JPH0787590B2 - Color signal processing circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a color signal processing circuit of a television signal for performing I-axis and Q-axis color demodulation using a motion adaptive Y / C separation circuit.

[Conventional technology]

In the current NTSC receiver, color signal (hereinafter referred to as C)
Is frequency-multiplexed with a luminance signal (hereinafter referred to as Y), which causes cross color interference and dot interference, resulting in deterioration of image quality.

A motion adaptive Y / C separation circuit is known as a means for realizing high image quality excluding these image quality deterioration factors.

It detects the motion of the image and performs Y / C separation by inter-frame processing using a frame comb filter in the still image area, line comb filter in the video area, or bandpass filter (hereinafter referred to as BPF). ), Y / C separation is performed by in-field processing using a low-pass filter (hereinafter referred to as LPF) to achieve high image quality.

As a color signal processing circuit using this type of Y / C separation circuit,
For example, those described in JP-A-58-129892 and JP-A-55-123280 can be mentioned.

[Problems to be solved by the invention]

In the NTSC system, (R
There are -Y) axis, (BY) axis, I axis, and Q axis.

The signals corresponding to the (RY) axis and the (BY) axis are both 0.
The signal corresponding to the I-axis is 1.5M while it has a band of 5MHz
The signal corresponding to the Hz and Q axes has a band of 0.5 MHz.

In general, the human eye has the visual characteristic that the color resolution is superior to orange and cyan (I axis), and a television that can realize high image quality by a motion adaptive Y / C separation circuit. In the receiver, I-axis and Q-axis demodulation with high color resolution is suitable.

However, in the above-mentioned conventional technique, no consideration has been given to I and Q axis demodulation.

In the Y / C separation in the field in the moving image area of the above-mentioned conventional technique, complete separation cannot be performed in principle, and dot interference and cross color interference are reduced.

Therefore, when I-axis and Q-axis demodulation is applied, crosstalk with the Y signal increases due to the wide band of the I signal, and the (RY) axis and (BY) axis demodulation in the moving image area. On the other hand, there is a problem that the image quality is deteriorated because the deterioration due to the cross color interference is larger than the improvement of the color resolution.

It is an object of the present invention to provide a color signal processing circuit that is suitable for a motion adaptive Y / C separation circuit that performs I-axis and Q-axis demodulation.

[Means for solving problems]

The above object is achieved by providing demodulation band varying means for varying the demodulation band of the I signal according to the control signal output from the motion detection circuit.

[Action]

The motion detection circuit detects motion from the difference in signal level between frames, and outputs the Y / C separation circuit between frames and Y in the field.
/ C Outputs a control signal for controlling the mixing ratio of the output of the separation circuit.

The demodulation band changing means changes the demodulation band to a wide band (for example, 0 to 1.5 MHz) in the still image region and a narrow band (for example, 0 to 0.5 MHz) in the moving image region based on the control signal.

As a result, the amount of cross color with the Y signal can be reduced in the moving image area, and cross color interference can be reduced.

〔Example〕

 Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a first embodiment of a color signal processing circuit according to the present invention, in which 1,18 are input terminals, 2, 4, 10, 17
Is a delay circuit, 3 is a subtractor, 5, 14 and 15 are output terminals, 6 is an inter-frame C separation circuit, 7 is an intra-field C separation circuit,
Reference numeral 11 is a mixer, 9 is a BPF composed of an acyclic (hereinafter referred to as FIR) type digital filter, 12 is a multiplexer, 13 is a color demodulation circuit, and 16 is a motion detection circuit.

In the figure, the A / D-converted digital composite video signal from the input terminal 1 is passed through a delay circuit 2 to a subtractor 3, an inter-frame C separation circuit 6, an intra-field C separation circuit 7, and a motion detection circuit 16. Given.

As the sampling frequency is selected in the A / D conversion, generally Iro含carrier frequency _SC (≒ 3.58 MHz) of three times the 3 _SC (≒ 10.74MHz) or 4 times 4 _SC (≒ 14.32MH
z) is available. Hereinafter, in the embodiment of the present invention, the sampling frequency is 4
The case of _SC is explained.

The inter-frame C separation circuit 6 is composed of a FIR type digital filter having a tap delay circuit of at least one frame period unit, and limits the band on the time-frequency axis to remove the color signal component from the composite video signal. It is to separate and extract.

The intra-field C separation circuit 7 is composed of an FIR type digital filter having one or both of 1H (H indicates a horizontal scanning period) or one pixel unit tap delay circuit, and a horizontal frequency axis and a vertical frequency axis. By performing the band limitation above, the color signal components are separated and extracted from the composite video signal.

In order to obtain color signals with high color resolution by performing color demodulation on the I axis and Q axis, the color signals obtained from the inter-frame C separation circuit 6 and the intra-field C separation circuit 7 are at least as components on the horizontal frequency axis. Is the color subcarrier frequency _SC (≈3.58MH
A band pass characteristic of ± 1.5MHz or more is required around z).

The motion detection circuit 16 is composed of an FIR type digital filter having a tap delay circuit of at least one frame period unit, detects the motion amount of the composite video signal, and outputs a control signal k for controlling the mixers 8 and 11. Is.

The color signal C _F obtained from the inter-frame C separation circuit 6 and the color signal C _f obtained from the intra-field C separation circuit 7 are applied to the mixer 8 at their inputs.

The mixer 8 has an addition ratio determined by the control signal k.
Add C _F and C _f . The control signal k has a value in the range of 0 ≦ k ≦ 1 so that the addition ratio of C _F is large when the motion amount is small and the addition ratio of C _f is large when the motion amount is large.

The color signal obtained from the output of the mixer 8 is the subtractor 3, BPF
9, given to the delay circuit 10.

The luminance signal is obtained by removing the color signal component in the composite video signal from the output of the subtractor 3, and the extracted luminance signal is output from the output terminal 5 via the delay circuit 4.

The BPF 9 limits the input color signal to a narrow band, and has a bandpass characteristic of about ± 0.5 MHz centering on the _SC , for example.

The delay circuit 10 corrects the delay time difference between the narrow band color signal obtained from the BPF 9 and the wide band color signal which is the input,
Actually, the tap delay circuit of BPF9 can be used instead.
In this case, it is not necessary to separately provide the delay circuit 10.

The mixer 11 as the demodulation band varying means receives the narrow band color signal obtained from the BPF 9 and the wide band color signal obtained from the delay circuit 10 as input, and changes the motion amount by the control signal k obtained through the delay circuit 17. When the amount is small, the addition ratio of the wideband color signals is increased, and when the amount of movement is large, the addition ratio of the narrowband color signals is increased, and both are mixed.

Here, when the sampling frequency at the time of A / D conversion is 4 _SC , four sampling points are obtained in one cycle of the color subcarrier. At this time, if the sampling clock is made to be a phase clock for the I axis and the Q axis, these four sampling points become I, Q, −I, −Q, and the sampling points for only the I component and the sampling points for the Q component only. It is obtained in time-division multiplexed form.

Therefore, the output of the BPF 9 is led to one input of the multiplexer 12, and the output of the mixer 11 is led to the other input, and this is input to the input terminal.
Controlled by the timing signal supplied from 18, the sample value of the Q component is alternately selected from the output of the BPF 9 and the sample value of the I component is alternately selected from the output of the mixer 11 in pixel units, and output to the color demodulation circuit 13.

The color demodulation circuit 13 has sampling points (-I, -Q) whose signs are reversed.
Inverts or thins out the sign of
Baseband I and Q signals are obtained by separating the sampled value sequence of the components.

The timing signal can be easily derived from a clock recovery circuit that recovers the sampling clock.

According to this embodiment, for the sampled value of the I signal, the demodulation band of the I signal can be made variable by changing the bandpass characteristic according to the motion.

Therefore, since the high frequency component of the I signal can be sufficiently attenuated in the moving image area, I
Cross-color interference can be reduced without losing the advantages of axis and Q axis demodulation.

FIG. 2 is a block diagram showing a second embodiment of the present invention, in which 19 is an inter-frame Y / C separation circuit and 20 is an intra-field Y / C.
Separation circuit, 21 and 22 are mixers, other symbols are first
Corresponds to the same parts as in the figure.

In the figure, the digital composite video signal from the input terminal 1 is applied to the inter-frame Y / C separation circuit 19, the intra-field Y / C separation circuit 20, and the motion detection circuit 16.

The inter-frame Y / C separation circuit 19 is a FIR type digital filter having a tap delay circuit of at least one frame cycle unit, and separates and extracts a luminance signal and a chrominance signal by performing band limitation on the time-frequency axis. It is a thing.

The intra-field Y / C separation circuit 20 is a FIR type digital filter having one or both of 1H-unit or 1-pixel-unit tap delay circuits, and is a luminance signal by band limitation on the horizontal frequency axis and the vertical frequency axis. The color signals are separated and extracted.

Also in this embodiment, the color signals obtained from the inter-frame Y / C separation circuit 19 and the intra-field Y / C separation circuit 20 must have the same band as in the first embodiment.

Luminance signals Y _F and Y _f obtained from each of the inter-frame Y / C separation circuit 19 and the intra-field Y / C separation circuit 20 are given to the input of the mixer 21, and the color signals C _F and C _f are mixed. Given to 22 inputs.

The mixers 21 and 22 are the same as those in the first embodiment in the motion detection circuit 1
The luminance signals are obtained from the mixer 21 and the color signals are obtained from the mixer 22 by adding at the addition ratio determined by the control signal k output from 6.

The chrominance signal obtained from the mixer 22 is given the narrow band chrominance signal and the wide band chrominance signal to the two inputs of the mixer 11 via the BPF 9 and the delay circuit 10 as in the first embodiment, and the delay circuit 17 The addition ratio is controlled by the control signal k obtained via

The multiplexer 12 and the color demodulation circuit 13, which receive the color signal obtained from the mixer 11 and the color signal obtained from the BPF 9, as input, perform the same operation as in the first embodiment to demodulate and output the I signal and the Q signal. .

Therefore, also in the present embodiment, the demodulation band of the I signal can be changed similarly to the first embodiment, and the cross color in the moving image area can be obtained without impairing the advantages of the I axis and Q axis demodulation in the still image area. Interference can be reduced.

FIG. 3 is a block diagram showing a third embodiment of the present invention, in which 23, 27 and 29 are delay circuits, 24, 25 and 26 are LPFs composed of FIR type digital filters, and 28 is a mixer. , And other symbols are the same as those in the previous embodiment.

In the figure, Y / C separation is performed by the delay circuit 2, the inter-frame C separation circuit 6, the intra-field C separation circuit 7, the mixer 8, the motion detection circuit 16, as in the first embodiment shown in FIG. The luminance signal from the output of the subtractor 3
The color signal is obtained from the output of.

The color signal obtained from the mixer 8 is given to the input of the color demodulation circuit 13. The Q signal obtained from the color demodulation circuit 13 is given to the LPF 24 having a pass band of approximately 0 to 0.5 MHz to remove the crosstalk component with the high frequency component (0.5 to 1.5 MHz) of the I signal, It is limited and output to the output terminal 14.

The I signal obtained from the color demodulation circuit 13 is LPF 25, 26.
Given to each input of. The LPF25 limits the I signal to a narrow band, and the pass band is, for example, 0 to 0.5M.
It can be done by setting to about Hz. The LPF 26 connects the I signal to a wide band, and the pass band is about 0 to 1.5 MHz.

The output of the LPF 26 is corrected by the delay circuit 27 for the delay time difference from the output of the LPF 25, and is given to one input of the mixer 28. The output of the LPF 25 is given to the other input of the mixer 28, and the addition ratio is controlled by the control signal k obtained through the delay circuit 23.

This operates to increase the addition ratio of wideband I signals when the amount of motion is small, and to increase the addition ratio of narrowband I signals when the amount of motion is large.

Therefore, also in the present embodiment, the demodulation band of the I signal can be changed according to the motion amount as in the previous embodiment, and the high frequency component of the I signal can be attenuated in the moving image area, so that cross color interference can be reduced. is there.

In this embodiment, if the sampling frequency is set to, for example, 4 _SC and the harmonics generated by demodulation can be treated in the same manner as the harmonics generated by sampling, the Y / C separation process in the previous stage is performed. The LPF 26 can be made unnecessary by performing the band limitation on the horizontal frequency axis of the color signal performed in step 1 in accordance with the demodulation band of the I signal determined by the LPF 26.

Further, when the LPF 26 is removed, the delay circuit 27 can substitute the tap delay circuit forming the LPF 25.

Further, as described above, when the sampling frequency is set to 4 _SC , the sample value of the I component and the sample value of the Q component are obtained in a time-division multiplexed form, so that the LPF25 and 26 are shared by the time-division processing. It is possible to reduce the circuit scale.

Further, the output of the mixer 22 shown in FIG. 2 is supplied to the color demodulation circuit shown in FIG.
It is obvious that the I-signal demodulation band varying means of this embodiment can be applied to the embodiment of the motion adaptive Y / C separation circuit shown in FIG. 2 by connecting it to 13 inputs.

FIG. 4 is a block diagram showing a fourth embodiment of the present invention, in which 30, 31, 32, and 34 are delay circuits, 33 is a BPF composed of a FIR type digital filter, and other symbols are the same as those in the previous embodiment. Same as the example.

In the figure, the inter-frame Y / C separation circuit 19 and the intra-field Y / C separation circuit 20 have the configurations described in the previous embodiments, and the digital composite video signal input from the input terminal 1 is used as a luminance signal. And color signals.

The luminance signal Y _F output from the inter-frame Y / C separation circuit 19 is given to one input of the mixer 21 via the delay circuit 30,
The color signal C _F is given to one input of the mixer 22 via the delay circuit 31.

Luminance signal Y _f output from Y / C separation circuit 20 in the field
Becomes the other input of the mixer 21 via the delay circuit 32, and the color signal C _f becomes the other input of the mixer 22 via the BPF 33.

The BPF 33 narrows the band of the wideband color signal extracted from the in-field Y / C separation circuit 20, and has a passband of about ± 0.5 MHz centering on _SC , for example.

The mixing ratios of the mixers 21 and 22 are controlled by the control signal k provided from the motion detection circuit 16 through the delay circuit 34 as in the previous embodiment, and the luminance signal is output from the output of the mixer 21 to the mixer 22. The color signal is obtained from the output of. The color signal obtained from the mixer 22 is demodulated and separated by the color demodulation circuit 13 into baseband I and Q signals.

According to this embodiment, by providing the narrow band BPF 33 in the path for supplying the color signal from the in-field Y / C separation circuit 20 to the mixer 22, the narrow band of the I signal in the moving image area can be achieved and the I signal can be narrowed. A mixer for changing the demodulation band of can be shared.

In addition, in the first embodiment of FIG.
By providing a narrow band BPF 33 as in the present embodiment in the path connecting the separation circuit 7 and the mixer 8, instead of the demodulation band variable means of the I signal in the embodiment of FIG. Obviously, the variable means can be applied.

FIG. 5 is a block diagram showing a fifth embodiment of the present invention, in which 35 and 36 are BPFs composed of FIR type digital filters, 37 and 4
2, 46, 50, 51, 52 are delay circuits, 38 is a multiplexer, 39 is a color demodulation circuit, 40 is an inter-frame C separation circuit, 41 is an intra-field C separation circuit, and 43 is an FIR type digital filter.
PFs, 44 and 53 are mixers, 45 is a demultiplexer, 48 is an inter-frame Y separation circuit, 49 is an intra-field Y separation circuit, and other symbols are the same as in the previous embodiment.

In the figure, the inter-frame Y separation circuit 48 and the inter-frame C separation circuit 40 are composed of FIR type digital filters having a map delay circuit of at least one frame period unit, and the luminance signal and the luminance signal are generated by band limitation on the time-frequency axis. The color signals are separated and extracted.

In-field Y separation circuit 49 and in-field C separation circuit
41 is composed of a FIR type digital filter having one or both tap delay circuits in 1H unit or pixel unit, and separates luminance signal and chrominance signal by band limitation on horizontal frequency axis and vertical frequency axis. , To be extracted.

The digital composite video signal input from the input terminal 1 is BP
It is given to each input of the motion detection circuit 16, the inter-frame Y separation circuit 48, and the intra-field Y separation circuit 49 via the F35 and the delay circuit 46.

Inter-frame Y separation circuit 48 and intra-field Y separation circuit 49
The outputs Y _F and Y _f of each of the signals are given to the input of the mixer 53 via the delay circuits 51 and 52, respectively, and the motion detection circuit 16 delays the delay circuit 50.
A luminance signal that has been added by the addition ratio determined by the control signal k given through the signal and adaptively separated is obtained at the output terminal 5.

The BPF 35 passes the color signals multiplexed in the input composite video signal, and the respective outputs are given to the input of the multiplexer 38 via the BPF 36 and the delay circuit 37.

The BPF 35 determines the demodulation band of the I signal, and has a pass band of about ± 1.5 MHz centering on the _SC , for example.

The BPF 36 determines the demodulation band of the Q signal, and has a pass band of about ± 0.5 MHz centering on the _SC , for example.

As described above, when the sampling frequency is 4 _SC , the sampled values of the I component and the Q component are obtained in a time division multiplexed form.

Therefore, the multiplexer 38 alternately selects the sample value of the Q component from the output of the BPF 36 and the sample value of the I component from the output of the delay circuit 37 on a pixel-by-pixel basis according to the timing signal supplied from the input terminal 18, and performs color demodulation. Output to circuit 39.

As a result, I in the color signal supplied to the color demodulation circuit 39
Independent band limitation can be performed for a component and a narrow band for the Q component.

The color demodulation circuit 39 demodulates the input color signal by the means described above, and does not separate them but time-division-multiplexes them, and inputs each of the inter-frame C separation circuit 40 and the intra-field C separation circuit 41. Given to.

The output C _F of the inter-frame C separation circuit 40 is given to one input of the mixer 44 via the delay circuit 42, and the output C _f of the intra-field C separation circuit 41 is given to the other input of the mixer 44 via the LPF 43. The mixer 44 adds the C _F and C _f at an addition ratio determined by the control signal k.

The output of the mixer 44 is applied to the demultiplexer 45, and is divided into a sampled value sequence of the I signal and a sampled value sequence of the Q signal by the timing signal and output.

The LPF 43 narrows the sampled value band of the I component, and has a band of about 0 to 0.5 MHz, for example.

Therefore, also in this embodiment, the demodulation band of the I signal in the moving image region can be narrowed, and the crosstalk can be reduced without impairing the advantages of the I axis and Q axis demodulation in the still image region.

FIG. 6 is a block diagram showing a sixth embodiment of the present invention, 54 is a color demodulation circuit, and other reference numerals are the same as those in the fifth embodiment of FIG.

In the figure, the luminance signal obtained at the output terminal 5 is obtained by the same operation as that of the fifth embodiment described in FIG.

The color demodulation circuit 39 uses the BPF 35, the delay circuit 37, the BPF 36, and the multiplexer to demodulate the color signal in which the sample value of the I signal limited to the wide band and the sample value of the Q signal limited to the narrow band are time-division multiplexed. The output is given to the inter-frame C separation circuit 40 of.

The color demodulation circuit 54 demodulates the color signal limited to the output of the BPF 36, and supplies the output to the intra-field C separation circuit 41.

This inter-frame C separation circuit and intra-field C separation circuit
The output of each of 41 is input to the mixer 44, and the motion detection circuit 16
The signals are added by the addition ratio determined by the control signal k output from the demultiplexer 45, and separated by the demultiplexer 45 into a sample value string of the I signal and a sample value string of the Q signal and output.

According to this embodiment, the inter-frame C separation circuit 40 can be preliminarily supplied with the wideband demodulated I signal and the intra-field C separation circuit 41 can be preliminarily supplied with the narrowband demodulated Q signal. It is possible to reduce the crosstalk color in.

〔The invention's effect〕

As described above, according to the present invention, cross color interference in the moving image area when I-axis and Q-axis demodulation is performed can be reduced, color resolution can be improved in the still image area, and I-axis and Q-axis demodulation can be performed. Since the advantages can be maximized, the image quality of the television receiver can be improved, the problems of the above-described conventional techniques can be solved, and a color signal processing circuit having a novel and excellent function can be provided.

[Brief description of drawings]

1, FIG. 2, FIG. 3, FIG. 4, FIG. 5, and FIG. 6 are block diagrams showing respective embodiments of the color signal processing circuit according to the present invention. 3 …… Subtractor 6,40 …… C separation circuit between frames 7,41 …… C separation circuit in field 8,11,21,22,28,44,53 …… Mixer 13,39,54 …… Color Demodulation circuit 16 …… Motion detection circuit 19 …… Y / C separation circuit between frames 20 …… Y / C separation circuit in field

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuo Nakagawa, 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa, Ltd. Home Appliances Research Laboratory, Hitachi, Ltd. (56) Reference JP-A-63-63295 (JP, A)

Claims (1)

[Claims] 1. An inter-frame color separation circuit for separating color signals multiplexed into a television signal, an intra-field color separation circuit, a motion detection circuit for detecting the motion of the television signal, and the motion detection circuit. A motion adaptive type three-dimensional YC separation circuit, which is at least composed of a mixer for mixing a color signal obtained from the inter-frame color separation circuit and a color signal obtained from the intra-field color separation circuit;
A television receiver provided with a color demodulation circuit for performing axis and Q axis color demodulation, comprising demodulation band varying means for varying a demodulation band of an I signal in accordance with a control signal from the motion detection circuit. Characteristic color signal processing circuit.