JP2979543B2 - Color video signal processing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color video signal processing device suitable for use in a video tape recorder or the like for long-time recording.

[Summary of the Invention]

The present invention provides a low-pass filter for preventing spectral aliasing by digitization so as to be common to one signal path including a memory in which a color video signal is digitized and written and another signal path not including the memory. , The required transmission characteristics are substantially equal between the two signal paths, and there is no need for compensation.

[Conventional technology]

Generally, a video tape recorder for long-term recording for monitoring or the like is an intermittent recording in which recording is performed with the tape stopped at the time of recording, the tape is sent at predetermined time intervals, and the tape is again stopped and recorded. The operation is repeated.
At the time of reproduction, a continuous reproduction mode tape is continuously fed to review the screen, and if there is a notable screen, so-called frame advance is performed in the vicinity of the screen so that the screen can be inspected.

In this case, it is desired that the screen has no noticeable noise even in the continuous reproduction mode, that it is compatible with general VIR, that the adjustment at the time of manufacturing is easy, and the like.

In view of this, the present applicant has disclosed in Japanese Patent Application No. 61-279215 that two pilot heads having a predetermined step are multiplexed with a video signal in a stationary state of a tape to record a plurality of pilot signals in a frame. A normal playback speed tape is run, and tracking control is performed so that each of the two rotating heads scans along a predetermined trajectory over a plurality of tracks so that a desired RF signal can be obtained using a pilot signal. We have proposed a "recording / reproducing device" that can make the bar noise appearing on the top and bottom of the screen almost invisible and obtain a continuous playback screen with little noise and easy to see.

[Problems to be solved by the invention]

However, in the above-described apparatus, in the continuous playback mode, each bed scans over two tracks, and tracking can be performed at the end of the track corresponding to the odd field and the start of the track corresponding to the even field. Therefore, the level of the reproduced RF signal at the beginning of the odd field and at the end of the even field is reduced, and there is a problem in that noise is generated at the upper and lower ends of the reproduced screen.

To solve this problem, the applicant of the present application has
In No. 204498, a plurality of pilot signals are multiplexed with a video signal in a stationary state of a tape using a pair of rotary heads having a predetermined step and different azimuth angles, and a plurality of pilot signals are framed and recorded. One of the magnetic heads scans the track corresponding to the inclined track on the tape running at the center and the tracking detection signal extracted at the center to reproduce the video signal of one field, and the period corresponding to the other field Has already proposed a video tape recorder for long-time recording in which a video signal of one field written in a memory is read out to obtain a continuous reproduction screen without noise.

First, the proposed video tape recorder will be described with reference to FIGS. 3 to 6. FIG.

 FIG. 3 shows a configuration example of the proposed device.

In FIG. 3, reference numeral (10) denotes a capstan servo circuit, which drives the capstan CP so that the magnetic tape MT runs at a normal reproduction speed during reproduction. Reference numeral (20) denotes an ATF tracking detection circuit. As shown in FIG. 5, predetermined four frequencies f ₁ , f ₂ , f ₃ and f ₃ sequentially and cyclically recorded on each track on the magnetic tape. The pilot signal of ₄ is reproduced, supplied from the reproduction system (30), and detected by the detection circuit (20).
Is supplied to the capstan servo circuit (10).

(30) shows the reproducing system as a whole, and a pair of magnetic heads
The outputs of HA and HB are the preamplifiers (31A) and (3
Via 1B), it is supplied to a changeover switch (32). 4th
As shown in the figure, both magnetic heads HA and HB have a step h corresponding to one track pitch on the tape, and have different azimuth angles from each other. The switch (32) is supplied with a switching pulse _PSW from a drum servo circuit (33), and the output of the switch (32) is supplied to a tracking detection circuit (20) via a low-pass filter (34). ,
It is supplied directly to the FM demodulator (35).

(40) is a memory system, and a field memory (4
1) It has an AD converter (42), a D-converter (43) and a changeover switch (44). The demodulated output Y of the demodulator (35) is supplied to the W-side fixed contact of the changeover switch (44).
It is supplied to a field memory (41) via a -D converter (42). Through the DA converter (43), the memory (4
The output of 1) is supplied to the R-side fixed contact of the switch (44).

Switching pulse P from drum servo circuit (33)
_{The SW} is supplied to the tracking detection circuit (20) and to the memory control circuit (45), and the control circuit (45)
Is supplied to the memory (41) and the switch (44).

Although not shown, low-pass filters for preventing aliasing of the frequency spectrum are provided between the input side of the AD converter (42) and the output side of the DA converter (43). Inserted.

 Next, the continuous reproduction operation of the already proposed example will be described.

In previously proposed example, as shown in FIG. 4 has a predetermined level difference, by the magnetic head of a different pair of azimuth angle, as shown in FIG. 5, the pilot signal ATF system on the tape f ₁ intermittent recorded video signal is continuously reproduced in ~f ₄ and frequency-multiplexed by frame.

As is apparent from FIG. 5, in the continuous reproduction (review) mode, the magnetic tapes continuously run at the standard speed, so that the scanning trajectories LA and LB of the magnetic heads HA and HB move on the stopped magnetic tape. Obliquely intersects with the center line of the recording track formed at the end.

For this reason, in the already-proposed example, as shown in the figure, offset control is performed so that tracking can be achieved at the center of the corresponding track T _1a , T _2a ,.

When the magnetic head is traveling along the center line of any track, the levels of the crosstalk components from both adjacent tracks are equal. When the magnetic head shifts to the upstream side of the tape, the level of the crosstalk component from the upstream track increases, and when the magnetic head shifts to the downstream side, the level of the crosstalk component from the downstream track increases.

In the proposed example, the switching pulse P _SW as shown in FIG.
Accordingly, as shown in FIG. 4B, a sampling pulse having a pulse width of about 0.2 field period is formed at the center of the odd field period, and the tracking detection output is sampled and held by this pulse. As a result, the reproduced RF signal obtained from one magnetic head HA as shown in FIG.
S _r1 , S _r2 , S _r3 are at both ends of one field period.
Although the level is slightly lowered, it is sufficient for most of the time.

On the other hand, the other magnetic head HB causes the corresponding recording tracks T _1b , T 1
Tracking can be taken at the center of the adjacent track T _2a ‥‥ behind _2b ‥‥. Therefore, the azimuth angle of the magnetic head differs between recording and reproduction, and as shown in FIG. C, a reproduced RF signal of a sufficient level cannot be obtained over the entire period of the field.

Therefore, in the review mode, high-level playback
Write the reproduced video signal of one field where the RF signal can be obtained to the memory, and replace the video signal read from this memory with the reproduced video signal of the other field where the reproduced RF signal is at a low level. Have gained.

Switching pulse P from drum servo circuit (33)
_SW is supplied to the memory control circuit (45). From the control circuit (45), as shown in FIG. 6D, a control circuit which becomes "Hi" in one field period corresponding to the track _T1a is supplied to the field memory (45). is supplied to the 41), field of the reproduced video type signal of the track T _1a is written in the memory (41). At the same time, is controlled by the output of the "Hi" of the memory control circuit (45), the switch (44) becomes a reverse connection state and shown, the reproduction of the track T _1a video signal S ₁ is output (4
It is derived in 6).

During the next one field period corresponding to the track T _1b , the output of the memory control circuit (45) becomes “Lo” and the switch (4
4) are both in a connected state shown, the reproduced video signal S _m1 of field of the track T _1a from the memory (41) is read, via the switch (44) is derived to the output terminal (46).

In the already proposed example, although not shown, address clear of the field memory (41) is performed using a switching pulse, and between the odd and even fields,
In order to ensure the interlaced relationship of the reproduced images, they are shifted by a half horizontal period (H / 2).

The above operation is repeated every two fields,
From the output terminal (46), as shown in FIG. 6E, a high-quality reproduced video signal based on the high-level reproduced RF signal of each odd field is directly delayed by one field or via the memory (41). Is derived.

By the way, the present applicant has disclosed in Japanese Patent Application No. 62-207848 a pair of rotating heads having different azimuth angles, and when the reproducing output level of one of the magnetic heads is equal to or less than a predetermined value, the other magnetic head is turned off. A video tape recorder that writes a reproduced video signal to a field memory and reads a video signal from the field memory instead of a reproduced video signal from one of the magnetic heads to obtain a reproduced screen without noise. Has already been proposed, and in the second already-proposed video tape recorder,
A memory system exactly the same as the memory system (40) shown in FIG. 3 is used.

However, since the already proposed example of FIG. 3 reproduces only the luminance signal Y, as is apparent from FIG. 3, only a black-and-white reproduced image is obtained, and there is a regret that the information amount of the image is insufficient. Was.

Therefore, the reproduction luminance signal Y is simply used for colorization.
And the reproduced carrier chrominance signal C are supplied to the memory system (40) shown in FIG. 3 by one-field delay via the memory (41) due to the group delay of the low-pass filter (not shown) for preventing spectrum aliasing. The phase of the obtained chrominance subcarrier is delayed by, for example, about 130 ° as compared with the directly derived chrominance subcarrier without passing through the memory (41).

If there is such a large phase jump in the color subcarrier for each field, the APC of the color receiver cannot cover the phase jump, causing a problem that color unevenness occurs in a reproduced image.

In order to eliminate the phase jump for each field of the color subcarrier, usually, as shown in FIG. 7, the group delay of the low-pass filters (47) and (48) for preventing spectral aliasing is compensated by: It is conceivable to construct a memory system (40A) in which a delay circuit (49) in the video band is directly inserted into the path from which a signal is directly derived, that is, a memory system (40A) inserted before the W-side fixed contact of the switch (44).

However, since the low-pass filters (47) and (48) have a variation in group delay, the delay circuit (9) needs to have a variable delay time in order to cope with this. However, there is a problem that the cost is high and an adjustment man-hour is required.

A similar problem also occurs in the second already-proposed example mentioned above.

In view of the foregoing, an object of the present invention is to substantially equalize required transmission characteristics between one signal path including a memory to which a color video signal is written and the other signal path not including the memory, An object of the present invention is to provide a color video signal processing device which does not require the compensation and is suitable for a video tape recorder or the like for long-time recording.

[Means for solving the problem]

In order to solve the above problems, the present invention provides a color video signal processing device having the following means. A first low-pass filter for extracting low-frequency components from an input composite video signal; an A / D converter for converting an output of the first low-pass filter into a digital signal; A field memory for storing one field of the output signal digitized by the above, an input to which the output of the A / D converter is directly supplied, an input to which the output from the field memory is supplied, and A changeover switch having an output for switching and outputting one of them; a memory control circuit for controlling the field memory and the changeover switch; and a D / D for converting the output of the changeover switch to an analog signal.
An A-converter, and a second low-pass filter for extracting a low-frequency component from the output of the D / A converter, wherein the clock frequency of the filter memory is adjusted by the A / D converter and the D / A converter. A color video signal processing device in which the frequency is set to a frequency that is a multiple of a sampling frequency of the filter and the cutoff frequency of the first and second low-pass filters is set to a value that can prevent spectral aliasing due to digitization. I do.

[Action]

Since the color video signal processing device of the present invention has the above-described configuration, the required transmission characteristics can be substantially achieved between the path passing through the field memory and the path from the A / D converter directly to the D / A converter. Since there is no significant difference, there is no need for compensation.

〔Example〕

An embodiment in which the color video signal processing apparatus according to the present invention is applied to a video tape recorder for long-time recording will be described below with reference to FIG.

FIG. 1 shows the configuration of an embodiment of the present invention. In FIG. 1, portions corresponding to FIGS. 3 and 7 are given the same reference numerals, and redundant description is omitted.

In FIG. 1, reference numeral 30C denotes a composite video signal reproducing system, which comprises an FM demodulator (35) and a frequency conversion circuit (36). FM luminance signal Y _FM separated from the output of switch (32) by high-pass filter (37) and band-pass filter (38)
And low-band carrier chrominance signal C _L is supplied to a demodulator (35) and frequency converting circuit (36). The luminance signal Y from the demodulator (35) and the carrier chrominance signal C from the frequency conversion circuit (36)
Are supplied to a Y / C mixing circuit (39) to form a reproduced composite video signal (Y + C).

In this embodiment, in the memory system (40C), the field memory (41) is a 6-bit memory, the output of the AD converter (42) is divided into two, and one is supplied to the memory (41). The other is supplied to the W-side contact of the switch (44), and the output of the memory (41) is supplied to the R-side contact. The composite video signal (Y + C) is supplied from the mixing circuit (39) to the A / D converter (42) via the low-pass filter (47), and the output of the switch (44) is D-
It is led to an output terminal (46) via an A converter (43) and a low-pass filter (48).

In the present embodiment, the frequency of the clock of the memory (41) is set to, for example, six times the chrominance subcarrier frequency f _SC , and its phase is synchronized with the reproduced chrominance subcarrier.

The sampling frequency of the AD converter (42) and the sampling frequency of the DA converter (43) are, for example, 3f _SC , respectively.
A low-pass filter (4
The cutoff frequencies of 7) and (48) are, for example, 4
It is set to about MHz, which also contributes to the prevention of S / N degradation.

Since the present embodiment is configured as described above, in the review mode, a digitized composite video signal for one field is directly output from the changeover switch (44) or via the memory (41). The signal is delayed by one field, alternately derived in two paths, and returned to an analog composite video signal by a DA converter (43). In the case of the present embodiment, the reduction filters (47) and (48) are connected to the switch (44).
The effect of the group delay of both filters (47) and (48) remains unchanged even when the switch (44) is switched, as in the case of the previously proposed example. It does not cause a phase jump of the color subcarrier for each field.

Although the delay of one clock cycle can occur at the maximum in the field memory (41), as described above, if the clock frequency is set as high as, for example, 6f _SC , the delay by the field memory (41) can be reduced. Does not matter at all.

In the above embodiment, 6 is used as the field memory (41).
The A / D and D / A converters (42) and (43) also have 6 bits, but the field memory (41) and the A / D and D- When using 8-bit A converters (42) and (42), the frequency response of the memory (41) and both converters (42) and (43) becomes wide, so that it is shown in FIG. As described above, the changeover switch (44) is moved between the DA converter (43) and the low-pass filter (48), and the output of the low-pass filter (47) is divided into two parts. (41) and both converters (4
2), switch (44) depending on the route through (43)
May be supplied to each of the contacts.

[Effects of the Invention] As described above in detail, according to the present invention, one signal path including a memory in which a color video signal is digitized and written is common to the other signal path not including the memory. As described above, since a low-pass filter for preventing spectral aliasing due to digitization is interposed, required transmission characteristics are substantially equal between both signal paths, and a color video signal processing apparatus which does not require compensation thereof. Is obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment in which a color video signal processing device according to the present invention is applied to a video tape recorder for long-time recording, and FIG. 2 is a block diagram showing a configuration of another embodiment of the present invention. FIG. 3 is a block diagram showing a configuration example of the proposed video tape recorder, FIG. 4 is a development view showing the configuration of a main part of the proposed example of FIG. 3, and FIG. FIG. 6 is a plan view showing the head trajectory according to the proposed example, FIG. 6 is a time chart for explaining the continuous reproducing operation of the already-proposed example in FIG. 3, and FIG. 7 is a block diagram for explaining the present invention. (10) is a capstan servo circuit, (20) is a tracking detection circuit, (30) and (30C) are reproduction systems, (40) and (40)
(A), (40C), (40D) are memory systems, (41) is a field memory, (42) is an AD converter, (43) is a DA converter, (44) is a changeover switch, (47) ) And (48) are low-pass filters.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) H04N 5/91-5/956 H04N 9/79-9/898 H04N 5/907

Claims (1)

(57) [Claims] A first low-pass filter for extracting a low-frequency component from an input composite video signal; an A / D converter for converting an output of the first low-pass filter into a digital signal; A field memory for storing the output signal digitized by the D converter for one field; an input to which the output of the A / D converter is directly supplied; an input to which the output from the field memory is supplied; A changeover switch having an output for switching and outputting one of two inputs; a memory control circuit for controlling the field memory and the changeover switch; and a D / A for converting the output of the changeover switch to an analog signal
A second low-pass filter for extracting a low-frequency component from the output of the D / A converter. The clock frequency of the field memory is adjusted by the A / D converter and the A / D converter. A color video signal processing apparatus wherein the frequency is several times higher than the sampling frequency and the cutoff frequency of the first and second low-pass filters is set to a value that can prevent spectral aliasing due to digitization.