GB1569042A

GB1569042A - Recording and reproduction of video signals

Info

Publication number: GB1569042A
Application number: GB266178A
Authority: GB
Original assignee: Sony Corp
Current assignee: Sony Corp
Priority date: 1977-02-24
Filing date: 1978-01-23
Publication date: 1980-06-11
Also published as: FR2382143B1; JPS53104214A; DE2759030A1; FR2382143A1; NL7802050A

Description

(54) IMPROVEMENTS IN OR RELATING TO THE RECORDING AND REPRODUCTION OF VIDEO SIGNALS (71) We, SONY CORPORATION. a Corporation organized and existing under the laws of Japan, of 7-35 Kitashinagawa.

SChome, Shinagawa-Ku. Tokio, Japan. do hereby declare the invention for which we pray that a patent may be granted to us. and the method by which it is to be performed.

to be particularly described in and bv the following statement: This invention relates to the recording (and reproducing) of television signals such as PAL or SECAM-type signals to permit the reduction of cross-talk from adjacent tracks.

It is well known to record video signals on magnetic tape or other forms of recording medium by scanning successive parallel tracks on the record medium with one or more transducers to which the video signals are applied. There has been a constant effort to improve the efficiency of use of the recording medium by packing the tracks as close together as possible. The packing density has always been limited by the fact that, during reproduction of the recorded signals, a reproducing transducer scanning each of the tracks in order could pick up signals or cross-talk from adjacent tracks.

One important step in minimizing crosstalk is to utilize the so-called H-alignment recording technique, in which horizontal synchronizing signals of the video signals recorded in the adjacent tracks are aligned in the transverse direction of the tracks.

Therefore, it is possible to record the tracks relatively closely to each other. Since the contents of the video signals recorded in the adjacent tracks are almost similar. the reproduced video signals will be hardlv disturbed by the cross-talk from the adjacent tracks.

However, signals such as PAL or SECAM (Registered Trade Mark) signals are different from NTSC type signals. In the PAL signals. the phase of one of the colour sub-carriers reverses at the end of each horizontal line interval. while in the SECAM signals the frequency modulated (R-Y) sub-carrier signals having frequency fr = 4.4()6MHz and the frequency modulated (B-Y) sub-carrier signals having fre quencv f,, = 4.25MHz are transferred linesequentially. This means that in the prior art the correlative relation of the chrominance components of the PAL or SECAM signals recorded in the adjacent tracks cannot be attained.

According to a first aspect of the invention. there is provided apparatus for recording a colour video signal. comprising chrominance components of which a parameter periodically varies from line to line and luminance components. on a plurality of tracks on a recording medium with a plurality of recording heads. the apparatus comprising means for disposing a first track recorded bv one of the heads in abutting or partially overlapping side bv side relationship with a second, adjacent track recorded bv the other or another of the heads and in which the arrangement is such that. in use.

chrominance components having the same property with respect to said parameter are aligned in said first and second tracks and circuitry for applying the video signals to the heads, the circuitry being adapted to preserve the variations of said parameter of the chrominance compoents.

According to a second aspect of the invention. there is provided apparatus for recording a colour video signal having chrominance components of which a parameter varies periodically from line to line and luminance components. the apparatus comprising a pair of recording heads having different azimuth angles arranged to form slanted tracks on a magnetic tape. the arrangement being such that. in use, the start of a track is shifted by a distance (m + 1/2)x H (where m is an integer and H the length of one horizontal line interval) from the starts of adjacent tracks such that tracks where odd fields of said video signal are recorded are aligned with the remaining tracks where even fields thereof are recorded, such that, for adjacent tracks where fields from the same frame are successivelv recorded, lines in which the chrominance components have the same property with respect to said parameter are aligned.

According to a third aspect of the invention, there is provided a method of recording colour video signals comprising chrominance components of which a parameter periodically varies from line to line and luminance components on tracks of a recording medium with a plurality of recording heads having different azimuth angles wherein the positions of the heads and their motions are such that a first track formed bv one of the heads is at least in abutting or partially overlapping relationship with a second track formed by another of the heads and in said tracks chrominance components having the same property with respect to said parameter are aligned with each other.

The invention will be further described with reference to the accompanying drawings, in which: Figure 1 shows schematicallv the disposition of a number of tracks of video signals recorded on a magnetic tape: Figures 2A and 2B are respectively horizontal sectional and side elevational views of a rotary head assembly for use in an embodiment of the present invention: Figure 3 shows the azimuth angles of the heads of Figures 2A and 2B: Figure 4 shows schematically the dispostion of tracks recorded using a prior recording apparatus: Figures 5 to 8 show the disposition of tracks recorded using embodiments of the present invention: Figure 9 shows in block form the circuitry of an embodiment of the present invention: and Figure 10 illustrates the operation of the embodiment of Figure 9.

Figure 1 shows schematicallv a number of tracks 3 of video information signals recorded on a record medium such as a tape 3.

such that each track contains the video informtion of one field of the video signal.

The tracks 3 are recorded in so called H-alignment. i.e. with the horizontal synchronizing signals Ph of corresponding line intervals of successive fields aligned with one another.

The following descripiton of the prior art and embodiments of the invention is given in terms of a SECAM video signal in which the B-Y -and R-Y signals are transmitted alternatively, for a line at a time and using different sub-carrier frequencies. The invention is. however applicable to other types of video signal in which a parameter of the chrominance components periodically varies such as for example the signals of PAL type.

Figures 2A, 2B and 3 show the head configuration of a rotary head assembly of a video tape recorder in which a pair of heads 1A and 1B are mounted on a rotary drum with an angular separation about the axis of the drum 1XO" + H and the tape 2 is guided along a part-helical path extending 1800 around the drum. As shown in Figure 3, the air gap G, of the head 1A is at an angle HI with respect to the line representing the direction of movement of the head and the air gap G1 of the head 1B is at an angle H, with respect to the line f t. The angles 8, and H, are known as the azimuth angles. Further. it is noted that the heads 1A and 1B are mounted with a height difference h with respect to the longitudinal direction of the drum.

Now. assuming H = (), h= 0 and Hl = = 90". a tracking pattern shown in Figure 4 will be formed bv the heads 1A and 1B, in which the head 1A could be used to trace the tracks 3A and the head lB could be used to trace the tracks 3B. Under these conditions. it is impossible to record the video signals in H-alignment. In other words. the horizontal synchronizing portions of the video signals recorded in the adjacent tracks are shifted by some amount. for example ().4H. In Figure 4. the colour sub-carrier signals (R-Y) are recorded in the hatched portions of the tracks 3 (assuming the video signal to be a SECAM signal). while the colour sub-carrier signals (B-Y) are recorded in the remaining portions thereof.

However. if as shown in Figure 2A, the head 1B is shifted bv an appropriate nonzero angle H in the counter-rotating direction. so that the starting points of the tracks 3B are delaved bv an amount which is determined by the angle H, the horizontal synchronizing signals recorded in the tracks 3A and 3B will be aligned with each other and the same colour sub-carrier signals will be arranged in line between the tracks 1A and 1B. as shown in Figure 5.

Suitably. as shown in Figure 3, the head 1B is raised by a height h. so that the track 3B formed bv the head 1B is formed abutting to the track 3A or even partially overlapping with the track 3A, as shown in Figure 6, to eliminate the guard bands between the two fields of each frame and so achieve a higher information signal density.

It should be noted that the two tracks, such as 3A1 and 3B1 corresponding to the two fields of a frame are disposed so that lines in these two fields having the same chrominance sub-carrier are aligned, so reducing the effects of cross-talk. However.

the adjacent fields such as 3B, and 3A2 of successive frames are not in such alignment and so the geometry of the rotary head assembly should be such as to ensure the formation of a guard band therebetween.

As a matter of practice, the heads 1A and 1B used should have different azimuth angles 9 and 02, so that the tracks formed by the heads 1A and 1B will be in a pattern such as is shown in Figure 7.

In the tracks 3A, the video signals are recorded with the head having the azimuth angle 91, while the video signals are recorded with the head having the azimuth angle 92 in the tracks 3B closely adjacent to the tracks 3A. The chrominance components (B-Y) and (R-Y) of the video signals are respectively aligned in the tracks 3A and 3B.

Figure 7 thus shows the recording pattern formed by a practical form of apparatus according to this invention. with which the colour video signals of PAL or SECAM format can be reproduced without the effects of cross-talk from the adjacent tracks.

As far as the luminance components of the video signals is concerned. the luminance components are frequency modulated on a carrier signal having a relatively high frequency, so that the cross-talk of the luminance components from the adjacent tracks are reduced to a great extent bv the azimuth loss of the heads, since the azimuth loss is proportional to the frequency of the recorded signal.

On the other hand, the chrominance components of the video signals are converted to the lower frequency band. so that the reduction of the cross-talk of the chrominance components by the azimuth loss cannot be expected. However. it is wellknown that when the frequency modulated signals including the cross-talks are demodulated in the reproducing process. the amplitude of the cross-talk is proportional to the frequency difference between the frequency modulated signals and the cross-talk signals. As described before. since the contents of the video signals recorded in the qiWdjacent tracks are quite similar. a great frequency difference does not exist between the frequency modulated chrominance components recorded in the tracks 3A and 3B.

This means that the effects of cross-talk of the chrominance components of SECAM signals are extremely small owing to the correlation of the aligned recorded signals.

Similar to the case of the luminance components. the guard band prevents crosstalk of the chrominance components between the adjacent tracks such as 3B1 and 3A. of successive frames.

By suitable choice of the parameters tf, h and the tape speed, a recorded pattern without any guard bands as shwon in Figure X can be obtained. Then. the cross-talk of the chrominance components between successive frames, such as the tracks 3B1 and 3A2 etc.. present a serious problem, because the same chrominance components are not aligned between the tracks 3B1 and 3A2 etc.

In order to avoid serious cross-talk from the non-aligned adjacent track. the frequencies of the chrominance components which are converted to the lower frequency band can be changed every field interval. In other words. the odd lines (3AI. 3B1, 3A3. 3B3 ---) of the video signals are frequency converted using a first carrier signal having a frequency (f + f,). while the even fields (3A1. 3B2, 3A4.3B4.---) thereof are converted with a second carrier signal having a frequency (fs + f). It should be noted that the frequency difference between the first and second carrier signals should be selected to be 1/4(2K - I )fh wherein K is an integer and fh is the horizontal line frequency. The 1/4(2K - I)fh frequency difference means that the converted chrominance components are inverted in phase every two horizontal intervals. Specifically. f, can be selected at (n + l/X)fh. and f at (n-liX)fh. (n=44).

The apparatus shown in Figure 9 comprises a rotary head assembly as shown in Figures 2A. 2B and 3 and associated tape transport and circuitrv 5(3 selectively operable bv means of switches 41-45 to record video signals on and reproduce video signals on and reproduce video signals from the tape 2. these signals being recorded in the format shown in Figure 8.

During recording a video signal is applied to the terminal 11 with the switches 41-45 in the positions shown. The luminance component of th signal is applied from the output of a low-pass filter 12 to the input of a luminance clamp 13 and vertical and horizontal synchronizing pulse separators 51 and 31 respectively.

The clamped luminance signal is passed iia a pre-emphasis circuit 14. a clipping circuit 15. a frequency modulator 16 and a high pass filter 17 to one input of an adder 18.

The chrominance components of the signal from terminal I1 pass through a band pass filter 21 and reversed-bell filter 22 to a frequency converter 23 to which a frequency converting signal is applied from a further frequency converter 33.

A pair of phase-locked loop circuits 35, 36, phase locked with the horizontal svnc.

pulses from the synchronisation separator 31 are used to produce a signal S1 having the frequency fl=(n+1/8)fh and S2 having the frequency 2= (n-1/8)flh respectively. The outputs of the circuits 35. 36 are alternatelv applied as indicated in Figure lOB via an electronically operated switch 37 to one input of the frequency converter 33. The switch 37 changes states at the frequency of a signal Sf (Figure 10A) applied to a control input thereof. Also applied to an input of converter 33 is the output having a frequency fs of a reference oscillator 34. The output applied as the frequency converting signal to the second input of converter 23 is thus a signal having the frequencies fs + f and fs + f2 alternately. The signal Sf has a frequency equal to the frame rate i.e. half the vertical frequency and so the signal (having a frequency fs + fl or fs + f. applied to converter 23 from converter 33 changes every frame as indicated in Figure tOC.

Figure 10D indicates the frequencies of the converted chrominance components fed to the second input of adder 18 to be applied with the processed luminance component and via amplifier 19 to the head 1A or 1B to be recorded on tape 2.

During recording. the vertical synchronizing signals from separator 51 are applied (after frequency division by two by divider 52) via an amplifier 57 to a head 58 bv means of which thev are recorded on the tape 2 as reference signals to identifv the tracks. They are also applied to a phase comparator 53 for comparison with reference signals picked up by a head 54.

amplified by amplifier 55 and indicating the positions of the heads 1A. 1B along their scanning paths. The ouptut of the phase comparator is applied via amplifier 56 to the rotary head drive motor 6 to ensure correct synchronization of the rotary head assembly.

Amplifier 55 also drives flip-flop 38 which controls the state of the switch 37. The flip-flop is triggered by the pulses from amplifier 55 to generate the signal Sf inverting its state energy frame. The bistable element is reset depending on the signal from switch 45.

In order to replay a recorded signal. the switches 41-45 are reversed so that the recorded synchronizing signals are reproduced by head 58. amplified bv amplifier 59 and applied to the phase comparator 53.

while the reproduced video signals from heads 1A. 1B are amplified bv amplifier 61 and applied to the high pass filter 62 and low pass filter 71. The reproduced luminance signals pass through filter 62 and a limiter 63 to be frequency demodulated and restored to their original frequency band by demodulator 64. After de-emphasis by deemphasis circuit 65, they are applied to one input of a summer 66, the output of which is connected to an output terminal 66.

The reproduced chrominance signals pass through filter 71 to frequency converter 72, the frequency converting signal for which is obtained from the output of converter 33.

The phase lock loop circuits 35. 36 which feed the converter 33 are phase locked to the horizontal synchronizing signals in the band-restored luminance signal at the output of de-emphasis circuit 65.

The converter 72 thus performs frequency reconversion of the chrominance components to their original frequency bands i.e. it performs a conversion which is the inverse of that performed by converter 23. After filtering by bell-filter 73. the band-restored chrominance components are applied to the other input of summer 66 so that the output at terminal 67 is the reproduced composite video signal.

In order to ensure that during reproduction the switch 37 is in the correct one of its states at any particular time (so ensuring that the frequency reconversion by converter 72 is performed using the appropriate frequency converting signal. the output of converter 72 is also applied to a bandpass filter 81 followed bv a level detector 82 to set or reset the flip-flop 38 to the correct state. Now, assuming that during reproduction. the head 1B is scanning the track 3B1 the chrominance components from track 3A2 will be reproduced as cross-talk mixed with the main chrominance components from the track 3B,. The converted chrominance components are reconverted in the converter 72 with a signal having the same frequency as that as was used in recording.

Accordinglv. the frequencies of the reconverted main and cross-talk chrominance components will be as shown in Figure tOE.

As apparent from Figure 1E. the (B - Y) cross-talk signals are mixed with the (R - Y) main signals and vice versa, and the frequencies of the cross-talk signals are offset by 1/4 of the line frequency. This means that the phase of the cross-talk in. for example, the 314-th line interval in inverted in comparison with that in the 316-th line interval. In other words. the cross-talk of the same chrominance component is inverted every two line intervals.

Therefore. since the cross-talk components for successive lines as displayed will be similar but inverted with respect to one another the cross-talk components will be visuallv concelled on the image picture.

WHAT WE CLAIM IS: 1. Apparatus for recording a colour video signal. comprising chrominance com

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. converting signal is applied from a further frequency converter 33. A pair of phase-locked loop circuits 35, 36, phase locked with the horizontal svnc. pulses from the synchronisation separator 31 are used to produce a signal S1 having the frequency fl=(n+1/8)fh and S2 having the frequency 2= (n-1/8)flh respectively. The outputs of the circuits 35. 36 are alternatelv applied as indicated in Figure lOB via an electronically operated switch 37 to one input of the frequency converter 33. The switch 37 changes states at the frequency of a signal Sf (Figure 10A) applied to a control input thereof. Also applied to an input of converter 33 is the output having a frequency fs of a reference oscillator 34. The output applied as the frequency converting signal to the second input of converter 23 is thus a signal having the frequencies fs + f and fs + f2 alternately. The signal Sf has a frequency equal to the frame rate i.e. half the vertical frequency and so the signal (having a frequency fs + fl or fs + f. applied to converter 23 from converter 33 changes every frame as indicated in Figure tOC. Figure 10D indicates the frequencies of the converted chrominance components fed to the second input of adder 18 to be applied with the processed luminance component and via amplifier 19 to the head 1A or 1B to be recorded on tape 2. During recording. the vertical synchronizing signals from separator 51 are applied (after frequency division by two by divider 52) via an amplifier 57 to a head 58 bv means of which thev are recorded on the tape 2 as reference signals to identifv the tracks. They are also applied to a phase comparator 53 for comparison with reference signals picked up by a head 54. amplified by amplifier 55 and indicating the positions of the heads 1A. 1B along their scanning paths. The ouptut of the phase comparator is applied via amplifier 56 to the rotary head drive motor 6 to ensure correct synchronization of the rotary head assembly. Amplifier 55 also drives flip-flop 38 which controls the state of the switch 37. The flip-flop is triggered by the pulses from amplifier 55 to generate the signal Sf inverting its state energy frame. The bistable element is reset depending on the signal from switch 45. In order to replay a recorded signal. the switches 41-45 are reversed so that the recorded synchronizing signals are reproduced by head 58. amplified bv amplifier 59 and applied to the phase comparator 53. while the reproduced video signals from heads 1A. 1B are amplified bv amplifier 61 and applied to the high pass filter 62 and low pass filter 71. The reproduced luminance signals pass through filter 62 and a limiter 63 to be frequency demodulated and restored to their original frequency band by demodulator 64. After de-emphasis by deemphasis circuit 65, they are applied to one input of a summer 66, the output of which is connected to an output terminal 66. The reproduced chrominance signals pass through filter 71 to frequency converter 72, the frequency converting signal for which is obtained from the output of converter 33. The phase lock loop circuits 35. 36 which feed the converter 33 are phase locked to the horizontal synchronizing signals in the band-restored luminance signal at the output of de-emphasis circuit 65. The converter 72 thus performs frequency reconversion of the chrominance components to their original frequency bands i.e. it performs a conversion which is the inverse of that performed by converter 23. After filtering by bell-filter 73. the band-restored chrominance components are applied to the other input of summer 66 so that the output at terminal 67 is the reproduced composite video signal. In order to ensure that during reproduction the switch 37 is in the correct one of its states at any particular time (so ensuring that the frequency reconversion by converter 72 is performed using the appropriate frequency converting signal. the output of converter 72 is also applied to a bandpass filter 81 followed bv a level detector 82 to set or reset the flip-flop 38 to the correct state. Now, assuming that during reproduction. the head 1B is scanning the track 3B1 the chrominance components from track 3A2 will be reproduced as cross-talk mixed with the main chrominance components from the track 3B,. The converted chrominance components are reconverted in the converter 72 with a signal having the same frequency as that as was used in recording. Accordinglv. the frequencies of the reconverted main and cross-talk chrominance components will be as shown in Figure tOE. As apparent from Figure 1üE. the (B - Y) cross-talk signals are mixed with the (R - Y) main signals and vice versa, and the frequencies of the cross-talk signals are offset by 1/4 of the line frequency. This means that the phase of the cross-talk in. for example, the 314-th line interval in inverted in comparison with that in the 316-th line interval. In other words. the cross-talk of the same chrominance component is inverted every two line intervals. Therefore. since the cross-talk components for successive lines as displayed will be similar but inverted with respect to one another the cross-talk components will be visuallv concelled on the image picture. WHAT WE CLAIM IS:

1. Apparatus for recording a colour video signal. comprising chrominance com

ponents of which a parameter periodically varies from line to line and luminance components, on a plurality of tracks on a recording medium with a plurality of recording heads, the apparatus comprising means for disposing a first track recorded by one of the heads in abutting or partially overlapping side by side relationship with a second.

adjacent track recorded by the other or another of the heads and in which the arrangement is such that, in use, chrominance components having the same property with respect to said parameter are aligned in said first and second tracks and circuitry for applying the video signals to the heads, the circuitry being adapted to preserve the variations of said parameter of the chrominance components.

2. Apparatus according to claim 1.

wherein the arrangement is such that, in use, guard bands are formed between adjacent tracks of which the chrominance components recorded therein are not aligned with respect to said parameter.

3. An apparatus according to claim 1 or 2 in which means are provided to frequency convert said chrominance components to a lower frequency band than that occupied by the luminance components immediatelv prior to recording using a carrier signal of which the frequency is changed by a predetermined amount when the chrominance components are recorded without alignment with respect to said selected parameter.

4. Apparatus according to claim 3 wherein, in use, the frequency of the carrier signal is changed in accordance with line synchronizing signals of the video signal.

5. Apparatus according to claim 3 or 4 wherein means are provided to derive the carrier signal by a frequency conversion of the output of a fixed frequency oscillator.

6. Apparatus according to claim 3. 4 or 5 wherein means are provided to derive the carrier signal by frequency multiplication of the line frequency.

7. Apparatus according to any one of claims 3 to 6 in which said predetermined amount is 1/4(2K-I) x fh where K is an integer and fh is the horizontal line frequency.

8. Apparatus according to any one of the preceding claims in which the arrangement is such that the start of a track is shifted by a distance of (m+ 112) x H (where m is an integer and H is the length of one line interval) from that of an adjacent track.

9. Apparatus according to any one of the preceding claims wherein means are provided to move the heads cvclicallv along respective, separate paths with respect to the recording medium. the disposition of the paths and heads and the motion of the heads m use being such as to ensure the alignment of recorded chrominance components having the same property with respect to said parameter in said first and second tracks.

tO. Apparatus according to claim 9, wherein the heads are mounted on a rotary head assembly at different angular positions around the axis of rotation of the head assembly.

11. Apparatus according to any one of the preceding claims and adapted for use with a magnetic recording medium.

12. Apparatus according to any one of the preceding claims and adapted to record a PAL type video signal.

13. Apparatus according to any one of claims l to It and adapted to record a SECAM type video signal.

14. Apparatus according to any one of the preceding claims and comprising circuitry for reproducing recorded video signals from the recording medium.

15. Apparatus according to claim 14 and any one of claims 3 to 7 and comprising a frequency reconverter arranged to bandrestore the chrominance components.

16. Apparatus according to any one of the preceding claims wherein the heads have different azimuth angles.

17. Apparatus for recording a colour video signal having chrominance components of which a parameter varies periodicallv from line to line and luminance components. the apparatus comprising a pair of recording heads having different azimuth angles arranged to form slanted tracks on a magnetic tape. the arrangement being such that. in use. the start of a track is shifted by a distance (m+1/2) x H (where m is an integer and H the length of one horizontal line interval) from the start of adjacent tracks such that tracks where odd fields of said video signal are recorded are aligned with the remaining tracks where even fields thereof are recorded. such that for adjacent tracks where fields from the same frame are respectively recorded. lines in which the chrominance components have the same property with respect to said parameter are aligned.

18. A method of recording colour video signals comprising chrominance components of which a parameter periodically varies from line to line and luminance components on tracks of a recording medium with a plurality of recording heads having different azimuth angles wherein the positions of the heads and their motions are such that a first track formed by one of the heads is at least in abutting or partially overlapping relationship with a second track formed by another of the heads and in said tracks chrominance components having the same property with respect to said parameter are aligned with each other.

19. Apparatus for recording a video signal constructed and arranged to operate substantially as hereinbefore described with reference to Figures 2A, 2B, 3 and 7 to tO of the accompanying drawings.

20. A method of recording a video signal substantially as hereinbefore described with reference to Figures 2A. 2B. 3 and 7 to 10 of the accompanying drawings.

21. A record of video signals made by the apparatus of any one of claims 1 to 17 or 19 or using the method of claim 18 or 20.