given in Fig. 5 no output signal is supplied through "and" port 56, no output signal is coming from circuit 61 and circuit 62 either. as shown in fig. 5-0. Thus, the bistable multivibrator 64 is not toggled and is therefore not reset by the circuit
69 signal generated from the trailing edge by differentiation
104. Thus, the output of the bistable multivibrator 64 is at zero level as shown in FIG. 5K and no signal is supplied to the deflection stop switch 23.



   Since no signal is present at output 70 of bistable multivibrator 64, output circuit 75 of the "and" gate will

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 72 do not change the scanned video signal. Thus, the original high-speed attack video signal 94-3 is supplied directly to the input of delay line 76, as shown in FIG. 5M, and is delayed therein by the time T, causing delay at output 34. signal 94-3D is supplied, as shown in Fig. 5N. by pulsv01'l! ler pul. Becomes 94-39
The pulse 94-33 supplied by the pulse shaper 65 is applied to the delay line 79 and delayed by time T, as shown at 94-3SD in FIG. 5P.

   The signals 105, 106 derived by the differential circuit 82 from the leading and trailing edges of delayed pulse 94-3SD are shown in FIG. 5Q. However, since no signals are supplied by the circuits 61, 63 to switch the bistable multivibrator 78, the signal 106 supplied by the circuit 82 will not switch back the bistable multivibrator 78 and thus the bistable multivibrator 78 does not produce an output signal. as shown in Fig. 5R.

   Thus, the output circuit 87 of "and" gate 84 does not affect the signal at output 34, with the result that the original high-speed scan video signal 94-3 is delayed by a time T by the delay line 76 at output 34. as shown at 94-3D in FIG. 5T.



   In FIG. 6, the operation of the video sample and video change circuits 29, 32 is depicted under the influence of an original fast scan white video signal such as 94-1, having a duration shorter than the respective monostable multivibrator pulse 93-1. The control signal

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 provided by the white level detector 52 in response to the video signal 94-1 is shown at 94-1C in FIG. 6B and its inversion supplied by inverter 54 at 107 in FIG. 6D. leading edge and trailing edge of the control signal 94-1C derived signals 108,

   109 are shown in FIG. 6E and the monostable multivibrator pulse 93-1 in FIG. 6C. It will be seen that the inverted signal 107 from inverter 54 applied to the "and" port 56 is shorter than the multivibrator signal 93-1 also applied to the output of "and" port 56 an output pulse 110. will occur, with a duration that is the difference between the duration of the inverted signal 107, and thus the duration of the control.

   signal 94-1C and the white level fast scan video signal 94-1, and the duration of the monostable multivibrator pulse 93-1. The pulse 94-18 supplied by the pulse shaping circuit 65 in response to the control signal 94-1C is shown in FIG. 6G, under control of which the timing signal 112 is controlled by the timer 66 and the threshold signal 113 by the threshold detector 68. as shown in FIGS. 6H and I, respectively.



   The output signal 110 appearing at the output of "and" gate 56 is differentiated by differential circuit 61 to produce signals 116, 117 from the leading and trailing edges as shown in FIG. 60. The signal 116 will switch the bistable multivibrator 64, causing a pulse 114 to appear at output 70, as in FIG.



  6K is shown. The signals 115, 116 supplied by the differential circuit 69 in response to the leading and trailing edges of the threshold signal 113 are shown in FIG. 6J; it

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 Signal 116 corresponding to the trailing edge of signal 113 resets bistable multivibrator 64, terminating pulse 114. Pulse 114 has a duration equal to the duration of the original fast scan white level video signal 94-1, with pulse 114 being applied to deflection stop switch 23 to interrupt the scan as described above.



   The output pulse 114 of the bistable multivibrator 64 is applied to "and" gate 72, thus supplying output 75 with the fixed DC voltage shown in FIG.



  6L at 115 is shown. As shown in FIG. 6N, the original white level video signal 94-1 with the first whiter than white level is supplied as an input to delay line 76, with output 30 then maintained at the intermediate @ third level of source 74, such as. in ìg.6M at 115M. Thus, the output of delay line 76 is the signal depicted in FIG. 6M delayed by a time T, as shown in FIGS. 6N at 94-1D and 115D. It is assumed that the signal through "and" gate 84 is not changed further.



   The signal 117 supplied by the circuits 61,63 is delayed by time T from the start of the fast scan signal 94-1. Signal 94-1S supplied by pulse shaping circuit 65 is passed through delay line 79 with time
T delayed, providing the delayed signal 94-1SD shown in FIG. 6P and the differentiating circuit
82 deduces signals 118, 119 therefrom, as shown in FIG. 6Q.

   The signal 117 passing through the differential chain 61 and the a ± cutting circuit 63 from the trailing edge of pulse 110

 <Desc / Clms Page number 26>

 is derived from the "and" gate 56, the bistable multivibrator 78 switches, initiating pulse 120 at its output 83, while the signal 119 derived by the differential circuit 82 from the back ± lank resets the bistable multivibrator 78, thereby pulse 120 is terminated, as shown in Fig. 6R. It can be seen from FIG. 6 that the pulse 120 supplied by the bistable multivibrator 78 has the same duration as the vit-level video signal 94-1 but is delayed by a time T relative thereto.



   Application of pulse 120 to "and" gate 84 causes the voltage from source 86 to be passed to output 87, as indicated at 122 in Fig. 6S. Since now the signal 94-1D, 115D will appear at the output 34 of the delay line 76, when there is no signal at the output 87 of "and" gate 84, and the fixed level of the DC voltage signal 122 appearing at the output 87 of "and" gate 84, coinciding with the delayed signal 94-1D, the output 34 is held at the voltage of source 86 during signal 122, with the result that output 34 is a composite altered video signal 94 -1M occurs, as indicated in fig.6T,

   which signal is at the level of the sources 74, 86, that is to say a level between black level 90 and vit level 94, and is twice as long as the video signal 94-1; the altered video signal 94-1K is composed of the latch signals 122M and 115D each of the same duration as the video signal 94-1, as described above.



     It now appears that 'When a video signal such as 94-1 has a duration shorter than the duration T' of the monostable

 <Desc / Clms Page number 27>

   multivibrator pulse 93-1, a deflection stop pulse 114 is generated, with the same duration as the video signal 94-1, which controls the deflection stop switch 23 to interrupt the deflection and change the video signal 94-1 to the video signal 94-1M with a third level which is between the white level 94 and the black level 96 and is twice as long as the video signal 94-1,

   that is, it has the same duration as it would have had if portion 89-1 of the scanned line had been scanned at the normal or slow speed.



   In Figure 7B, the same original video signal as shown in Figure 4B is shown. The signals generated from the preflash by the differential circuit 57 are shown in Fig. 7E and the monostable multivibrator pulses 93 in Fig. 7C. The signals 110 appearing at the output 62 of "'and" gate 56 in response to original fast scan white level video signals, and respectively having a duration shorter than the monostable multi-vibrator pulses 93, are shown in FIG. .7F shown,

   the pulse 94-S supplied by the pulse shaping circuit 65 is shown in FIG. 7G and the timing signals supplied by the timing circuit 66 in response to the pulses 94-S are shown in FIG. 7H.



  The resulting threshold signals are shown in Figure 7I and the deflection stop pulses 114 in Figure 7L; The input of delay line 76 is shown in FIG. 7M and the output of delay line 76 (when this output is not latched by the output of "and" gate 84) is shown in FIG. 7N. Finally, the latch signal supplied by "and" gate 84 is shown in FIG. 73 and the resulting composite video signal applied to output 84.

 <Desc / Clms Page number 28>

 appears in Fig. 7T.

   The composite video signal of Figure 7T resulting from the video signal of Figure 7B includes a sync signal 92 with a fourth level video signal 94-1M having a third level corresponding to the video signal. channel 94-1, a second level black video signal 96-1M corresponding to the black video signal 96-1, a white video signal 94-2M with a third level corresponding to the video signal 94-2, a black level video signal 96-2M which corresponds to the black video signal 96-2, a white video signal 94-3D with a first level corresponding to the white video signal 94-3,

     a second level black video signal 96-3M corresponding to the black video signal 96-3 and a third level white video signal 94-4M corresponding to the video signal 94-4.



   The composite video output signal shown in FIG. 7T includes four levels, including a first white level. level in fast scan, a second or black level in normal scan, a third level in normal scan, and a fourth sync level.

   It is a requirement of the system that a deflection stop signal 114 be generated with a duration such that, added to the duration of an original white level video signal in fast scan, which is shorter than the predetermined time T, the same proportion to the duration of the original. white level video signal at fast scan occurs when the ratio between the fast scan speed and the small scan speed is, and the original video signal at fast scan is changed to a third level video signal,

   with a duration equal to the duration of the original

 <Desc / Clms Page number 29>

 video signal plus the duration of the deflection stop signal. In the exemplary embodiment shown in Fig. 3, the ratio between the high scan speed and the small scan speed was 2: 1 and thus the duration of the deflection stop pulse 114 was equal to the duration of the original white level video signal at fast scan and the resulting third level video signal had a duration that is twice as long as the duration of the original video level video signal.



   According to FIG. 8, the same composite video signal is received at the receiving station 35 as the signal transmitted from the transmitting station 20 and shown in FIG. 7T. The sync decoder 36 separates the sync signals 92 from the other video signals in a known manner, with the result that the three-level video signal shown in FIG. 8B appears at the output 39 of the circuit 36.
The level detector circuit 49 is set to a threshold level such that it can detect the video level video signals at fast scan, as indicated by the dotted line 50 in FIG. 8B.

   The signal 94-3D from a fast scan of a white information has a first level that exceeds the threshold level 50 of the detector 49, as indicated at 117, thereby creating a fast a ± bend pulse 118 shown in FIG. 8D. is generated, influencing switch 45 to connect fast deflection timing circuit 46 to deflection elements 48 of picture tube 40.

 <Desc / Clms Page number 30>

 



   The video pulse generator circuit 42 is set to a threshold level such that all white video signals are detected, both the fast scan-related white signals and the slow scan-related white signals, as indicated by the dotted line 43 in Figs. 2 and 8B. . Thus, all white video signals of the three-level video signal will exceed the threshold level 43, thereby providing the respective vit-video pulses 119-1, 119-, 119-3, 119-4 of Fig. 8C.



   The switch 45 connects the normal deflection timing circuit 47 to the deflection elements 48 of the picture tube 40 when there is no fast deflection signal 118 present, and thus the electron beam in the picture tube 40 will move at normal or slow fieless during the occurrence of the white video signals 119-1 and 119-2 and the black signals 96-1M and 96-2M.



  Upon the occurrence of signal 118, switch 45 connects
 EMI30.1
 the fast deflection timing circuit 46 with the deflection elements 48 generating a fast deflection, while switch 45 during the occurrence of the black signal 96-3M and the white signal 119-4 the normal a ± deflection time circuit 47 with the deflection elements 48 connection, creating the line shown in Fig. 8E on the picture tube. It will be seen from FIGS. 8F and FIG. 4A that the line depicted in FIG. 8E is the duplicate of the scanned line in the camera tube 21, but delayed in time by delay T.

   However, it will be seen that the video signals generated in the transmitting station 20 in the manner described above and causing the line generation in the picture tube 40 were transmitted in a significantly shorter time than would be required in the uniform rate scan. -

 <Desc / Clms Page number 31>

 The scan was slow enough to permit transmission of the video signals over a medium of narrow bandwidth.



   It is important that both the camera tube 21 and the picture tube 40 explore at the same deflection speed. The scan spot contains both vertical and horizontal components, and thus, as in the system of the invention, when the horizontal scan speed is increased, the vertical scan speed must be increased proportionally; if this ratio is not kept constant, the distance between adjacent lines will vary. For example, if only the speed of the horizontal deflection is increased, the distance between adjacent scan lines will be the smallest in an image area where the least detail occurs, so that maximum vertical definition would occur where it is least needed.

   Thus, in order to maintain a constant horizontal-vertical relationship, the a ± bending wave ± shapes must be controlled together.



   In FIG. 9A the same video signal as in FIG. 7B is shown and in FIG. 9B the resultant bend stop signals 114 corresponding to FIG. 7L are shown. A deflection voltage for the video signal depicted in FIG. 9A and the deflection stop signals depicted in FIG. 9B is shown in FIG. 9C, where this waveform relates to both the horizontal and vertical deflection circuits of the camera tube 21.



  The beam moves at the high speed indicated by ramps 120-1, 120-2, 120-3 and 120-4 during white video signals 94-1, 94-2, 94-3 and 94-4; the scan is

 <Desc / Clms Page number 32>

 broken during deflection stop signals 114-1, 114-2 and 114-3 as indicated at 122-1, 122-2 and 122-3, and the beam is moving at the normal speed indicated by ramps 123-1, 123 -2 and 123-3 during the remaining intervals of the black video signals 96-1, 96-2 and 96-3.



   Generation of the waveform shown in Fig. 9C can be easily accomplished by changing the time constant in the deflection circuit. Referring to FIG. 10, the fast and normal scan timing circuits 24, 25, consisting of resistors cooperating with timing capacitor 124, are shown to provide a high and low scan rate. Switch 26 is operated by a relay, such as a reed spring relay 125, which relay is energized by output 53 of video sample circuit 29. During the intervals of normal or slow scanning, resistor 24 is disconnected and capacitor 124 charges across resistor 25. , creating the normal a ± probe speed.

   However, when a fast sense signal is detected by the white level detector 52 (FIG. 3), relay 125 is energized and switch 26 closes, connecting the two resistors 24, 25 in parallel and causing the fast deflection.



   Stop switch 23 is operated by another relay 126 which is energized by deflection stop signals 114. Energizing relay 126 by a deflection stop signal 114 opens deflection stop switch 123, disconnecting charge capacitor 124 from the charge circuit and interrupting the scan. It will be appreciated that separate circuits, as shown in Fig. the vertical and horizontal deflection are used, with corresponding

 <Desc / Clms Page number 33>

 shells in the fields of resistors 24, 25 and capacitor 124,

   but whose switches 26 and deflection stop switches 23 are operated simultaneously in response to the fast deflection signals and the deflection stop signals.



  The circuit shown in FIG. 10 is given by way of example only, and other circuits may be used to generate the fast and slow bend.



   In FIG. 9D the same received composite video signal is depicted as in FIG. BA and the corresponding deflection voltage for the picture tube 40 is shown in FIG. 9E, this waveform being related to the horizontal and vertical deflection circuits. Here, the beam in the picture tube 40 is moved at the slow or normal speed, equal to the movement in the camera tube 21, during the occurrence of the normal scan rate video signals 94-1M,
 EMI33.1
 94-2bi and 94-4M and during black video 96-1M, 96-21 and 96-3M, as indicated by slopes 127-1 and 127-2.

 <Desc / Clms Page number 34>

 



  However, upon detection of a high scan rate white video signal 94-3D by the detector 49, the switch 45 is actuated which connects the fast deflection timing circuit 46 to the deflection elements 48 of the picture tube 40, causing rapid deflection, as indicated by the slope 128 in FIG. 9E. The fast and slow deflection timing circuits 46, 47 of the picture tube 40 may be identical to the fast and slow deflection timing circuits 24, 25 of the camera tube 21, with the deflection stop switch 23 being omitted, of course, since the picture tube 40 does not interrupt the deflection.

   The shown in FIG. The fast and slow deflection circuits shown are given by way of example only and can also be replaced by other circuits serving the same purpose by those skilled in the art.



   Bi;' In the system according to the invention, it is an imperative requirement that the deflections of the camera tube 21 and of the picture tube 40 are synchronized. Since in this system the time between the synchronizing signals will vary depending on the type of the document to be transferred, namely an all-white line will be transmitted twice as fast as an all-black line, the use of local synchronized oscillators is not possible, and to control the horizontal and vertical deflection, the synchronizing pulses must be accurately transmitted.

   This can be easily achieved by using synchronizing pulses with a fourth level, as described above; however, this requires an increase in the signal-to-noise ratio at an equivalent channel capacity, and it is therefore desirable to provide synchronization signals that can use the same three levels as for the video.

 <Desc / Clms Page number 35>

 signals are applied.



   From an examination of the device shown in FIG. 7T and FIG. 8A depicted broadcast and received video wave waveforms shows that during normal transmission of video signals there are only three transitions in the signal level; namely, from normally scanned white to black, 129 in FIG. 11A, from black to quickly scanned white, 130 in FIG. 11A, and quickly scanned from white to black,
 EMI35.1
 132 in FIG. ll.

   From 'ig. 7T, FIG. 8A and FIG. 11 further shows that there are four transitions in the signal level which do not occur during normal video signal transmission, namely, black to normal scanned white immediately followed by normal scanned white to fast scanned white, 133 and 144 in FIG. 11A and vice versa, namely quickly scanned to white
 EMI35.2
 normally scanned from immediately gE r 1gd by normal scanned white to black, 145 n 146 .in ri. 11A. Broadcasting ,. in three levels, us can place V: nae-rr through the. n! lrOn: l.aa1il.e- from .chronisatáesà. alen et to encode unused transitions described above.

   Thus, when a sync language is used to transmit pulse 147 in FIG. 11A, which is made up of four transitions 133, 144, 145 and 146, and this pulse is differentiated in the receiving station 35, a set of positive signals 148, 149 is produced immediately followed by a set of negative signals 150, 151. which can be used to recognize a sync pulse 147 and generate a sync signal in response.
 EMI35.3
 n In Fig. 12, a circuit is shown for encoder 33 of FIG. 1 is appropriate and the encoded sync pulse 147 of FIG. 11A will generate in response to a sync. signal.

     It uses a common differential circuit 152 connected to a monostable multivibrator 153, which generates a pulse whose duration is equal to the third.

 <Desc / Clms Page number 36>

 level pulse 154 of the coded synchronization signal 147 in response to signal 155 occurring as a result of the leading edge of the differentiated signal. The output 156 of the monostable multivibrator 153 is connected to "and" gate 157, the other input of which is connected. to a long DC voltage source 158 of the third level, namely the level of pulse 154. The output 159 of "and" gate 157 is connected to output 34.

   Thus, the generation of the pulse by the monostable multivibrator 153 will result in the output 34 being latched by source 158, providing the third level pulse 154 of the encoded sync pulse 147.



   Connected to the output 156 of the monostable multivibrator 153 is another monostable multivibrator 160 which generates a pulse in response to the trailing edge of the pulse generated by the monostable multivibrator 153. The output 162 of the monostable multivibrator 160 is connected to "and" port 163, the other input of which is connected to a source of a fixed DC voltage, to the first level of pulse 161,164. The output 165 of "and" port 163 is connected to the output 34.

   Generating the pulse by; thus, the monostable multivibrator 160 in response to the termination of the pulse generated by the monostable multivibrator 153 will cause output 34 to be latched to the voltage of source 164, first level, causing the first level pulse 161 of the coded sync pulse 147 will be delivered.



   Connected to the output 162 of the monostable multivibrator 160 is a third monostable multivibrator 166 which generates a pulse in response to the termination of the monostable multivibrator 160.

 <Desc / Clms Page number 37>

   stable multivibrator 160 excited pulse. The exit 168
 EMI37.1
 of the monostable multivibrator 166 is connected to the output 156 of the monostable multivibrator 153 and to the "and" port 157.

   Upon termination of the pulse supplied by the monostable multivibrator 160, which provided the first level pulse 161 of the coded sync pulse 147, the. monostatic multivibrator 166 generate a pulse that causes output 34 to latch back to the level of source 158, thus providing the third level pulse 167 of coded sync pulse 147.



   In fig. 13 shows a chain suitable for the
 EMI37.2
 synchronization decoding circuit 36 of Fig. 2 for decoding the encoded synchronization pulses 147. The differentiating circuit 169 differentiates the received video signal and the
 EMI37.3
 coded synchronization signal 147, whereby the system shown in FIG. 11D, signals 147, 148, 149 and 150 shown are generated. Three bistable multivibrators 170, 172 and 173 are provided, each providing a zero output signal.

   The output 174 of the bistable multivibrator 172 is connected to the "and" port 175 through an inverter 176, and the other input of "and" port 175 through an inverter 177, of the differential circuit 169, while the output 178 of this "and" port 175 is connected to the bistable multivibrator 170. The first going positive signal 147 will output "and" port 175, causing bistable multivibrator 170, whose output 179 is connected to "and" port 180, to output an output signal. The other input of "and" gate 180 is connected to output 177 of differentiating circuit 169 and output 182 is connected to bistable multivibrator 172.

   The second turning positive signal 148 will signal "and" gate 180, causing the bistable multi

 <Desc / Clms Page number 38>

 vibrator 172 generates an output signal. The output of bistable multivibrator 172 blocks "one" port 175, but enables port 183. The other input of "and" gate 183 is connected through inverter 184 to the output 177 of differentiating circuit 169 and thus becomes the first negative. applied the signal 149 to the bistable multivibrator 173, thereby providing an output signal that enables "and" gate 184.

   The other input of "and" gate 184 is connected to inverter 184, supplying the second and last negative signal 150 to "and" gate to provide the sync signal 185 to output 38, thereby providing the prior art. mode the deflection is reset. The signal 185 also appearing in circuit 181 resets the bistable multivibrator 170, 172, 173 to their initial position with zero output signals at 174, 179, 191.



   In fig. 14 shows a modified form of video sample and change circuit 29, 32 in which corresponding elements are indicated by the same reference characters. In this circuit, a delay line 79 is connected to the output
186 of the threshold detector 68 instead of the output 80 of circuit 65 as in the embodiment of FIG. 3 was the case, and so the entire threshold signal is over time
T delayed. The delay line 79 is connected to the differer.



   tiering circuit 82, which itself is connected to the reset circuit of the bistable multivibrator 78. The output 83 of multivibrator 78 is connected to elan "and" port 187, the other input 188 of which is a source of a fixed equal. voltage is connected to a third level 189 and the output
190 of "and" port 187 is connected to output 34.



   In fig. 15 are shown with FIG. 6 corresponding signals are indicated by the same reference characters. FIG. 15 indicates the signals contained in the circuit of FIG. 14 attend the performance

 <Desc / Clms Page number 39>

 A high-scan original white video signal 94-1 having a duration shorter than the pulse 93-1 supplied by the mono stable multivibrator 59, respectively. The deflection top signal 114 is generated in the same manner as that in the embodiment of FIG. 3 d happened.

   However, the threshold signal 113 is now delayed by delay line 79 by a time T to produce the delayed threshold signal 113 D, of which signals 192 and 193 are generated by differentiation by the differential circuit 82 from the leading and trailing edges. . The signal 117 supplied by the differential circuits 61,63 in response to the trailing edge of pulse 110 switches the bistable multivibrator 78, while the signal 193 derived from the trailing edge of delayed threshold signal 113 D, the bi-stable multivibrator. 78, thereby generating pulse 194.

   This pulse has the same duration as the threshold signal 113, but is generated only that the original fast scrap white video signal 94-1 has a duration shorter than the bar. timing pulse 93-1, generating pulse 110. The application of the bistable multivibrator pulse 194 to "and" gate 187 releases this gate, latching output 34 to the third level voltage of source 189, as shown in FIG. 158 and T at 195. The third level signal 195 has the same duration and level as the altered video signal 94-1M of FIG. 6.



   In fig. 16, in which with FIGS. 13 and 14, the same reference character is used, a modification of the video sample and video change circuit 29, 32 is shown, which is adapted to a ratio between the high and low scan speed of 311.

 <Desc / Clms Page number 40>

   ference circuit 181 is connected to output 53, while also connected to clipping circuits 191, 201 and mono stable multivibrator 59 is connected to clipping circuit 191.

   The timer 196, which may be similar to the timer 66 of the preceding figures, is connected to the pulse former 65 and to the cut-off circuit 201 to generate a first time signal having a duration twice the duration of the pulse generator. the pulse shaper 65 supplied.



  Threshold detector 197 is connected to timer 196 to generate a corresponding threshold signal, and to threshold detector 197 is connected a differential circuit 198 to derive signals from the leading and trailing edges of the signal supplied by detector 197. The biostable multivibrator 199 setting circuit is connected to the differential and clipping circuit 198 so that the signal derived from the leading edge switches the beet stable multivibrator 199.



     The setting circuit of another bistable multivibrator 200 is connected to the clipping circuit 201, whereby this malt! Vibrator is set by the signal derived from the trailing edge circuit 201 supplied by circuit 201. The reset chain of! the bistable multivibrator 200 is connected to the differentiating and clipping circuit 198, thereby resetting the bistable multivibrator 200 by the signal derived from the trailing edge by circuit 198 '.

   The output 202 of the bistable multivibrator 200 is with a different timer 203! connected, which may be time chain 196, of which; timer 203 is connected to the reset circuit with circuit 198 so that it is reset by the signal derived therefrom from the rear edge. The timing chain 203 thus wakes up

 <Desc / Clms Page number 41>

 a time signal of twice the duration of the pulse supplied by the bistable multivibrator 200. The timer 203 is connected to another threshold detector 204 which generates a corresponding threshold signal which is differentiated by the differentiating and clipping circuit 205.

   Circuit 205 is connected to the reset circuit of the bistable multivibrator 64 and to the reset circuit of the bistable multivibrator 199. The signal derived from the trailing edge differential by circuit 205 resets the bistable multivibrator 64, thereby canceling the deflection stop pulse. terminates and also resets the bistable multivibrator 199, terminating the pulse generated thereby. The output 206 of the bistable multivibrator 199 is connected to the delay line 79 which is itself / by the differentiating and clipping circuit 82 connected to the reset circuit of the bistable multivibrator 78.



   From fig. 17. wherein the different signals are provided with the same reference characters as in FIG. 15, and depicting the signals contained in the circuit of FIG. 16 are present upon the occurrence of a high-speed scan-generated native white video signal 94-1 having a duration shorter than the duration of the respective monostable multivibrator pulse 93-1, it is found that the timing circuit 196 generates a timing signal 207. which has the same duration as the time signal 112 of FIG. 5, namely twice the duration of the pulse 94-1S.

   Threshold detector 197 generates a corresponding threshold signal 208 from which differential and clipping circuit 198 generates signals 209 and 210, respectively, in response to the leading and trailing edges.



   The signal 109 passed through the differential circuit 57

 <Desc / Clms Page number 42>

 bistable multivibrator 200 switches, initiating pulse 212, which pulse is terminated by the signal supplied by differentiating circuit 198.
210. Thus, the pulse has the same duration as pulse 94-13. Thus, timing circuit 203 generates a timing signal 213 of duration twice the duration of pulse 212 and pulse 94-1S, and threshold detector 204 provides a corresponding threshold signal 214. Differential circuit 205 derives from the leading and trailing edges of the threshold signal 214 outputs the signals 215,216.

   The bistable multivibrator 64 is toggled by pulse @ 110 and reset by signal 216, thereby providing deflection stop pulse 217. Pulse
217 has the same duration as the threshold signal 214 and the time signal 213, that is, twice the duration of the fast scan video signal 94-1, and thus the deflection stop pulse 217 corresponds to the requirement that the duration of the deflection stop signal set at the The duration of the fast scan white video signal should have the same ratio to the duration of a fast scan video signal when the ratio between the fast scan speed and the slow scan speed is 2: 1 in the present example.



   The signal supplied by the differential circuit 198
209 turns on the bistable multivibrator 199, causing pulse
218 is initiated, signal 216 supplied by differential circuit 205 terminates pulse 218, and it will now be seen that pulse 218 has a duration equal to the duration of the fast scan white video signal 94-1 plus the duration. of the deflection stop signal 217.



   Pulse 218 is delayed by delay line 79 by a time T, creating delayed pulse 218D. The signal 17 supplied by the differential circuit 63 switches the bistable multivibrator 78, while the

 <Desc / Clms Page number 43>

 signal 219 derived by differential circuit 82 from the trailing edge of delayed pulse 218D resets bistable multivibrator 78, providing output pulse 220 to output 83 of bistable multivibrator 78.

   The output pulse 220 has the same duration as pulse 218, i.e. the duration of the fast scan white video signal plus the duration of the deflection stop pulse 217, but pulse 220 is generated only when the fast scan white video signal 94-1 has a duration that is shorter than the duration of the respective monostable multivibrator pulse 93-1, thus generating pulse 110. Applying the bistable multivibrator pulse 220 to "and" gate 187 allows this gate to lock output 34 to the third @ level voltage of source 189, as shown in FIGS. 17S and T at 222.



   It will now be understood that the duration of the altered third level video signal 222 has the same ratio to the duration of the fast scan white video signal 94-1 when the ratio between the high and low scanning speed is 3. : 1.



   The system of FIG. 16 can be further modified to allow for greater ratios between high and low scan rate, by cascading the desired number of bistable multivibrators, timing chains, threshold detectors, and differential and clipping circuits corresponding to 200,203, 204 and 205, respectively.



   It will now be readily seen that the transmission time reduction system of the present invention offers a number of advantages over prior systems. The system of the present invention does not employ shift registers or other memory devices that make up most of the cost of the

 <Desc / Clms Page number 44>

 similar prior systems, and the system according to the invention can be readily incorporated into existing television broadcast systems of the type described in the aforementioned Belgian Patent 641 584 and of the conventional slow scan type.

   Sampling of the video signal is not used in the system of the invention, thus avoiding the above discussed reduction in definition due to quantization. Finally, the system lends itself not only to the transmission of black and white information but also to the transmission of all shades of gray.



   Although the principles of the invention have been described above with reference to special equipment, this should not be construed as limiting the scope of the invention, as this description has been given by way of example only.

 

Claims (1)

C O N C L U S I E S. 1. Television system, characterized in that therein is a camera tube having means for converting an optical image into a corresponding electric characteristic pattern and a sensing means for converting this pattern into a time-based video signal having a first extreme level in response to the presence in the image of information with predetermined characteristics; a deflection generating means for selectively influencing the deflection means at a high and a low speed; means for influencing the deflection generating means to provide a fast deflection speed in response to the first level video signal and for producing a low deflection speed in the absence of the first level video signal; means for supplying a first control signal in response to a first level video signal having a duration shorter than a predetermined time; means for providing, in response to the first control signal, another control signal of such duration as <Desc / Clms Page number 45> added to the duration of the first level video signal, the same ratio occurs with the duration of the first level video signal when the ratio between the high scan speed and the low scan speed is; means for interrupting the timing in response to the other control signal; means for changing the first level video signal in response to the first control signal to provide a second level video signal having a duration equal to the duration of the first level video signal plus the duration of the said first level video signal. another control signal, wherein said changing means passes the video signals in unaltered form in the absence of the first control signal; means for outputting the modified and unaltered video signals and means for receiving the same, a signal-to-image converter including another sensing means for converting the received video signals into an optical image; another deflection generator for selectively operating the other scanner at the high and low speed and means for operating the other scanner at the high speed in response to the reception of a first level video signal, and running the other scanner at low speed when no first level video signals are received. 2. A television system, characterized in that therein is provided: a camera tube having an output circuit, the camera tube including means for converting an optical image into a corresponding electrical characteristic pattern and a sensing means for converting this pattern into a video signal at the same time. time base in the output chain, varying * between a first and a second extreme level and corresponding non-first and second contrasting characteristics, respectively, of the image; deflection generator for selectively operating at the high and the low speed <Desc / Clms Page number 46> the sensing member; first means for developing a first controller in response to and during a video signal having a first level; means for connecting the first developing means to the deflection generator to operate it at the high speed in response to the first control signal and at the low speed in the absence of this first control signal; second means for developing a second control signal in response to a video signal having a first level d lasting less than a predetermined time; a third means for developing, in response to the second control signal, a third control signal having a duration which, added to the duration of the first level video signal, gives the same ratio to the duration of the first level video signal as the ratio between the high and low scanning speed is; a means connecting the third developing means to the deflection generator to interrupt the scan in response to and during the third control signal; means connected to the output circuit for modifying the first level video signal in response to the second and third control signals to provide a third level video signal intermediate between the first and second levels and having a duration which is equal to the duration of the original video signal by the first level plus the duration of the third control signal, this changer passing the original video signal unaltered when the second and third control signals are not present; means connected to the modifier for outputting the modified and the unmodified video signal; means for receiving the broadcast video signals; <Desc / Clms Page number 47> a signal-to-image converter connected to the receiver and including another sensing means for converting the received video signals into optical images; another deflection generator for selectively operating the high and low speed of the other deflection means; fourth means for developing a fourth control signal in response to and during a received video signal, having the first level; and means for connecting the fourth developer to the other deflection generator $ to produce a fast scan speed in response to the fourth control signal and a slow scan speed in the absence of this signal. 3. System according to claim 2, characterized in that the converter converts both a received first level video signal and a received third level video signal into an optical image having a first characteristic. A system according to claim 2, characterized in that the first developing means includes a first examining means connected to the output circuit for examining the level of the original video signals, the second developing means including a second examining means connected to the first examiner in order to probe the duration of the original first level video signals, the third developer including a member connected to the first and second probes, and the altering means including a member which is associated with the first, second and third investigational bodies. <Desc / Clms Page number 48> 5. System according to claim 2, characterized in that one of the characteristics is "black" and the other is "white". System according to claim 2, characterized in that one of the characteristics is "black" and the other is "white", wherein the optical image is composed of black and white information only and the converter receives the video signals with the first and third levels. converts both into an optical image with the first characteristic. 7. The system of claim 2, wherein the first developing means includes an examining means connected to the output circuit for examining. knowing the level of the original video signals; wherein the second developing means includes a first pulse generating means connected to the examining means for generating a first pulse of the duration of the predetermined time in response to the first control assignat and a means connected to the examining means and to the first pulse generating means connected to compare the first control signal to a bar. first pulse, providing a second control signal when the first control signal has a shorter duration than the first pulse; and wherein the third developing means includes a second pulse generating means connected to the examining means for generating, in response to a first control signal, a second pulse having a duration that, when called at the duration of the first control signal, has the same ratio to the duration of the respective . first control signal as the ratio of the high scan. speed to the slow scan rate and a third pulse generator connected to the comparator and to the second pulse generator and including means for initiating a third pulse in response to the second pulse. <Desc / Clms Page number 49> control signal and for terminating the third pulse in response to termination of the second pulse, which third pulse constitutes the third control signal. 8. The system of claim 2, wherein the changer comprises a video delay means connected to the output circuit for delaying the original video signals by the predetermined time and a means connected to the delay means for said delay. latching the video signal to a fixed voltage for a period of the same duration as the duration of the video signal with the first level plus the duration of the third control signal, which period is initiated after the predetermined time following the start of a video signal with a first level, which fixed voltage then forms the video signal with the third level, 9. A system according to claim 7, characterized in that the changer includes a first signal delay means whose input is connected to the output circuit and which has an output circuit, the first delay means delaying the original video signals by the predetermined time. and means for connecting the third pulley generator to the input of the first delay means to lock said input at a fixed voltage in response to the third control signal; a second signal delay means, the input of which is connected to the examiner and which has an output circuit, the second delay means delaying the first control signal by the predetermined time, a fourth pulse generator connected to the comparator and to the output circuit of the second delay means for initiating a fourth pulse in <Desc / Clms Page number 50> EMI50.1 response to the second control signal and to terminate the fourth pulse in response to termination of the pulse EMI50.2 delayed first control signal, and means connecting the fourth pulse generator to the output circuit of the first delay means, for latching that circuit to the fixed voltage in response to the fourth pulse, where the fixed voltage is the third level video signal. 10. System according to claim 2, characterized in that the first and the second contrasting characteristics are respectively. are "white" and "black" and the optical image is made up of black and white information only; wherein the first developing means includes means for detecting original video signals of the first level; wherein the second developing means includes a first monostable pulse generating means connected to the detection means for generating a first pulse of the duration of the predetermined EMI50.3 time in response to the initiation of a first bite control signal; a member connected to the detection member for EMI50.4 inverting the first beat control means; a first gate connected to the first pulse generator and to the inverter for providing the second controls EMI50.5 signal when an inverted first control signal has a duration shorter than the reap. first pulse; at which EMI50.6 the third developing means includes a second pulse generating means connected to the detection means for generating, in response to the first control signal, a second pulse having a duration set to the duration of the strip. first EMI50.7 control signal gives the same ratio to the duration of this first beat signal when the ratio is between the high and low scan speed, and the third is at the same time. EMI50.8 stable pula generator with the first adder and with <Desc / Clms Page number 51> the second pulse generator is connected to initiate a third control signal in response to the initiation of a second control signal and to interrupt the third control signal in response to termination of resp. second pulse; wherein the changer comprises a first signal delay circuit, the input of which is connected to the output circuit and which has an output circuit, which first delay means delays the original video signals from the camera tube by the predetermined time, and a first source of a fixed DC voltage with the third level, a second gate circuit connecting the first source and the third pulse generator to the input of the first delay means, thereby latching this input to the first DC voltage in response to a during the third control signal; a second signal delay circuit, the input of which is connected to the detection means and which has an output circuit for delaying the first control signals by the predetermined time, a fourth bistable pulse generator connected to the first gate means and to the output circuit of the second, delay means for initiating a fourth pulse in response to the inputting of the second control signal and for terminating this fourth pulse in response to the termination of a resp. delayed first control signal, a second source of a fixed voltage of the third level, and a third gate circuit connecting the second source and the fourth pulse generator to the output of the first delay member to lock this output to the second voltage. in response to and during the fourth pulse and wherein the converter divides both first level video signals and third level video signals into white information in the <Desc / Clms Page number 52> optical image converting. i 11. The system of claim 2, wherein further comprising: a synohro-; nization signal generator connected to the first deflection generator, an encoder connected to the synchronization. generator and is connected to the changer so as to generate an encoded video signal in response to the sync signal with discrete steps having first, second and third levels and a decoder connected to the receiver for decoding the encoded video signal. and for outputting another synchronization signal in response, the decoder connected to the other deflection generator. 12. The system of claim 11, wherein the encoded video signal comprises steps of the second, third, first, third and second levels in sequence. 13. The system of claim 2, wherein the changer has an output connected to the transmission means and further includes a blanking and synchronizing signal generating means connected to the camera tube and the first. deflection generator for quenching the camera tube to provide a second level video signal and for resetting the deflection generator, encoders being connected to the quench and sync signal generator and to the output circuit for the response to the quench and synchronization signal generator. providing a synchronizing signal of an encoded video signal in the form of a first signal with a third level, a second signal with the first level and a d .; rth signal with the third level, taking the first, second and third signals immediately after each other <Desc / Clms Page number 53> occur and the first signal is immediately preceded and the third signal is immediately followed by second level video signals and the deode encoder is coupled to the receiver to provide another sync signal in response to the encoded video signal which decoder with the other deflection generator is connected. The system of claim 12, characterized in that the encoder includes a first monostable pulse generator for generating a first pulse in response to the initiation of the blanking and synchronizing signal, and a first fixed voltage source at the third level, a first gating circuit connected to the first monostable pulse generator and to the first source for producing the first signal in response to on during the first pulse, a second monostable pulse generator for generating a second pulse in response to terminating the first pulse, a second source with fixed! voltage with the first level, a second gating circuit connected to the second monostable pulse generator and to the second source for providing a second signal in response to the second pulse and a third monostable pulse generator connected to the second monostable pulse generator to generate a second pulse generator. third pulse in response to termination of the second pulse, the third monostable pulse generator connected to the first gate circuit to provide the third signal in response to the third pulse. 15. A system according to claim 13, wherein the decoder includes means for differentiating the video signal, whereby the encoded video signal is first and second consecutive signal. <Desc / Clms Page number 54> peaks of one polarity, followed by third and fourth consecutive peaks of the opposite polarity, and a gate connected to the differential means for transmitting the first signal peak, a first bistable pulse generator connected to the first gate, means for initiating a first pulse in response to the first signal peak, a second gate circuit connected to the first bistable pulse generator and to the differential means for transmitting the second signal peak in the presence of the first pulse, a second bistable pulse generator connected to the second gate circuit for initiating a second pulse in response to the second signal peak, said second bistable pulse generator connected through a first inverter to the first gate circuit to disable said first gate circuit, a third gate circuit connected to the second bistable pulse generator and to the differentiating means connected to a second inverter for passing the third signal peak, a bistable pulse generator connected to the third gate circuit for initiating a third pulse in response to the third signal peak and a fourth gate circuit connected to the third bistable pulse generator and the second inverter for transmitting the fourth signal peak, whereby the other sync signal is supplied. A system according to claim 2, characterized in that the first characteristic is "white" and the second characteristic is "black" and the optical image is composed of black and white information only, the fourth developing means including a first means for detecting. received video signals having the first level and further comprising means for connecting the signal-to-image converting means to the receiving means and a second means <Desc / Clms Page number 55> is provided for detecting received first and second level video signals and providing video output signals in response thereto, the signal-to-image converting means including means for converting the video outputs into white information in the optical image. 17. A television transmission method, characterized in that it consists of the following steps: converting an optical image into a corresponding electric characteristic pattern; generating an electron beam; deflecting the beam normally at a first scan rate, thereby generating an original time-based video signal that varies between a first and a second extreme level that stripe. matches the first and second contrasting characteristic of the image; detecting generating a video signal with the first extreme level and, in response, deflecting the beam at a second scan rate greater than the first scan speed; detecting the generation of a first level video signal having a duration shorter than a predetermined time and, in response, interrupting the beam deflection for a period of time added to the duration of the first level video signal having the same ratio has up to the duration of the shorter first level video signal when the ratio between the second and the first scan speed is; changing the shorter first level video signal in response to the latter detection to provide a third level video signal intermediate between the first and second levels and having a duration equal to the duration of the timeout plus the duration of the shorter first level original video signal; broadcasting the changed and unchanged <Desc / Clms Page number 56> video signals; receiving the broadcast video signals and applying them to a signal-to-picture converter; deflecting the other beam normally at the first scan rate, thereby converting the received video signals into an optical image; and detecting the presence in the received video signals of a video signal having a first level and, in response, deflecting the other beam at the second rate. 18. The method according to claim 17, wherein the video signals with the second and third levels are converted into information with the first characteristic in the optical image. EMI56.1 19. Television transmission method, characterized in that this method consists of the following steps; converting an optical image into a corresponding electrical characteristic pattern; generating an electron beam; deflecting this beam normally with a first scan rate to produce a time-based video signal that is variable between a first and a second extreme level, respectively. corresponds to a first and a second contrasting characteristic of the image; detecting the generation of an original video signal with the first "extreme level" and, in response, deflecting the beam "at a second scan rate greater than the first scan rate; generating a first signal of predetermined duration in response to a video signal of the first level; comparing the duration of the video signal at the first level with the duration of the first signal when the first video signal has a duration that is shorter than the duration of the first signal; generating a third signal <Desc / Clms Page number 57> in response to the second signal having a duration that added to the duration of the shorter first level video signal gives the same ratio to the duration of the shorter first level video signal if the ratio between the second and the first scan rate is; interrupting the beam deflection in response to and during the third signal; changing the shorter first level video signal in response to the second signal to a third level video signal intermediate between the first and second levels and having a duration equal to the duration of the original shorter video signal by the first level plus the duration of the third signal; transmitting the changed and the unchanged video signals; receiving the broadcast video signal and applying it to a signal-to-image converter; generating another electron beam; normally deflecting the beam at a first scan rate, thereby converting the received video signals into an optical image; and detecting the presence of a video signal of the first level in the received video signals and, in response, deflecting the other beam at the second scan rate. 20. The method of claim 19, characterized in that the change consists in latching the original video signal to a fixed voltage at the third level and delaying the video signal by the predetermined time. 21. The method according to claim 19, characterized in that it further comprises the following steps: generating first synchronizing signals and resetting the deflection of the first beam in response <Desc / Clms Page number 58> thereupon, in response to the first sync signals, generating coded sync signals including discrete steps having the first, second, and third levels; transmitting the coded sync signals, decoding the received coded sync signals to provide second sync signals in response, and resetting the deflection of the other beam in response to the second sync signals. 22. A method according to claim 21, characterized in that the encoded synchronization signals consist of steps with the second, third, first, third and second levels.