JP2000134510A - Circuit for removing noise of video signal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain high S/N even in the case of a weak electric field by detecting the electric field strength of an input video signal through the use of a signal which is included in the vertical synchronizing period or equalizing period of the input video signal and outputting it to a motion detecting means. SOLUTION: A frame memory 4 inputs a video signal output (c) outputted from an adder 3 and outputs a memory output (d) after one frame delay. The motion detecting circuit 5 detects a difference between framed by pixel unit through the use of a video signal input (a) and the memory output (d), judges whether the pixel is an animation or a still image and outputs a cyclic coefficient control signal (f) to multipliers 1 and 2. An electric field strength detecting circuit 6 detects the signal level of the input video signal within a detection period which is provided in the vertical synchronizing period or vertical equalizing period of the inputted video signal, judges the electric field strength of the input signal from the detection result and outputs an electric field strength detection output (g) for controlling a cyclic coefficient.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise removing circuit for removing noise from a video signal of a television receiver.

[0002]

2. Description of the Related Art In recent years, a television receiver has a large screen.
With an increase in image quality, a noise removing circuit that effectively removes noise generated on a screen is regarded as important. There are many methods for this noise elimination circuit. For example, as a frame recursive noise elimination circuit using the correlation between frames of a video signal, the Journal of the Institute of Television Engineers of Japan, Vol. 4
(1979).

An example of a conventional frame recursive noise elimination circuit will be described below with reference to the drawings. FIG. 6 is a block diagram of a conventional frame recursive noise elimination circuit.

In FIG. 6, reference numeral 1 denotes a multiplier, which attenuates an input video signal a by (1−K) times when a cyclic coefficient of a frame cycle is K. Symbol 2 is also a multiplier, and the memory output d output from the frame memory 4 is represented by K
Multiply. Reference numeral 3 denotes an adder that adds the multiplied output b output from the multiplier 1 and the multiplied output e output from the multiplier 2 to output a video signal output c from which noise has been removed. Reference numeral 4 denotes a frame memory which receives the video signal output c output from the adder 3 and outputs a memory output d after a delay of one frame. Reference numeral 5 denotes a motion detection circuit which detects a difference between frames on a pixel-by-pixel basis using the video signal input a and the memory output d to determine whether the pixel is a part of a moving image or a part of a still image. Then, a cyclic coefficient control signal f is output to the multipliers 1 and 2.

[0005] The operation of the frame cyclic noise elimination circuit configured as described above will be described below. Generally, the video signal has a strong correlation of video information between frames, and the noise component is a random signal with little correlation.If the video signal is averaged for each frame period, the video component of the input signal changes little. Instead, only the noise component can be reduced. In FIG. 6, a luminance signal, a color difference signal, or an RGB
A signal or the like is input, attenuated by (1−K) times by the multiplier 1 and input to the adder 3.

On the other hand, the noise-removed video signal output c is delayed by one frame in the frame memory 4 and a memory output d is output from the frame memory 4 as a video signal of the previous frame. After that, the multiplier 2 attenuates K times,
It is input to the adder 3. In the adder 3, the above (1-
K) The uncorrelated noise is removed from the frame by adding the multiplied video signal and the video signal of the previous frame multiplied by K,
The video signal output c is output. In this way, the frame is of a cyclic type in which the information of the previous frame and the information of the current frame are processed.

Here, when the input video signal is a still image, since the frame correlation is large, the noise is Δ ((1-
K) / (1 + K)). The theoretical degree of S / N improvement by this frame recursive noise elimination circuit is 10
g ((1 + K) / (1-K)). Here, the value of K is 0 <K <1.

However, a video signal generally includes a moving image portion in addition to a still image, and a moving image has an extremely small frame correlation. When a video signal including such a moving image is processed by a frame cyclic circuit as shown in FIG. 6, an afterimage like tailing occurs on the screen. Here, if the cyclic coefficient K is increased, the noise removal effect increases but the afterimage increases. Conversely, if K is reduced, the afterimage becomes less noticeable but the noise removal effect decreases. For this reason, since a residual image does not occur in a still image portion, it is necessary to increase the value of the cyclic coefficient K to increase the noise removal effect, and to reduce the value of K in the moving image portion to suppress the residual image as much as possible.

Therefore, the motion detection circuit 5 of FIG. 6 calculates a difference between frames from the video signal input a and the video signal d of the previous frame in pixel units. If the difference is small, the pixel is a still image, and Is large, it is determined that the image is a moving image. The result after this determination is output to multipliers 1 and 2 as a cyclic coefficient control signal f, and controls the value of cyclic coefficient K.

In this way, by controlling the cyclic coefficient K for a still image and a moving image, it is possible to obtain an image with little afterimage and high S / N.

[0011]

However, in the above configuration, the control of the cyclic coefficient K is performed only by the detection result from the motion detection circuit 5 for determining whether the image is a still image or a moving image. There is a possibility that the noise removal operation may fail depending on the S / N ratio. For example, the electric field strength of a signal input from a television antenna to a television receiver is low, and as a result, the S /
When the N ratio is low, noise is distributed over the entire screen, which is very unsightly.

In such a case, the screen becomes easier to see if the noise removal effect is increased, even if the occurrence of some afterimages is sacrificed. However, when such a signal is input, the noise component included in the input signal is considerably large. Therefore, when the difference between the input video signal a and the previous frame video signal d is calculated by the motion detection circuit 5, it is a still image portion. Even so, the frame difference becomes large due to the influence of noise, and the image is erroneously determined to be a moving image. As a result, the value of the cyclic coefficient K becomes small, and there is a problem that sufficient noise cannot be removed.

[0013]

In order to solve the above-mentioned problems, a video signal noise elimination circuit according to the present invention is a video signal noise elimination circuit for eliminating a noise component contained in an input video signal. A frame memory for storing an output signal of the noise elimination circuit; motion detection means for detecting whether the input video signal is a moving image or a still image from the input video signal and an output signal of the frame memory; A first multiplier for multiplying the output signal of the frame memory by a coefficient of 1; a second multiplier for multiplying an output signal of the frame memory by a second coefficient; and an output of the first multiplier and the second multiplication. An adder that adds the output of the input video signal and outputs the output signal as an output signal of the noise removal circuit, and detects an electric field strength of the input video signal using a signal included in a vertical synchronization period or an equalization period of the input video signal. , Serial characterized by comprising a field strength detection means for outputting a movement detector.

According to the present invention, a low residual image and a high S / N ratio noise elimination process based on the original motion detection are performed at the time of a strong electric field, and the noise of a video signal at which a higher S / N ratio can be obtained at a weak electric field than before. An elimination circuit can be provided.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a block diagram showing a configuration of a video signal noise elimination circuit according to a first embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a multiplier, which attenuates an input video signal a by (1−K) times when a cyclic coefficient of a frame cycle is K. A multiplier 2 also multiplies the memory output d output from the frame memory 4 by K. Reference numeral 3 denotes an adder that adds the multiplied output b output from the multiplier 1 and the multiplied output e output from the multiplier 2 to output a video signal output c from which noise has been removed. Reference numeral 4 denotes a frame memory which receives the video signal output c output from the adder 3 and outputs a memory output d after a delay of one frame.

Reference numeral 5 denotes a motion detection circuit which detects a difference between frames on a pixel-by-pixel basis using the video signal input a and the memory output d to determine whether the pixel is a moving image or a still image. And outputs a cyclic coefficient control signal f to the multipliers 1 and 2. Reference numeral 6 denotes an electric field strength detection circuit which detects a signal level of an input video signal within a detection period provided in a vertical synchronization period and a vertical equalization period of an input video signal, and detects an electric field of the input signal from the detection result. The strength is determined, and an electric field strength detection output g for controlling the cyclic coefficient is output.

The operation of the video signal noise elimination circuit configured as described above will be described below with reference to the drawings. FIG. 2 is an enlarged view of the vertical blanking period of the NTSC signal. Here, in the vertical synchronization period and the equalization period, a cutting pulse and an equalization pulse are inserted, but there is basically no signal component in a portion other than those pulses. However, at the time of a weak electric field, noise is mixed in the entire video signal, so that a noise component also appears in this portion. Therefore, the electric field strength of the input video signal can be detected by detecting the signal level of a portion other than the cut pulse and the equalization pulse.

FIG. 3 is a diagram for explaining this electric field strength detection method. In the vertical synchronization period and the equalization period of the input video signal, a detection period is provided at an arbitrary position in a portion other than the cutting pulse and the equalization pulse, and the electric field strength detection circuit 6 in FIG. The maximum value of the signal level of the video signal is detected. In the electric field strength detection circuit 6, the larger the maximum level, the larger the noise component, and it is determined that the electric field strength of the input video signal is weak. Conversely, when the maximum level is small, it is determined that the noise component is small and the electric field strength of the input video signal is strong.

As described above, according to this embodiment, the electric field strength of the input video signal is determined by detecting the maximum value of the input signal level within an arbitrary detection period of the vertical blanking period. , The cyclic coefficient K is adaptively controlled, whereby a frame cyclic noise removal process capable of effectively removing noise even in a weak electric field can be performed.

(Embodiment 2) FIG. 4 is a diagram showing another detection method of the electric field strength detection circuit according to the second embodiment of the present invention. In the first embodiment, the maximum value of the signal level of the video signal within an arbitrary detection period is detected. However, according to this method, if there is a noise with a fast rising that instantaneously peaks, If the response of the maximum value detection is poor, this peak cannot be detected, which may cause erroneous detection of the electric field intensity.

Therefore, in the second embodiment, as shown in FIG. 4, the signal levels of all the pixels in the detection period are added, and the sum is divided by the number of pixels to calculate the average value of the signal levels. The electric field strength is calculated from the average value. This configuration enables stable electric field strength detection regardless of the responsiveness of the circuit. By using this electric field strength detection result to adaptively control the cyclic coefficient K, an effect can be obtained even in a weak electric field. It is possible to perform frame cyclic noise elimination processing capable of effective noise elimination.

(Embodiment 3) FIG. 5 is a diagram showing another detection method of the electric field strength detection circuit according to a third embodiment of the present invention. In the second embodiment, the average value of the signal level of the video signal within an arbitrary detection period is detected.
In this method, an adder having a relatively large circuit scale is required to add all the signal levels of all the pixels in the detection period.

Therefore, in the third embodiment, as shown in FIG. 5, a circuit configuration for detecting where all the pixels in the detection period are distributed between some preset threshold values is provided. As a result, the electric field strength is calculated from the magnitude of the level in the threshold range where the distribution is the largest. With such a configuration, stable electric field strength detection can be performed with a relatively small-scale circuit, and the cyclic coefficient K is adaptively controlled using the electric field strength detection result, which is effective even in a weak electric field. It is possible to perform frame cyclic noise elimination processing capable of effective noise elimination.

In the above description, a frame recursive noise elimination circuit using a frame memory has been described. This is a field recursive noise elimination circuit using a field memory, or a line cyclic noise elimination circuit using a line memory. Similar effects can be obtained in the removing circuit.

[0026]

As described above, according to the present invention, the provision of a multiplier, an adder, a frame memory, a motion detection circuit, and an electric field intensity detection circuit provides a low afterimage and a high S by the original motion detection in a strong electric field. / N noise elimination processing, and it is possible to provide a noise reduction circuit for a video signal capable of obtaining a higher S / N ratio than before in a weak electric field.

[Brief description of the drawings]

FIG. 1 is a block diagram of a video signal noise removal circuit according to a first embodiment of the present invention.

FIG. 2 is an enlarged view of a vertical blanking period in the NTSC broadcasting system.

FIG. 3 is an operation explanatory diagram of the electric field strength detection circuit according to the first embodiment of the present invention;

FIG. 4 is an operation explanatory diagram of the electric field strength detection circuit according to the second embodiment of the present invention;

FIG. 5 is an explanatory diagram of an operation of the electric field strength detection circuit according to the third embodiment of the present invention.

FIG. 6 is a block diagram of a conventional noise removal circuit.

[Explanation of symbols]

 1 Multiplier ((1-K) times) 2 Multiplier (K times) 3 Adder 4 Frame memory 5 Motion detection circuit 6 Electric field strength detection circuit

Claims (5)

[Claims] 1. A noise reduction circuit for a video signal for removing a noise component included in an input video signal, comprising: a frame memory for storing an output signal of the noise removal circuit; and an output of the input video signal and an output of the frame memory. Motion detection means for detecting whether the input video signal is a moving image or a still image from a signal and a first coefficient for multiplying the input video signal by a first coefficient
, A second multiplier for multiplying the output signal of the frame memory by a second coefficient, and adding the output of the first multiplier and the output of the second multiplier to obtain the noise. An adder that outputs as an output signal of the removal circuit; and an electric field that detects an electric field intensity of the input video signal using a signal included in a vertical synchronization period or an equalization period of the input video signal, and outputs the electric field intensity to the motion detection unit. A noise removal circuit for a video signal, comprising: an intensity detection unit. 2. The image according to claim 1, wherein the electric field intensity detecting means detects the electric field intensity using a signal component other than a pulse included in the vertical synchronization period or the equalization period. Signal noise removal circuit. 3. The video signal noise according to claim 2, wherein said electric field intensity detecting means detects an electric field intensity based on a maximum value of a signal level in said vertical synchronization period or said equalization period. Elimination circuit. 4. The video signal noise according to claim 2, wherein said electric field intensity detecting means detects an electric field intensity based on an average value of signal levels in said vertical synchronization period or said equalization period. Elimination circuit. 5. The apparatus according to claim 1, wherein the electric field intensity detecting means detects the electric field intensity based on the number of pixels whose signal level exceeds a predetermined threshold value in the vertical synchronization period or the equalization period. Item 3. A video signal noise removing circuit according to Item 2.