JP2583877B2 - Noise suppression device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise suppression circuit that can function as a noise reducer and a noise canceller.

[Prior Art] In general, a television signal has a stronger correlation between frames than between lines and between frames than between fields.
Various noise suppression devices have been proposed which suppress the noise by utilizing the characteristic characteristic of the video signal and utilizing the difference in the degree of correlation. The conventional noise suppressor 1 shown in FIG. 3 is called a noise reducer, and a video signal to be subjected to noise reduction is cyclically added to a video signal substantially one field period or one frame period ago at an appropriate ratio. By adding to
This is to perform a cyclic noise reduction process. Input video signal Vi
(T) is supplied to the addition circuit 3 through the coefficient circuit 2 having a positive coefficient (1−K) of 1 or less. This addition circuit 3
Is delayed by a delay circuit 4 having a delay time of approximately one field period or one frame period, and is multiplied by K by a coefficient circuit 5 to obtain a delayed output video signal V ₀ (t−τ) as (1-K) It is added to the doubled input video signal Vi (t), and the added output is taken out to the outside as an output video signal V ₀ (t), and is also supplied to the delay circuit 4 at the same time. That is,
The relationship V ₀ (t) = (1−K) Vi (t) + KV ₀ (t−τ) holds between the output video signal V ₀ (t) and the input video signal Vi (t). Here, τ is a delay time in the delay circuit 4 and indicates an integer (262 or 263 in the NTSC system) line period or one frame period closest to one field. As is well known, the degree of noise suppression by this noise reducer is ｛(1−K) / (1+
K)｝ ^1/2 , and the noise suppression effect can be increased as the value of the coefficient K approaches 1.

[Problems to be Solved by the Invention] The conventional noise suppression device 1 of the cyclic noise reduction system is
While the S / N ratio of the video signal can be greatly improved, if the coefficient K is increased to increase the S / N ratio improvement, there is a problem that an afterimage generated particularly in a rapidly moving image is conspicuous and the image quality is rather deteriorated. Therefore, for example, the third
As shown by the one-dot chain line in the figure, the difference between the input video signal Vi (t) and the delayed output video signal V ₀ (t) is calculated, and the larger the difference signal serving as a barometer indicating the degree of image motion is, the larger the difference is. , A coefficient switching circuit 6 for switching the value of the coefficient K to a smaller value, or for a video signal of originally high quality, the noise reduction itself is stopped by forcing the coefficient to zero. A plan was taken.

For this reason, in a device such as a home magnetic recording / reproducing device that does not include noise suppression means other than a noise reducer, the SN ratio between when the cyclic noise reduction processing is executed and when it is not is improved. There is a problem in that a gap arises in a method of coping with the problem, and users who strongly desire high-quality image reproduction complain.

Japanese Patent Application Laid-Open No. 56-169917 discloses an automatic equalizer, in which means for performing linear or non-linear conversion on a tap gain sequence is provided in the automatic equalizer, and the automatic equalizer is provided in a non-cyclic type (feedforward type). After the tap gain sequence is determined by operating in the configuration, the converted tap gain sequence is given to a transversal filter, and the automatic equalizer is switched to a cyclic (feedback) configuration. The disclosed hybrid ghost canceller is disclosed.

However, it uses a reference signal waveform (the leading edge of the vertical synchronizing waveform of the video signal) periodically present in the received television signal, and automatically equalizes the linear distortion of the transmission system on the receiving side. Is a ghost canceller that employs a hybrid method that combines both cyclic ghost removal performance and non-cyclic stability.However, when switching to the cyclic type, noise or band limiting of the input signal is required. It is premised that the tap gain sequence is set to an ideal value so as not to oscillate under the influence of the above. Therefore, the automatic equalizer is first operated in a non-recursive type (feedforward type) configuration and determined in this non-cyclic type configuration. The tap gain sequence without the risk of oscillation is linearly or non-linearly converted and applied to a transversal filter, and is simultaneously switched to a cyclic configuration. Therefore, instead of switching between the non-cyclic configuration and the cyclic configuration according to the level of linear distortion of the transmission system, the non-cyclic configuration is temporarily used for the purpose of searching for a tap gain sequence that does not oscillate the main cyclic configuration. And it is not a configuration in which the non-recursive configuration and the cyclic configuration are switched and selected in an equal relationship with each other according to the ghost occurrence situation, so that the advantage of both configurations is not fully utilized. It was something to hold.

The present invention has two noise reducers and noise cancellers.
It is an object of the present invention to provide a noise suppression device that enables the role to make the most of the advantages of both.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides an input video signal multiplied by a coefficient (1-K) of 1 or less and an output video signal in a delay circuit for approximately one field period or A delay output video signal multiplied by a coefficient K equal to or less than 1 after being delayed by one frame period is added in an adder circuit to obtain the output video signal, and the coefficients (1-K) and K are determined according to a target noise suppression degree.
And a noise reducer that cyclically reduces noise included in the input video signal, and a noise reducer that is provided between the addition circuit and the delay circuit. Alternatively, if the target noise suppression degree requires 1/3 <K ≦ 1, the switch is switched to the addition output selection side, and the target switch is configured to selectively supply the addition output of the addition circuit. When the noise suppression degree requires 0 ≦ K ≦ 1 /, the coefficient K is forcibly switched to about 1/2, and the switch is switched to the input video signal selection side, so that the noise reducer is switched. And a noise suppression mode switching circuit that functions as a noise canceller that performs a non-recursive noise reduction process.

[Operation] According to the present invention, when a signal approximately one field or one frame period earlier is added to a video signal to be noise-reduced, a cyclic coefficient K is discriminated as a threshold value and cyclic addition and non-recursive addition are performed. Either of the type additions is selected, and one device can perform two functions of a noise reducer and a noise canceller.

Embodiment An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a circuit configuration diagram showing one embodiment of the noise suppression device of the present invention, and FIG. 2 is an SN ratio diagram showing the noise suppression degree of the noise suppression device shown in FIG.

In FIG. 1, a noise suppression device 11 performs a non-recursive noise reduction process by cutting off a repetition of an output video signal V ₀ (t) based on a conventional noise suppression device 1 known as a noise reducer. A noise suppression mode switching circuit 12 for changing from a noise reducer to a noise canceller is added. That is, the coefficient circuit 2 and the delay circuit 4 necessary for the noise reducer use the conventional ones as they are, while adding the above-described noise suppression mode switching circuit 12 and the switching switch 13 as means for functioning as a noise canceller. It is. Selector switch
Reference numeral 13 is connected between the addition circuit 3 and the delay circuit 4 so that either the output of the addition circuit 3 or the input video signal can be selected. The noise suppression mode switching circuit 12 switches the noise suppression mode depending on whether the addition output of the addition circuit 3 is cyclic or non-cyclic. In this embodiment, the noise suppression mode switching circuit 12 determines whether the motion signal detected by itself is large or small. Also, mode switching is performed according to a switching operation from outside.

In other words, when K must be used at 1/3 or less in order to suppress the afterimage while using as a noise reducer, the switch is switched to the use as a noise canceller by switching the changeover switch 13. And K to maximize the noise suppression
It is fixed at 1/2. Of course, the changeover of the changeover switch 13 can be performed from the outside. In this case, K is fixed to 1/2 when used as a noise canceller.

Here, when the changeover switch 13 is switched to the addition circuit 3 side as shown in FIG. 1, the cyclic noise reduction processing is executed as the noise reducer described above. On the other hand, when the noise suppression mode switching circuit 12 switches the changeover switch 13 to the input video signal side, the cyclic loop up to that point is cut off and functions as a noise canceller that performs a non-cyclic noise reduction process.
In this case, the output video signal V ₀ (t) and the input video signal Vi
The relationship of V ₀ (t) = (1−K) Vi (t) + KVi (t−τ) holds between (t), but the noise suppression mode switching circuit 12
However, the coefficient K is set to 1 /
Since it is switched to 2, the relationship is actually V ₀ (t) = (1-2) Vi (t) + (1/2) Vi (t−τ).

By the way, regarding the signal component of the video signal, by setting Vi (t) = Vi (t−τ) in the above equation, V ₀ (t)
= Vi (t) is obtained. On the other hand, as for the noise component N ₀ (t) having no correlation, even if it is assumed that there is no change in the noise level, the sum of the amplitudes is not obtained, and (1-K) Ni (t) + KN
It is represented by the sum of the powers of i (t−τ). That is, the average amplitude of the noise component N ₀ (t) is {(1−K) ² + K ² )} ^1/2 N
It is represented by i (t). Therefore, by setting K to 1/2, the noise suppression degree becomes 1/2 ^1/2 .

Here, the noise suppression degree as a noise canceller 1/2 ^1/2
When the noise reduction ratio {(1-K) / (1 + K)} ^1/2 as the noise reducer described above is converted into an SN ratio and compared, as shown in FIG. It is clear that the noise suppressor of the noise reducer exceeds the noise canceller in the range exceeding. However, in the case of a noise canceller that does not require much attention to the occurrence of an afterimage, a noise suppression effect of about 3 dB can always be obtained. For this reason, as described above, when K must be used at 1/3 or less in order to suppress the occurrence of afterimages during use as a noise reducer, the noise canceling mode switching circuit 12 outputs the noise canceller. It is used as. That is, 1/2 of the input video signal Vi (t)
By adding 1/2 of the delay input video signal Vi (t−τ) to the maximum, the maximum afterimage suppression by the non-cyclic noise suppression is achieved.

Regardless of the motion of the image, that is, the magnitude of the motion signal, the noise suppression degree is fixed to 1/2 ^1/2 even when the noise suppression mode switching circuit 12 is externally actuated and forcedly switched to the noise canceller. However, afterimage suppression with little afterimage is possible.

As described above, in the noise suppression device 11, the noise suppression mode switching circuit 12 switches the changeover switch 13 according to the value of the coefficient K required by the target noise suppression degree, and performs one of the cyclic addition and the non-cyclic addition. By selecting, a single device can perform the dual role of a noise reducer and a noise canceller. When used as a noise reducer, image quality may deteriorate due to an afterimage, or when used as a noise reducer, noise suppression K ≦ 1 where the degree is below 2dB
For example, when it is necessary to accept / 3, by switching to a non-recursive configuration so as to function as a noise canceller, it is possible to increase the constant noise suppression effect without occurrence of afterimages. It can be used as a noise canceler for video signals with high quality originally, and as a noise reducer with high noise suppression for video signals contaminated with noise. Fine noise suppression according to the quality is possible.

[Effects of the Invention] As described above, the present invention provides an input video signal Vi
(T), the the output video signal V ₀ (t) is delayed by approximately one field period or a delay circuit having a delay time of one frame period delayed output video signal V ₀ (t-τ), respectively A coefficient (1-K) of 1 or less is multiplied by a coefficient K and added by an adder circuit to obtain an output video signal V ₀ (t), where V ₀ (t) = (1−
K) An operation of Vi (t) + KV ₀ (t−τ) is performed, and at that time, a target value of the noise suppression degree {(1−K) / (1 + K)} ^1/2 , that is, a target noise suppression degree is calculated. Coefficient (1-K)
And K are linked and variably set, and the input video signal Vi (t)
For a noise reducer that cyclically reduces noise included in the delay circuit, a switch that selectively supplies an input video signal or an addition output of the addition circuit to the delay circuit between the addition circuit and the delay circuit. When the target noise suppression degree requires 1/3 <K ≦ 1, the changeover switch is switched to the addition output selection side, and the target noise suppression degree is set to 0.
When ≤K≤1 / 3, the coefficient K is forcibly set to approximately 1
/ 2, and switch the switch to the input video signal selection side so that the noise reducer functions as a noise canceller that performs acyclic noise reduction processing. By switching the changeover switch according to the value of the required coefficient K and selecting one of the cyclic addition and the non-recursive addition, a single device can perform a dual role of a noise reducer and a noise canceller. When used as a noise canceler, the image quality may be degraded due to afterimages, or when used as a noise reducer, the noise suppression must accept K ≤ 1/3 below 3 dB. By switching to a non-recursive configuration to function, For example, a noise reducer that can obtain a high noise suppression degree for a video signal that is originally contaminated with noise, for example, as a noise canceler for a video signal of originally high quality. It is possible to selectively use such as, for example, and to provide excellent effects such as fine noise suppression according to the signal quality of the input video signal.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of the noise suppression device of the present invention, FIG. 2 is an SN ratio diagram showing the degree of noise suppression of the noise suppression device shown in FIG. 1, and FIG. FIG. 2 is a circuit configuration diagram illustrating an example of a conventional noise suppression device. 2,5,13 ... coefficient circuit 3 ... addition circuit 4 ... delay circuit 11 ... noise suppression device 12 ... noise suppression mode switching circuit 13 ... switch

Claims (1)

(57) [Claims] 1. An input video signal multiplied by a coefficient (1-K) of 1 or less, and a coefficient K of 1 or less after delaying an output video signal by approximately one field period or one frame period in a delay circuit.
And a delay output video signal obtained by multiplying the input video signal by an adder circuit to obtain the output video signal, and variably set the coefficient (1-K) and K in accordance with a target noise suppression degree. A noise reducer for cyclically reducing noise included in the input signal and the delay circuit; and selectively supplying the input video signal or the addition output of the addition circuit to the delay circuit. When the target noise suppression degree requires 1/3 <K ≦ 1, the changeover switch is switched to the addition output selection side, and the target noise suppression degree is 0 ≦ K ≦ 1/3. When requested, the coefficient K is forcibly switched to about 1/2, the switch is switched to the input video signal selection side, and the noise reducer performs a non-recursive noise reduction process. Noise suppression apparatus characterized by comprising a noise suppression mode switching circuit to function as a canceller.