DE1230845C2 - Circuit arrangement for regulating the level of a video signal - Google Patents

Description

signal component one of two different values. These regulations take place with a certain

assumes, depending on whether during the duration of the delay. If several successive previous image signal components of the first or the images of the film 3 had an extremely low transparency, the second operating state was present. By means of the, then the actual value of the Maxiser control voltage is reduced, a switching stage is controlled, ₅ times values. By the onset control operation over which the integration element substantially increases a certain _w i _r d is the gain of the amplifier 7 of time after the transition from the first operating states, and thereby the actual value of the maximum level in the second operating state with a value to the constant set value of the maximum -Capacitor is connected. Approximated by this condensation value. (The constant setpoint of the sator becomes the time constant of the integration _{element 10} maximum value, however, is usually increased significantly because of the. In this way, after a limited control range with a given Transdem, the transition from the first operating state to the parenz of the film is not achieved). Since the control of the second operating state begins with a delay during the first, the amplification during the operating state is the most recently existing control state images that still maintain a certain time on the images with extremely low transparency. ₁₅ follow, impermissibly high.

The invention thus provides the advantage of Dj _e F i g. 2 and 3 show a video signal 19 with

That in the case of the occurrence of strong brightness vertical blanking components 20, image signal components 21 jumps, especially with black or white fades _{un (} j horizontal sync pulses 22 by sampling a g of interfering in excess of the natural positive film ₂₀ and the video signal 19 to F i. 3 brightness impression by switching the control obtained by sampling a negative film,
time constant is avoided. With regard to these video signals, two different

In the following, a distinction is made between the invention and the various operating states, which are now examples of the same with reference to FIGS. 1 to 7 on the basis of FIGS. 2 and 3 are explained. In the explained, with several figures shown scanning of the positive film (FIG. 2), a first identical components or pulse sequences with the same operating state are given when the maximum drawing characters are identified. It shows a value Ma of an image signal component 21 greater than a

F i g. 1 is a known television system for outputting a predetermined threshold value S. On the other hand, the scanning of films is in a schematic representation, the second operating state with the scanning of

F i g. 2 and 3, when scanning positive 30 positive films, if the maximum value Ma or negative films obtained video signal, the video signal component 21 is smaller than the specified

F i g. 4 and 5 television systems for scanning bene threshold value S is. In this case, the maximum value of films in a schematic illustration, wherein the Ma and the threshold value 5 from the reference potential level 23 of video signals measured in accordance with the invention of which is equal to the regulated Schwarzpoten-way 35 is TiAl.

F i g. 6 Details of the circuitry 25 and When scanning negative films is a first

16 according to FIG. 4, the operating status is given when the minimum

F i g. 7 pulse trains which, during operation, generate the sound value Mi (FIG. 3) of an image signal component 21 larger processing arrangement according to FIG. 6 occur. as a predetermined threshold value S is. Against it is

The representation according to FIG. 1 shows a television 40 the second operating state when scanning from the transmission system with a lamp 1, a lens 2 negative film given when the minimum value Mi for illuminating the film 3, which is smaller than the front lens 4 and the using a video signal component 21 TV camera 5 scanned given threshold value S is. The minimum becomes. A video signal obtained in this way is measured via value Mi and the threshold value 5 from the reference potential of the amplifiers 6, 7 via a switchable polarity 45 24, which is equal to the white value. Inverter 8 and via the output amplifier 9 to the threshold value S should be slightly smaller than the maxi television receiver 11 and made visible on the video signal level P (Fig. 2, 3) to be adjusted on the screen. It is believed to be.

the film 3 is printed by the interlace method. The illustration according to FIG. 4 shows a television button is, so that the image signal components of the video system 50 for scanning films, in addition signals successive fields to the in F i g. 1 devices shown a control speech, level 25 is provided, which is based on the maximum value

The video signal control is acted on via the node 12. This control stage 25 is fed a video signal 19 to the input 26 via the inputs 14, 14 'of the circuit arrangements. The 16 or 16 'is supplied, and via the outputs 18 55 output 27 is connected to the circuit arrangement 16 or 18' a control voltage is connected to the amplifier. This control stage 25 causes that after ker 7 and 6 respectively. By means of the control span transition from the first operating state to the voltage of the circuit arrangement 16, the amplified second operating state is automatically adjusted during the first beker 7 in such a way that the maximum operating state is maintained for an approximately constant time over a given value of the image signal components. Remains to carry out. By means of these measures in the circuit arrangement 16, depending on the control voltage obtained, the amplifier 6 maximum value Ma of the image signal component 21 is automatically regulated in such a way that the minimum value circuit arrangement 16 maintains a control voltage of the image signal components at constant potential and via an invegration element the strengthened. It is thus fed using a 65 ker 7 which regulates the level of the video signal clamping stage (not shown) to a keyed one. Due to the dimensioning of this Integra black level maintenance, whereby the clamping element is given a certain time constant, the potential of the clamping stage is changed. After the transition from the first operating state to

the second operating state, this integration element can be connected to a capacitor, which increases the time constant of the integration element significantly.

By means of the control stage 25, however, it can also be ensured that after the transition from the first operating state to the second operating state, a control state independent of the maximum value Ma of the image signal component 21 is maintained for a certain period of time. This can be done in that the circuit point 14 is conductively connected to a circuit point of constant potential by means of the control stage 25.

The video signal from which the control voltage is derived can be taken from the output of the Amplifier 7, as already described, or taken from the output of the polarity reverser 8 and the circuit arrangement 16 are supplied.

It would also be possible to control the level of the video signal using the amplifier 28 to make, which affects the current through the lamp 1! In this case the outcome could be 18 of the circuit arrangement 16 to the input of the amplifier 28 and not to the input of the amplifier 7 be connected.

The video signal which is fed to the control stage 25 can either be outside of a control loop (Amplifier 7, circuit arrangement 16, input 14, output 18, amplifier 7) or within a control loop (amplifier 7, input 14, output 18, amplifier 28, lamp 1, camera 5, amplifier 7) can be removed.

The illustration according to FIG. 5 shows a television system for scanning films, in which, in addition to the in FIG. 1 a control stage 25 'is provided, which is used to improve the minimum value control. A video signal 19 is fed to this control stage 25 'via the input 26'. The output 27 'is connected to the circuit arrangement 16'. This control stage 25 'has the effect that, after the transition from the first operating state to the second operating state, the control state present during the first operating state is maintained for a certain period of time. Therefore, depending on the minimum value Mi of the image signal component 21, a control voltage is derived by means of the circuit arrangement 16 'and fed to the controllable amplifier 6 via an integration element. After the transition from the first operating state to the second operating state, this integration element can be connected to a capacitor which significantly increases the time constant of the integration element.

By means of the control stage 25 ', however, similar to the control stage 25, it can also be effected that a control state which is independent of the minimum value Mi of the image signal component 21 is maintained for a certain time. This can be done in that the circuit point 14 'is conductively connected to a circuit point of constant potential by means of the control stage 25'.

The video signal from which the control voltage is derived can either be taken from the output of the Amplifier 7 or removed from the output of the polarity reversing stage 8 and the circuit arrangement 16 'are fed.

In a preferred exemplary embodiment of the invention, both circuit arrangements 26 and 16 (FIG. 4) for regulating the amplifier 7 as well as circuit arrangements 25 'and 16' for regulating of the amplifier 6 is provided. The circuit arrangement is by means of a first or second switch 25 or 25 'can be switched on or off. In addition, a third switch is provided by means of which the polarity of a video signal which is transmitted via the polarity reverser 8 is reversible

ίο will. Here are the first switch, the second Switch and the third switch are coupled in such a way that when the third switch is in a switch position (for the scanning of positive film) the control stage 25 is switched on and the control stage 25 'is switched off

X ₅ is, whereas in the other switch position of the third switch (for scanning negative film) the control stage 25 'is switched on and the control stage 25 is switched off.

The circuit arrangement according to FIG. 6 shows the circuit arrangement 16 and the control stage 25 in FIG more detailed presentation. The control stage 25 consists essentially of a peak rectifier 29, a charging capacitor 31, a gate 32, an impedance stage 33, a further charging capacitor

as 34, a further gate 35, an amplifier stage 36, a pulse shaper 37, a further impedance converter 38, a transistor 39 (type SFT 229) and a capacitor 40 according to FIG. 4 is won. This video signal 19 is fed to the diodes 42, 43 (type IN914) via the capacitor 41. Due to the rectified action of these diodes, the charging capacitor 31 is charged to the maximum value Ma of the video signal 19.

The voltage of the charging capacitor 31 is at the base of the transistor 44 (type BSy 80), which is with the resistors 44 'and 45 forms a gate which conducts during the duration of the pulses 46. The impulses 46 occur with vertical rate pulse repetition rate, and their duration is equal to 3% of Duration of a field. These pulses 46 are fed to the pulse shaper 37 and the pulses 47, 48.49 derived. This pulse shaper 37 consists of the transistors 50, 51, 52 (all of the Type SFT 229), also from the resistors 53, 54, 55, 56, 57, 58 and from the capacitors 59, 60, 61. The pulses 46 are supplied via terminal 62 and by means of the capacitor 59 and the Resistance 53 differentiated, so that the pulses 47 result, which in the further sequence in the Pulses 48 are transformed.

The pulses 46 are also fed to the base of transistor 51 via capacitor 60, see above that of the collector, the pulses 49 can be removed, which differ only in terms of their polarity from the Distinguish impulses 46.

Finally, the pulses 46 are also fed to the emitter of the transistor 44 via the resistor 58. You control the gate 32, which is open during the duration of these pulses 46, so that on Collector of transistor 44 the pulses 64 arise, the amplitude of which depends on the voltage on Charging capacitor 31 is dependent.

It is initially assumed that the maximum value Ma exceeds the predetermined threshold value S. During this first operating state, the pulses 64 have a relatively large amplitude Λ.

309 628/443

9 10

These are fed to the impedance converter 33. _{It would also be} conceivable by means of the transistor 39

consisting of the transistor 65 (708 2 N) and the resistance _{to the} node 70 was at a node 66th _{Connect the} output of this impedance- _fixed potential. In this case, the converter is connected to the gate 35, which consists of _{ten mu} ß _the capacitor 40 and the transistors 71, the diodes 67,68 (type IN 914) and are Iassen from _{5 72 we} gg _e. For example, resistor 69 could be formed. This gate 35 is controlled node 70 to the tap of a voltage by the pulses 49, which can be connected via the con- _divider, the ends of the poles with capacitor are supplied to 74th In this way _an operating voltage source is connected. On the charging capacitor 34 during the duration of the pulses _{this way,} a 49 to the _ege po- _io R (open gate 35) lspannung _{can be} charged _via terminal 18 instead of a constant voltage to the TiAl the emitter of transistor 65th Amplifier 7 according to FIG. 4 can be submitted. This voltage of the charging capacitor 34 is applied to the control stage 25 '(FIG. 5) differs from

the base of transistor 75 (Type 2 N 708), of the 25 blocks the requirements made _{of the} control stage with respect to the peak-lower (relatively large _{rectifier 29, and} with regard to the setting of the target amplitude A of the pulses 64). The amplifier _{value s The 36 used in the control stage} 25 ', which consists of the transistor 75 and the resistive peak rectifier, is designed in such a way that it consists of 76, 77, 78, 79, and thus only responds _{to the} image signal components 21 (but not the base of the transistor 39 a positive control voltage _{on the entire} video signal 19) and that the charging connector + U and blocks its emitter-collector _{capacitor on a path} from the reference potential 24 (FIG. 3). However, the charging capacitor 31 is _2o Senen _from g _Emes maximum value is charged. The nominal value S used during the duration of the pulses 48 is periodically reloaded in the control stage 25 by the formation of the transistor 52, so that the operating point of the transistor 75 is set using the maximum value Ma of the video signal 19 of _the resistors 77, 79. The control stage 25 'always relates to the respective preceding image signal - thus it differs from the control stage 25 and also relates to the proportion of the video signal. _{$ 2} regarding the dimensioning of these resistors

The stage 16 is used in a manner known _{per se to 77>} 79 jy _ie circuit arrangement 16 'is similar to the generation of a control voltage, the maximum essential of the circuit arrangement 16, where value Ma of _{the image signal portion of} the video signal 19 also here only the image signal portions 21 for generation is dependent. This video signal is _{supposed to contribute from the output of the} control voltage, of the amplifier 7 (Fig. 4) via an amplitude _{. By means of the control stage} 25 ' , either a limiter and a further amplifier (not shown, _the time constant of the integration element 86, 87 is provided) Terminal 14 is fed to stage 16. The control voltage, which is essential during the second operating state, is increased by peak rectification, or the circuit point can be conductively connected using the diodes 83, 84 (Type 1N 914), 70 with a circuit point of constant potential further using the capacitors 86 and _35.

of the resistor 87 derived and via the output The illustration according to FIG. 7 illustrates one

output 18 to amplifier 7 (FIG. 4). Control process using the circuit

According to a second operating state, order 16 or 16 'and the control stage 25 or 25'. provided that the maximum value Ma of the video signal 19 with the video signal components 21/0, signal component 21 is less than the predetermined threshold ₄₀ 2I / I, 21/2, 21/3, 21/4, 21/5, 21 / 6 is now evaluating S is. In this case the pulses 64 have shown a more detailed one. Below this is the course of the relatively small amplitude a, so that control voltage U can be seen in the following. The switch 98 is to charge the capacitor 34, the emitter-collector path of the pulse 49 is only charged to a voltage during the duration of the import _d i _e switching states, transistor 39 symbolize.

the amount of which is relatively small. However, the emitter of the transit ₄₅ During the image signal portions 21/0, 21/1, 21/5, sistors 75 is such a bias, 2I / 6, the maximum value exceeds the relevant that the emitter-collector path of this transistor image signal components of the predetermined threshold value S, 75 conducts at this small voltage. In another _{so that the first} operating state is against. During the sequence, a negative of _the image signal components 21/2, 21/3 and during a relative control voltage - U are applied to the base of the transistor 39 _{50 v} i _e ] _he intermediate image signal components up to 21/4 , which works in switching mode. As a result, _the maximum value is smaller than the specified value, the emitter-collector path conducts this Tran threshold value S, so that the second operating state sistor 39. As long as this emitter-collector path is present. Is locked, the transition from the first operating state, the time constant is (1 second) of the _{m the zwe} ith operating state thus occurs Zvi integration member by the dimensioning of the _{55 sc} h _s of the image signal portions 21/1 and 21/2, where capacitor 86 (1 μΡ) and the resistor 87 against the transition from the second operating state to (lMOhm). If, on the other hand, the emitter conducts _{the first} operating state between the image-collector path of the transistor 39, then signal components 21/4 and 21/5 are going on. If the two capacitors 40 (100 μΡ) and 86 are alike, the change in the control voltage and the resistor 87 is an integration _{combination, 6o from the} amount + U to the amount - U and from the lower time constant (100 seconds) substantially _lazy _ j / _{to the} Amount + U each delayed by the duration greater than the time constant of the integration _{element e} ines image signal component 21. 86, 87 is. Thus, upon switching of the transistor 39. _{In the} R i _{of the} level of the video signal 19 _{ege ung}

no surges of over clamp _is in terms _of the transition from the frame signal of 21/1 to the output control voltage 18 may occur, which is _6; . following image signal portions 21/2, 21/3 particularly kri capacitor 40 _illustrates the interposition of the _{impedance-Durcll d} ie negative control voltage - U passes danzwandlers 38 (with the transistors 71, 72) _the emitter-collector path of the transistor 39 resulting in the respective control voltage charged. during the duration of the video signal component 21/3, see above

that the capacitor 40 is connected in parallel with the capacitor 86. And the time constant of the integration combination 86, 87, 40 is much greater than the time constant of the integration element 86, 87. Auf this way, after the transition from the first operating state (during the duration of the image signal

part 21/1) in the second operating state (during the duration of the video signal part 21/3) of the Maintain the control status present during the first operating mode. This will be Excessive levels in the transition from the video signal component 21/4 to the video signal component 21/5, 21/6 are avoided.

1 sheet of drawings

Claims (14)

Patent claims: 1. Circuit arrangement for regulating the level of a video signal, which consists of image signal components and blanking signal components exist in which a first or a second operating state is given when the 'extreme value of an image signal component is greater or less than a predetermined one Threshold value is characterized by that after the transition from the first operating state to the second operating state either during the first operating state last existing control status or one of the extreme values of the relevant video signal components:, independent rcgol / state essentially maintained and after returning to the first state the previous control state is restored. 2. Circuit arrangement according to claim 1, according to which as a function of the extreme value of the image signal components a control voltage derived and via an integration element with a certain Time constant is fed to an amplifier which regulates the level of the video signal, characterized in that a certain duration after the transition from the first operating state in the second operating state the integration element (86, 87) with such a switching element (40) is conductively connected so that an integration combination (86,87,40) is created, the time constant of which much larger - preferably 50 to 150 times larger - than the time constant of the integration member (86, 87). 3. Circuit arrangement according to claim 1, according to which a control voltage is derived and one Amplifier is fed which regulates the level of the video signal, characterized in that a certain period after the transition from the first operating state to the second operating state a circuit point (18) of the control voltage transmission channel conductive with a Circuit point (70) constant potential is connected. 4. Circuit arrangement according to claim 1, characterized in that a control stage (25, 25 ') is provided, in which a control voltage (U) is derived which has one of two different values (+ U or - U) during the duration of an image signal component. assumes, depending on whether the first or the second operating state was present during the duration of the previous video signal component. 5. Circuit arrangement according to claim 2 and 4, characterized in that a switching stage (39) is controlled by means of the control voltage (U) which causes the conductive connection of the switching element (40) to the integration element (86, 87). 6. Circuit arrangement according to claim 3 and 4, characterized in that a switching stage (39) is controlled by means of the control voltage (U) and thereby the circuit point (18) of the control voltage transmission channel is conductively connected to a circuit point (70) of constant potential. 7. Circuit arrangement according to Claim 4, characterized in that the image signal components (21) of a video signal (19) are fed to a charging capacitor (31) via a peak rectifier (29), which is thereby applied to the respective extreme value (Ma, Mi) of the image signal components (21 ) is charged that the charging capacitor (31) is connected to a gate (32) which is periodically open during a time between two successive image signal components (21), that the output of the gate (32) with a storage device (34, 35) is connected, which stores a voltage which is proportional to the voltage on the charging capacitor (31) during the duration of each image signal component (21), and that the control voltage (U) is derived as a function of the stored voltage by comparison with a predetermined constant voltage . 8. Circuit arrangement according to claim 7, characterized in that the charging voltage of the charging capacitor (31) is periodically cleared. 9. Circuit arrangement according to claim 7, characterized in that the control voltage (U) is fed to the base of a transistor (39) operating in switching mode, the emitter-collector path of which connects the integration element (86, 87) to a capacitor (40). 10. Circuit arrangement according to claim 9, characterized in that the emitter-collector path of the transistor (39) is bridged by an impedance converter (38) in such a way that the capacitor (40) continuously to the respective control voltage during the first operating state is reloaded. 11. Circuit arrangement according to claim 7, characterized by such a predetermined constant voltage that the threshold value (S) is somewhat smaller than that smallest maximum value (P) which is still regulated by the controllable amplifier. 12. Circuit arrangement according to claim 4, according to which a control stage for deriving a Control voltage is provided, characterized in that a first such control stage (25) and a second such control stage (25 ') are provided, of which the first control stage (25) when scanning positive film and the second control stage (25 ') when scanning Negative film is turned on. 13. Circuit arrangement according to claim 12, characterized in that the first control stage (25) or the second control stage (25 ') by means of a first switch or second switch can be switched on that a polarity reversal stage (8) is provided, which when a third Switch reverses the polarity of a signal and that the first switch, the second switch and the third switch are coupled in such a way that when the third switch is in a switch position, the first Control stage (25) is switched on and the second control stage (25 ') is switched off, whereas at the other switch position of the third switch, the second control stage (25 ') switched on and the first control stage (25) is switched off. 14. Circuit arrangement according to claim 1, characterized in that the amount of the Threshold value (S) equal to 10 to 40% - preferably approximately 20% - of that potential difference which is given by the difference between the potentials of the white value (24) and the black value (23). The invention relates to a circuit arrangement for regulating the level of a video signal, which consists of image signal components and blanking signal components. Such a video signal can, for example by film scanning or by slide scanning using television cameras or light point scanners can be obtained. When scanning positive film in television studios - for example in the context of television advertising - the individual scenes are often made up of a sequence of "black" film images (Black Fade) that last for about 1 to 2 seconds and have low transparency. A control voltage is usually used as a function of the maximum value of the image signal components derived and thus the gain of the amplifier is regulated in such a way that the maximum value is approximated remains constant. If now the entire surface of several successive film frames one has extremely low transparency, then the maximum value of the relevant image signal components is reduced of the video signal. As a result of the control process that begins, the gain is increased significantly. Since the If the regulation starts with a delay, the amplification is during the first film frames that affect the film frames Follow extremely low transparency, too high, so that the level of the video signal is impermissibly high. The As a result, the images following the black screen are transmitted much too brightly so that the impression of a flash of light is created. This brightening is so annoying that you can click automatic control of the image brightness is dispensed with and manual control is used instead. Similar difficulties can arise when scanning negative film. Finally do it Disturbances of this kind are also noticeable when shooting scenes directly with television cameras if the Exposure of the scene is temporarily changed for some reason. A control problem of a similar kind occurs with film scanners whose image pickup tube is a so-called CPS-Emitron is. This tube is very sensitive to overexposure and goes when exceeded of a certain brightness level into a different stability position. To a stability now to ensure the operation of such tubes when the average image brightness is a certain Value exceeds what z. B. can happen with negative films when switching on a white screen has a regulation of the brightness of the lamp illuminating the film is made. But since the Regulation of an incandescent lamp is generally relatively sluggish, the control voltage was not dependent on that just scanned film frame, but derived from one of the previous frames of the film loop. The lamp is therefore already darkened before the jump in transparency becomes visible in the image. So that will but before a white fade the picture is already darkened, before a black fade it is already brightened, before the change in brightness of the film appears. Both are the natural impression of the picture disturbing effect. This control device also requires a special construction of the film projector, so that the control voltage from the film removed a few images in front of the projection window can be. Since such image pickup tubes of the CPS-Emitron type are no longer used today this control method is also of no technical importance. Furthermore, a circuit arrangement with an image pickup tube of the Vidikon type has become known, in which a control voltage is derived with the help of the signal current, which provides the bias voltage the signal plate of the pickup tube controls so that the mean signal current is independent of the respective scene brightness remains approximately constant. The time constant of the The rectifier for the video voltage is much larger, but at least ten times as large as that Be the scanning duration of the image. Even when using such a control circuit in film scanners and the like. The initially mentioned disturbing effect occurs a ₅ , which is associated with the fact that the large control time constant required to avoid visible fluctuations in the image brightness when sudden changes in brightness occur, such as. B. black fades in the film is too large, so that the natural course of brightness is falsified. The aim of the invention is to provide a circuit arrangement in which the above-mentioned difficulties be avoided. In particular, the invention aims to provide a circuit arrangement for scanning of films containing several "black" or "white" film frames. The invention is based on the knowledge that the regulation of the level of video signals, which in particular obtained by film scanning only makes sense if the extreme value of the Image signal components of these video signals exceed a certain predetermined threshold value. It will a distinction is therefore made between a first and a second operating state, depending on whether the Extreme value of an image signal component is larger or smaller than a predetermined threshold value. the The invention is also based on the knowledge that it is advantageous if the television picture is always appears black when the extreme values of the image signal components are below the specified threshold value sink. According to the invention, after the transition from the first operating state to the second operating state either the control status that was last present during the first operating status or a essentially maintained the control state independent of the extreme value of the relevant video signal component and after returning to the first state, the previous control state is restored. In a preferred embodiment of the In accordance with the invention, a control voltage is derived as a function of the extreme value of the image signal components and fed via an integration element with a certain time constant to an amplifier, which the Controls the level of the video signal. A control stage is provided in which a control voltage derived during the duration of an image