JPH04246975A - Television receiver - Google Patents

Abstract

PURPOSE:To effectively reduce large random noise with large amplitude at the time of receiving satellite broadcasting in a weak electric field and to prevent the deterioration of resolution. CONSTITUTION:A detection circuit 1 outputs a detection signal B more than a white component detection level and less than a black component detection level, and a pulse width detection circuit 2 outputs a detection signal C equivalent to prescribed continuous time width. A differential operation circuit 4 separates noise by the inter-frame non-correlation of noise and outputs a noise detection signal D. Thus, a switch circuit 7 is switched to the side of a low pass filter 5 only at the time of noise by a noise detection signal D and a reduced video signal E in a noise part is outputted. Namely, an output video signal is corrected in a video signal part passing through the low pass filter 5 only at the time of detecting noise.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] This invention relates to the reduction of noise components in video signal processing circuits of video-related equipment such as television receivers and video tape recorders that have built-in tuners for receiving satellite broadcasting.

0002

[Prior art] As a noise reduction circuit for video signals, there are ■high-frequency component removal type and ■
There are frame memory types, etc. The high-frequency component removal type (■) removes only the high frequency of small-amplitude signals, which causes some resolution deterioration, and is also effective against large-grain, large-amplitude noise such as noise when receiving satellite broadcasts in weak electric fields. No reduction effect was observed. Regarding the frame memory type (2), cyclic or acyclic frame memory type noise reduction circuits have been developed by utilizing the non-correlation of noise components between frames. However, if the feedback rate is increased in the recursive frame memory type in order to effectively suppress large-grain, large-amplitude noise during satellite broadcast reception, it has the disadvantage that afterimages occur in moving parts of the image.

0003

[Problems to be Solved by the Invention] The present invention has been made in view of the conventional example, and effectively reduces large-grain, large-amplitude random noise when receiving satellite broadcasting in a weak electric field, and prevents deterioration of resolution. The aim is to improve overall image quality by doing so.

0004

[Means for Solving the Problems] The present invention provides a black or white grain noise detection circuit of a predetermined level tailored to the characteristics of random noise during reception of satellite broadcasting in a weak electric field, a pulse width detection circuit of predetermined width noise, and a frame memory. The noise component is detected through a difference calculation circuit according to the method, and the output video signal is corrected only when noise is detected using the video signal section that has passed through a low-pass filter.

[0005]

[Operation] As shown in FIG. 1, there is a detection circuit 1 for black and white grain noise, a pulse width detection circuit 2 for large grain noise having a duration of a predetermined width in one horizontal scanning line, and a difference calculation circuit 4 using a frame memory 3. , consists of a circuit configuration of a low-pass filter 5 that inputs the video signal A and a delay circuit 6, and the switch circuit 7 is connected to the terminal on the low-pass filter 5 side only when noise is detected by the noise detection signal D output from the difference calculation circuit 4. a and outputs a video signal E with reduced noise.

[0006]

[Example] In order to effectively detect random noise when receiving satellite broadcasting in a weak electric field, the characteristics of the noise
Black or white grain noise, ■Large grain noise that has a certain duration in one horizontal scanning line, ■Utilizes non-correlation between frames (no noise exists at the same point in the previous frame or the next frame), etc. do.

1 in FIG. 1 indicates the retrace period (H
2 is a detection circuit that detects a white component above a predetermined level and a black component below a predetermined level in a video signal period excluding (VBLK), and 2 transmits only pulses having a duration within a set range in the output signal B of the detection circuit 1. A pulse width detection circuit, 3 is a frame memory for one frame delay, and 4 is a difference calculation that separates noise and outputs a noise detection signal D based on the difference between the current frame signal input to the frame memory and the previous frame signal output from the same frame memory. 5 is a low-pass filter that has a delay time equal to the delay time of the noise detection signal D with respect to the input video signal A and outputs only the low frequency component of the video signal A; 6 is a noise detection signal D with respect to the input video signal A; The delay circuit 7 has a delay time equal to the delay time of the noise detection signal D, and 7 is a high-speed switching switch circuit that switches to the terminal a on the output signal side of the low-pass filter 5 to interpolate the signal only when the noise detection signal D is output.

FIG. 2A shows operating waveforms A, B, C, D, and E of each part of the circuit for the display screen 10. 11 is a black or white random noise having a predetermined range of duration (several hundred to several thousand ns) when receiving satellite broadcasting in a weak electric field, 12 is a white signal with the same duration, and 13 is the same duration. This is a black level signal whose length exceeds the width. Assuming that A is the video signal of the L-L1 line on the display screen 10, the detection circuit 1 outputs a detection signal B that is higher than the white component detection level WL and lower than the black component detection level BL, and the pulse width detection circuit 2 continues for a predetermined period. A detection signal C corresponding to a time width is output, and a difference calculation circuit 4 separates noise by inter-frame decorrelation of noise and outputs a noise detection signal D. Therefore, the switch circuit 7 is switched to the low-pass filter 5 side only in the case of noise by the noise detection signal D, and the video signal E with the noise portion n reduced is output. Note that (b) in Fig. 2 shows 1 where no noise is observed.
It is a waveform diagram of each part operation before a frame.

[0009]

As described above, the present invention provides a black or white grain noise detection circuit of a predetermined level tailored to the characteristics of random noise during reception of satellite broadcasting in a weak electric field, a pulse width detection circuit of a predetermined width noise, and a frame memory. Noise components are detected through a differential calculation circuit that uses noise to separate them, and only when noise is detected, the output video signal is corrected in the video signal section that passes through a low-pass filter, effectively reducing noise. However, there is no afterimage of moving parts of the image, and the overall image quality can be improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a noise reduction circuit in a video signal circuit.

FIG. 2 is a diagram of operation waveforms of various parts on a display screen for explaining FIG. 1;

[Explanation of symbols]

1. Detection circuit for black and white grain noise 2 Pulse width detection circuit 3 Frame memory 4 Frame difference calculation circuit 5 Low pass filter 6 Delay circuit 7 Switch circuit

Claims (1)

[Claims] 1. In a video signal processing circuit such as a television receiver with a built-in tuner for receiving satellite broadcasting, detection of a white component above a predetermined level and a black component below a predetermined level in a video signal portion of an input video signal excluding the flyback period. a pulse width detection circuit that transmits only pulses having a duration within a predetermined range;
A frame difference calculation circuit using a frame memory is connected in series, and a delay circuit output signal of the input video signal having a predetermined delay time and a delay circuit output signal of the input video signal having a predetermined delay time are determined by a noise detection signal output from the difference calculation circuit. A television receiver that selects a band pass filter output signal.