JPS62227295A - Noise removing circuit - Google Patents

Abstract

PURPOSE:To obtain sufficient effect in a noise removal at the state of a reduced conversion carrier chrominance signal, by using a signal separated by one frame+ or -1H, and a present signal, in a carrier chrominance signal of reduced conversion carrier frequency with a relation of l/4 line offset. CONSTITUTION:When a chrominance subcarrier frequency fc sets a horizontal frequency as fH, a signal having the l/4 offset as fc=(2m-l)fH mu1/4, is converted to a digital signal at an A/D converter 12, and the digital signal is delayed by one frame+ or -1H by a delay means 14. A difference between the digital signal from the converter 2, and the signal whose phase is inverted and that is delayed by one frame+1H from a phase inversion means 15, or the signal delayed by one frame-1H from an extending meas 14, is taken at the first subtraction means 16, and the output of the difference is subtracted from the digital carrier chrominance signal from the A/D converter 12 by the second subtraction means 13, then being provided. A part having no correlation is extracted as the noise. And by subtracting those from the present signal, it is possible to remove the noise.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention is directed to, for example, a color video signal reproduced from a popular VTR in which the color subcarrier frequency is recorded after being converted to a low frequency, especially when the noise is lower than that of the carrier color signal. This invention relates to a noise removal circuit that removes noise.

[Summary of the invention]

In this invention, the color subcarrier frequency of the color video signal is fc=
(2m 1) rs (fo is the horizontal frequency), which allows noise removal using frame correlation while the frequency is still low-frequency converted to fc, where fo is the horizontal frequency.
Since the frequency re is a 1/4 line offset, the noise component is extracted from the current signal and a signal delayed by 1 frame + 1H (H is the horizontal period) and/or l frame - 1H, and this is used as the current signal. The noise is removed by removing it from the .

[Conventional technology]

In the case of a skin type home VTR, due to the limitations of the recording and reproducing band, the color subcarrier frequency of the carrier color signal is set to the lower frequency side of the frequency modulated luminance signal, for example, 688kllz in the case of an NTSC color video signal. Convert and record/play.

By the way, noise removal is performed on the reproduced color video signal from the VTR by taking advantage of the fact that the frame correlation is strong.

In this case, when considering noise removal using frame correlation for a carrier color signal, the phase of the color subcarrier with respect to the line must be considered, but in the case of an NTSC color video signal, the color subcarrier has a 1/2 line offset relationship. Since the frequency is 3.58 MIIz, the line one frame before is in a phase-inverted relationship with respect to the current line.

Therefore, in the past, the carrier frequency of the carrier color signal in the reproduced color video signal from the VTR was returned to the original 3.58 MIIz, and the noise component was obtained from the difference between the current signal and a signal obtained by inverting the phase of the signal one frame before. , this noise component is subtracted from the current signal to perform noise removal.

That is, FIG. 3 is an example of a conventional noise removal circuit of this type, in which the input terminal (1) has a color subcarrier frequency of 3.58.
The reproduced carrier color signal Sc returned to Mtlz is supplied.

This carrier color signal Sc is converted into a digital carrier color signal DSc in an A/D converter (2), and this signal DSc
is written to the frame memo (January 4) via a noise removal subtraction circuit (3) which will be described later. This frame memory (
4) constitutes a delay circuit, from which the input signal is 1
A signal extended by 525 HJ for one frame is obtained. As described above, in the case of the carrier color signal of the NTSC signal, this delayed digital signal has a phase inverted with respect to the input carrier color signal Sc.

Therefore, this delayed digital signal is phase-inverted through the inverter (5) and brought into phase with the input carrier color signal Sc.

The delayed digital signal from the inverter (5) and the digital carrier color signal DSc from the A/D converter (2) are then supplied to a subtraction circuit (6) to produce a signal with no frame correlation. is extracted as noise.

After the noise extracted in this way is multiplied by a predetermined coefficient K for adjusting the noise removal effect in the coefficient circuit (7),
The signal is supplied to a noise removal subtraction circuit (3) and subtracted from the digital carrier color signal DSc from the A/D converter (2) to remove noise.

From the above, from the frame memo January 4) the input signal S
c is delayed by one frame and a noise-removed digital signal is obtained, which is sent to the D/A converter (8).
is returned to an analog signal, and a noise-removed carrier color signal is obtained at the output terminal (9).

[Problems to be solved by the invention]- As mentioned above, conventional carrier color signal noise removal is performed with the color subcarrier frequency returned to 3.58 MIIz, so the A/D converter (2) The sampling frequency of the D/A converter (8) was more than twice as high as 3.58 MIIz, and the large number of samples required a large capacity frame memory (4) and high-speed calculation. .

All of the above points can be improved by removing noise from the carrier color signal while the color subcarrier frequency reproduced by the VTR is still low frequency converted.

However, the carrier frequency re of the low-pass converted carrier color signal is
In order to avoid bright and dark dot interference caused by the mixing of frequency components twice the color subcarrier into the reproduced luminance signal on the reproduced screen, fc = (2m-1) in the color video signal of the NTSC system. f.

In this way, re becomes (odd number x -) (i!i) of fH, resulting in a 1/4 line offset.

Therefore, the phase of this low-frequency conversion carrier color signal with respect to the line goes around every four frames as shown in FIG. 4, and the phase inversion occurs two frames apart.

Therefore, when the noise removal shown in FIG. 3 is performed using the low-pass converted carrier color signal as it is, noise is extracted by correlating between signals two frames apart, and sufficient noise removal cannot be achieved.

As is clear from Figure 4, there is a 90 degree phase difference between signals that are one frame apart, so it is possible to shift the phase of the signal delayed by one frame by 90 degrees to bring it into phase with the input signal. , more accurate than the phase inversion circuit
It is quite difficult to construct a degree phase shift circuit, and it is difficult to achieve a sufficient noise removal effect, so it is not generally used.

The present invention aims to provide a noise removal circuit that can be expected to have a sufficient noise removal effect on low-frequency conversion carrier color signals without causing the above-mentioned drawbacks.

[Means for solving problems]

In this invention, the color subcarrier frequency fc is fc=
(2m 1) an A/D converter (12) that converts the carrier color signal low frequency converted into a digital signal;
a delay means (14) for delaying this digital carrier color signal by one frame ±111; a phase inversion means (15) for inverting the phase of the signal delayed by one frame from this delay means (14); a first subtraction that takes the difference between the digital carrier color signal from the A/D converter (12) and the signal from this phase inversion means (15) or the signal delayed by 1 frame-1H from the delay means (14); means (16);
A second subtraction means (13) is provided for removing noise by subtracting the difference output from the first subtraction means (16) from the digital carrier color signal from the A/D converter (12).

[Effect]

At the low-pass conversion color subcarrier frequency, there is a 1/4 line offset relationship, so as is clear from Figure 4, the phase of the signal delayed by 1 frame + I II is inverted with respect to the input current signal. , and the one-frame-IH delayed signal is in phase with the input current signal.

In video signals, there is a strong correlation between frames and also between lines. Therefore, there is a strong correlation between the input current signal and these signals that are one frame ±LH apart.

Therefore, by inverting the phase of the signal delayed by 1 frame by 1H, and taking the difference from the input signal while leaving the signal delayed by 1 frame by 1HJ, it is possible to extract uncorrelated parts as noise. The noise can be removed by subtracting this from the current signal.

〔Example〕

FIG. 1 shows an embodiment of the circuit according to the invention, with a Kugata terminal (1
1) is supplied with a low frequency converted carrier color signal SLc of an NTSC signal with a carrier frequency of 688kllZ. This low-pass conversion carrier color signal SLc is converted into a digital low-pass conversion carrier color signal DSLc in an A/D converter (12), and this signal DSLc is passed through a noise removal subtraction circuit (3) to be described later to 526H (one frame +lH) Memory (14)
will be written to.

This memory (14) constitutes a delay means, from which the input signal is delayed by 525H (1 frame), a signal So, 524H (1 frame-II-1) delayed, signal S1, and 526H (1 frame). frame+1H) delayed signal S2 is obtained.

The signal SO delayed by 525 H is sent to the D/A converter (1
8) and is converted back into an analog signal and sent to the output terminal (1
9), a noise-removed low-frequency conversion carrier color signal is obtained as described later.

The signal S delayed by 52411 hours and the signal S2 whose phase is inverted by the inverter (15) are added by the adding circuit (20), and the added signal is sent to the averaging circuit (21). Supplied and level 1/2
be made into

Here, as mentioned above and as shown in FIG.
The current signal DSLc from the /D converter (12) and the signal s1 delayed by 524H are in phase, and
5261 from the signal DSLc (the phase inverted signal "T" of the delayed signal S2 is also in phase with the current signal DSLc,
The spatial relationship between the signals S1 and s2 on the line is that the signal S1 is shifted up by one line with respect to the line containing the signal DSLc, and the signal S2 is shifted down by one line. It is a line signal. And signal S1
An averaging circuit (2
The output of 1) is pseudo-coupled with the line of signal S1 and the line of signal S2.
This means that it is a signal on the line in the middle of the line of signal DSLc, and is a signal on the previous line of one frame that is spatially the same as the line of signal DSLc.

Therefore, the signal DS from the A/D converter (12)
When the difference between Lc and the output signal of the averaging circuit (21) is obtained by the subtraction circuit (16), noise, which is an uncorrelated part of both signals, is extracted as the difference.

The noise extracted in this way is multiplied by a predetermined coefficient K for adjusting the noise removal effect in the coefficient circuit (17), and then supplied to the noise removal subtraction circuit (13).
It is subtracted from the digitally reduced converted carrier color signal DSLc from the converter (12) to remove noise.

From the above, the signal S from frame memory (14)
A digital low-pass conversion carrier color signal from which noise has been removed is obtained as o.

FIG. 2 shows another example of the present invention, in which the circuit also serves as a time axis error correction circuit for reproduced signals, and the same parts as in the example of FIG. 1 are denoted by the same reference numerals.

In this example, an adding circuit (20) and an averaging circuit (20) are used.
1) Instead of taking the weighted average of signals S1 and 32,
These two signals S1 and 82 are switched to 1 by the switch (22).
The signal is alternately switched and supplied to the subtraction circuit (16) every frame. In this way, the output of the switch (22) becomes equal to the weighted average over a long period of time due to the eye's integral effect, and a noise removal effect similar to that of the example in FIG. 1 can be obtained.

In this example, the color sending signal for reduction conversion from the input terminal (11) is sent to the write clock generation circuit (23).
The horizontal synchronizing signal (ID) which is supplied to the
). This write clock generation circuit (23
), a clock signal synchronized with the reproduced horizontal synchronizing signal HD and the phase of the burst signal in the carrier color signal, that is, a clock signal WCK having the same time axis error as the reproduced signal is obtained.

This clock signal WCK is then applied to the A/D converter (
12) as its sampling clock, and the memory (14) as its write clock.

On the other hand, the reference signal REF is
4), from which a read clock signal RCK with the same frequency as the signal WCK and no time axis error is obtained,
This clock signal RCK is supplied to the memory (14) as its read clock, and is also supplied to the D/A converter (18) as its sampling clock.

In this way, signals with time axis errors are sequentially written into the memory (14) by the write clock signal WCK, but when reading, the carrier color signal is written into the memory (14) by the read clock signal RCK with this time axis error removed.
(14).

In the above example, the weighted average of the signals S1 and 32 was taken to further improve the noise removal effect, but the signal S
1 and signal S2 are signals that have a strong correlation with the current signal, as described above, so even if noise is extracted by taking the difference between either signal S1 or signal S2 and the current signal, good.

Further, in the example shown in FIG. 1, the output digital low frequency conversion carrier color signal may be obtained from the subtraction circuit (13).

Furthermore, when obtaining the noise-removed output from the subtraction circuit (13), the memory (14) is provided with an A/D converter (1
The output of 2) may be written directly.

〔Effect of the invention〕

In this invention, in the case of a carrier color signal of a reduced converted carrier frequency with a relationship of 1/4 line offset, (1) Taking advantage of the fact that signals 111 points apart on a frame are in phase or in opposite phase, these 1 frame ±1H By extracting noise from the distant signal and the current signal, a sufficient noise removal effect can be achieved.
This is what can be obtained in the state of a reduced conversion one-shell color forwarding signal.

Since noise can be removed in the state of the reduced conversion carrier color signal,
The sampling frequency for digitization is low (often
It has the advantage that it requires less memory capacity and the calculation speed can be slower than before.

[Brief explanation of drawings]

Figure 1 is a block diagram of one embodiment of this inventive circuit, Figure 2 is a block diagram of another example of this inventive circuit, Figure 3 is a block diagram of an example of a conventional circuit, and Figure 4 is a low frequency conversion color FIG. 3 is a diagram showing the phase of subcarriers with respect to a line. (12) is an A/D converter, (13) is a second subtraction circuit, (14) is a memory as a delay means, (15) is an inverter, and (16) is a first subtraction circuit.

Claims (1)

[Claims] (a) Color subcarrier frequency f_c is f_c=(1/4)
(2m-1) An A/D converter that converts the carrier color signal low frequency converted to f_H (f_H is the horizontal frequency) into a digital signal; a delay means for delaying by (c
) a phase inversion means for inverting the phase of the signal delayed by 1 frame + 1H from the delay means; (d) a digital carrier color signal from the A/D converter and a signal from the phase inversion means or the delay means; (e) a first subtraction means for taking the difference from the signal delayed by 1 frame - 1H; (e) the difference output from the first subtraction means is sent to the A/D;
and a second subtraction means for removing noise by subtracting it from the digital carrier color signal from the converter.