JPH022358B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention separates a luminance signal and a chrominance signal and records and reproduces them in separate heads, and in particular records and reproduces a carrier chrominance signal by superimposing a single carrier wave of a higher frequency on the carrier chrominance signal. The present invention relates to a video signal recording and reproducing method that allows high-quality color video to be easily obtained.

At present, magnetic recording and reproducing equipment (hereinafter referred to as VTR)
The mainstream is the helical scan type, in which a rotating head forms an image track diagonally on the tape. In particular, home VTRs are compact and high-density. For example, in a VHS VTR, two video heads are placed at 180° intervals around a rotating cylinder with a diameter of 62 mm, and the video signal is transmitted into a 1/2-inch width. Recorded diagonally to the tape. In addition, for broadcasting VTRs, news editing (ENG) portable
For VTRs, there is a strong desire for smaller size and lighter weight, and 3/4 inch U
Standard VTRs have also made considerable inroads. VTR for ENG
In addition to being small and lightweight, it is also required to have high image quality because it is used for broadcasting. The 3/4-inch U standard VTR has a cylinder diameter of 110 mm and a tape width of 3/4 inch, so there are limits to miniaturization. Since a method is used in which a carrier color signal converted to a low frequency band is superimposed after removing the low frequency band, the bands of the luminance signal and the color signal are limited, and the image quality is not sufficient for broadcasting. Figure 1 shows the recording pattern of an NTSC 3/4 inch U standard VTR. In FIG. 1, T _W , T _P , and T _S represent video track width, video track pitch, and space, respectively, and are approximately T _W =85 μm, T _P =137 μm, and T _S =52 μm.

Taking the above points into consideration, the present invention has developed a compact and lightweight
The present invention provides a video signal recording and reproducing method that allows high-quality reproduced images to be obtained using a VTR.

According to the present invention, high-quality images can be obtained even with a cylinder diameter and cassette of the same size as a VHS system VTR, and the VTR can be made smaller and lighter than conventional ENG VTRs.

Figure 2 shows the arrangement of the heads on the cylinder.
FIG. 3 is a front view of the head. Also, the fourth
Fig. 5 shows an example of a recording pattern on a magnetic tape according to the present invention, Fig. 5 shows a configuration of an embodiment of the invention, and Fig. 6 shows a spectrum of a recording signal in Fig. 5, respectively.

In FIGS. 2 and 3, A, A' and B, B' represent two sets of heads arranged at the same height and 180 degrees apart, respectively, on the circumference of the cylinder.
Further, a, a' and b, b' in FIG. 4 represent trajectories drawn by heads A, A' and B, B', respectively.

In Figures 3 and 4, T _A and T _B are, respectively,
The track width of heads A (A') and B (B') is represented by T _P and T _S is the track pitch and space, respectively. now,
By appropriately determining the diameter of the cylinder, the number of rotations, the values of x and y in Fig. 3, the values of T _A , T _B , and T _S , the tape speed, and the angle formed by the tape and the recording trajectory, the second
With the head arrangement as shown in FIG. 3 and FIG. 3, a trajectory as shown in FIG. 4 can be obtained. In this way, for example, it is possible to construct a VTR that has a cylinder with a diameter comparable to that of a VHS system VTR and is capable of recording approximately 20 minutes on a VHS cassette.

When recording and reproducing color video signals using the recording and reproducing apparatus described above, head A (A') records and reproduces a luminance signal (frequency modulated wave), and head B
At (B'), the conveyed color signal is recorded and reproduced. In this way, the track width of the luminance signal can be increased, and since the color signal is not superimposed on it, the band can be widened, and a reproduced image with high S/N and high resolution can be obtained. In addition, the bandwidth of the carrier color signal can be widened for color signals, and as will be described in detail later, a single carrier wave with a higher frequency than the carrier color signal can be superimposed and recorded, resulting in a high S/N in a high band. It is possible to obtain a playback signal of

According to the system of the present invention, a VHS cassette is used with a cylinder of the same diameter as a VHS system VTR, and approximately 20
This makes it possible to record minutes, making it possible to construct a VTR for news coverage of broadcasting stations that is smaller, lighter, and of higher quality than before. The present invention will be explained in detail below with reference to FIGS. 4 to 6.

In Fig. 5, 1 is a color camera, 2 is a synchronization signal generator, and 3 converts the three primary color signals of R, G, and B from the camera into a luminance signal (also called a Y signal) and a color signal (I, Q signal). 4 is a frequency modulator for frequency modulating the Y signal; 5 is a head for recording and reproducing the Y signal; 6 is a signal supplying signal to the head 5 during recording, and a signal to the head 5 during reproduction.
7 is a frequency demodulator for the reproduction signal, 8 is an adder for interposing the Y signal and the carrier color signal, and 9 is a switch for extracting the I and Q color signals from the color subcarrier (the frequency is 10 is _a frequency divider for dividing the color subcarrier, 11 and 12 are frequency converters, 1
3 is an adder for adding the carrier color signal converted to a low frequency band and a single carrier wave of a high frequency;
14 is a color signal recording/reproducing head; 15 is a recording/reproducing switch; 16 is a low frequency filter for extracting only the carrier color signal converted to a low frequency; 17 is for extracting only a single carrier wave. Bandwidth wave device, 1
8 is an envelope detector, 19 is a gain control amplifier, 20
is a frequency converter, 21 is an amplitude limiter, and OUT is an output terminal. Further, in FIG. 6, 22 is the recording and reproducing spectrum of the Y signal, 23 is the recording and reproducing spectrum of the color signal, 24 is the low-pass converted carrier color signal, 25 is the single carrier wave, 26,
27 is a component generated by third-order distortion of the tape head during reproduction.

The synchronization signal generator 2 normally uses four times the color subcarrier frequency ( _fsc ), that is, _4fsc , as a fundamental oscillation, and counts down the fundamental oscillation to form horizontal and vertical synchronization signals. The color camera 1 is driven by the synchronization signal generated by the synchronization generator 2, and three primary color signals of R, G, and B are obtained as the output of the color camera 1. This is led to the matrix circuit 3 to obtain three signals Y, I, and Q. After the Y signal is modulated by a frequency modulator 4, it is recorded on a tape by a head 5 via a switch 6. The Y signal has a band of approximately 4MHz, and in order to record and reproduce this signal with good performance, the frequency shift of the modulation is, for example,
It is set like 4.4MHz to 6MHz. The recorded signal spectrum is as shown in FIG. 6 , 22 . The I and Q signals are also guided to a balanced modulator and each 90°
A quadrature two-phase modulated wave, that is, a carrier color signal, is obtained at the output of the balanced modulator 9. It is not a good idea to record and reproduce this carrier color signal as it is on a tape head system because it is very difficult to absorb high frequency jitter and the frequency characteristics of the tape head deteriorate as the frequency increases. . Therefore, conventionally, home VTR,
In the aforementioned 3/4-inch VTR, this carrier color signal is converted to a low frequency signal and recorded. However, for home use
VTRs and 3/4-inch VTRs superimpose the frequency-modulated Y signal and the low-frequency carrier color signal and record and reproduce them in the same head.
Both color signals have limited bands, making it impossible to obtain sufficiently satisfactory image quality. In view of these points, the present invention
The luminance signal and color signal are recorded in separate heads, and both have a wider band than the home VTR or 3/4-inch VTR, in an attempt to obtain high-quality images. Therefore, the frequency for low frequency conversion is also suitable for home use.
It can be selected higher than the 629KHz of a VTR or 688KHz of a 3/4 inch VTR and has a wide color signal band. By the way, in home VTRs and 3/4 inch VTRs, the low frequency converted carrier color signal and the frequency modulated Y signal are recorded simultaneously, so the low frequency converted carrier color signal is converted into the frequency modulated wave of the frequency modulated Y signal. Therefore, AC bias recording is performed, and recording is performed very efficiently. Similarly, the present invention also proposes AC bias recording of the low frequency conversion carrier color signal. Home VTR for AC bias recording
It is a well-known fact that it is not necessary to use a frequency modulated wave as in the case of a 3/4-inch VTR, and a single carrier wave having a higher frequency than the low frequency conversion carrier color signal is sufficient. The above-mentioned low-pass conversion color signal carrier wave and AC bias single carrier wave can be freely selected, but should be determined with the following four points in mind.

[1] When recording and reproducing by superimposing a low-pass conversion carrier color signal and a single carrier wave for AC bias, tape
Components caused by third-order distortion caused by the hysteresis characteristics of the head should not be mixed into the low-frequency conversion carrier color signal. (If mixed, it becomes beat,
Significantly degrades image quality. ) [2] When regenerating the low-pass converted carrier color signal and returning it to the original carrier color signal whose carrier frequency is _fsc , the regenerated single carrier wave can be used effectively. Select low-pass conversion color signal carrier and single carrier.

[3] When obtaining a carrier color signal with a carrier frequency of f _sc using a single carrier wave, if the single carrier wave is not synchronized with the color signal carrier wave, the phase relationship between the single carrier wave and the carrier color signal will be The energy concentration of the phase component is poor due to randomness, and the so-called PM noise component deteriorates. If they are synchronized, they have a constant phase relationship and no extra noise is picked up, which improves the S/N ratio of the phase, that is, the hue. Therefore, it is desirable that the single carrier, the low-pass conversion color carrier, and the color subcarrier be in a synchronous relationship.

[4] In order to ensure the resolution of the color signal, it is better to raise the low-pass conversion carrier frequency and have a sufficient color signal band.
It is easily affected by jitter, and the S/N ratio deteriorates due to the poor high-frequency characteristics of the tape head system. Therefore, there are limits to the selection of the low-frequency conversion carrier frequency.

An example of a configuration that considers the above four points is shown in Figure 5-10.
13 and the frequency settings shown in FIG .
Current tape, head, and VHS format NTSC
When recording and reproducing a low frequency converted carrier color signal using a home VTR, it is appropriate to set the low frequency converted color signal carrier at approximately 1 MHz from the viewpoint of S/N.
Assuming that f _sc =3.58 MHz, if we search for a low-frequency conversion color signal carrier wave that has a synchronous relationship with this, we obtain 2/7 f _sc ≈1.02 MHz. Also, regarding the single carrier wave, from the points mentioned in point [2], the frequency f _sc should be set by subtracting the frequency 2/7 f _sc of the low-pass conversion color signal carrier wave from the single carrier frequency f _o . The circuit configuration is the simplest.
Therefore, f _c −2/7 f _sc = f _sc ∴ f _c = 9/7 f _sc ≒4.60MHz (mixture of NTSC systems)
It is reasonable to choose.

When the low frequency conversion color signal carrier wave and the AC bias single carrier wave are determined in this way, the components caused by the third-order distortion caused by the hysteresis characteristic of the tape head are as shown in FIGS. 26 and 27. 26 is the difference between the second harmonic of the single carrier (9/7f _sc ) and the low-pass converted carrier color signal (carrier frequency 2/7f _sc ), i.e. 9/7f _sc -2×2/7f _sc =5/7f 3 that appears with a color signal bandwidth centered on _sc
The first-order distortion component, 27, is the third harmonic of the low-pass conversion carrier color signal, that is, the third harmonic that appears with the bandwidth of the color signal centered at 3×2/7f _sc =6/7f _sc .
This is the second distortion component. As is clear from Figure 6,
In the case of the NTSC system, if the color signal band is approximately 700 KHz, the third-order distortion component described above will not be mixed into the low-frequency conversion carrier color signal.

FIG. 5 configured under the conditions described above will be further explained. The frequency divider 10 obtains 2/7f _sc , and this and the color subcarrier f _sc are added to the frequency converter 11 to extract the component of 2/7f _sc +f _sc =9/7f _sc . This is led as a single carrier signal to one input end of the adder 13 and also to the frequency converter 12, where it is used to obtain a low frequency converted carrier color signal at the output of the frequency converter 12. The carrier color signal that has been low-pass converted is subjected to appropriate band limiting using a bandpass filter (2/7f _sc ±700K in the case of NTSC).
Hz) is applied to the other input terminal of the adder 13, and the output of the adder 13 can provide a single carrier wave and a low-pass converted carrier color signal as shown in FIG. 6, 23 . This signal is recorded via switch 15 and head 14. Switches 6 and 15 are interlocking switches, and both the Y signal and color signal are recorded on the tape in the form shown in FIG. In FIG. 4, a and a' are Y signal recording trajectories, and b and b' are color signal recording trajectories.

During reproduction, the Y signal reproduced from the head 5 is demodulated by the frequency demodulator 7 and guided to the adder 8.
On the other hand, from the signal reproduced from the head 14, a low frequency converter 16 extracts a low frequency converted carrier color signal, and a band frequency converter 17 extracts a single carrier wave, thereby completely separating the two. In this example, it is appropriate for the low-band waver 16 to have a band of about 2 MHz, and the band waver 17 is preferably a narrow-band type that extracts 9/7 f _sc ±Δf (Δf is a jitter component). The low frequency converted carrier color signal outputted from the low frequency converter 16 is transmitted to the tape during playback,
There are level fluctuations due to changes in the sliding condition of the head, etc. Since quadrature two-phase modulation is also amplitude modulation, when this level fluctuation is added to the low-pass conversion carrier color signal, it becomes a noise component when detected, and the S/
Degrades N. It is considered that this level fluctuation also appears in the single carrier wave output from the band wave transmitter 17. Therefore, the level fluctuation of this single carrier wave is detected by the envelope detector 18, and this is inputted to the control terminal of the gain control amplifier 19 to correct the level fluctuation of the low-pass converted carrier color signal. In this way, the output of the gain control amplifier 19 provides a low frequency converted carrier color signal with suppressed level fluctuations. According to experimental results, by installing the level fluctuation suppression circuit in this manner, an improvement in S/N of approximately 3 dB was observed. The single carrier wave used to suppress level fluctuations is applied to an amplitude limiter 21 to make the amplitude constant, and then applied to a frequency converter 20 together with the output signal of the gain control amplifier 19. At the output of the frequency converter 20, the frequency of the difference between the low-pass converted carrier color signal and the single carrier is extracted.
In other words, the original carrier signal centered at 9/7f _sc -2/7f _sc =f _sc is obtained. When this signal is added together with the aforementioned Y signal in adder 8, a composite signal is obtained at its output.

In the above explanation, the NTSC system was mainly described, but it can also be applied to the PAL system and other similar systems. Further, the structure of the head is not limited to that shown in FIGS. 2 and 3, and the recording pattern is not limited to that shown in FIG. 4.

As explained above, according to the present invention, VHS
It is possible to obtain high-quality reproduction signals for both brightness and color signals with a compact and lightweight VTR that is constructed with a head cylinder that is about the same size as a standard VTR. In particular, for color signals, there is an advantage that a signal with a good S/N ratio can be obtained that does not contain unnecessary components due to third-order distortion of the head/tape system.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a recording pattern of a conventional VTR, FIGS. 2 and 3 are a layout diagram and a front view of a recording/reproducing head according to an embodiment of the present invention, and FIG. 4 is a diagram showing a recording pattern of a conventional VTR. FIG. 5 is a block diagram showing the circuit configuration of one embodiment of the present invention, and FIG.
It is a figure which shows the frequency spectrum of the recording and reproduction signal of a figure. 4...Y signal frequency modulator, 5...Y signal recording/reproducing head, 7...Y signal frequency demodulator, 8...
Adder, 9... Balanced modulator, 11, 12... Frequency converter, 14... Color signal recording/reproducing head, 16
...Low frequency converter for extracting carrier color signal for low frequency conversion, 17
... Bandwidth detector for single carrier wave extraction, 18 ... Envelope detector, 19 ... Gain control amplifier, 20 ... Frequency converter, 22 ... Frequency modulated Y signal spectrum, 23 ... Recording and reproducing Spectrum of color signal at time, 24...Low frequency conversion carrier color signal, 25
...Single carrier wave, 26, 27...Components caused by third-order distortion.

Claims (1)

[Scope of Claims] One or more sets of a first head and a second head having different heights are provided on the circumference of a cylinder, a modulated luminance signal is recorded and reproduced by the first head, and a modulated color signal is recorded and reproduced by the first head. is a recording/reproduction method using the second head, and the modulated color signal is obtained by low-band converting a carrier color signal modulated by a color subcarrier, and converting the low-band converted carrier color signal and the low-band converted carrier color. Frequency multiplexing is performed with a single carrier wave having a higher frequency than the signal, and the difference between the carrier frequency of the low-pass converted carrier color signal and the number of single carrier frequencies becomes the frequency of the color subcarrier. After demodulating the modulated luminance signal and separating the modulated color signal into the low-pass converted carrier color signal and the single carrier wave, by taking the difference between the low-pass converted carrier color signal and the single carrier wave. A video signal recording and reproducing system characterized in that the carrier color signal is frequency-converted to the original carrier color signal, and the carrier color signal and the demodulated luminance signal are combined.