JPS62136175A - Noise reducing device - Google Patents

Abstract

PURPOSE:To reduce the unnatural property of noises caused by the switching of still pictures, by controlling the coefficient of a constant multiplier by means of both of the difference signal of a delayed video signal which is at least one period earlier than present and the current input video signal and a delayed difference signal which is obtained by delaying the said difference signal at least one period. CONSTITUTION:When video signals are changed from an animation to a still picture, a ROM 8 makes the coefficient to be given to a difference signal larger so as to increase S/N improvement, since the difference between the one-frame preceding video signal and current video signal in the case of a still picture. However, a large value cannot be taken immediately, because the ROM 8 is controlled by an one-frame preceding difference signal which is the output of a frame memory 7 and the one-frame preceding difference signal is larger. When the still picture continues to the next frame, the S/N improvement is improved by making the coefficient to be given to the difference signal at the ROM 8 larger by a time constant which is determined by the coefficient of another ROM 9. When such operations are made, a change in S/N which is smooth to a picture can be obtained when the animation is switched to the still picture.

Description

【発明の詳細な説明】 産業上の利用分野 本発明は、テレビジョン映像信号に於ける雑音を低減す
る雑音低減装置に関するものである。DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a noise reduction device for reducing noise in television video signals.

従来の技術 テレビジョン映像信号はフレーム周期で画像情報が繰り
返す信号であり、そのフレーム間の自己相関性は非常に
強いといえる０しかし、映像信号に含まれる雑音成分は
一般にその自己相関性がほとんど無いことから、映像信
号を時間的にフレーム周期ごとに平均化すると、信号成
分のエネルギーはほとんど変化しないで、雑音成分のエ
ネルギーのみが低くなる。この雑音低減装置の一構成を
第２図に示す。１は入力端子、３は減算器、４は加算器
、１２は入力に係数として定数に−ｉ与えるＲＯＭ（リ
ードオンリーメモリ）、５は１フレームの遅延をおこな
うフレームメモリ１１は出力端子である。入力端子１よ
り入力された現在の入力映像信号と、１フレームメモリ
６の出力信号である現在より１フレーム過去の信号とが
減算器３で減算されて差信号が求められる。差信号はＲ
ＯＭ１２によって係数を与えられ、現在の入力信号に加
算器４で加算される。加算器の出力が１フレームメモリ
５に入力されると同時に出力端子１ｏから雑音の低減し
た信号として出力される０この回路は入力映像信号をフ
レーム周期ごとに時間的に平均化する回路で、ＲＯＭ１
２において、差信号に与える係数Ｋが映像信号の時間的
な平均化の重みであり、Ｓ／Ｎ改善度を決定する。入力
映像信号が完全な静止画像とすると、この回路のＳ／Ｎ
改善度は、 Ｓ／Ｎ改善度＝１ｏ　６ｏｇ（１＋Ｋ）／（１−Ｋ）（
ｄＢ）となる。以上は静止画像の場合であり、一般に映
像信号はフレーム間で変化する部分すなわち動画部分を
含んでいるので次の様な問題を生ずる０動画部分を含む
映像信号をこの回路に通すと動画の部分は前フレームと
相関が無いので残像効果が現れる。その時定数は、 Ｔ　＝　−１／　（ｌｎＫ）　Ｘ　１．’ｓｏ　（ｓｅ
ａ）となる。以上のようにこの回路においては、Ｋを大
きくすることでＳ／Ｎ改善度が良好となるが残像効果も
増大する。その対策として、ＲＯＭ４で差信号に与える
係数Ｋを第３図の様に、差信号の値で変化させる。差信
号は前述の様に、１フレーム過去の信号と現在の信号と
の差であり、フレーム間自己相関の無い雑音成分と、信
号成分のフレーム間で変化した差分とを含む。一般に、
前者は静止画部分で得られ、その値は小さく、後者は動
画部分で得られ、その値は大きい。この差信号の値が小
さいときＫの値を犬にして、映像信号の時間的な平均化
を充分に行いＳ／Ｎ改善度を上げ、差信号の値が大きい
ときには、Ｘの値を零とし、入力信号の変化をそのまま
出力する（ＴＶ学会誌３３・４（１９７９）２９６〜３
００Ｐ参照）。Conventional technology A television video signal is a signal in which image information repeats at a frame period, and the autocorrelation between frames can be said to be very strong.However, noise components included in video signals generally have very little autocorrelation. Therefore, when the video signal is temporally averaged for each frame period, the energy of the signal component hardly changes, and only the energy of the noise component decreases. One configuration of this noise reduction device is shown in FIG. 2. 1 is an input terminal, 3 is a subtracter, 4 is an adder, 12 is a ROM (read only memory) which provides a constant -i as a coefficient to the input, and 5 is a frame memory 11 which delays one frame as an output terminal. A subtracter 3 subtracts the current input video signal input from the input terminal 1 and the output signal of the one frame memory 6, which is one frame past the current signal, to obtain a difference signal. The difference signal is R
A coefficient is provided by OM 12 and added to the current input signal in adder 4. The output of the adder is input to the 1-frame memory 5, and at the same time, it is output from the output terminal 1o as a signal with reduced noise.0 This circuit temporally averages the input video signal for each frame period.
In step 2, the coefficient K given to the difference signal is a weight for temporal averaging of the video signal, and determines the degree of S/N improvement. If the input video signal is a completely still image, the S/N of this circuit is
The improvement degree is S/N improvement degree = 1o 6og (1 + K) / (1-K) (
dB). The above is the case of a still image, and generally a video signal includes a part that changes between frames, that is, a moving part, so if a video signal that includes a moving part is passed through this circuit, the following problem will occur. Since there is no correlation with the previous frame, an afterimage effect appears. Its time constant is T = -1/(lnK) x 1. 'so (se
a). As described above, in this circuit, increasing K improves the degree of S/N improvement, but also increases the afterimage effect. As a countermeasure, the coefficient K given to the difference signal in the ROM 4 is changed according to the value of the difference signal, as shown in FIG. As described above, the difference signal is the difference between the signal of one frame past and the current signal, and includes a noise component with no interframe autocorrelation and a difference in signal components that has changed between frames. in general,
The former is obtained in the still image portion and its value is small, and the latter is obtained in the moving image portion and its value is large. When the value of this difference signal is small, the value of K is set to dog, and the video signal is sufficiently averaged over time to increase the S/N improvement degree, and when the value of the difference signal is large, the value of X is set to zero. , outputs changes in the input signal as they are (TV Society Journal 33, 4 (1979) 296-3
(See 00P).

発明が解決しようとする問題点 しかしながら上記のような構成では、動いている物体が
停止して静止状態になる時や、その逆の場合で、制止し
た物体が動き出す時に、動画部分と静止画部分では前述
の様にＳ／Ｎ改善度が違うため、急激なＳ／Ｎの変化を
ともない画像に不自然さを生ずる０ 本発明はかかる点に鑑み動画、静止画の切り換えによる
雑音の不自然さを減少する雑音低減装置を提供すること
を目的とする０ 問題点を解決するための手段 本発明は、現在より少なくとも１周期過去の遅延映像信
号と現在の入力映像信号との差信号を得る減算器と、前
記差信号を少なくとも１周期遅延して遅延差信号を得る
遅延素子と、前記差信号に係数を与える係数器と、入力
映像信号と係数を与えた差信号を加算する加算器と、加
算器の出力を遅延して前記遅延映像信号を得る遅延素子
とを備え、差信号と遅延差信号との両者で、係数器の係
数を制御する手段を備えたことを特徴とする雑音低減装
置である。Problems to be Solved by the Invention However, with the above configuration, when a moving object stops and becomes stationary, or vice versa, when a stopped object starts moving, the moving image part and the still image part are separated. As mentioned above, since the degree of S/N improvement is different, sudden changes in S/N cause unnaturalness in images. SUMMARY OF THE INVENTION It is an object of the present invention to provide a noise reduction device that reduces noise by a subtraction method that obtains a difference signal between a delayed video signal that is at least one cycle past the current input video signal and a current input video signal. a delay element that delays the difference signal by at least one period to obtain a delayed difference signal; a coefficient unit that applies a coefficient to the difference signal; and an adder that adds the input video signal and the difference signal to which the coefficient has been applied; A noise reduction device comprising: a delay element that delays the output of an adder to obtain the delayed video signal; and means for controlling coefficients of a coefficient multiplier using both a difference signal and a delayed difference signal. It is.

作用 本発明は、前記した構成により、動画から制止面への切
り換わり時のＳ／Ｎ改善度を徐々に増大することによっ
て、動画から静止画へのＳ／Ｈの変化をなめらかにして
、画像の不自然さを取り除くものである。静止画から動
画への切り換わりにおいては、徐々にＳ／Ｎ改善度を減
少した場合Ｓ／Ｎの変化はなめらかになるが、残像効果
が目立ち、画像の不自然さを取り除くとは一概に言えな
いＯ 実施例 この発明の一実施例について、第１図を参照しながら説
明する。入力端子１に入力される映像信号はフレーム周
期を持つ映像信号とする。入力端子１に入力された映像
信号は、ム／Ｄ変換器２でデジタル信号に変換され、加
算器４．減算器３に入力される。減算器３は、入力映像
信号から、フレームメモリ６の出力の１フレーム過去の
映像信号を減算し、差信号として、ＲＯＭＢとピット数
低減器６とに出力する。ビット数低減器は、差信号のピ
ット数を低減し、加算器１０に出力する。Effect of the Invention With the above-described configuration, the present invention gradually increases the degree of S/N improvement when switching from a moving image to a stopping surface, thereby smoothing the change in S/H from a moving image to a still image, and improving the image quality. It removes the unnaturalness of When switching from a still image to a video, if the S/N improvement rate is gradually reduced, the change in S/N will be smoother, but the afterimage effect will be noticeable and it cannot be said that the unnaturalness of the image will be removed. Embodiment One embodiment of the present invention will be described with reference to FIG. The video signal input to the input terminal 1 is assumed to have a frame period. The video signal input to the input terminal 1 is converted into a digital signal by the MU/D converter 2, and then sent to the adder 4. It is input to the subtracter 3. The subtracter 3 subtracts the video signal of one frame past, which is output from the frame memory 6, from the input video signal, and outputs the result to the ROMB and the pit number reducer 6 as a difference signal. The bit number reducer reduces the number of pits of the difference signal and outputs it to the adder 10.

加算器１０は′、ピット数が低減した差信号と、ＲＯＭ
９が係数を与えた１フレーム過去のピット数を低減した
差信号とを加算し、フレームメモリ７に出力する。ＲＯ
Ｍ８は入力した差信号に、フレームメモリ７の出力であ
る１フレーム過去の差信号と、自身の振幅とに従った係
数を与えて、加算器４に出力する。加算器４は、係数を
与えられた差信号と入力信号を加算して、フレームメモ
リ６と、Ｄ／Ａ変換器１０に出力する。フレームメモリ
５は、入力された信号を１フレーム遅延して減算器３に
出力する。Ｄ／人変換器は、加算器４の出力をアナログ
信号に変換し、出力端子１１に出力する。以上で出力端
子１１に、雑音を低減した信号を得る。The adder 10 inputs the difference signal with a reduced number of pits and the ROM
9 gives a coefficient and a difference signal in which the number of pits of one frame past is reduced is added and outputted to the frame memory 7. R.O.
M8 gives the input difference signal a coefficient according to the difference signal of one frame past, which is the output of the frame memory 7, and its own amplitude, and outputs it to the adder 4. The adder 4 adds the difference signal given the coefficient and the input signal and outputs the result to the frame memory 6 and the D/A converter 10. The frame memory 5 delays the input signal by one frame and outputs the delayed signal to the subtracter 3. The D/person converter converts the output of the adder 4 into an analog signal and outputs it to the output terminal 11. In the above manner, a signal with reduced noise is obtained at the output terminal 11.

本発明の要点である映像信号が動画から静止画に変化し
た時の本実施例の雑音低減装置の動作を説明する。The operation of the noise reduction device of this embodiment when the video signal changes from a moving image to a still image, which is the main point of the present invention, will be explained.

静止画では１フレーム過去の映像信号と、現在の映像信
号との差は小さいので、減算器３で得られる差信号は小
さく、従来例と同じ（、ＲＯＭＢで差信号に与える係数
を第５図の様に犬にして、Ｓ／Ｎ改善度を上げる。しか
し、ＲＯＭＢは、フレームメモリ７の出力である１フレ
ーム過去の差信号で制御されており、今１フレーム過去
では、入力映像信号が動画であったとしているので、１
フレーム過去の差信号は犬であり、第４図の様に’　　
　ＲＯＭａで差信号に与える係数は差信号が小さくとも
１フレーム過去の差信号が犬であるので、すぐには大き
な値をとらない。次のフレームで、静止画が続けば、Ｒ
ＯＭ９の係数で決まる時定数によって、徐々にＲＯＭ５
で差信号に与える係数を上げて、Ｓ／Ｈの改善度を上げ
ていく。この動作によって、動画から静止画への切り換
わり時で、画面になめらかなＳ／Ｎの変化が得られる。In a still image, the difference between the video signal of one frame past and the current video signal is small, so the difference signal obtained by the subtracter 3 is small, and is the same as the conventional example (Fig. 5 shows the coefficient given to the difference signal by ROMB). However, the ROMB is controlled by the difference signal of one frame past, which is the output of the frame memory 7, and the input video signal is currently one frame past. Since it is assumed that 1
The difference signal in the past frame is a dog, as shown in Figure 4.
Even if the difference signal is small, the coefficient given to the difference signal by ROMa does not take a large value immediately because the difference signal of one frame past is a dog. If the still image continues in the next frame, R
ROM5 is gradually increased by the time constant determined by the coefficient of OM9.
By increasing the coefficient given to the difference signal, the degree of improvement in S/H is increased. This operation provides a smooth S/N change on the screen when switching from a moving image to a still image.

静止画から動画への切り換わりでは、１フレーム前の差
信号が小さくても、動画であるため差信号が太き（、Ｒ
ＯＭＢで与える係数をほとんど零としているので、従来
の雑音低減装置と変わらない。本実施例では、残像効果
を考慮して、静止画から動画への切り換わりのＳ／Ｎ変
化をなめらかにすることはおこなわない。When switching from a still image to a video, even if the difference signal from one frame before is small, the difference signal is thick because it is a video (, R
Since the coefficients given by OMB are almost zero, this is no different from conventional noise reduction devices. In this embodiment, in consideration of the afterimage effect, smoothing of the S/N change when switching from a still image to a moving image is not performed.

フレームメモリ？、ＲＯＭ９．加算器１ｏは巡回型のフ
レームメモリを構成しており、１フレ一ム以上過去の差
信号の情報をも持つ様にしている。Frame memory? , ROM9. The adder 1o constitutes a cyclic frame memory, and is configured to have information on past difference signals of one or more frames.

ピット数低減器６では、差信号のピット数を減らす。こ
れは、フレームメモリ７、ＲＯＭ９．加算器１０の容量
を減らす効果と、ＲＯＭ５での係数の制御は、多ビット
は必要ないためである。−例として、Ａ／Ｄ変換器が８
ビツトであれば、ビットを減らした差信号は４ピツトで
問題ない。また、１フレーム過去の差信号でのＲＯＭＢ
の制御は、主に動画、静止画の区別ができればよく、ピ
ット数低減器に第６図の様な、最大値を制限する動作を
持たす。A pit number reducer 6 reduces the number of pits in the difference signal. This includes frame memory 7, ROM 9. The effect of reducing the capacity of the adder 10 and controlling the coefficients in the ROM 5 is because a large number of bits is not required. - As an example, if the A/D converter is 8
If it is a bit, the difference signal with fewer bits has no problem with 4 pits. In addition, ROMB with the difference signal of one frame past
The control mainly needs to be able to distinguish between moving images and still images, and the pit number reducer has an operation to limit the maximum value as shown in FIG.

加算器１０での演算結果にも最大値を持たし、動画から
制止面への切り換わり時の時定数の最大値を制御する。The calculation result of the adder 10 also has a maximum value, and controls the maximum value of the time constant when switching from a moving image to a stopping surface.

本実施例では、動画から静止画への切り換わシだけを制
御したが、静止画から動画への切り換わり時の制御も同
様にしておこなえる。In this embodiment, only the switching from a moving image to a still image is controlled, but the switching from a still image to a moving image can also be controlled in the same way.

発明の詳細 な説明したように、本発明によれば、簡易な構成で画面
の動画から静止画への切り換わり時に起こるＳ／Ｎの変
化をなめらかにして、画面の不自然さを取り除くことが
でき、その実用的効果は太きい。As described in detail, according to the present invention, it is possible to smooth the change in S/N that occurs when the screen changes from a moving image to a still image and eliminate unnaturalness on the screen with a simple configuration. It can be done, and its practical effects are significant.

【図面の簡単な説明】[Brief explanation of drawings]

第１図は本発明の一実施例における雑音低減装置のブロ
ック図、第２図は同装置の入力差信号−係数特性図、第
３図は同装置の入力差信号−ピット数低減差信号の特性
図、第４図は従来の雑音低減装置のブロック図、第６図
は従来の雑音低減装置の入力差信号−係数特性図である
０ ８．９・・・・・・ＲＯＭ、ａ・・・・・・ビット数低
減器、１ｏ・・・・・・加ＪＩ器％　７・・・・・・フ
レームメモリ０代理人の氏名　弁理士　中　尾　敏　男
　ほか１名第１図 第２図 第３図FIG. 1 is a block diagram of a noise reduction device according to an embodiment of the present invention, FIG. 2 is an input difference signal-coefficient characteristic diagram of the same device, and FIG. 3 is a diagram of input difference signal-pit number reduction difference signal of the same device. FIG. 4 is a block diagram of a conventional noise reduction device, and FIG. 6 is an input difference signal-coefficient characteristic diagram of a conventional noise reduction device. ...Bit number reducer, 1o...Additional JI device% 7...Frame memory 0 Name of agent Patent attorney Toshio Nakao and 1 other person Figure 1 Figure 2 Figure 3

Claims (1)

【特許請求の範囲】[Claims] 周期を持つ映像信号を入力映像信号とし、現在より少な
くとも１周期過去の遅延映像信号と現在の入力信号との
差信号を得る減算器と、前記差信号を少なくとも１周期
遅延して、遅延差信号を得る少なくともひとつの遅延素
子と、前記差信号に係数を与える係数器と、現在の入力
映像信号と係数を与えられた前記差信号とを加算する加
算器と、加算器の出力を少なくとも１周期遅延して、前
記遅延映像信号を得る遅延素子とを備え、前記差信号と
、前記遅延差信号との両者によって、前記係数を制御す
る手段を備えたことを特徴とする雑音低減装置。a subtracter that takes a video signal with a period as an input video signal and obtains a difference signal between a delayed video signal at least one cycle past the current input signal and a current input signal; and a subtracter that delays the difference signal by at least one cycle to produce a delayed difference signal. at least one delay element that obtains a coefficient, a coefficient unit that provides a coefficient to the difference signal, an adder that adds the current input video signal and the difference signal that has been given the coefficient, and an adder that adds the output of the adder for at least one period. 1. A noise reduction apparatus, comprising: a delay element that delays and obtains the delayed video signal; and means for controlling the coefficients using both the difference signal and the delayed difference signal.