JPH0346466A - Noise reduction circuit - Google Patents

Abstract

PURPOSE:To send an excellent signal without deteriorating resolution by reducing shot noise remarkable depending on kinds of films by means of a band pass filter means when a film is picked up and it is used as a source of a TV signal. CONSTITUTION:An original signal, a signal through a 1H delay circuit 7-1 and a signal through 1H delay circuits 7-1, 7-2 are fed to a multiplier circuit 7-3 in a vertical direction band pass filter 71 and calculated in the circuit 7-3. In this case, the signal through the circuit 7-1 and signals on 3 scanning lines on and above/below the signal are multiplied. Then signals through vertical and horizontal band pass filters 71, 72 are applied to a time direction averaging circuit 9 to obtain a signal averaged with a signal of, e.g. one preceding frame and the result is inputted to an adder circuit 10. Then the addition is applied in a way of applying some correction to the output of a subtraction circuit 8. The signal through the circuit 9 is subject to noise reduction in the band.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a circuit for effectively reducing grain noise when imaging photographic film with a TV camera.

[Prior Art] As a signal source at a TV broadcasting station, there are an imaging signal from a camera and a signal obtained by applying photographic film to an imaging device. The latter are called film programs, and together with VTR programs, they make up the majority of TV programs. When a program made using photographic film, particularly positive film, is imaged and transmitted, the graininess of the film is poor, causing image deterioration on the receiving side. Therefore, it is necessary to reduce grainy noise in positive films, but conventionally, instead of a dedicated circuit for this purpose, a normal noise reduction circuit as shown in FIG. 4 has been used. In Fig. 4, 1 is a terminal for separating and inputting only the luminance signal among the film camera output signals, 2 is a high-pass filter, 3 is a low-pass filter, 4 is a slice circuit, and 5 is a superposition circuit. , 6 indicates a luminance signal output terminal. In FIG. 4, only the luminance signal is inputted and separated into a high frequency signal and a low frequency signal by a filter 2.3. Since noticeable noise is concentrated in the low-level part of the high-frequency signal, it is removed by the slice circuit 4 and adjusted to the zero-order level, and then superimposed with the output signal of the low-pass filter 3 by the superimposition circuit 5. The signal from which noise has been removed is output from the terminal 6.

[Problems to be Solved by the Invention] The noise reduction circuit shown in FIG. 4 has a sufficient effect on images taken by a TV camera, but is not sufficient for image signals taken from film. Ta. This is because the circuit shown in FIG. 4 performs amplitude processing in the time axis direction, and high frequency information is lost due to image blurring of the image pickup device. Therefore, depending on the circuit shown in FIG. 4, an image with reduced resolution can only be obtained, which is a drawback especially when high fidelity is required as in recent years.

SUMMARY OF THE INVENTION An object of the present invention is to improve the above-mentioned drawbacks and to provide a noise reduction circuit that processes signals obtained by imaging a positive film so that a good signal can be transmitted without deteriorating the resolution.

[Means for Solving the Problems] FIG. 1 is a diagram showing the basic configuration of the present invention. In Fig. 1, ■ is a luminance signal input terminal, 6 is a luminance-signal output terminal, 7 is a diagonal mid-range bandpass filter, 8 is a subtraction circuit, and 9
indicates a time direction averaging circuit, and lO indicates an addition circuit.

The present invention has the following configuration. That is, a diagonal mid-band bandpass filter 7 to which a luminance signal obtained from a photographic film camera serving as a TV signal source is applied, and a subtraction circuit 8 that subtracts the output signal of the bandpass filter 7 from the luminance signal. , a temporal averaging circuit 9 to which the output signal of the bandpass filter 7 is applied, and an adding circuit 10 for adding the output of the subtracting circuit 8 and the output of the temporal averaging circuit 9, The object is to obtain a luminance signal with reduced grain noise at the output of the circuit 10.

[Operation] For one frame of the film to be imaged, the state of granular noise is measured using an image signal measuring device (for example, an oscilloscope). In the frequency domain diagram shown in Figure 2, the noise is usually most noticeable in the intermediate band (not hatched) for both horizontal frequency (H) and vertical frequency (V), and that band is diagonally divided into the intermediate band. That's what it means. In order to extract only that band signal, the center frequency of the band pass filter 7 is selected to be that frequency, and then the luminance signal of the film image signal is inputted from the terminal 1. Since the output signal that has passed through the band-pass filter 7 is the unhatched portion of the input luminance signal, it is applied to the subtraction circuit 8 so as to subtract it from the input luminance signal. Therefore, the subtraction circuit 8
The output signal is a partial signal subjected to hunting.

Note that for I and Q signals other than the luminance signal, it is only necessary to give a predetermined delay such as an IH waiting time.The output signal of the bandpass filter is also applied to the time direction averaging circuit 9. Here, since a signal is obtained by averaging the signal state one frame before and the current signal, a signal with reduced granular noise is obtained for the signal in the non-hatched portion shown in FIG. 2. Next, in the adding circuit 10, the output signal of the subtracting circuit 8 and the output of the temporal averaging circuit 9 are added, and a luminance signal with reduced noise in the non-hunted portion of FIG. 2 is obtained at the output terminal 6. I can do it.

[Example] FIG. 3 is a configuration diagram showing an embodiment of the present invention.

In FIG. 3, 71 is a vertical band pass filter;
2 indicates a horizontal band-pass filter, and 71 and 72 are combined to form a diagonal mid-range band-pass filter. 7-1.7-2 is an IH delay circuit, 7-3 are signal multiplication circuits, and 7-4 is a delay circuit with a time approximately equal to the delay time of the horizontal band-pass filter.
9-1, 9-4 is an adder circuit, 9-2 is a coefficient unit, 9-3 is a frame memory, and 11 is a delay circuit, the delay time of which is approximately the same as the delay time in the time direction averaging circuit 9. Shows what is set equal.

In FIG. 3, the vertical band-pass filter 71 separates the original signal, the signal passed through the IH delay circuit 7-1, and the IH delay circuit? -1, 7-2 and the multiplier circuit 7-3.
At this time, the signal passed through the IH delay circuit 7-1 is multiplied by the signals of the three scanning lines above and below the IH delay circuit 7-1. For example, the center frequency of the obtained bandpass filter is 525/
Set 4 CP H. Here, CPH indicates the number of cycles in which black and white patterns repeatedly exist within the vertical size (height H) of the screen. If the center frequency of the filter 71 is to be changed, it is sufficient to add the two upper and lower signals of the horizontal scanning line one field before to the signal multiplier circuit 7-3 and change the multiplier.

Next, the center frequency of the horizontal band-pass filter 72 is selected to be, for example, 1.5 MHz for a 16 m positive film. The signal passing situation at the output of the horizontal band-pass filter 72 is as shown in the vicinity of the filter, and the unhatched portion is the frequency range in which the signal passes. That is, because of the band pass filters 71 and 72 in each of the vertical and horizontal directions, signals in a portion without hunting are passed through. Next, in the subtraction circuit 8, the signals passed through the filters 71 and 72 are subtracted from the original luminance signal from the terminal 1. Therefore, the signal that has passed through the subtraction circuit 8 loses the intermediate band.
As shown in the vicinity, this is a signal in which the hunting part is missing.

Next, the signals that have passed through the filters 71 and 72 are applied to the time direction averaging circuit 9 to obtain a signal that is averaged with the state of the signal one frame before, for example. That is, the frame memory 9-
3, the signal is delayed by one film frame, and the addition circuit (actually operates as a subtraction circuit) 9-4
In , the current signal is operated on. The signal is multiplied by a predetermined coefficient by the coefficient unit 9-2, and then the adder circuit 9-2
After performing subtraction processing using 1, the signal is input to the next addition circuit 10. Addition processing is then performed with some correction added to the output of the subtraction circuit 8. The signal that has passed through the temporal averaging circuit 9 has reduced noise within its band.

Although an example has been described in which the band-pass filters are connected in cascade in the vertical and horizontal directions, the same effect can be obtained even if this order is changed.

[Effects of the Invention] Thus, according to the present invention, especially when film is imaged and used as a TV signal source, the grain noise that is noticeable depending on the type of film is reduced by the band-pass filter means, so that the resolution can be improved. There is little deterioration, and it is possible to send out a good signal on the image sending side. Since the processing is performed by a band-pass filter means, it is possible to easily deal with different types of films being used.

[Brief explanation of drawings]

Figure 1 is a diagram showing the principle configuration of the present invention, Figure 2 is an explanatory diagram of the operation of Figure 1, Figure 3 is a diagram showing the configuration of an embodiment of the present invention, and Figure 4 is a diagram showing a conventional noise reduction circuit. FIG. 1-...-Luminance signal input terminal 6...Luminance signal output terminal 7--...Diagonal mid-pass filter 8--Subtraction circuit 9...Temporal direction averaging circuit■ 1. Addition circuit

Claims (1)

[Scope of Claims] A diagonal mid-range bandpass filter to which a luminance signal obtained from a photographic film camera serving as a TV signal source is applied; and a subtractor for subtracting the output signal of the bandpass filter from the luminance signal. a time-direction averaging circuit to which an output signal of the band-pass filter is applied; and an addition circuit that adds the output of the subtraction circuit and the output of the time-direction averaging circuit; A noise reduction circuit characterized by obtaining a luminance signal with reduced noise.