JPH0678181A - Noise removing circuit - Google Patents

Abstract

PURPOSE:To obtain a noise removing circuit capable of executing digital arithmetic processing by increasing the gradation of an image part in a video signal (luminance signal). CONSTITUTION:The image part (from a pedestal to a white peak) of a luminance signal is pedestal-clamped and amplitude-adjusted by a claming/ amplitude-adjusting circuit 4 so that the amplitude of the image part is set up to the one regulated by an A/D converter 6. When a luminance signal is supplied to an input terminal 1, change-over switches 2, 5 are connected to the b sides, pedestal clamping and amplitude adjustment are executed by the circuit 4, the image part of the luminance signal is converted into a digital signal by the converter 6 and the digital signal is supplied to an arithmetic circuit 7 to execute noise removing processing utilizing line correlation or the like. The luminance signal whose noise is removed by the circuit 7 is converted into an analog signal by a D/A converter 9, a composite synchronizing signal is added to the analog signal by a synchronizing signal adder 10 and the added signal is outputted from an output terminal 11.

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 (luminance signal) by digital processing.

[0002]

2. Description of the Related Art FIG. 2 is a block diagram showing a conventional noise removing circuit. In the figure, 21 is an input terminal,
The luminance signal supplied to the input terminal 21 is supplied to the clamp circuit and the amplitude adjusting circuit 22. In this circuit 22, so-called sync-chip clamping and amplitude adjustment are performed so that the sync-chip level becomes a predetermined value, and the amplitude of the brightness signal, that is, the amplitude from the sync-chip to the white peak of the brightness signal is A / D described later. The amplitude (dynamic range) specified by the converter 23 is adjusted.

The luminance signal output from the circuit 22 is an A / D
It is converted into a digital signal by the converter 23 and supplied to the digital arithmetic circuit 24. This digital arithmetic circuit 24
Then, as is well known in the art, noise is removed from the luminance signal by digital arithmetic processing utilizing line (field, frame) correlation. This digital arithmetic circuit 2
The noise-removed luminance signal output from the A / D converter 4 is converted into an analog signal by the D / A converter 25 and is output to the output terminal 26.

[0004]

Since the conventional noise removing circuit is configured as described above, all the amplitude of the luminance signal (from the sync tip to the white peak) is converted into a digital signal for noise removal processing. Therefore, there is a problem that the gradation of the image portion is reduced.

The present invention has been made in order to solve such a problem, and provides a noise removing circuit capable of performing digital arithmetic processing by increasing the gradation of a video portion of a video signal (luminance signal). The purpose is to do.

[0006]

A noise removing circuit according to the present invention is an A / D converter for converting a video portion of an input video signal into a digital signal, and a digital video signal output from the A / D converter. A digital operation circuit for removing noise by digital operation processing, a D / A converter for converting the noise-removed digital video signal output from the digital operation circuit into an analog signal, and the D / A converter And a synchronization adding circuit for adding a synchronization signal to the output analog video signal to obtain an output video signal.

[0007]

According to the present invention, since the video portion of the video signal, that is, the pedestal to the white peak of the video signal is converted into a digital signal and subjected to digital arithmetic processing, the gradation of the video portion of the video signal is increased to be digital. It becomes possible to perform arithmetic processing.

[0008]

EXAMPLES Example 1. FIG. 1 is a block diagram showing an embodiment of a noise removing circuit according to the present invention. In the figure, an input terminal 1 is connected to a movable terminal of a changeover switch 2, and fixed terminals on the a side and the b side of the changeover switch 2 are connected to a clamp circuit and amplitude adjusting circuits 3 and 4, respectively.

In the circuit 3, so-called sync chip clamping and amplitude adjustment are performed so that the sync chip level becomes a predetermined value, and the amplitude of the composite color video signal, that is, the amplitude from the sync chip to the white peak of the color video signal is determined. It is adjusted to have an amplitude (dynamic range) defined by an A / D converter 6 described later. On the other hand, in the circuit 4, so-called pedestal clamping and amplitude adjustment are performed so that the pedestal level becomes a predetermined value, and the amplitude of the image portion of the luminance signal, that is, the amplitude from the pedestal to the white peak of the luminance signal is A / D converted. It is adjusted so that the amplitude (dynamic range) specified by the device 6 is obtained.

The output signals of the circuits 3 and 4 are supplied to fixed terminals on the a side and the b side of the changeover switch 5, respectively, and the signal obtained at the movable terminal of the changeover switch 5 is converted into a digital signal by the A / D converter 6. Convert to digital operation circuit 7
Supply to. The change-over switches 2 and 5 are a when the composite color video signal is supplied to the input terminal 1, respectively.
On the other hand, when the luminance signal is supplied to the input terminal 1, it is connected to the b side.

Further, the input terminal 1 is connected to the horizontal AFC circuit 8. The horizontal AFC circuit 8 extracts the horizontal synchronizing signal from the composite color video signal or the luminance signal and outputs a frequency signal that is n times the horizontal synchronizing signal. The frequency signal output from the horizontal AFC circuit 8 is supplied to the digital arithmetic circuit 7 as a reference synchronizing signal. When the composite color video signal is supplied to the input terminal 1, the digital arithmetic circuit 7 performs a conventionally known three-dimensional YC separation process and outputs a luminance signal and a color signal. On the other hand, when a luminance signal is supplied to the input terminal 1, the digital arithmetic circuit 7 performs noise removal processing using conventionally known line (field, frame) correlation.

After the signal output from the digital arithmetic circuit 7 is converted into an analog signal by the D / A converter 9, it is led to the output terminal 11 via the synchronization adding circuit 10. Further, the input terminal 1 is connected to the synchronization generating circuit 12. The sync generation circuit 12 generates a composite sync signal synchronized with the luminance signal,
This composite synchronizing signal is supplied to the synchronization adding circuit 10. The synchronization adding circuit 10 operates only when the luminance signal is supplied to the input terminal 1, and performs the processing for adding the synchronization signal.

Next, the operation will be described. When the composite color video signal is supplied to the input terminal 1, the changeover switches 2 and 5 are connected to the side a, and the sync tip clamp and the amplitude adjustment are performed in the circuit 3. (Including) is converted into a digital signal by the A / D converter 6, and the digital arithmetic circuit 7
And YC separation processing is performed. Then, the luminance signal and the chrominance signal output from the digital arithmetic circuit 7 are converted into analog signals by the D / A converter 9 and led to the output terminal 11 via the synchronization adding circuit 10.

On the other hand, when the luminance signal is supplied to the input terminal 1, since the changeover switches 2 and 5 are connected to the b side and the pedestal clamp and the amplitude adjustment are performed in the circuit 4, the image portion of the luminance signal is The signal is converted into a digital signal by the A / D converter 6 and supplied to the digital arithmetic circuit 7, where noise removal processing using line correlation or the like is performed. Then, after the noise removal processed luminance signal output from the digital arithmetic circuit 7 is converted into an analog signal by the D / A converter 9, a synchronization signal is added by the synchronization adding circuit 10 and is derived to the output terminal 11. It

[0015]

As described above, according to the present invention, an A / D converter for converting a video portion of an input video signal into a digital signal, and a digital operation from a digital video signal output from the A / D converter. A digital arithmetic circuit that removes noise by processing, a D / A converter that converts the noise-removed digital video signal output from this digital arithmetic circuit into an analog signal, and an output from this D / A converter Since a sync addition circuit for adding a sync signal to the analog video signal to obtain an output video signal is provided,
Since the video part of the video signal, that is, the pedestal to the white peak of the video signal is converted into a digital signal for digital calculation processing, the gradation of the video part of the video signal is increased to perform digital calculation processing for noise removal. There is an effect that can be done.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a noise removal circuit according to the present invention.

FIG. 2 is a block diagram showing a conventional noise removal circuit.

[Explanation of symbols]

 1 Input Terminal 2, 5 Changeover Switch 3, 4 Clamp Circuit and Amplitude Adjustment Circuit 6 A / D Converter 7 Digital Operation Circuit 8 Horizontal AFC Circuit 9 D / A Converter 10 Synchronization Addition Circuit 11 Output Terminal 12 Synchronization Generation Circuit

Claims (1)

[Claims] 1. An A / D converter for converting a video portion of an input video signal into a digital signal, and a digital arithmetic circuit for removing noise from a digital video signal output from the A / D converter by digital arithmetic processing. , D for converting the noise-removed digital video signal output from the digital arithmetic circuit into an analog signal
A noise removal circuit comprising a / A converter and a synchronization adding circuit for adding a synchronization signal to an analog video signal output from the D / A converter to obtain an output video signal.