JP2987891B2 - Color video signal playback device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a color video signal reproducing apparatus for reproducing a color video signal composed of a frequency-multiplexed signal of an FM modulated luminance signal and a chromaticity signal on a low frequency side thereof. About.

[Summary of the Invention]

The present invention relates to a color video signal reproducing apparatus for reproducing a color video signal composed of a frequency multiplexed signal of an FM-modulated luminance signal and a chromaticity signal on a low frequency side thereof, wherein the level of the reproduced chromaticity signal is higher than a reference level. Is detected, the characteristics of the color field noise reducer are controlled in accordance with the level of the reproduced luminance signal obtained by performing FM demodulation on the reproduced FM modulated luminance signal. /
N and color reproducibility can both be improved.

[Conventional technology]

In the conventional VTR, during recording, the luminance signal is FM-modulated and the carrier chrominance signal is low-frequency-converted so that it is on the low-frequency side of the FM-modulated luminance signal. A color video signal composed of a frequency multiplexed signal of a carrier color signal is recorded on a magnetic tape so as to form an inclined track.

In a conventional VTR, during reproduction, an FM modulated luminance signal is supplied to an FM recovery circuit for demodulation, and a low-frequency converted carrier color signal is subjected to high-frequency conversion to convert the original frequency carrier color signal. Then, the carrier color signal is supplied to a color field noise reducer to remove (reduce) noise.

The color field noise reducer obtains a difference signal between the current carrier color signal and the carrier color signal one field before, supplies the difference signal to a limiter, and the level of the input difference signal is inside the positive / negative reference level. Sometimes, the input difference signal is output as the output difference signal,
When the level of the input difference signal is outside the positive / negative reference level, the output difference signal is set to zero, the output of the limiter is regarded as noise, and the output is subtracted from the current carrier color signal or the carrier color signal one field period earlier. It is configured as follows.

According to such a conventional VTR, a high S / N ratio is obtained by a bias effect by an FM modulated luminance signal during recording and a noise removal effect by a color field noise reducer during reproduction.
Can be obtained.

[Problems to be solved by the invention]

However, since the frequency of the FM-modulated luminance signal changes in accordance with the level change of the luminance signal, the bias effect on the carrier chrominance signal also changes. That is, the higher the frequency of the FM modulated luminance signal, the higher the bias effect becomes, and the lower the frequency, the lower the bias becomes.

Therefore, if the reproduced carrier color signal is supplied to the color field noise reducer and the noise is reduced (reduced) uniformly, when the frequency of the FM modulated luminance signal during recording is high,
In particular, when the high-frequency period is long to some extent, the S / N of the reproduced carrier chrominance signal is high. Therefore, when the reproduced carrier chrominance signal is supplied to the color field noise reducer to remove noise, the effective component of the reproduced carrier chrominance signal is reduced. And the color reproducibility may be reduced. Also, when the frequency of the FM modulated luminance signal at the time of recording is low, especially when the low-frequency period is long to some extent, the S / N of the reproduced carrier color signal is low, so such a reproduced carrier color signal is used as a color field noise reducer. When the noise is removed by the supply, the S / N of the reproduced carrier color signal may not be improved to the left.

In view of the above, the present invention provides a color video signal reproduction for reproducing a color video signal composed of a frequency multiplexed signal of an FM-modulated luminance signal and a chromaticity signal on the low frequency side thereof, and the S / N of the reproduced chromaticity signal and An object of the present invention is to propose a device capable of improving both color reproducibility.

[Means for solving the problem]

The present invention relates to a color video signal reproducing apparatus for reproducing a color video signal composed of a frequency multiplexed signal of an FM modulated luminance signal and a chromaticity signal on a low frequency side thereof, and a color field noise reducer to which a reproduced chromaticity signal is supplied. A first level detection circuit for detecting a level of a reproduced chromaticity signal; an FM demodulation circuit to which a reproduced FM modulated luminance signal is supplied;
A second level detection circuit for detecting the level of the reproduced luminance signal from the demodulation circuit, and when the first level detection circuit detects that the level of the reproduced chromaticity signal is higher than the reference level, The characteristic of the color field noise reducer is controlled based on the detection output of the second detection circuit.

[Action]

According to the present invention, when the first level detection circuit detects that the level of the reproduced chromaticity signal is higher than the reference level, the color field noise reducer is output based on the detection output of the second detection circuit. Is controlled.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. This embodiment shows a helical scan type VTR reproducing system to which the present invention is applied. On a magnetic tape (not shown), a color video signal composed of a frequency-multiplexed signal of an FM-modulated luminance signal and a low-frequency converted carrier chrominance signal on the low-frequency side is provided.
The color video signal recorded on the magnetic tape is reproduced by a rotating magnetic head (one or a pair of rotating magnetic heads) H. The reproduced color video signal is supplied to a high-pass filter (2) and a low-pass filter (5) through a reproduction amplifier (1), where an FM-modulated luminance signal and a low-frequency converted carrier color signal are separated. .

The FM modulated luminance signal from the high-pass filter (2)
The luminance signal is supplied to the luminance signal processing circuit, where the amplitude is limited by a limiter, FM demodulation is performed by an FM demodulator, de-emphasis is performed by a de-emphasis circuit, and the like, and a luminance signal is output to an output terminal (4).

The luminance signal from the luminance signal processing circuit (3) is supplied to a pedestal clamp circuit (6) and pedestal clamped, and then supplied to a white clip and synchronization signal removing circuit (7) to obtain a high luminance peak waveform. 50% of white level to avoid malfunction due to over-level
And the horizontal and vertical synchronizing signals are removed as necessary in order to increase the accuracy of detecting the level of the luminance signal.

The white side clip and the luminance signal from the synchronization signal removal circuit (7) are supplied to an integration circuit (9) through an on / off switch (8), and are integrated over a predetermined several to several tens field periods. The level is supplied to a level discriminating circuit (10) including a hysteresis circuit for avoiding a malfunction due to unnecessary noise, the level is discriminated, and the characteristic of the color field noise reducer (13) is controlled by the discrimination output having the hysteresis characteristic.

On the other hand, the low-pass conversion carrier color signal (including the burst signal) from the low-pass filter (5) is supplied to the ACC circuit (11). The output of the ACC circuit (11) is supplied to a carrier chrominance signal processing circuit (12), where processing such as high-frequency conversion (inverse conversion) is performed, and a carrier chrominance signal (including a burst signal) output therefrom. But color field noise reducer (13)
Supplied to Color field noise reducer (1
The output of 3) is supplied to the output terminal (14). A specific configuration example of the color field noise reducer (13) will be described later with reference to FIGS. 2 and 3.

The carrier chrominance signal from the carrier chrominance signal processing circuit (12) is output to a burst signal extraction circuit (15) and an envelope detection circuit (1).
7) supplied to. The burst signal output from the burst signal sampling circuit (15) is supplied to a burst signal level detection circuit (16), the level of which is detected, the detection output is integrated for a predetermined number of field periods, and the integration output is output. Is supplied to the ACC circuit (11) as a gain control signal,
The ACC circuit (1
6) The gain is controlled.

The detection output from the envelope detection circuit (17) is supplied to a level discrimination circuit (18) to discriminate the level, and the discrimination output is supplied as a switch control signal to an on / off switch (8). And an on / off switch (8)
Is turned on when the level of the carrier color signal is equal to or higher than a predetermined level that is sufficiently high, and when the level is lower than the predetermined level,
Turned off.

Next, a specific example of the color field noise reducer (13) in FIG. 1 will be described with reference to FIG. A carrier chrominance signal (including a burst signal) from the carrier chrominance signal processing circuit (12) is supplied to an A / D converter (21) through an input terminal (20) and is converted into a parallel 8-bit digital signal. ,
The digital carrier chrominance signal from the A / D converter (21) is supplied directly to the subtracter (23), and is also supplied to the field memory (2).
After being supplied to (2) and delayed by one field period, it is supplied to a subtractor (23), and the latter is subtracted from the former, and the parallel 9-bit subtraction output is used as an address signal to form a ROM (limiter). 24).

As shown in FIG. 4, when the level of the input signal supplied to the ROM (24) as an address signal is inside the positive / negative reference level, the ROM (24) as the limiter
The relationship between the level of the input signal and the level of the output signal is linear, and when the level of the input signal is outside the positive / negative reference level, regardless of the increase in the absolute value of the level of the input signal, The level becomes 0, and the positive and negative reference levels can be varied according to a control signal as an address signal supplied from the level discriminating circuit (10) to the ROM (24) through the input terminal (24a). A bit digital output signal is stored.

In this case, the lower the level of the luminance signal, the greater the absolute value of the positive and negative reference levels, that is, the greater the noise reduction effect of the color field noise reducer (8). When the level of the luminance signal changes, or at predetermined intervals, the positive and negative reference levels are changed so that the absolute value of the reference level becomes small, that is, the noise reduction effect of the color field noise reducer (8) becomes small. It can be varied discretely.

In this case, when the switch (8) in FIG. 1 is off, the curve b is selected as the input / output characteristic of the ROM (24) as a limiter, the switch (8) is on, and the level of the luminance signal is changed. Is higher than a predetermined level, a curve a having a smaller noise removal effect than the curve b is selected. If the luminance signal level is less than the predetermined level, a curve c having a larger noise removal effect than the curve b is selected. Is to be chosen. It should be noted that the number of input / output characteristic curves of the ROM (24) as the limiter may be increased to more than three, so that switching may be performed in more stages.

Then, the parallel 8-bit digital output signal from the ROM (24) is regarded as a noise signal and supplied to the subtracter (25) together with the digital carrier color signal from the field memory (22). Is subtracted. Subtractor (9)
Are output to a bit compressor (26), where they are bit-compressed into parallel 8-bit digital carrier chrominance signals (including digital burst signals) and then sent to a D / A converter (27). The converted carrier chrominance signal (including the burst signal) is supplied and converted into an analog signal, and is supplied to the output terminal (14) of FIG. 1 through the output terminal (28).

Next, another specific example of the color field noise reducer (13) shown in FIG. 1 will be described with reference to FIG. 3. In FIG. 3, the parts corresponding to those in FIG. Then, a duplicate description will be partially omitted. The parallel 8-bit digital carrier color signal from the A / D converter (21) is supplied directly to the subtracters (29) and (30). The parallel 9-bit subtraction output from the subtractor (29) is supplied to a bit compressor (26), bit-compressed into a parallel 8-bit digital signal, and then supplied to a field memory (22). Field period is delayed. The output of the field memory (22) is supplied to a D / A converter (27) and a subtractor (3
0) and is subtracted from the digital carrier chrominance signal (including the digital burst signal) from the A / D converter (21),
The parallel 9-bit subtraction output is stored in ROM as a limiter.
(24).

Then, the parallel 8-bit digital output signal from the ROM (24) is regarded as a noise signal and supplied to the subtractor (29), where the digital carrier color signal (digital signal) from the A / D converter (21) is output. (Including burst signals).

According to the above-described color video signal reproducing apparatus, in a color video signal reproduction for reproducing a color video signal composed of a frequency modulated signal of an FM-modulated luminance signal and a low-frequency converted carrier color signal on a lower side thereof, When the color signal level is detected to be higher than the reference level, the characteristics of the color field noise reducer are controlled according to the level of the reproduced luminance signal obtained by FM demodulating the reproduced FM modulated luminance signal. Therefore, both the S / N and the color reproducibility of the reproduced chromaticity signal can be improved.

〔The invention's effect〕

According to the present invention described above, in a color video signal reproducing apparatus for reproducing a color video signal composed of a frequency-multiplexed signal of an FM-modulated luminance signal and a chromaticity signal on the lower frequency side, the level of the reproduced chromaticity signal is a reference. When it is detected that the level is higher than the level, the characteristics of the color field noise reducer are controlled according to the level of the reproduced luminance signal obtained by FM demodulating the reproduced FM modulated luminance signal. Both the signal S / N and the color reproducibility can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIGS. 2 and 3 are block diagrams showing specific examples of a color field noise reducer, and FIG. 4 is a curve diagram showing characteristics of a limiter. . (3) is a luminance signal processing circuit (including an FM demodulator), (6)
Is a clamp circuit, (7) is a white side clip and sync signal removal circuit, (8) is an on / off switch, (9) is an integration circuit, (10) is a level discrimination circuit, (11) is an ACC circuit, and (1).
2) Carrier color signal processing circuit (including high-frequency converter), (1)
3) is a color field noise reducer, (17) is an envelope detection circuit, and (18) is a level discrimination circuit.

Claims (3)

(57) [Claims] 1. A color video signal reproducing apparatus for reproducing a color video signal comprising a frequency multiplexed signal of an FM modulated luminance signal and a chrominance signal on the reduction side thereof, wherein a color field noise reducer to which the reproduced chromaticity signal is supplied is provided. A first level detection circuit for detecting the level of the reproduced chromaticity signal; an FM demodulation circuit to which a reproduced FM modulated luminance signal is supplied; and a second level detection circuit for detecting the level of the reproduced luminance signal from the FM demodulation circuit. When the first level detection circuit detects that the level of the reproduced chromaticity signal is higher than a reference level, the first level detection circuit detects the level of the reproduced chromaticity signal based on a detection output of the second detection circuit. A color video signal reproducing apparatus for controlling the characteristics of the color field noise reducer. 2. The color video signal reproducing apparatus according to claim 1, wherein the second level detection circuit detects that the level of the reproduced luminance signal is lower than a predetermined level. An apparatus for reproducing a color video signal, wherein the characteristic of the field noise reducer is set to a characteristic having a large noise removing effect. 3. The color video signal reproducing apparatus according to claim 1, wherein the characteristic of the color field noise reducer is controlled at predetermined intervals based on the detection output of the second detection circuit. A color video signal reproducing apparatus characterized by the following.