JP3050497B2 - Video signal receiving device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal receiving apparatus for receiving a video signal and reproducing an image signal from the received video signal. More specifically, the present invention relates to an image mute based on a video signal reception level. The present invention relates to a video signal receiving device for performing the operation.

[0002]

2. Description of the Related Art When a video signal is received, if the level of the received signal is lower than a prescribed value, it is impossible to perform reception while maintaining a predetermined S / N ratio, and a reproduced image is unclear due to noise. It becomes an image. For this reason, in a device that receives a video signal, such as a portable television or a BS tuner, when a reception level is lower than a specified value, an unclear image is displayed by setting the image to a mute image such as a blue screen. Is prevented from being done.

[0003]

However, in the above configuration, an inconvenience may occur depending on the receiving situation. For example, when an automobile equipped with a portable television travels on an iron bridge or the like, a radio wave to be received is often blocked by a bridge structure. Therefore, the reception level decreases a plurality of times at short time intervals. As a result, an image indicating a normal image and an image serving as a blue screen are alternately displayed many times in a short time, and the television screen is hard to see. Also BS
In the case of a tuner, the reception level may be equal to the identification level at which the image is switched to the blue background depending on the strength of the rainfall. In such a case, when the reception level slightly changes, the image is switched from a normal image to a blue-back image or from a blue-back image to a normal image. As a result, a situation occurs in which switching of images occurs many times in a short time, and the television screen is difficult to see.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and an object of the present invention is to provide an image processing apparatus that is capable of displaying an image when a period in which a reception level is lower than an identification level continues for a longer period than a set period. By starting mute,
It is possible to prevent the image mute and the mute release from being repeated in a short cycle without causing an unnecessary increase in the image mute period, and to reduce the sharpness of the image when the reception level becomes lower than the identification level. Accordingly, an object of the present invention is to provide a video signal receiving apparatus capable of reducing discomfort of displayed image noise due to delay of image mute. Further, an object of the invention described in claim 2 is that, when the reception level becomes particularly low, the image mute is quickly performed so that the noise image is displayed even when the image mute is configured to be delayed. It is an object of the present invention to provide a video signal receiving device capable of preventing such a problem.

[0005]

According to a first aspect of the present invention, there is provided a video signal receiving apparatus which receives a video signal and reproduces an image signal from the received video signal. Applied to an apparatus that outputs an image signal, a level detection unit that detects a reception level of the video signal, and a first comparison that outputs a decrease signal when the reception level is lower than a first identification level set in advance. And when the period during which the decrease signal is output lasts longer than a preset period, the signal output by the signal processing circuit is changed from the image signal to a mute signal indicating a screen mute, and the signal processing is performed. While the circuit is outputting the mute signal, when the decrease signal is no longer output, the signal output by the signal processing circuit is converted from the mute signal to the image signal. When a mute control unit for exposed and ,, the reduced signal is output, it has a configuration having a sharpness control unit to reduce the sharpness of the image signal. Further, the video signal receiving apparatus according to the second aspect of the present invention, when the second identification level is a level lower than the first identification level, a warning signal when the reception level is lower than the second identification level in the previous period. The signal processing circuit includes a second comparing unit that outputs the mute signal, and the mute control unit outputs the mute signal from the signal processing circuit when the warning signal is output.

[0006]

The operation of the first aspect of the invention will be described below. The mute control unit changes the signal output by the signal processing circuit from an image signal to a mute signal when the period during which the decrease signal is output lasts longer than a preset period. For this reason, for example, even if the reception level decreases for a short period with a fixed period, the mute signal is not output,
The image signal continues to be output. As a result, an image is continuously displayed on the television screen displaying the output of the signal processing circuit without interruption. Only when the reception level decreases, the image noise only increases. In addition, the mute control unit changes the signal output from the signal processing circuit from a mute signal to an image signal when the signal processing circuit outputs the mute signal and the reduction signal is not output. As a result, since the radio wave is blocked by a building or the like, the period during which the reception level is reduced is prolonged, and even if the television screen is muted, when the reception level exceeds the first identification level, a normal image is not generated. It is immediately displayed on the TV screen.

Further, the invention of claim 1 has the following operation. The sharpness of the image displayed on the TV screen is
The optimum value changes depending on the S / N ratio of the image signal, and image noise is less noticeable on a screen with low sharpness. That is, when the S / N ratio is deteriorated, a screen with low sharpness is easier to see than a screen with high sharpness. The image signal obtained when the decrease signal is output is S
The image signal has a poor / N ratio. For this reason, when the reduction signal is output, if the sharpness of the image signal is reduced,
An image signal with reduced sharpness is a signal that is easy to see.

The operation of the invention described in claim 2 will be described below.
The warning signal is output when the reception level is lower than the second identification level, and the image signal at this time has an extremely poor S / N ratio. In other words, the image signal when the warning signal is output is an image signal that occupies most of the image noise and is not worth displaying. Therefore, when the reception level is lower than the second identification level, the mute control unit prevents a display of an image in which the image noise occupies most by displaying a signal output from the signal processing circuit as a mute signal.

[0009]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an electrical configuration of an embodiment of a video signal receiving apparatus according to the present invention.
Specifically, it shows a television.

The tuner section 4 has a UHF band and a VHF band.
It is a block that receives the video signal of the band and detects the received video signal, and sends out a detection output to the level detection unit 3 and the signal processing circuit 7. Signal processing circuit 7
Is a block that performs predetermined signal processing on the detection output output from the tuner unit 4 to generate R, G, and B color signals, and sends the generated color signals to the drive circuit 8. Also, a sharpness circuit (not shown) for changing the sharpness of an image, and a generation circuit (not shown) for generating a mute signal for image mute
It has. Hereinafter, the color signal transmitted to the drive circuit 8 will be referred to as an image signal.

The drive circuit 8 is an amplifier circuit that amplifies the image signal output from the signal processing circuit 7 to a predetermined level, and drives the CRT 10 with the amplified image signal.
The synchronizing signal circuit 9 is a block that generates a horizontal synchronizing signal and a vertical synchronizing signal based on the signal output from the signal processing circuit 7.
Send to 10. The level detector 3 is a block that detects the level of the video signal received by the tuner unit 4 by detecting the level of the synchronization signal in the detection output output from the tuner unit 4. To the first comparison unit 1 and the second comparison unit 2.

The first comparing section 1 is a block for comparing a predetermined first identification level with a reception level, and generates a decrease signal when the reception level becomes lower than the first identification level. I do. The generated decrease signal is sent to the timer unit 11 and the sharpness control unit 6 in the mute control unit 5. The first identification level is set to a value indicating the reception level when the S / N ratio of the video signal in the detection output from the tuner unit 4 becomes poor and the image noise starts giving an unpleasant impression. Also, the drop signal is
It is shown at the H level at output 101.

The second comparing section 2 is a block for comparing a predetermined second identification level with a reception level, and generates a warning signal when the reception level becomes lower than the second identification level. I do. The generated warning signal is sent to one of the inputs of the OR gate 12 in the mute control unit 5. Note that the second identification level is the tuner unit 4
Is set to a value indicating the reception level when the S / N ratio of the video signal in the detection output from the image signal becomes extremely poor, and image identification becomes difficult due to image noise. The warning signal is indicated by the H level at the output 201.

When the period in which the first comparator 1 outputs the lowering signal lasts longer than the preset period, the mute controller 5 outputs the signal output from the signal processing circuit 7 to the driving circuit 8. The image signal is changed to a mute signal indicating a screen mute. When the signal processing circuit 7 is outputting the mute signal, and when the lowering signal is not output, the signal output from the signal processing circuit 7 is changed from the mute signal to the image signal. When a warning signal is output from the second comparison unit 2, the signal output from the signal processing circuit 7 to the drive circuit 8 is used as a mute signal. More specifically, the mute control unit 5 includes a timer unit 11 and an OR gate 12, and the timer unit 11 determines whether a period during which the decrease signal is continuously transmitted is longer than a preset period. Is determined. That is, the timer unit 11 starts the measurement operation when the decrease signal is transmitted, and immediately initializes the measurement operation when the output of the decrease signal is stopped before the measurement is completed. The OR gate 12 is connected to the second comparison unit 2
Is output to the signal processing circuit 7. Note that the period measured by the timer unit 11 is, for example, in the case of being applied to a portable television, for example,
It is set to about 2 seconds.

The sharpness control section 6 includes a first comparison section 1
Is output from the signal processing circuit 7, a block for reducing the sharpness of the image signal output from the signal processing circuit 7 is sent to the signal processing circuit 7 for reducing sharpness.

FIG. 2 is a timing chart showing waveforms of main signals in the embodiment. The operation of the embodiment will be described with reference to FIG. The output 3 shown in FIG.
01 indicates the reception level detected by the level detection unit 3, where level L1 indicates the first identification level and level L2 indicates the second identification level.

When a vehicle equipped with the embodiment travels on an iron bridge, radio waves are interrupted for a short period in a short period by a structural material in a vertical direction of the iron bridge. At time T1, due to such a situation, the reception level becomes the first identification level L1.
This shows the timing when it began to become lower. A period t1 starting at time T1 is a short period, and is 0.5
About 1 second.

In a period t1 when the reception level is lower than the first discrimination level L1, the output 101 of the first comparator 1 becomes
It goes to H level indicating a decrease signal. Therefore, the timer unit 11
Means that when the output 101 becomes H level (time T1),
Start timing. However, the H level indicating the lowering signal returns to the L level at time T2 before the elapse of 2 seconds, which is the measurement period of the timer section 11. Therefore, the timer unit 11 does not output the H level to the OR gate 12. Therefore, the signal processing circuit 7 continues to send the image signal to the drive circuit 8 without generating a mute signal. In the period t1, the sharpness control unit 6 gives an instruction to the signal processing circuit 7 to reduce the sharpness.

As a result, a screen based on an image signal is displayed on the CRT 10 without image muting also during the period t1. However, in the period t1, the CRT 10
Is a screen mixed with some image noise because the reception level is lowered. However, since this screen has a reduced sharpness, the image noise is less noticeable. That is, when the period during which the reception level is lower than the first identification level L1 is shorter than 2 seconds, which is the measurement period of the timer unit 11, the screen by the image signal is continuously displayed on the CRT 10. When the reception level is the first identification level L
During periods of less than 1 and some increase in image noise, sharpness is reduced, making the image noise less noticeable.

A period t2 indicates a period during which the car is traveling in an area where radio waves are blocked by a building or the like, and a period during which the reception level is lower than the first identification level L1 is two.
Longer than seconds. For this reason, in the period t3 (2 seconds) starting at the time T3, a screen with reduced sharpness is displayed on the CRT 10 as in the period t1. Then, at time T4 when the period t3 has elapsed, the timer unit 11 sends the H level to the OR gate 12. Therefore, the output of the OR gate 12 also becomes H level, so that the signal processing circuit 7 stops outputting the image signal and sends out the mute signal to the drive circuit 8. That is, the period t3 has elapsed and the time T3
When the number is 4, the screen of the CRT 10 is an image mute (blue-back screen).

When the time t4 has elapsed and the time T5 has elapsed, the reception level exceeds the first discrimination level L1, and no lowering signal is transmitted (the output 101 goes to the L level). As a result, the timer unit 11 quickly changes the output to the L level and changes the output of the OR gate 12 to the L level. Therefore, the signal processing circuit 7 changes the signal sent to the drive circuit 8 from a mute signal to an image signal. That is, after the time T5, the CRT 10
A screen with high sharpness is displayed by the image signal.

A period t5 indicates a period during which the vehicle is traveling in an area where radio waves are extremely difficult to reach, such as in a tunnel, and in the period t5, the reception level is lower than the second identification level L2. Therefore, when the reception level becomes lower than the second identification level L2 (time T6),
The output 201 of the second comparison unit 2 becomes H level indicating a warning signal. Therefore, the output of the OR gate 12 becomes H level, and the signal processing circuit 7 changes the signal to be sent to the drive circuit 8 from the image signal to the mute signal promptly. As a result, at time T6, the screen of the CRT 10 becomes an image mute and becomes a blue-back screen.

When two seconds have elapsed from the time T6, the output of the timer unit 11 goes high, but the output of the OR gate 12 is already at the high level.
Does not affect the output of the OR gate 12. Then, at time T7, the output of the timer unit 11 and the output 201 change to the L level at substantially the same timing. Therefore, the signal processing circuit 7 changes the signal sent to the drive circuit 8 from a mute signal to an image signal. As a result, after the time T7, a screen with high sharpness by the image signal is displayed on the CRT 10.

The present invention is not limited to the above embodiment,
As other devices, for example, a video cassette recorder, a BS tuner, and the like can be similarly applied.

[0025]

The video signal receiving apparatus according to the first aspect of the present invention is applied to a device that receives a video signal, reproduces an image signal from the received video signal, and outputs the reproduced image signal. A level detection unit that detects a reception level of the video signal; and a first detection unit that outputs a decrease signal when the reception level is lower than a preset first identification level.
And when the period during which the drop signal is output lasts longer than a preset period, the signal output from the signal processing circuit is changed from an image signal to a mute signal indicating a screen mute, and the signal processing circuit And a mute control unit that changes the signal output from the signal processing circuit from a mute signal to an image signal when the decrease signal is no longer output while the mute signal is being output. That is, even when the reception level is lower than the preset level, the image signal is continuously output if the period during which the reception level is low is short. Even when the image is muted, the image signal is output immediately when the reception level is restored. Therefore, it is possible to prevent the image mute and the mute release from being repeated in a short cycle without causing an unnecessary increase in the image mute period.

Furthermore, the video signal receiving apparatus according to the first aspect of the present invention includes a sharpness control unit that reduces the sharpness of the image signal when the reduction signal is output. For this reason, when the screen has an increased image noise, the sharpness becomes lower and the image noise becomes less noticeable. Therefore, it is possible to reduce the discomfort of the displayed image noise due to the delayed image mute. .

In the video signal receiving apparatus according to the second aspect of the present invention, when a level lower than the first identification level is set as the second identification level, a warning signal is issued when the reception level becomes lower than the second identification level. A second comparison unit for outputting the signal is provided, and the mute control unit is configured to output a mute signal from the signal processing circuit when the warning signal is output. That is, when the reception level is extremely low and image degradation is severe, the image is muted, so that it is possible to prevent a noise image from being displayed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an electrical configuration of an embodiment of a video signal receiving apparatus according to the present invention.

FIG. 2 is a timing chart showing waveforms of main signals according to the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st comparison part 2 2nd comparison part 3 Level detection part 5 Mute control part 6 Sharpness control part 7 Signal processing circuit

Claims (2)

(57) [Claims] An apparatus for receiving a video signal, reproducing an image signal from the received video signal, and outputting the reproduced image signal, a level detection unit for detecting a reception level of the video signal, When the level is lower than a preset first identification level, a first comparing unit that outputs a lowering signal, and when a period during which the lowering signal is output lasts longer than a preset period, a signal processing circuit The output signal is changed from the image signal to a mute signal indicating a screen mute, and when the signal processing circuit is outputting the mute signal, when the decrease signal is no longer output, the signal processing circuit A mute control unit for changing a signal to be output from the mute signal to the image signal, and when the decrease signal is output, Video signal receiving apparatus characterized by comprising a sharpness control unit to reduce the sharpness of the signal. 2. A method according to claim 1, wherein a level lower than said first discrimination level is a second level.
A second comparing unit that outputs a warning signal when the reception level is lower than the second determination level, wherein the mute control unit outputs the signal when the warning signal is output. 2. The video signal receiving device according to claim 1, wherein the mute signal is output from a processing circuit.