JP2007306173A - Television signal processor and processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce degradation of image quality even when reception state of a television signal is deteriorated. <P>SOLUTION: In the television signal processor receiving a composite video signal from a television signal receiver; a color signal is extracted from the composite video signal in a first frequency band when the reception state of the television signal is in a first reception state, and extracted in a second frequency band narrower than the first frequency band when the reception state is in a second reception state lower than the first reception state. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a television signal processing apparatus that extracts a color signal and a luminance signal from a composite video signal, and in particular, television signal processing that changes a frequency band for extracting a color signal according to a reception state of the television signal. The present invention relates to an apparatus and a television signal processing method.

  In general, a television device includes a television signal receiving device, a television signal processing device, a display device, and the like. First, a television signal receiver receives a high-frequency television signal, converts it to an intermediate frequency signal, extracts a composite video signal from the intermediate frequency signal, and outputs it. An example of such a television signal receiving apparatus is described in Patent Document 1.

The composite signal output from the television signal receiving device is input to the television signal processing device. The television signal processing device extracts a luminance signal, a color signal, and a synchronization signal from the composite video signal, and outputs an RGB signal and a synchronization signal based on the luminance signal and the color signal to the display device. The display device displays the received television image on the screen based on the RGB signal and the synchronization signal.
JP 2001-313881 A

  However, when the reception state of the television signal deteriorates, the quality of the displayed image is deteriorated due to noise included in the received radio wave. In particular, when a television signal processing apparatus extracts a color signal and a luminance signal from a composite video signal, if a lot of noise is mixed in the color signal, the deterioration of the color quality of the video becomes remarkable. For example, a color different from the color that should be output is output, and the user looks uncomfortable.

  Furthermore, in a television device installed in a vehicle that has become widespread in recent years, since the electric field strength of the received radio wave changes as the vehicle moves, the reception state deteriorates when moving to a weak electric field region. Video degradation is likely to occur.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a television signal processing apparatus and a television signal processing method that can reduce deterioration in video quality even when a television signal reception state deteriorates.

  In order to achieve the above object, according to a first aspect of the present invention, in a television signal processing device that receives a composite video signal input from a television signal receiving device, the reception state of the television signal is first. The color from the composite video signal is in the first frequency band in the second reception state, and in the second frequency band narrower than the first frequency band in the second reception state worse than the first reception state. It has the signal extraction part which extracts a signal, It is characterized by the above-mentioned. The television signal processing apparatus outputs a video signal based on the luminance signal obtained by removing the color signal from the composite video signal and the color signal.

  According to the first aspect, when the reception state of the television signal is good, that is, when the S / N ratio (signal-to-noise ratio) of the entire received television signal is large, the color signal in the first frequency band. Is separated from the composite video signal, and when the reception state deteriorates and the S / N ratio of the entire received television signal decreases, the color signal is separated from the composite video signal in the second frequency band narrower than the first frequency band. Extract. Therefore, even when the reception state is bad, the S / N ratio (signal-to-noise ratio) of the extracted color signal can be improved.

  According to the present invention, even when the S / N ratio of the entire television signal is lowered, the S / N ratio of the extracted color signal can be improved, and the deterioration of the color quality of the video can be reduced.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the technical scope of the present invention is not limited to these embodiments, but extends to the matters described in the claims and equivalents thereof.

  FIG. 1 is a diagram for explaining the configuration of a television signal processing apparatus according to the present embodiment. The television signal processing device 200 processes the composite video signal CMVS input from the television signal receiving device 100 to generate RGB signals R, G, and B, and outputs them to the display device 400 as video signals. The television signal receiving device 100, the television signal processing device 200, and the display device 400 constitute a television device mounted on a vehicle.

  In the television signal receiving apparatus 100, the tuner 10 extracts the frequency band of the channel selected by the user from the high-frequency (frequency band 90 to 700 MHz) television signal received by the antenna 11, and converts it into an intermediate frequency signal. The intermediate frequency signal output from the tuner 10 is amplified by the intermediate frequency signal amplifier 12 and input to the video detector 14. The video detector 14 extracts a video intermediate frequency signal which is a carrier signal from the intermediate frequency signal. Part of the video intermediate frequency signal is input to an AGC (Automatic Gain Control) 20, and part of the video intermediate frequency signal is amplified by the video amplifier 16 and output to the television signal processing device 200 as a composite video signal CMVS.

  The AGC 20 controls the gain of the tuner 10 and the intermediate frequency signal amplifier 12 based on the video intermediate frequency signal input from the video detector 14 in order to keep the output of the video detector 14 constant. Specifically, an AGC signal that obtains a larger gain as the video intermediate frequency signal is smaller is output to a high-frequency amplifier and intermediate frequency signal amplifier 12 (not shown) of the tuner 10. The AGC signal is also output to the control unit 28 of the television signal processing apparatus 200, and the control unit 28 controls the operation of the signal extraction unit 22 in accordance with the AGC signal, as will be described later.

  The electric field strength detector 18 detects the electric field strength of the received signal of the tuner 10 and outputs an electric field strength signal that is the detected electric field strength to the control unit 28 of the television signal processing device 200. As will be described later, the control unit 28 controls the operation of the signal extraction unit 22 in accordance with the electric field strength signal.

  In the television signal processing device 200, the signal extraction unit 22 and the synchronization signal separation unit 30 receive the composite video signal CMVS from the video amplifier 16. The signal extraction unit 22 includes a band-pass filter 23 and a subtracting circuit (not shown). The band-pass filter 23 is configured by a digital filter that can change the pass bandwidth by a control signal from the control unit 28. The signal extraction unit 22 first extracts the color signal C from the composite video signal CMVS by passing through the pass band set in the bandpass filter 23, and subtracts the color signal C from the composite video signal CMVS to obtain the luminance. The signal Y is extracted.

  The extracted luminance signal Y is input to the matrix circuit 26 after noise in the color burst signal section is detected by the noise detection unit 25, as will be described in detail later. The color signal C is input to the color demodulator 24, and the color demodulator 24 further extracts a color difference signal from the color signal C, that is, a blue difference signal Cb and a red difference signal Cr, and inputs them to the matrix circuit 26. The matrix circuit 26 generates RGB signals R, G, and B corresponding to the input luminance signal Y and color difference signals Cr and Cb, and outputs them to the display device 400.

  The sync signal separator 30 to which the composite video signal CMVS is input takes out the horizontal sync signal and the vertical sync signal from the composite video signal CMVS, and inputs the horizontal sync signal to the PLL circuit 32. The PLL circuit 32 generates a reference clock CLK that is synchronized with the horizontal synchronization signal and outputs the reference clock CLK to the control unit 28, the color demodulation unit 24, the matrix circuit 26, and the display device 400. The control unit 28 and the like perform processing in accordance with the reference clock CLK, and the display unit 400 displays images corresponding to the RGB signals R, G, and B based on the reference clock CLK.

  In the in-vehicle television device having the above configuration, the electric field strength of the received radio wave changes as the vehicle moves, so that the magnitude of the received television signal also changes. Then, the reception state of the television signal in the television signal receiving apparatus 100, that is, the S / N ratio between the received television signal and the noise included therein also changes according to the electric field strength. An operation in which the signal extraction unit 22 extracts the color signal C according to the change in the electric field strength will be described below.

  First, looking at the frequency components of the luminance signal Y and the color signal C included in the composite video signal CMVS, the luminance signal component YS is distributed in a frequency band of 0 to 4.2 MHz as shown in FIG. The color signal component CS is distributed in a frequency band of ± 0.5 MHz centering on 3.58 MHz. Note that the noise component NS is distributed over the entire frequency band. Therefore, first, the control unit 28 of the television signal processing apparatus 200 has a problem that the noise component NS is a problem when the electric field strength is sufficiently strong and the S / N ratio of the television signal is large, that is, compared with the frequency component of the received television signal. When the amount is not so small as shown in FIG. 2A, as shown in FIG. 2A, the pass band of the band pass filter 23 of the signal extraction unit 22 is passed through the color signal C with a pass band width W of 1 MHz centered on 3.58 MHz. The portion that does not pass through is extracted as the luminance signal Y.

  However, when the electric field strength decreases, the received television signal decreases, and the amount of the noise component NS relatively increases as shown in FIG. Then, the S / N ratio of the color signal C extracted in the passband W as described above, that is, the area S of the portion not overlapping with the noise component NS of the distribution curve CS of the color signal component, and the noise component NS overlap. The ratio of the area N of the shaded portion decreases. In particular, in the frequency components in the frequency bands F1 and F2 separated from 3.58 MHz, the ratio of the noise component NS is large, and the S / N ratio is extremely low. Therefore, when the color signal C is extracted with the pass bandwidth W, the signals of the frequency bands F1 and F2 with extremely low S / N ratios are included, and colors corresponding to these signals cannot be output accurately. .

  Therefore, as shown in FIG. 2C, the television signal processing apparatus 200 has a pass band narrower than a pass band width W of 1 MHz centered on 3.58 MHz. The color signal C is extracted with the width N changed. By doing so, the signal components of the frequency bands F1 and F2 having an extremely low S / N ratio are not taken in as the color signal components, but the S / N ratio of the extracted color signal C, that is, the distribution curve C of the color signal component It is possible to improve the ratio of the area (S1) of the portion that does not overlap with the noise component NS and the area (N1) of the shaded portion that overlaps with the noise component NS.

  Since the color signal extraction unit 22 uses the signal that does not pass through the bandpass filter 23 as the luminance signal Y, noise components existing in the frequency bands F1 and F2 are mixed into the luminance signal Y. However, the influence of noise on the color signal C is remarkable in appearance that an image having a color different from the original color of the image is displayed. It is relatively inconspicuous, brighter and darker than brightness. Therefore, even if the influence of noise components in the frequency bands F1 and F2 mixed in the luminance signal is subtracted, the improvement effect of the video quality by improving the S / N ratio of the color signal C is greater. For this reason, in the present embodiment, the narrowing of the pass band of the band pass filter 23 and the extraction of the color signal C in a narrow frequency band can reduce the deterioration of video quality.

  The above operation is realized by controlling the operation of the signal extraction unit 22 based on the electric field strength signal received by the control unit 28 from the electric field strength detector 18. For example, as shown in FIG. 3A, when the electric field strength signal exceeds the threshold value THV, that is, when the electric field strength is sufficiently strong, if the electric field strength signal is equal to or lower than the threshold value THV. The signal extraction unit 22 is controlled so that the narrow passband N is set in the bandpass filter 23.

  The bandpass filter 23 is a digital filter that attenuates a certain frequency band by multiplying an input signal by a plurality of coefficients, and the attenuated frequency band differs depending on the number of coefficients and the value of the coefficients. Therefore, as shown in FIG. 4A, the control unit 28 stores the coefficient group 1 and the coefficient group 2 in the coefficient table 29, and inputs these coefficient groups to the bandpass filter 23 according to the electric field strength. To control the passband. For example, when the coefficient group 1 is input, the band pass filter 23 multiplies the input composite video signal CMVS by the coefficient group 1 to extract the color signal C in the band W (FIG. 4B), When a coefficient 2 that attenuates the high-frequency part and the low-frequency part is input, the input signal is multiplied by the coefficient group 2 and the color signal C is output in the passband N (FIG. 4B). In this way, by setting an appropriate coefficient in the band pass filter 23, the pass band W or the pass band N can be switched.

  The control unit 28 may receive the AGC signal from the AGC 20 and control the passband of the bandpass filter 23 based on the AGC signal. If the electric field strength of the television signal is strong, the gain of the intermediate frequency signal amplifier 12 and the like is large, so the AGC signal is a signal that obtains a small gain. If the electric field strength is weak, the gain of the intermediate frequency signal amplifier 12 and the like is small. The AGC signal is a signal for obtaining a larger gain. Therefore, the control unit 28 can use the AGC signal as a parameter indicating the electric field strength, and when the gain obtained from the AGC signal falls below a certain threshold, the normal passband W and the gain obtained from the AGC signal exceed the threshold. If so, a coefficient group corresponding to the narrow pass band N is input to the band pass filter 23 and the pass band of the band pass filter 23 is switched.

  Further, when the PLL circuit 32 generates the clock CLK having the same phase as the horizontal synchronization signal separated by the synchronization signal separation unit 30, the control unit 28 determines the passband of the bandpass filter 23 according to the lock rate of the PLL circuit 32. May be controlled. Here, the lock rate refers to a ratio within a certain period of time that the state in which the phase of the reference clock CLK generated by the PLL circuit 32 and the phase of the horizontal synchronizing signal coincide (lock state) continues.

  When the electric field strength of the received signal is weak, if the phase of the horizontal synchronizing signal is disturbed due to the influence of noise, a phase difference between the horizontal synchronizing signal input to the PLL circuit 32 and the reference clock CLK is generated. The locked state is released, and the PLL circuit 32 operates to synchronize the phase of the reference clock CLK with the horizontal synchronizing signal. On the contrary, when the electric field strength is strong, the phase of the horizontal synchronizing signal is stabilized and the locked state is maintained. Therefore, the control unit 28 can use the lock rate of the PLL circuit 32 as a parameter indicating the electric field strength. Upon receiving the lock rate detected by the PLL circuit 32, if the lock rate is higher than the threshold, the normal passband If W and the lock rate are equal to or lower than the threshold, a coefficient group corresponding to a narrow pass band N is input to the band pass filter 23, and the pass band of the band pass filter 23 is switched.

  In this way, even when the control unit 28 does not receive the electric field strength signal or the AGC signal from the television signal receiving apparatus 100, the control unit 28 sets the pass band corresponding to the reception state of the television signal based on the composite video signal CMVS. The filter 23 can be set.

  The control unit 28 may control the passband of the bandpass filter 23 based on the color burst signal used when the color demodulation unit 24 extracts the color difference signals Cb and Cr from the color signal C. The color burst signal is included in the composite signal, and the phase of the burst signal is used as a reference when the color demodulation unit 24 performs phase selective detection of the color difference signals Cb and Cr from the color signal C. As shown in FIG. 5A, in the composite signal CMVS1 corresponding to one line of video, the color burst signal CB is approximately 4 between the horizontal sync signal HS and the composite signal of the color signal C and the luminance signal Y. It is inserted as a 3.58 MHz signal in 7 μS.

  The composite video signal CMVS1 (FIG. 5A) is separated into a color signal C, a color burst signal CB (FIG. 5B), and a luminance signal Y (FIG. 5C) by the signal extraction unit 22. The color burst signal section CBP into which the color burst signal CB is inserted corresponds to about 4.7 μS following the horizontal synchronizing signal HS of the luminance signal Y (FIG. 5A). Therefore, the noise detection unit 25 to which the luminance signal Y extracted by the signal extraction unit 22 is input detects the color burst signal interval CBP based on the reference clock CLK synchronized with the horizontal synchronization signal HS, and detects the frequency component in that interval. (FIG. 5C). Since no signal originally exists in the color burst signal section of the luminance signal Y from which the color signal C and the color burst signal have been removed, the signal detected in this section is a noise component. Since the amount of noise component is a measure of the amount of noise component mixed in the color signal C, the S / N ratio of the received signal deteriorates if the noise component in the color burst signal section CBP is large.

  Therefore, the color demodulator 24 detects a signal at 4.7 μS after the reference clock CLK received from the PLL circuit 32, and when a noise component is detected, inputs the component amount to the controller 28. Then, the control unit 28 selects a coefficient group corresponding to the normal passband W if the noise component amount of the color burst signal section received from the color demodulator 24 is smaller than the threshold, and the narrow passband N if the noise component is greater than the threshold. The signal is input to the band pass filter 23 and the pass band of the band pass filter 23 is switched.

  Further, since the color burst signal CB is inserted so that the phase is reversed for each line, the phase difference between the color burst signal of one line and the color burst signal of the next line must be 180 degrees. The phase of the color burst signal is disturbed due to the noise, that is, the S / N ratio of the received signal is lowered. Therefore, the color demodulator 24 detects a color burst signal of continuous lines from the color signal C based on the reference clock CLK, and inputs the phase difference between the color burst signals to the controller 28. When the phase difference is 180 degrees, the control unit 28 inputs the coefficient group corresponding to the normal pass band W, and when the phase difference is not 180 degrees, the narrow pass band N is input to the band pass filter 23. The pass band of the filter 23 is switched.

  As described above, the control unit 28 can set the passband of the bandpass filter 23 in accordance with the electric field strength of the television signal or various parameters correlated with the electric field strength.

  In the above example, the control unit 22 sets two types of coefficient groups in the bandpass filter 23, thereby setting a pass band corresponding to each coefficient group. Such coefficients are stored in the coefficient table 29 in advance, but the coefficient table can be stored in a rewritable nonvolatile storage device so that the coefficient group can be set appropriately. By doing so, for example, at the time of factory shipment, the control unit 28 calculates the optimum coefficient according to the hardware characteristics of the bandpass filter 23 by the benchmark test and stores the calculated coefficient in the coefficient table 29. It is possible to change the pass band of the band pass filter 23 by setting the stored coefficient group.

  Further, the CPU 34 may obtain a coefficient group corresponding to the electric field strength or the like by calculation. By doing so, as shown in FIG. 3B, when the electric field strength falls below the threshold value THV, the CPU 34 sets the pass band of the band pass filter 23 according to the electric field strength signal, the AGC signal, the PLL lock rate, and the like. The coefficient for setting the passband is calculated and set in the bandpass filter 23. By doing so, a step-by-step pass band can be set according to a change in electric field strength, and video quality can be improved step by step. Furthermore, as a modified example in that case, when the control unit 28 changes the pass band of the band pass filter 23, the switching may be performed in a hysteresis manner.

  FIG. 6 is a diagram for explaining the operation of the control unit 28 that changes the passband of the bandpass filter 23 in a hysteresis manner. 6A is a flowchart for explaining the operation procedure of the control unit 28, and FIGS. 6B and 6C are diagrams showing the relationship between the electric field strength and the pass bandwidth.

  First, FIG. 6B shows a case where the control unit 28 does not perform switching of the pass band of the bandpass filter 23 in a hysteresis manner. The control unit 28 uses the electric field strengths V1 and V2 as thresholds, and sets the pass band to W when the electric field strength signal is larger than the electric field strength V1, and N to pass the band when the electric field strength signal is smaller than the electric field strength V2. A coefficient is set in the pass filter 23. And between electric field strengths V1 and V2, the pass band is controlled so that the pass band changes linearly from W to N according to the electric field strength signal. However, in this method, when the electric field strength fluctuates in an unstable manner between the threshold value V1 and the threshold value V2, the pass band of the bandpass filter fluctuates in an unstable manner in accordance with the fluctuation of the electric field strength signal, and is displayed as a result. The video becomes unstable. Therefore, the operations shown in FIGS. 6A and 6C are performed.

  First, the control unit 28 determines the passband set in the bandpass filter 23 (S10 in FIG. 6A). When the wide passband W is set ((W in S10 in FIG. 6A, B10 in FIG. 6C)), the electric field strength signal becomes equal to or lower than the threshold value V1 ((FIG. 6 ( A) YES in S20), the CPU 34 calculates a coefficient for setting a pass band according to the electric field strength (weak electric field), and sets the coefficient in the bandpass filter 23 (S22 in FIG. 6A). 6 (C) B22) When the pass band is set to a narrow pass band N, the change of the pass band is terminated (S24 in FIG. 6A, B12 in FIG. 6C)).

  On the other hand, when the narrow passband N is set ((N in S10 in FIG. 6A, B12 in FIG. 6C)), when the electric field strength signal becomes larger than the threshold value V3 (( 6), the CPU 34 calculates a coefficient for setting a pass band according to the electric field strength (strong electric field), and sets the coefficient in the band-pass filter 23 (FIG. 6A). S32, B32 in FIG. 6C) When the passband is set to a wide passband W, the change of the passband is terminated (S34 in FIG. 6A, B10 in FIG. 6C). ).

  With the above operation, the passbands W and N of the bandpass filter 32 can be switched in a hysteresis manner. That is, the control unit 28 maintains the pass band W between the electric field strengths V1 and V3 when operating in the direction of narrowing the pass band, and when operating in the direction of widening the pass band. N is maintained. By doing so, even when the electric field strength fluctuates in an unstable manner between V1 and V3, it is avoided that the image becomes unstable by switching the pass band sensitively according to the fluctuation of the electric field strength signal. can do.

  As described above, according to the television signal processing apparatus in the present embodiment, even when the S / N ratio of the entire television signal is reduced, the S / N ratio of the extracted color signal can be improved. It is possible to reduce the color quality degradation of the video.

It is a figure explaining the structure of the television signal processing apparatus in this Embodiment. It is a figure explaining the frequency component of a composite video signal. It is a figure explaining the pass band of the band pass filter 23 according to electric field strength. FIG. 6 is a diagram for explaining the frequency characteristics of the output of the bandpass filter 23. It is a figure explaining the waveform of a composite video signal. It is a figure explaining operation | movement of the control part 28 which performs the change of the pass band of the band pass filter 23 like a hysteresis.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100: Television signal receiver 200: Television signal processor 22: Signal extraction part 23: Band pass filter 28: Control part CMVS: Composite video signal C: Color signal Y: Luminance signal

Claims (6)

A television signal processing device for receiving composite video signal input from a television signal receiving device,
When the reception state of the television signal is the first reception state, the first frequency band is used. When the second reception state is worse than the first reception state, the second frequency band is narrower than the first frequency band. A signal extraction unit for extracting the color signal from the composite video signal in a frequency band;
A television signal processing apparatus that outputs a video signal based on a luminance signal obtained by removing the color signal from the composite video signal and the color signal. In claim 1,
The first reception state is when the electric field intensity of the television signal is a first intensity, and the second reception state is when the electric field intensity is a second intensity that is weaker than the first intensity. A television signal processing apparatus characterized by the above. In claim 1,
The first reception state is when the AGC signal of the television signal receiving apparatus is a signal for setting the first gain, and the second reception state is a state where the AGC signal is larger than the first gain. A television signal processing apparatus, wherein the signal has a gain of 2. In claim 1,
A PLL circuit for inputting a synchronization signal extracted from the composite video signal and outputting a clock signal synchronized with the synchronization signal;
The first reception state is when the lock rate, which is the ratio of the lock time within a predetermined time of the PLL circuit, is the first lock rate, and the second reception state is the lock rate of the PLL circuit. The television signal processing apparatus according to claim 1, wherein the second lock ratio is smaller than the first lock ratio. In any one of Claims 1 thru | or 4,
When the frequency band for extracting a color signal is switched from the first frequency band to the second frequency band, the signal extraction unit has a first correspondence relationship between the frequency band for extracting the color signal and the reception state. When the frequency band is switched from the second frequency band to the first frequency band, the frequency band from which the color signal is extracted and the reception state indicate a second correspondence relationship. . A television signal processing method for processing a composite video signal output from a television signal receiver,
When the reception state of the television signal is the first reception state, the first frequency band is used. When the second reception state is worse than the first reception state, the second frequency band is narrower than the first frequency band. Extracting the color signal from the composite video signal in a frequency band;
Removing the color signal from the composite video signal to extract a luminance signal;
A television signal processing method comprising: outputting a video signal based on the color signal and the luminance signal.

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