JPH0475714B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a secondary beat cancel circuit suitable for application to a VTR that records a low frequency converted carrier color signal together with a luminance signal.

BACKGROUND TECHNOLOGY AND PROBLEMS In VTRs, in which the conveyed color signal is low-frequency converted and then recorded on the tape along with the luminance signal, the tape/rotating magnetic head system has nonlinear characteristics.
As shown in FIG. 1A, the secondary beat component C _B of the carrier color signal C that has been low frequency converted leaks into the reproduced luminance signal (FM signal) Y-FM. For this reason, this FM
When the signal Y-FM is demodulated, along with the luminance signal Y,
Since the secondary beat component C _B centered at 2fc (fc is the reduced conversion frequency) is also demodulated (Figure 1B), diagonal beat stripes appear on the screen due to this secondary beat component C _B. image quality.

For this reason, conventionally, a reproduction system is provided with a secondary beat cancel circuit for canceling this secondary beat component C _B. FIG. 2 shows a circuit configuration showing an example of this.

In Fig. 2, the data reproduced by the magnetic head H
The FM signal Y-FM and the low frequency converted carrier color signal C are passed through a preamplifier 1 to a bandpass filter 2.
The low frequency converted carrier color signal C is separated, and this is supplied to the frequency conversion circuit 3, and then to the demodulator 4 to generate a pair of component color signals, for example, red and blue color difference signals. R-Y,
B-Y is demodulated.

The output of preamplifier 1 is further passed through high pass filter 6.
, the FM signal Y-FM is separated, and this is supplied to the demodulator 7 for FM demodulation, and then supplied to the secondary beat cancel circuit 10 to separate the secondary beat component C _B contained in the luminance signal Y. is canceled and a luminance signal Y containing no secondary beat component is output from the terminal 8.

The secondary beat cancel circuit 10 has a non-correlated signal detection circuit 11. Uncorrelated signal detection circuit 11
consists of a delay circuit 12 for one horizontal period (1H), an inverter 13, and an adder circuit 14 that synthesizes the current luminance signal and a signal delayed by 1H. Therefore, from this adder circuit 14, the luminance signal In addition to the secondary beat component C _B included in Y, an edge signal at the time of vertical uncorrelation (signal corresponding to the edge part of the luminance signal)
A decorrelation signal containing ΔY is output. If there is vertical correlation, edge signal ΔY is not output.

The non-correlated signal composed of the secondary beat component C _B and the edge signal ΔY is supplied to the limiter amplifier 16 via the bandpass filter 15, and the edge signal ΔY above a predetermined level is limited. The limited uncorrelated signal is supplied to a level control circuit 17 composed of, for example, an AM modulator, and its level is controlled by the envelope output of the carrier color signal output from the envelope detection circuit 19, and then the subtraction circuit 18 and is added to the current luminance signal with the polarity shown. Note that 30 is a delay element for compensating the delay time caused by insertion of the bandpass filter 15, limiter amplifier 16, etc.

The level control circuit 17 is for controlling the level of the uncorrelated signal to a value that can cancel the secondary beat component C _B included in the luminance signal Y.

By the way, when there is a vertical correlation, the edge signal ΔY is not output, and in this case, the level control circuit 17 outputs only the secondary beat component C _B whose level has been controlled based on the envelope output. The edge part does not deteriorate at all.

However, when recording a color image with a diagonal striped pattern as shown in Figure 3, for example, there is no vertical correlation, and in this case the edge signal ΔY is also output at the same time. As a result of level control of the signal ΔY based on the envelope detection output, even this edge signal ΔY may be subtracted from the current luminance signal Y, causing deterioration of the edge portion.

For example, in the case of a color image with a diagonal striped pattern as shown in FIG. 3, the current luminance signal Y is the signal shown in FIG. Figure A) is obtained. Therefore, the adder circuit 14 outputs a secondary beat signal C _B including the edge signal ΔY as shown in C in the figure.
As a result of this being limited by the limiter amplifier 16, a tragic correlation signal as shown in figure D is obtained.

In the level control circuit 17, when the envelope output of the carrier color signal is large, the output level is controlled to increase correspondingly. is small, the amount of the edge signal ΔY subtracted from the luminance signal Y in the subtraction circuit 18 also increases. Therefore,
As a result of outputting a luminance signal Y with degraded edge portions as shown in FIG. 4E to the terminal 7, the reproducibility of the edge portions is poor and an image with blurred edge portions is obtained.

Therefore, in order to avoid the deterioration of the edge portion that occurs during such secondary beat cancel processing,
The applicant previously proposed a circuit as shown in FIG.

This circuit is configured to inhibit the secondary beat cancel operation when the edge signal ΔY obtained from the vertical decorrelation section is present. Therefore, as shown in FIG. 5, an inhibiting circuit 20 is provided to control the level control state to the minimum level or zero when the edge signal ΔY is obtained.

The uncorrelated signal is supplied to a band eliminate filter 22 via an amplifier 21, and the secondary beat component C _B contained in the uncorrelated signal is eluted. The edge signal ΔY (FIG. 6E) outputted from this filter 22 is supplied to a double-wave detection circuit 23 and subjected to double-wave detection. This double-wave detection output ΔY′ (G in the same figure) is the envelope detection output S _E of the carrier color signal C.
The signal is also supplied to an AND circuit 24, and its AND output is supplied to a level control circuit 17 as a level control signal.

The detection output ΔY', which has been subjected to double-wave detection to become a negative polarity pulse, is used as an AND gate pulse, and therefore, the envelope output S _E is not supplied to the level control circuit 17 during the section where the edge signal ΔY is obtained. At this time, the level control circuit 17 does not output a non-correlation signal, and therefore no subtraction processing with the current luminance signal is performed in this section.

On the other hand, in sections other than the edge portion, the envelope output S _E itself is supplied to the level control circuit 17 via the AND circuit 24, so the level of the uncorrelated signal changes according to the level of the envelope output S _E. At this time, a secondary beat cancel operation similar to that explained in FIG. 2 is performed.

As a result, the edge portion of the brightness signal Y obtained at the terminal 8 is exactly the same as the current brightness signal as shown in FIG. 6H, and the deterioration of the edge portion caused by the secondary beat cancel processing can be avoided.

By the way, when the secondary beat cancel circuit 10 shown in FIG. 5 is used, the following problem occurs.

That is, since the band eluminate filter 22 is for eluminating the secondary beat component C _B , when a trap circuit that traps the secondary beat frequency 2c is used as this filter ₂₂ , When the wavelength is λ, the edge signal ΔY is as shown in Figure 7C,
If the pulse width is λ/2 or a pulse width in the vicinity thereof, even this edge signal ΔY will be emitted regardless of the level of the edge signal ΔY.

In such a case, since the detected output ΔY' cannot be obtained, a secondary beat cancel operation is performed. Therefore, as in the conventional case, the edge portions of the luminance signal Y deteriorate.

Purpose of the Invention In consideration of these points, the present invention makes it possible to prohibit the secondary beat cancel operation in the case of vertical uncorrelation, regardless of the pulse width of the edge signal ΔY, thereby preventing deterioration of the edge portion of the luminance signal. This was done to prevent this from happening.

SUMMARY OF THE INVENTION Therefore, in the present invention, an uncorrelated signal is obtained from a reproduced luminance signal, which includes a secondary beat component of a low-frequency converted carrier chrominance signal and an edge signal corresponding to an uncorrelated part of the luminance signal. A signal detection circuit, a band-pass filter that outputs a non-correlated signal in the band containing the secondary beat component from this non-correlated signal, an envelope detection circuit for the carrier color signal, and a level control of the band-pass output using this envelope output. a horizontal correlation circuit that detects the secondary beat component from the level-controlled bandpass output;
A subtraction circuit that subtracts the secondary beat component obtained from this from the luminance signal to cancel the secondary beat component included in the luminance signal, and an inhibition circuit that prohibits the level control while the edge signal is obtained. This constitutes a secondary beat cancel circuit.

In this way, if a horizontal correlation circuit is provided after the level control circuit, the edge signal ΔY is a signal with no horizontal correlation, so even if the detected output ΔY′ cannot be obtained, it will be included in the level-controlled bandpass output. Since the edge signal ΔY that is generated is not supplied to the subtraction circuit, the above object can be achieved.

Embodiment Next, a case in which an example of the secondary beat cancel circuit according to the present invention is applied to the circuit of FIG. 2 will be described in detail with reference to FIG. 8 and subsequent figures.

In this invention, as shown in FIG. 8, in addition to the configuration shown in FIG. 5, a horizontal correlation circuit 40 is provided between the level control circuit 17 and the subtraction circuit 18.

The horizontal correlation circuit 40 is supplied with a pair of series-connected delay elements 41 and 42 having a delay time of λ/2, an input signal of the delay element 41, and each output signal of the pair of delay elements 41 and 42, respectively. horizontal correlation means 43.

Now the level controlled bandpass output
S ₁ and this bandpass output i.e. the input signal
Assume that S ₁ is a secondary beat component C _B including an edge signal ΔY having a pulse width of λ/2 as shown in FIG. 9A. The input signal S ₁ is the first stage delay element 41
and is delayed by λ/2. If this output signal is S ₂ (FIG. 9B), the output signal actually obtained from this delay element 41 is the phase inverted signal S ₂ , so this output signal ₂
(FIG. 9C) becomes an input signal to the delay element 42 at the subsequent stage. Therefore, the output signal S ₃ (FIG. 9D) is obtained from the delay element 42 by delaying the output signal ₂ by λ/2 and inverting the phase.

These signals S ₁ , ₂ , delayed by λ/2, respectively
S ₃ is supplied to horizontal correlation means 43 and the correlation between signals S ₁ to _{S 3} is detected. The horizontal correlation means 43 is configured as an AND circuit, and therefore the horizontal correlation means 4
3, a correlation signal _SHC shown in FIG. 9E is obtained.

That is, the edge signal ΔY has no horizontal correlation and is therefore not output. In contrast, the secondary beat component
Since C _B is a continuous wave of the low frequency conversion signal, the secondary beat component C _B is output as is.

In this way, in the case of the edge signal ΔY having a pulse width of λ/2, the level control circuit 17
Even if a bandpass output _S1 as shown in FIG. 9A is output from the horizontal correlation circuit 40, the edge signal ΔY
is removed, so the edge portions of the luminance signal Y do not deteriorate.

Further, according to this configuration, the level of the edge signal ΔY is changed to the secondary beat component C _B as shown in FIG. 9A.
Whether it's larger or smaller than the level of
Since the edge signal ΔY can be removed in both cases, edge deterioration can be avoided regardless of the level of the edge signal ΔY.

When the pulse width of the edge signal ΔY is larger than λ/2, the inhibition circuit 20 operates as in the case of FIG. 5, and no subtraction processing is performed at the edge portion. Regardless of the pulse width and level of ΔY, it is possible to always prohibit the secondary beat cancel operation at the time of vertical decorrelation, and it is possible to reliably avoid deterioration of the edge portion.

FIG. 10 shows a specific example of the above-mentioned inhibition circuit 20. The edge signal ΔY output from the band elminate filter 22 is supplied to the terminal 25, and it is composed of a pair of transistors Q ₁ and Q ₂ . A phase-inverted edge signal (FIG. 5F) is obtained from the collector of one transistor _Q1 , and an in-phase edge signal ΔY is obtained from the collector of the other transistor _Q2 . . These in-phase and anti-phase edge signals ΔY are supplied to a double wave detector 23B to which the emitters of a pair of transistors Q ₃ and Q ₄ are commonly connected. A detection output ΔY′ obtained by double-wave detection is obtained from the collector.

Note that the capacitor 27 connected to the emitter side of the pair of transistors Q ₃ and Q ₄ is for slightly widening the pulse width of the detected output ΔY'.

The AND circuit 24 includes a pair of transistors Q ₅ and Q ₆
The emitters are commonly connected, and the collectors are commonly connected. Therefore,
If the detection output ΔY' is supplied to the base of one transistor Q ₅ and the envelope output S _E is supplied to the base of the other transistor Q ₆ , transistor Q ₅ will be turned on in the section where the detection output ΔY' is low level. ,
The gate output obtained at the terminal 28 becomes low level. On the other hand, when the detection output ΔY' is at a high level, the transistor _Q5 is off and a level corresponding to the envelope output S _E is obtained at the terminal 28, so the level control circuit 17 shown in FIG. It will be controlled based on this envelope output S _E.

Note that the AND circuit 24 used in this circuit can also be used as an AND circuit constituting the horizontal correlation means 43 described above.

Effects of the Invention As explained above, according to the configuration of this invention,
The secondary beat component C _B included in the luminance signal Y can be completely canceled. Furthermore, according to the configuration of the present invention, regardless of the pulse width and level of the edge signal ΔY, it is possible to always prohibit the secondary beat cancel operation at the time of vertical decorrelation, thereby reliably avoiding deterioration of the edge portion. can do.

In this way, in this invention, in order to eliminate blurring in minute parts of the luminance signal, secondary beat canceling is prohibited in uncorrelated parts of the luminance signal, and secondary beat cancellation is performed only in large area parts, which improves image quality. It is possible to improve the

[Brief explanation of the drawing]

Figure 1 is a frequency spectrum diagram of a color video signal, Figure 2 is a system diagram showing an example of a conventional secondary beat cancel circuit, Figures 3 and 4 are diagrams for explaining its operation, and Figure 5 is a diagram of this circuit. A system diagram showing an example of a secondary beat cancel circuit to explain the invention, FIGS. 6 and 7 are waveform diagrams to explain its operation, and FIG. 8 shows an example of a secondary beat cancel circuit according to the invention. A system diagram, FIG. 9 is a waveform diagram for explaining its operation, and FIG. 10 is a connection diagram showing an example of a prohibition circuit. 10 is a secondary beat cancel circuit, 11 is a non-correlation signal detection circuit, 15 is a band pass filter, 1
6 is a limiter amplifier, 17 is a level control circuit, 20 is an inhibition circuit, 22 is a band eluminate filter, 23 is a double wave detection circuit, 19 is an envelope detection circuit for the carrier color signal, 40 is a horizontal correlation circuit, 41 and 42 are delays Element 43 is a horizontal correlation means.

Claims (1)

[Scope of Claims] 1. In a secondary beat cancel circuit of a recording/reproducing device configured to record a low-frequency converted carrier color signal together with a luminance signal, an uncorrelated signal detection circuit that obtains an uncorrelated signal including a beat component and an edge signal corresponding to an uncorrelated part between lines of a luminance signal; and an uncorrelated signal in a band that includes a secondary beat component from the uncorrelated signal. an envelope detection circuit for the carrier color signal; a level control circuit for controlling the level of the bandpass output signal of the bandpass filter based on the output of the envelope detection circuit; a horizontal correlation circuit that detects the beat component from the bandpass output signal; and a horizontal correlation circuit that subtracts the secondary beat component obtained from the horizontal correlation circuit from the luminance signal to cancel the secondary beat component included in the luminance signal. an extraction circuit that extracts the edge signal included in the uncorrelated signal; and an inhibition circuit that prohibits operation of the level control circuit based on the output signal of the extraction circuit. A secondary beat cancel circuit for a recording/reproducing device characterized by: