JPH0385971A - Noise reduction circuit - Google Patents

Abstract

PURPOSE:To eliminate noise even without use of a post processing circuit without losing spatial sense of resolution by extracting a picture element from adjacent scanning lines in a frame, using a picture element with the largest correlation in both brightness and chromaticity so as to apply logic filter processing. CONSTITUTION:The circuit is provided with an input terminal 1 receiving an NTSC system composite signal, a 1st delay line 21 retarding the signal fed to the input terminal 1 by 262 scanning line periods, a 2nd delay line 22 receiving the output of the delay line 21 and retarding it further by 262 scanning line periods, a logic filter receiving the input and output of the delay line 21 and the output of the delay line 22 and outputting a median of the data, and an output terminal 4 extracting the output of the logic filter 3 to an external device. Then picture elements in which the phase of a color subcarrier is arranged are selected from plural adjacent fields and logical filter processing is applied to the picture element group. Thus, noise is effectively eliminated without losing the resolution considerably in the timewise direction and the spatial direction.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a noise removal circuit that removes noise in an image signal, and particularly relates to a noise removal circuit that removes impulsive noise mixed in with current NTSC signals. .

[Summary of the Invention] The present invention relates to a circuit that uses a logical filter to remove noise mixed in image data, and is a circuit that removes noise mixed in image data using a logical filter. By selecting aligned pixels and applying logical filter processing to these pixel groups, noise can be effectively removed without significantly impairing the resolution in the temporal and sky directions.

[Prior Art] Conventionally, when applying logical filter processing to a color television signal using a median filter, a maximum value (minimum value) filter, etc., for example, a composite signal is once converted into an R, G, B signal or a Y signal. .

A method is known in which the signals are decoded into 1.Q component signals, each of these signal channels C is subjected to logical filter processing, and then these signals are encoded again. Furthermore, a method (L
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[Problem to be solved by the invention] In the conventional method of once decomposing a composite signal into component signals and processing them, the same processing unit must be prepared for each channel, and the NTSC
The disadvantage is that it requires a decoder and an encoder, making it impractical for use as a receiver.

On the other hand, in the conventional method of performing logical filter processing within the field, since the color signal band is narrow, at the normal sampling rate (14,3M) H. Every two scanning lines in the vertical direction (with respect to scanning line C within a frame), and if used as is, the image quality will deteriorate significantly. Therefore, post-processing such as replacing only the parts where the difference between the output of this processing and the original image is large with the processed image is usually required, but even if this post-processing is performed, for example, the C/N of satellite broadcasting When processing relatively low-amplitude impulsive noise contained in a degraded image, a drawback has been found that it is difficult to improve the degradation at the edges of the image where the brightness and saturation change significantly.

Therefore, in view of the above points, an object of the present invention is to provide a noise removal circuit that can process an NTSC composite signal without substantially impairing spatial resolution and without requiring any post-processing. It's about doing.

[Means for Solving the Problem] A noise removal circuit according to the present invention includes a plurality of data delay means for inputting an NTSC system composite signal and sequentially delaying the signal by a predetermined scanning line period, and a plurality of data delay means. The system is equipped with a logical filter that manually processes each output of the input data and performs logical processing on the input data.

[Function] The present invention selects pixels whose color subcarriers have the same phase from among a plurality of adjacent fields in the current NTSC television signal, and performs logical filter processing on these pixel groups. , it is possible to effectively remove noise without significantly impairing resolution in the temporal and spatial directions.

[Example] Hereinafter, the present invention will be described in detail based on Examples.

FIG. 1 shows an embodiment of a noise removal circuit to which the present invention is applied. This embodiment has an input terminal 1 which inputs an NTSC composite signal, and a first delay line 21 which delays the applied signal by 262 scanning line periods.
Then, using the output of the delay line 21 as input, this is further processed by 262
a second delay line 22 that delays the scanning line period; and a delay line 21.
The output terminal 4 includes a logic filter that receives the human output of the input signal and the output of the delay line 22 and outputs an intermediate value (median) from these data, and an output terminal 4 that takes out the output of the logic filter 3 to the outside.

Next, the circuit operation of this embodiment will be explained.

In general, points where the phases of color subcarriers in the NTSC system match are shown as shown in FIG. 2 or FIG. 3. Since this is superimposed on the luminance signal of the image, if logical filter processing, which is a waveform operation, is performed in the same manner as for the luminance signal, significant image deterioration will occur.

On the other hand, as shown in Figure 3, if we include the time direction,
It can be seen that the phases of the color subcarriers at points separated by 262 scanning lines always match. Moreover, the distance between pixels in the vertical direction at this time is only one scanning line within a frame, which is very preferable in terms of processing since the effective processing area can be narrowed.

Furthermore, in logical filter processing, unlike linear filter processing in which deterioration always occurs at the edges by the shape of the processing area, the edges are preserved, so there are three field taps in the time direction. Even if it does, it will not directly lead to motion blurring of the entire screen.

Note that the logic filter 3 is not limited to the 3-tap median filter shown in FIG. 1, but may be one that outputs different rank data with different tap lengths.

[Effects of the Invention] As explained above, according to the present invention, by extracting pixels from adjacent scanning lines within a frame, luminance and
Since the logical filter processing is performed using the pixel with the greatest correlation with chromaticity, it is possible to create NTSC composites with almost no loss of spatial resolution and without the use of any post-processing circuits. Able to process signals.

In particular, when processing a composite signal, compared to the method of converting it to a component signal and then processing it, the circuit required for three channels can be reduced to one channel, and at the same time, a decoder is not required, and the circuit scale is small. Become.

On the other hand, compared to intra-field processing, there is less deterioration in image quality in the kth spatial direction using pixels with higher correlation, and furthermore, there is no need for a circuit to determine whether or not it is noise by post-processing.

Therefore, when applying a logical filter to a composite signal, it is possible to obtain much better performance than conventional filters in terms of circuit scale and less deterioration in image quality.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of a noise removal circuit according to the present invention. FIG. 2 is a diagram for explaining the pixel arrangement in which the phase of color subcarriers in an NTSC composite signal matches in the field. , 'g13 shows the same phase-matched pixel arrangement of the color subcarriers in the NTSC composite image over time.
It is a figure for demonstrating in a vertical direction. 1...Composite signal input terminal, 21.22...262 line delay line, 3...Logic filter, 4...Processing output terminal.

Claims (1)

[Scope of Claims] 1) A plurality of data delay means for inputting an HTSC system composite signal and sequentially delaying it by a predetermined scanning line period, and inputting each output from the plurality of data delay means for delaying the input data. A noise removal circuit characterized by comprising a logic filter that performs logic processing in between. 2) The noise removal circuit according to claim 1, wherein the scanning line period is 262 scanning line periods.