GB2086171A

GB2086171A - Video Signal Reproducing Apparatus

Info

Publication number: GB2086171A
Application number: GB8125444A
Authority: GB
Original assignee: Sony Corp
Current assignee: Sony Corp
Priority date: 1980-08-20
Filing date: 1981-08-20
Publication date: 1982-05-06
Also published as: NL192556C; DE3129292C2; JPS5739677A; NL8103894A; DE3129292A1; NL192556B; AT388634B; ATA363181A; GB2086171B

Abstract

An apparatus such as a VTR for reproducing a video signal recorded on tracks T formed obliquely in H alignment on a tape 1 includes a first main rotary head A for scanning the tracks T, a second main rotary head B having a different azimuth angle from that of the first head A and an auxiliary rotary head A' having the same azimuth angle as that of the first head A. For slow motion playback, tape driving means 11, 12, 13 including a capstan motor 8 intermittently drives the tape 1 by an amount corresponding to a predetermined number of the tracks T. Head control means controls the operation or selection of the first and second main rotary heads A, B and the auxiliary rotary head A' such that the video signal is reproduced by the first main rotary head A and the auxiliary rotary head A' when the tape 1 is stopped and is reproduced by the first and second main rotary heads A, B during movement of the tape 1. The video signal reproduced from the first and second main rotary heads A, B and the auxiliary rotary head A' is processed such that a colour sequence such as a phase alternation line sequence of a chrominance signal is maintained. <IMAGE>

Description

SPECIFICATION Video Signal Reproducing Apparatus This invention relates to video signal reproducing apparatus. Embodiments of the invention may, for example, comprise apparatus for reproducing PAL or SECAM video signals recorded on a tape in such a manner that slowmotion reproduction can be achieved without guard-band noise and disturbance of colour sequence.

In a helical scan type video recording and reproducing apparatus, video signals are successively recorded by two rotating heads on a magnetic tape in record tracks extending obliquely with respect to the longitudinal direction of the tape. Usually, to achieve high density recording, the two rotating heads have different azimuth angles, adjacent tracks of the tape being in an abutting or partially overlapping relation with each other. In this way, cross-talk signals from adjacent tracks can be effectively reduced as a result of azimuth loss of the heads.

For slow motion reproduction of these recorded video signals, the tape is driven at a speed which is slower than that used in the recording mode (or normal reproducing mode).

During slow motion reproduction, the rotating heads repeatedly trace the respective tracks a plurality of times, whereby the reproduced picture has a slower motion than it would have if reproduced in the normal reproducing mode. In this manner, slow-motion reproduction is achieved. Moreover, when the tape is stopped, a single track is repeatedly traced by the rotating heads to reproduce a still picture.

In the slow-motion reproducing mode or the still picture reproducing mode, the rotating heads rotate at the same speed as in the normal reproduction mode, while the tape is driven at a speed slower than that in the normal reproducing mode or is even stopped completely. As a result, the angle of inclination of the track traced by the rotating head on the tape in the slow-motion and still picture reproduction modes differs from the angle of inclination of the track in the recording mode (or normal reproducing mode), which difference in inclination gives rise to tracking deviation.

During reproduction when one of the rotating heads having one azimuth angle deviates from the track to be scanned and crosses an adjacent track which has been recorded by the other rotating head having another azimuth angle, a noise bar is generated in the reproduced picture.

In order to overcome the above-described disadvantage, an improved apparatus has been proposed, as described in US patent 4 190 869, in which the tape is intermittently driven or shifted by controlling a motor to drive a capstan intermittently when movement of the tape is stopped, and the same tracks are scanned a plurality of times by the rotating heads each having an azimuth angle corresponding to the track to be scanned, whereby still reproduction is achieved. On the other hand, when the tape is moved at a normal speed, normal reproduction is carried out by the rotating heads. Thus, slowmotion reproduction is performed as a combination of still and normal reproduction. It should be noted that the number of fields reproduced from the same track during the still reproduction part of the operation depends on the slow-motion speed.

With the above apparatus, even if one of the rotating heads having one azimuth angle does not cross the adjacent or wrong track recorded by the other rotating head having a different azimuth angle, the one rotating head sometimes traces a larger portion of the adjacent or wrong track because of the difference in inclination between the record track angle and the head scanning angle. This results in a reduction of the reproduced signal level, causing a lowering of the signal to noise ratio of the reproduced signal and a consequent deterioration of the reproduced picture.

In order to overcome the above-described disadvantage, an improved apparatus has been proposed wherein an additional or auxiliary head (A'-head) having the same azimuth angle as that of a first of the heads (A-head) is installed at substantially the same position as the other of the heads (B-head). In still picture reproduction using the above apparatus, the tape stopping position is controlled so that the A-head scans the centre of an A track, and the A-head and A'-head alternately scan the A-track, that is, so-called field still operation is carried out. In slow-motion reproduction, the field still operation and the approximately normal reproduction during intermittent moving of the tape is already described are alternately carried out at a time ratio slow speed.In that approximately normal reproduction, the A-head and A'-head may be alternately used, or the A-head and B-head may alternately used. A video signal reproducing apparatus (for example, a video tape recorder (VTR)), having an auxiliary head provides a still picture or a slow-motion picture of high quality.

With the above VTR, the additional head A' is generally disposed adjacent to the main head B such that the head A' can trace the same track as that scanned by the main head A. However, if the main head B is arranged to be diametrically opposed to the main head A, as in the case of the conventional VTR, the recording track recorded by the main head A cannot be in Halignment with the recording track recorded by the main head B under a specified tape speed. If the video signals are not recorded with H-alignment, it is necessary to provide a special circuit for compensating skew of the reproduced video signal at times when the head crosses from a first track and then another of the nearby tracks which have the positions of the recorded horizontal synchronizing pulses offset, for example, by 1/2 the horizontal period.

Further, it is impossible to select an angular displacement between the main head B and the additional head A' of an amount corresponding to an integral multiple of the horizontal period. This causes difficulty in adjustment of the positions of the heads upon constructing the head drum.

According to the present invention there is provided apparatus for reproducing a video signal recorded on tracks formed obliquely on a tape, the apparatus comprising: a first main rotary head for scanning the tracks; a second main rotary head having a different azimuth angle from that of the first main rotary head and being angularly displaced by 2N-1 (1800+ H) 2 from the first main rotary head, where N is an integer and H is an angle corresponding to one horizontal period; an auxiliary rotary head having the same azimuth angle as that of the first main rotary head and being displaced by M.H from the second main rotary head, where M is an integer;; tape driving means including a capstan motor for intermittently driving the tape by an amount corresponding to a predetermined number of the tracks during each of a plurality of predetermined time intervals; head control means for controlling the operation of the first and second main rotary heads such that the video signal is reproduced by the first main rotary head and the auxiliary rotary head when the tape is stopped and is reproduced by the first and second main rotary heads during movement of the tape: and a circuit for processing the video signal reproduced from the first and second main rotary heads and the auxiliary rotary head such that the colour sequence of the video signal is maintained.

The invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a schematic block diagram of a tape drive system of a video tape recorder constituting an embodiment of the invention; Figure 2 is a plan view illustrating the arrangement of magnetic heads mounted to a rotating drum of the system shown in Figure 1; Figures 3A and 38 are front views of magnetic heads; Figure 4 is a diagram illustrating a pattern recorded on a magnetic tape by an A-head and a B-head shown in Figure 2; Figure 5 is a diagram obtained by connecting tracks of Figure 4 in the head scanning direction; Figures 6A to 6F are time-charts illustrating the operation of the tape drive system shown in Figure 1; Figure 7 is a circuit diagram of a head switching circuit;; Figures 8A to 8B are a diagram illustrating the relation of tracks and head scanning paths on the tape during still picture reproduction and slowmotion reproduction; Figures 9A to 9D are time-charts showing the phase of reproduced signals during still picture reproduction; Figures 1 OA to 1 0D are time-charts illustrating signal processing during still picture reproduction; Figures 1 1A to 1 D are time-charts showing the phase of reproduced signals during slowmotion reproduction; Figures 1 2A to 1 2E are time-charts illustrating signal processing during slow-motion reproduction; and Figure 13 is a block diagram of a reproducing system of the video tape recorder.

Figure 1 diagrammatically shows a tape drive system of a VTR embodying the present invention. The VTR of this embodiment is designed for recording and reproducing CCIR video signals such as PAL or SECAM signals. A magnetic tape 1 is obliquely wound through an angular range of about 1800 around a head drum device comprising an upper drum 2 and a lower drum 3. An A-head 4 and a double-gap head 5 comprising an A'-head and a B-head are installed at the lower surface of the upper drum 2. The upper drum 2 is driven at 30 Hz by a drum motor 6. The magnetic drum 2 is driven at 30 Hz by a drum motor 6. The magnetic tape 1 is moved by a capstan 7 which is rotated at a prescribed speed by a capstan motor 8.

The rotational phase of the drum motor 6 is detected by a PG (pulse generator) head 9, the detected output PG of which represents the rotational phase of the magnetic head. As the tape 1 is moved, a control (CTL) signal recorded on the side edge of the tape is reproduced by a control (CTL) head 10. The reproduced output (PB.CTL) of the CTL head 10 represents the phase of a recording track T formed on the tape 1.

The outputs of the PG head 9 and the CTL head 10 are used, respectively, for changeover (RF switching) of the A and B heads and for a tracking servo in normal reproduction as well as for control of intermittent drive and stopping position of the tape 1 in still picture reproduction and slowmotion reproduction. Referring to Figure 1 , the output of the PG head 9 is supplied to an intermittent driving pulse generator 11 where intermittent driving pulses ware generated as hereinafter described. The pulses w are supplied to a positive input terminal of a motor drive circuit 12. An output of the motor drive circuit 12 drives the capstan motor 8 intermittently by one pitch of the CTL signal (two track intervals corresponding to one frame) in synchronization with the rotational phase of the head.

The reproduced output of the CTL head 10 during intermittent movement of the tape 1 is supplied to a brake pulse generator 13 where brake pulses V are foamed in synchronization with the reproduced CTL signal in the manner described hereinafter. The pulses v are supplied to a negative input terminal of the motor drive circuit 12, the output of which provides the capstan motor 8 with reverse torque (braking torque). The stopping position of the tape 1 is thereby so controlled that the A-head 4 scans the A-track.

Slow-motion reproduction without a noise band can be effected by controlling the timing of the start of intermittent drive and the stopping position of the tape 1.

Figure 2 is a plan view illustrating the arrangement of the magnetic heads mounted on the rotating drum of Figure 1, and Figures 3A and 38 are plan views of the heads shown in Figure 2.

Referring to Figure 2, the B-head 17 is arranged at an angular position of (1800+cut~) with respect to the A-head 4 in the direction of rotation of the drum, as indicated by an arrow R, wherein cr is an angle corresponding to one half of an angular interval (H) of 1800 divided by 312.5 (the number of scanning lines in one field). The A-head 4 and the B-head 17 have respective azimuth gaps 4a and 17a which are of opposite direction to one another, as shown in Figures 3A and 38.

The A'-head 18 is disposed near the B-head 1 7. The A'-head 1 8 is used in place of the B-head 17 during still picture reproduction or slowmotion reproduction. A gap 1 8a of the A'-head 18 has the same azimuth angle as that of the Ahead 4 as shown in Figure 3B. The A'-head 18 is arranged at an angular position of (180 ~13) with respect to the A-head 4 in the direction of rotation of the drum, as shown in Figure 2. The angular spacing or interval between the heads 17 and 18 must be of a magnitude equal to an integral multiple of the angular interval H so that the A'head 18 can be used in place of the B-head 17.

Since a is selected to be equal to 0.5H, p must be equal to 0.5x(2N--1)H wherein N=0, 1, 2,... The angular interval corresponding to p=0.5H is selected in this embodiment according to the requirements that the A'-head and B-head constitute the integral double-gap head 5 as shown in Figure 28 and that the difference in the number of horizontal synchronizing signals of reproduced signals between the A-head scanning period and the B-head scanning period must be minimized.

Figure 4 shows a pattern recorded on the magnetic tape 1 by the A-head 4 and the B-head 17 in Figure 2. Odd field tracks (A-tracks) T,, T3,...

are recorded by the A-head 4 and even field tracks (B-tracks) T2, T4,... are recorded by the Bhead 17. The A-tracks and B-tracks are recorded in accordance with the gaps 4a and 17a shown in Figures 3A and 38, respectively, to have different azimuth angles as shown in a recording trace PH of a horizontal synchronizing signal in Figure 4.

When the inclination of the tracks is so selected that the deviation or off-set between the A-track and the B-track is equal to 1 H, as can clearly be seen from Figure 2, the B-head 17 begins to scan earlier than the A-head 4 by 0.5H while the Ahead 4 begins to scan later than the B-head by 0.5H, whereby the deviation is alternately set to 0.5H and 1.5H as shown in Figure 4. Between adjacent tracks, therefore, the recording trace PH of the horizontal synchronizing signal is aligned in a direction perpendicular to the longitudinal direction of the track. In other words, recording is effected in an H-alignment pattern.

When PAL signals are recorded, one of two chrominance components in PAL signals, for example a V signal component, is transmitted with alternate phase inversion at every scanning line. Viewed from the chrominance signals, the recording pattern is arranged in reverse phase (V and Vì. For every interval of 1 H, as shown in Figure 4.

Figure 5 shows a diagram formed by connecting successive tracks of Figure 4 in the head scanning direction. Tracks shown in solid lines in Figure 5 are A tracks T1,T3,... having the same azimuth angle as that of the A-head and the A'-head, while shown in dotted lines are B tracks T2, T4,... having the same azimuth angle as that of the B-head. Each of the tracks TX, T2,T3,... is designated only by a numeral corresponding to the field number. The head scanning patterns in reproduction are shown by solid arrow lines. In normal reproduction, the track and the head scanning path S, coincide in the track inclination.

Viewed from the reproducing heads, the tracks T1, T2, T3,... on the tape are continuous by connecting each end point to a subsequent starting point.

Reproduced signals are therefore obtained by alternate scanning of the Ahead and B-head in similar manner to the recording mode.

In still picture reproduction, the scanning path is as represented by the line S2 in Figure 5, where, for example, only the A-track T1 is scanned by repeated alternation of the A-head and A'-head. A noise band does not occur in the still picture reproduction because reproduction is effected without intersecting the B-track shown by a dotted line.

In slow-motion reproduction, the scanning path is as represented by the line S3 in Figure 5, a combination of still picture reproduction and normal reproduction being carried out. In the stopped state of the tape, the A-track T, is scanned alternately by the A-head and the A'head and still picture reproduction is effected.

Immediately after the scanning of the A-head, the tape is driven. The A-track T1, B-track ckT2andA- track T3 are reproduced, as in the normal reproducting mode, by the A-head, B-head and Ahead, respectively. The tape is stopped at a position where the A-track T3 can be scanned under the control of the control circuit shown in Figure 1, and then the A-track T3 is reproduced in the still picture, reproducing mode by alternation of the A'-head and A-head. When scanning of the A'-head is finished again, the tape is moved. A similar operation is repeated whereby slowmotion reproduction is effected at a desired playback speed.

Since scanning is effected without intersecting a track having a different azimuth angle in slowmotion reproduction as described above, a noise band does not occur on the reproduced picture.

In Figure 5, a line S4 represents a scanning path for reverse reproduction. In this case, tracks T1(A), T,(B), T~,(A).T,(B), T~,(A) . . . are reproduced by alternation of the A-head and Bhead. A line S5 represents a scanning path for reverse slow-motion reproduction, in which still picture reproduction and reverse reproduction are effected alternately by driving the tape intermittently in the reverse direction. A line Sss represents a scanning path for reproduction at double speed, where tracks T,(A), T3(A) T5(A)...

are scanned by alternation of the A-head and A' head. A line S, represents a scanning path for reproduction at three times normal speed, where tracks T,(A), T4(B), T7(A),T10(B)... are scanned alternately by the A-head and B-head. In the case of any of these reverse-motion, slow-reverse motion, double speed fast-motion and triple speed fast-motion reproduction modes, through the scanning paths S4, S5, S, and S7, the reproduced picture is obtained without a noise band by suitably selecting the A, A' and B heads and suitably controlling the timing of the starting of the tape and the tape stopping position.

Figures 6A to 6F show time-charts illustrating operation of the tape drive system shown in Figure 1 for slow-motion reproduction, and Figure 7 shows a head switching circuit. Figure 6A shows a A-head/B-head switching pulse (RF switching pulse) train formed by the output of the PG head 9 shown in Figure 1. High level intervals in the head switching pulse train RF-SW correspond to the B-head (or A'-head) scanning periods. The head switching pulse train RF-SW is supplied to a head changeover switch 19, whereby the A-head 4 and B-head 17 (or A'-head 18) are selected alternately.

The output of the PG head 9 is supplied to the intermittent driving pulse generator 11 of Figure 1, and intermittent drive pulses w (Figure 6B) having a preset pulse width and period are formed at a preset time lag after trailing edges of certain of the head switching pulses RF-SW. The period of the intermittent drive pulses w determines the speed ratio of slow-motion reproduction. Since each intermittent drive pulse w is supplied through the drive circuit 12 to the capstan motor 8, the tape 1 is driven by one CTL-pitch just after the scanning of the A'-head (B-head). Since the tape drive system has inertia, the period during which the tape 1 is moving has a width M of about three fields, as shown in Figure 6B, which is longer than that of the drive pulse w. In the period S (Figure 6B) before the motor 8 is supplied with the next pulse, the tape 1 is stopped.

In the tape movement period M, the reproduced CTL signal shown in Figure 6C is obtained through the CTL head 10 shown in Figure 1. The reproduced CTL signal is supplied to the brake pulse generator 13, where brake pulses v (Figure 6D) having a preset time delay and pulse width are formed in synchronization with negative pulses of the CTL signal. Each brake pulses v is supplied through one input of the drive circuit 12 to the capstan motor 8, whereby the electromagnetic brake acts on the motor 8 and the tape 1 is stopped. The tape stopping position is determined in relation to the CTL signal so that the tape 1 is stopped at a position where the Ahead can scan the centre of the A track.

As shown in a time-chart of Figure 6E, approximately normal reproduction by the Ahead, B-head and A-head is effected during the tape movement period M, and still picture reproduction by the A'-head, A-head and A'-head is effected during the tape stopping period S.

Furthermore, based on the intermittent drive pulses w (Figure 6B) and the head switching pulses RF-FW, A'head/B-head switching pulses f (Figure 6F) are formed in a head switching pulse generator (not shown). The switching pulses fare supplied to a head changeover switch 20 in Figure 7, whereby the B-head 17 is selected during the B-head scanning period during normal reproducing operation in the tape movement period M, while the A'-head 18 is selected in place of the B-head during the B-head scanning period during still picture reproducing operation in the tape stopping period.

In the above-described manner, slow-motion playback is carried out at a desired speed. In the example shown in Figure 6E, the tape 1 is transferred by two tracks (two fields) during the total period in M+S=6 fields, resulting in 1/3 normal speed slow-motion reproduction. If the period of the intermittent drive pulses win Figure 6B is changed, the period of the still picture reproduction S is varied whereby a slow-motion picture without a noise band is obtained at another speed.

In still picture reproduction, field still operation by the A-head and A'-head in the abovementioned slow-motion reproduction is performed repeatedly. The tape stopping position upon changing the VTR from the standard playback mode into the still picture mode is determined by the brake pulses v, based on the reproduced CTL signal, in similar manner to slowmotion reproduction, and the tape is stopped at the A-track scanning position.

Figures 8A to 8D show diagram illustrating the relation between tracks and head scanning paths formed on the tape 1 in still picture reproduction and slow-motion reproduction. As already shown in Figure 4, the tracks T1,T2. .. are recorded in an H-alignment state. In Figures 8A to 8D, a solid line I represents horizontal periods where the V component of the chrominance signal is of positive phase, and a dotted line I represents horizontal periods, corresponding to the hatched portion in Figure 4, where the V component is of negative phase.

In still picture reproduction, the A-head 4 scans a path SA in Figure 8A from 0 to X during one field period. Since the A'-head 18 is disposed to have a phase of (1800 -0.5H) with respect to the A-head, viewed from a particular point on the track (for example, the track starting point), the A'-head scans a path SAt, from 0 to X in Figure 8B during one field period with a time delay of 0.5H with respect to the A-head. Since the B-head 17 is disposed to have a phase of (1800+0.5 H) with respect to the A-head, it scans a path SB from, 0 to X in Figure 8C with a lead in time of 0.5H with respect to the A-head.

Figure 8D shows head scanning paths for slow-motion reproduction. If the tape 1 is driven in the direction of the arrow shown in the Figure just after scanning of the A'-head, the A-head scanning path SA is bent towards the direction opposite to the direction of movement of the tape and approximately coincide with the A-trackT1 at the rear portion thereof. The end point of the scanning path SA coincides with that of the track T,. Since the tape 1 is moved at approximately normal speed in the next reproducing field, the Btrack T2 is scanned by the B-head as shown at SB.

If the B-head is disposed to have plane of 1800 with respect to the A-head, the B-head scanning path SB coincides with the B-track T2 at both its starting and end points. Since, however, there is a phase difference of 0.5H between the A and Bheads, the reproducing scanning is carried out according to Figure 8D in the phase from 0 to X.

In the next reproduction field, the A-track T3 is reproduced by the A-head. The tape 1 is decelerated and then stopped by the brake pulse such that the A-head scanning path SA approximately coincides.with the track T3, as shown in Figure 8D. The playback operation is returned to still picture reproduction like the state of Figure 8A. The starting point of the scanning path SA coincides with that of the track T3.

Figures 9A to 9D show time-charts illustrating the phase variation of reproduced signals during still picture reproduction. The time-charts can be understood by referring to Figures 8A to 8C.

Figure 9A shows the head switching pulse train RF-SW formed from the output of the PG head 9.

Figure 9B shows the phase of vertical synchronizing signals reproduced by the A-head and A'-head. If a vertical synchronizing signal V SYNC is recorded at the starting point of the track as shown in Figures 8A and 8B, reproduction of the A-head supplies a reproduced vertical synchronizing signal V-SYNC with a phase difference of 0.5H from the leading edge of the pulse of the head switching pulse train RF-SW.

Reproduction by the A'-head supplies a reproduced vertical synchronizing signal V SYNC with a phase difference of 1 H from the leading edge of a head switching pulse.

As the head switching pulses occur at regular intervals (Figure 9A), the number of reproduced horizontal synchronizing signals is not constant for each reproducing field and the phase of the vertical synchronizing signals vary for each field. If such reproduced signals are displayed on the monitor picture, jitter will occur on the picture and the picture will fluctuate in the vertical direction for each field. In order to reduce the jitter, regenerated vertical synchronizing signals are inserted in the reproduced signals. If a regenerated vertical synchronizing signal to be inserted during reproduction by the A-head is taken as a reference signal, the phase of synchronizing signal to be inserted during reproduction by the A'-head must be set to have a time delay of 0.5H with respect to the reference signal.For example, if a regenerated synchronizing signal is set to have a position of 7 H from the leading edge of a head switching pulse RF-SW upon reproduction by the A-head, it must be disposed to have a position equal to 7.5 H from the head switching pulse upon reproduction by the A'-head. In still picture reproduction, the two above sorts of regenerated vertical synchronizing singal are inserted alternately into the reproduced signals for each field.

Figure 9C shows the phase of reproduced horizontal synchronizing signals (H-SYNC) and chrominance signals. The phase of reproduced horizontal synchronizing signals can best be understood by referring also to Figures 8A and 8B. Since the A'-head has an angular deviation of 0.5H with respect to a position displaced by 1 800 (312.5H) from the A-head, phase continuity of the horizontal synchronizing signals is held at each reproducing field as shown in Figure 9C.

However, as for the chrominance signals (V and V), the line sequence with respect to alternate phase inversion per horizontal interval is broken at the transition of reproduction from the A'-head to the A-head as can clearly be seen also from Figure 9C.

In order to preserve the line sequence, the chrominance signals must be delayed by one horizontal period H (or by an integral multiple of H), as shown in Figure 9D, in an A-head reproducing period shown by an arrow in Figure 9C. The line sequence of the chrominance signal is naturally held when the reproduction is changed from the A-head to the A'-head.

However, as a time delay of the chrominance signal by 1 H is effected in the previous A-head reproduction, the time delay of 1 H must be effected also in the A'-head reproduction so as to hold the line sequence. When the time delay of the chrominance signal is effected in the A'-head reproducing period, the line sequence is held at the transition to the next A-head reproduction without time delay. Thus, a chrominance signal having a correct line sequence with respect to phase alternation per H-period can be obtained, as shown in Figure 9D. Thus, a time delay of the chrominance signal by 1 H is required alternately per one frame (A-head reproduction+A'-head reproduction).

Figures 1 OA to 1 OD show time-charts summarizing signal processing during still picture reproduction. Figure 1 OA shows the head switching pulse train RF-SW. Figure 1 OB shows heads to be selected for reproduction. Figure 1 OC shows the phase of regenerated vertical synchronizing signals to be inserted into the reproduced video signal. Figure 1 OD shows a delay control signal for the chrominance signal.

The control signal may be of reverse polarity.

Figures 1 1A to 11 D show time-charts illustrating the phase variation of reproduced signals during slowmotion reproduction, similarly to Figures 9A to 9D. The time-charts of Figures 11 A to 11 D can best be understood by referring to Figure 8D. As shown in Figure 11 B, vertical synchronizing signals V-SYNC reproduced by the A-head and A'-head in the still picture reproducing period have phase differences of 0.5H from the leading edge of the head switching pulse RF-SW in alternate reproducing fields, in the same manner as Figure 9B. In the normal reproducing period by the A-head and B-head, a vertical synchronizing signal appears with an 0.5H delay in the first scan by the A-head and appears without delay (OH) at the next scan of the track T2 by the B-head.As alternate deviations of 0.5H and 1.5H are provided to alternate tracks as shown in Figure 8D, a synchronizing signal is disposed at the start of the scanning path SB.

Therefore, in the second reproduction of the track T3 by the A-head, a vertical synchronizing signal appears at the start of the scanning path SA.

Regenerated synchronizing signals are formed to offset vertical jitter of the reproduced picture due to the phase variation of the vertical synchronizing signals in Figure 11 B. If the phase of the regenerated vertical synchronizing signal during A-head reproduction in the still picture reproducing period is taken as a reference value (OH), the phase of the regenerated synchronizing signals are in the order: OH(A), +0.5H(A'), OH(A), -0.5H(B),-O.5H(A),+0.5H(A'),OH(A):... If the phase of OH is 7H from the leading edge of a pulse of the head switching pulse train RF-SW, -0.5H corresponds to a phase of 6.5 H and +0.5H to a phase of 7.5H.

Chrominance signals are reproduced with a discontinuous phase sequence shown in Figure 11 C. In order to correct the line sequence into a normal phase alternation line sequence, the chrominance signal is provided with a time delay of 1 H alternately per one frame period during still picture reproduction by the A. head and A'-head, in the same manner as in the case of Figure 9D. In the subsequent normal speed reproduction during three fields on the A-track T1,B-track T2 and A trackT3 by the A-head and B-head, the phase alternation line sequence is held without time delay when the 1 H time delay is applied to the chrominance signal just before that normal reproduction. In the still picture reproduction after the normal reproduction, the A-track T3 is scanned.On the track3, the chrominance signals are recorded with an opposite phase sequence to the A-track T. The reproduced chrominance signal shows an inverted phase relative to the previous still picture reproduction as shown in Figure 11 C. Therefore, a 1 H delay of the chrominance signal is required to keep the correct phase alternation line sequence in the first reproducing period by the A-head and the next reproducing period by the A'-head.

If the time delay is not effected in the still reproduction on the A-track T1 by the A and A'head just before the normal reproduction, the phase alternation line sequence will be held by a 1 H delay of the chrominance signal during the three fields of that normal reproduction on the tracks1, T2 and T3. In that case, the line sequence is held by providing a 1 H delay to the first reproducing period on the A-track T3 by the A'-head just after the normal reproduction. A time delay is not required for the chrominance signal in the subsequent reproduction on the A-track T3 by the A-head and A'-head.

Figures 12A to 12E show diagrams summarizing signal processing during slowmotion reproduction, similarly to Figures 1 OA to 1 OD. Figure 1 2B shows the head switching pulse train. Figure 12C shows the phase of regenerated vertical synchronizing signals corresponding to Figure 128. Chrominance delay is controlled by a control signal shown in Figure 12D or another signal of reverse polarity. The control illustrated in Figure 12D is formed based on a 1/2 RF-SW signal obtained by dividing the frequency of the head switching pulse train in a ratio of 1/2, and a frame pulse (FR) formed in the normal reproducing interval is shown in Figure 12E.

Figure 13 is a block diagram of a reproducing system of the VTR for performing the signal processing of Figures 10 and 12. The A-head 4, A'-head 18 and B-head 17 are selected by a switching circuit 21 comprising the changeover switches 1 9, 20 described above. Head switching pulses RF-SW and fare formed in a switching pulse generator 22 based on mode selecting signal M for still picture/slow-motion, an RF-SW pulse and a frame pulse FR.

The output of the switching circuit 21 is supplied to a processing circuit 23, where processing such as demodulation of an FM luminance signal, frequency band conversion of a lower-band chrominance signal, and removal of cross-talk from an adjacent track are carried out.

A reproduced chrominance signal C obtained from the processing circuit 23 is supplied directly to a b-terminal of a changeover switch 26 and is supplied to an a-terminal of the switch 26 through an amplifier 24 and a 1 H delay circuit 25.

The changeover switch 26 is changed by a control signal u (Figures 1 OD and 1 2D) from a chromatic delay control circuit 27, so that a phase alternation line sequence of the chrominance signal is held or preserved as shown in Figures 9D and 11D.

The chromatic delay control circuit 27 forms the delay control signal u corresponding to the head switching condition based on a control signal rfrom the head switching pulse generator 22. The chromatic delay control circuit 27 is also controlled by a detected signal q from a jump detecting circuit 28. The jump detecting circuit 28 detects disorder in the line sequence of the chrominance signal, for example, when interval track scanning is effected at triple speed playback as on tracks T1 - T4(B) - T7(A) . . . as shown in Figure 5. When the chrominance signal is recorded in the pattern shown in Figure 4, disorder in the line sequence of the chrominance signal may occur upon transition from reproduction of the track t4 by the A-head into reproduction of the track T7 by the B-head or upon transition from the track T2 to the track T5. The disorder of the line sequence is detected by the jump detecting circuit 28, and the reproduced chrominance signal is corrected by a delay of 1 H in response to the detected output q. The jump detecting circuit 28 performs the detection based on the chrominance signal C and the horizontal synchronizing signal.

A luminance signal Y obtained from the processing circuit 23 of Figure 13 is provided to a vertical synchronizing signal inserting circuit 29, where regenerated vertical synchronizing signals V' of phase compensated as shown in Figures 1 0C and 12C are inserted. The regenerated synchronizing signals V' are formed in a vertical synchronizing signal generator 30, which is operated in correspondence with the head changing condition based on an output p of the head switching pulse generator 22.

The luminance signal from the vertical synchronizing signal inserting circuit 29 and the chrominance signal from the changeover switch 26 are mixed in a mixer 31, and the reproduced composite colour video signal is fed to a TV, monitor.

In the above description, the present invention has been described by way of example with reference to still picture reproduction and slowmotion reproduction of PAL signals. However, similar signal processing can be performed also for reproduction in reverse slow-motion, doublespeed fast-motion, triple-speed fast-motion, reverse-motion, cue-playback, review-playback, and furthermore for reproduction of SECAM signals at various tape speeds.

Claims

1. Apparatus for reproducing a video signal recorded on tracks formed obliquely on a tape, the apparatus comprising:- a first main rotary head for scanning the tracks; a second main rotary head having a different azimuth angle from that of the first main rotary head and being angularly displaced by 2N- -1 (1800±--#-.H) 2 from the first main rotary head, where N is an integer and H is an angle corresponding to one horizontal period; an auxiliary rotary head having the same azimuth angle as that of the first main rotary head and being displaced by M.H from the second main rotary head, where M is an integer;; tape driving means including a capstan motor for intermittently driving the tape by an amount corresponding to a predetermined number of the tracks during each of a plurality of predetermined time intervals; head control means for controlling the operation of the first and second main rotary heads such that the video signal is reproduced by the first main rotary head and the auxiliary rotary head when the tape is stopped and is reproduced by the first and second main rotary heads during movement of the tape: and a circuit for processing the video signal reproduced from the first and second main rotary heads and the auxiliary rotary head such that the colour sequence of the video signal is maintained.

2. Apparatus according to claim 1 wherein the tape driving means includes a drive pulse generating circuit for generating motor drive pulses in response to head switching pulses, and a brake pulse generating circuit for generating motor brake pulses in response to control signal reproduced from the tape, the arrangement being such that the tape is intermittently driven by alternately supplying the motor drive pulses and motor brake pulses to the capstan motor.

3. Apparatus according to claim 2 wherein the head control means includes a first switch circuit operative to switch one of the outputs from the second main rotary head and the auxiliary rotary head in response to a switching signal, and a second switch circuit operative to switch one of the output of the first main rotary head and the first switch circuit in response to said head switching pulse.

4. Apparatus according to claim 3 wherein the head control means includes a switching signal generating circuit connected to receive a signal indicative of movement of the tape and the head switching pulses for producing a switching signal indicating a duration wherein the second main rotary head should be switched, the switching signal being generated from the motor drive pulses.

5. Apparatus according to any one of claims 1 to 4 wherein the processing circuit includes a delay circuit for delaying the reproduced video signal by one horizontal duration and a switch means operative to switch the output of the delay circuit and the reproduced video signal in response to a control signal.

6. Apparatus according to claim 5 wherein said control signal is arranged to be generated by frequency-dividing by two the head switching pulses when the tape is stopped.

7. Apparatus according to claim 6 wherein the processing circuit includes a circuit for producing a quasi-vertical sync signal from the head switching pulses and a circuit for adding the quasi-vertical sync signal to the reproduced video signal after the latter signal has passed through said switch means.

8. Apparatus for reproducing a video signal recorded on tracks formed obliquely on a tape, the apparatus being substantially as herein described with reference to the accompanying drawings.