JPH04211590A - Noise removing circuit - Google Patents

Abstract

PURPOSE:To provide the noise reduction circuit of a video signal recording and reproducing device which is suppressed in the deterioration of the vertical resolution of a reproducing screen and an increase in rainfall noise and to simplify the circuitry thereof. CONSTITUTION:The noise reduction circuit of the reproducing system of a VTR is constituted of the combination of the noise reduction circuits (8 to 12) of a recursive type and the noise reduction circuits (12 to 16) of a nonrecursive type. The noise reduction circuits (8 to 12) of the recursive type function as vertical deemphasis circuits to apply vertical deemphasis on reproduced brightness signals. On the other hand, the noise reduction circuits (12 to 16) of the nonrecursive type cancel the noise components having no line correlation characteristics from the reproduced brightness signals subjected to the vertical deemphasis. The vertical deemphasis and the noise reduction are separately executed in such a manner and, therefore, the image quality is improved.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise removal circuit in a recording/reproducing apparatus such as a VTR.

0002

[Prior Art] For example, Japanese Patent Application Laid-Open No. 57-211885 (
H04N5/93) discloses a so-called recursive type noise removal circuit. This is an nH delay line (for example, a 1H delay line, where H is the horizontal period of the video signal)
is used to circulate the luminance signal and remove noise components with no vertical correlation.

In this type of noise removal circuit, when the noise reduction effect is increased, the resolution in the vertical direction deteriorates, and only the line-correlated components of the noise are emphasized, causing a so-called rain noise that lingers in the vertical direction. It has the disadvantage of being conspicuous (see the upper right column of page 3 of the aforementioned bulletin)
.

[0004] In order to improve image quality, VHS-HQ VTRs use a recursive type that applies vertical emphasis to the luminance signal during recording, and simultaneously performs de-emphasis and noise removal on the vertical emphasis on the playback side. A configuration in which a noise removal circuit is provided is adopted.

[0005]

[Problem to be solved by the invention] That is, VHS-H
In a Q-type VTR, a recursive type noise removal circuit performs both de-emphasis and noise removal operations, so the noise reduction rate is inevitably large. Therefore, as mentioned above, there are drawbacks such as deterioration of the vertical resolution of the reproduced signal and conspicuous rain noise.

[0006]

[Means for Solving the Problems] Accordingly, in the present invention, the circuit configuration on the reproduction side is realized by a combination of recursive type and non-recursive type noise removal circuits.

[0007]

[Operation] The recursive type noise removal circuit is provided with a de-emphasis characteristic corresponding to vertical emphasis, and the combined non-recursive type noise removal circuit removes noise.

[0008] The non-recursive type noise removal circuit does not cause deterioration of vertical resolution or increase of rain noise, and therefore does not have the problems of the prior art.

[0009]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the invention, FIG. 2 is a characteristic diagram for explaining the configuration of the embodiment of the invention, and FIG. 3 is a block diagram showing a second embodiment of the invention.

In FIG. 1, 1 is an input terminal for recording luminance signals, 2 is a first (nH) delay line (CCD delay line), 3 is a first adder, 4 is a first limiter, and 5 is a first multiplier. , 6 is a second adder, and the above constitutes a vertical emphasis circuit during recording. 7 is a block representing a configuration in which modulation/demodulation and recording/reproduction are executed.

8 is a third adder, 9 is a second limiter, 10
is the second multiplier, 11 is the fourth adder, 12 is the second (nH)
This is a delay line, and the above constitutes a recursive type noise removal circuit on the reproduction side.

13 is a fifth adder, 14 is a third limiter,
15 is a third multiplier, 16 is a sixth adder, and the above configuration and the second (nH) delay line 12 constitute a non-recursive type noise removal circuit. Further, 17 is an output terminal for the demodulated luminance signal.

That is, during recording, vertical emphasis is applied to the luminance signal by a non-recursive type emphasis circuit, as in the conventional case. The transfer function from the input terminal 1 to the second adder 6 can be expressed by the following equation.

[0014]

[Math 1]

[0015] Therefore,

[0016]

[Math 2]

Note that V6 is the output of the second adder 6, V1 is the input luminance signal, and K1 is the coefficient of the first multiplier 5.

On the reproduction side, transfer functions are determined separately for a recursive section that performs de-emphasis corresponding to vertical emphasis and a non-recursive section that performs line noise cancellation.

The transfer function from block 7 to the fourth adder is determined as follows.

[0020]

[Math 3]

[0021] Therefore,

[0022]

[Math 4]

Here, V11 is the output of the fourth adder 11,
V7 is the reproduced output signal of block 7, and K2 is the coefficient of second multiplier 10.

The transfer function from the fourth adder 11 to the output terminal 17 is determined as follows.

[0025]

[Math 5]

[0026] Therefore,

[0027]

[Math 6]

Here, V17 is the final output, and K3 is the coefficient of the third multiplier 15. In order for the characteristics to be complementary between the vertical emphasis during recording and the recursive type noise removal circuit on the playback side, K1 and K2 should be set to H6(ω)*H.
It may be determined so that 11≒1. That is, it becomes as shown in the following formula.

[0029]

[Math 7]

By determining in this way, it is possible to suppress the deterioration of the vertical resolution and the increase in rain noise caused by the recursive type. Then, the next connected non-recursive type noise removal circuit (line noise canceler) can cancel the component whose frequency is shifted by (1/2) fH.

FIG. 2 shows K1=0.5 in the configuration of FIG.
, K2=0.33, and K3=0.164, the frequency-amplitude characteristics are compared with those of a conventional configuration. Here, as already explained in the conventional configuration, there are no components 13 to 16 in FIG. 1, and in order to achieve the same effect as in FIG. I can imagine it happening. Also, in this conventional example,
Since K1≦K2/(1-K2), the de-emphasis amount is larger than the emphasis amount.

As is clear from FIG. 2 (in the figure, the broken line a represents the present embodiment, and the solid line b represents the conventional example), (1/
2) When the attenuation amount at frequencies separated by fH is the same, according to the embodiment, the passband is wider and the original luminance signal can be passed through more. In other words, unnecessary components can be removed using a non-recursive type noise removal circuit without increasing the noise reduction amount of a recursive type noise removal circuit, which eliminates the problems of the conventional technology (vertical resolution and Rain noise) can be solved.

Furthermore, in the embodiment shown in FIG. 1, the 1H delay line 12 is shared by the recursive type vertical de-emphasis circuit and the non-recursive type noise removal circuit, which simplifies the overall circuit configuration. ing.

Next, FIG. 3 is a schematic block diagram showing a second embodiment of the present invention. In FIG. 3, the vertical emphasis circuit (
Elements 1 to 6) in FIG. 1 are not illustrated and their descriptions are also omitted.

The second embodiment shown in FIG. 3 is basically the same as the embodiment shown in FIG. 1, and consists of a recursive type vertical de-emphasis circuit at the front stage and a non-recursive type noise removal circuit at the rear stage. However, the difference from the embodiment shown in FIG. 1 is mainly that one adder is used in common as adders 8 and 13 in FIG.

Referring to FIG. 3, during reproduction, the luminance signal supplied from the modulation/demodulation and recording/reproduction block 7 and subjected to vertical emphasis and containing noise is sent to the seventh adder 21.
and the eighth through the delay equalizer 27.
It is applied to an adder 25. The seventh adder 21 subtracts the output of the third (nH) delay line 26 from the reproduced luminance signal to extract a component without line correlation. A chroma signal component based on frequency interleaving during recording remains in this extracted component. Therefore, during playback, the third (nH
) Due to the phase shift caused by the delay line 26, the remaining chroma signal component may be emphasized by the recursive type vertical de-emphasis circuit at the front stage and the non-recursive type noise removal circuit at the rear stage.

Therefore, during reproduction, the subcarrier frequency fsc (3.58M
The chroma carrier is removed by a trap circuit 22 that traps the signal at Hz). This prevents the chroma signal from being emphasized due to the non-recursive type noise removal circuit. Further, the aforementioned delay equalizer 27 is provided to adjust the time delay caused by this trap circuit 22.

The component having no line correlation outputted from the trap circuit 22 is passed through the fourth limiter 23 to the coefficient K2.
' is applied to the fourth multiplier 24, and its level is attenuated. Then, the attenuated component is then transferred to the eighth adder 25.
given to. On the other hand, the eighth adder 25 is given the reproduced luminance signal from the modulation/demodulation and recording/reproducing block 7, and as a result, the eighth adder 25 extracts components without line correlation from the current reproduced luminance signal. Subtract. In this way, the reproduced luminance signal in which components without line correlation have been reduced is provided to the ninth adder 30, and the third (nH
) is applied to delay line 26. Thereafter, the series of operations described above are repeated. As described above, the seventh adder 21,
Trap circuit 22, fourth limiter 23, fourth multiplier 24
, the eighth adder 25, the third (nH) delay line 26, and the delay equalizer 27 are recursive type noise removal circuits (
vertical de-emphasis circuit).

On the other hand, the component having no line correlation outputted from the trap circuit 22 is applied to the fifth multiplier 29 via the fifth limiter 28, and its level is attenuated. The attenuated component is then provided to a ninth adder 30. On the other hand, the ninth adder 30 is given the reproduced luminance signal from the eighth adder 25, and as a result, the ninth adder 30
subtracts the noise component from the reproduced luminance signal subjected to vertical de-emphasis. In this way, the third (nH) delay line 26, the seventh adder 21, the trap circuit 22, the fifth limiter 28, the fifth multiplier 29, and the ninth adder 30 constitute a non-recursive type noise removal circuit. do.

In this second embodiment, the fourth multiplier 24
The coefficient K2' is preferably set to K2'<1.0, and in particular, is usually set to K2'≦0.5. Also, the fifth multiplier 2
The coefficient K3' of 9 is set to K3'≦0.5. Furthermore, the coefficient K3' of the fifth multiplier 29 of the second embodiment is
Unlike the coefficient K3 of the third multiplier 15 in the embodiment, the fifth multiplier 29 inputs the noise component extracted from the recursive type noise removal circuit, and therefore, the second embodiment differs from the first embodiment. In comparison, the amount of noise components input to the subsequent non-recursive type noise removal circuit increases. Therefore, the coefficient K of the fifth multiplier 29 of the second embodiment
3' is set smaller than the coefficient K3 of the third multiplier 15 in the first embodiment. For example, the third multiplier 15 of the first embodiment
The second coefficient corresponding to the case where the coefficient K3 of is set to 0.164
The optimum coefficient K3' for the fifth multiplier 29 of the embodiment is 0.1
Becomes 64 or less.

In the first and second embodiments, the recursive type vertical de-emphasis circuit and the non-recursive type noise removal circuit each include a limiter and a multiplier; It is also possible to configure the order of the noise removal circuit in reverse.

[0042] Furthermore, since the configurations of the noise removal circuit on the recording side and the noise removal circuit on the playback side are almost the same,
It can also be composed of common parts. In this case, only one delay line is required and the overall circuit configuration can be made smaller, making it suitable for IC implementation.

Further, although the delay line in the embodiment is an (nH) delay line, it may be a 1H (n: natural number) delay line.

[0044]

As described above, according to the present invention, in a recording and reproducing apparatus that applies vertical emphasis to a video signal during recording, noise is removed by combining recursive type and non-recursive type noise removing circuits on the reproducing side. Therefore, unnecessary noise in the reproduced signal can be removed without deterioration of vertical resolution or increase in rain noise as in the conventional example, which is effective in improving image quality.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a characteristic diagram for explaining the configuration of an embodiment of the present invention.

FIG. 3 is a block diagram showing a second embodiment of the present invention.

[Explanation of symbols]

8 Third adder 9 Second limiter 10 Second multiplier 11 4th adder 12 Second (nH) delay line 13 Fifth adder 14 3rd limiter 15 Third multiplier 16 Sixth adder 21 7th adder 22 Trap circuit 23 4th limiter 24 4th multiplier 25 8th adder 26 Third (nH) delay line 27 Delay equalizer 28 5th limiter 29 Fifth multiplier 30 9th adder

Claims (2)

[Claims] Claim 1: In a noise removal circuit for a magnetic recording and reproducing device that applies vertical emphasis to a video signal during recording, a noise removal circuit on the playback side is configured by combining a recursive type noise removal circuit and a non-recursive type noise removal circuit. , A noise removal circuit characterized in that the characteristics of the recursive type noise removal circuit are substantially equal to the characteristics of the vertical emphasis. 2. The noise removing circuit according to claim 1, wherein the non-recursive type noise removing circuit receives as input a noise component extracted from a recursive type noise removing circuit.