JP3351630B2 - Y / C separation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an NTSC system and a PAL system.
The present invention relates to a Y / C separation circuit capable of separating a luminance signal and a chrominance signal with high accuracy even when the correlation between horizontal lines of an input composite video signal of a system is small.

[0002]

2. Description of the Related Art FIG. 12 is a block diagram showing a conventional NTSC system Y / C separation circuit for luminance and chrominance signals. Bandpass filter BPF20 for input composite video signal
5 and one horizontal period (H) are supplied to the delay circuit 201. The output signal of the delay circuit 201 is connected to a bandpass filter BPF20.
7 and one horizontal period (H) delay circuit 20
Supply to 3. The output of this delay circuit 203 is
Supply to filter BPF209.

[0003] Bandpass filters BPF205, 207,
At 209, the color signal wave band of each horizontal line is extracted. Here, these signals are called H0, H1, and H2, respectively.
Hereinafter, H1 (= b) is handled as current data. In order to match the phase of the color subcarrier with H1, the phases of H0 and H2 are inverted by inverter circuits 215 and 217, respectively, to be a and c, respectively. Also, adders 211 and 21
Extract d = (a + b) / 2 and e = (b + c) / 2 using 3. These a, b, c, d, and e are input to a 5-tap median filter 219, and the third largest signal level among a, b, c, d, and e is selected and output as a color signal (C). . Then, the 1H delay circuit is generated by the subtractor 221.
The luminance signal (Y) is obtained by subtracting the color signal (C) output from the median filter 219 from the output signal of 201. But,
If the data correlation between the horizontal lines of the input composite video signal is small, the median filter 219 may not extract the desired color signal. In this case the median filter
The dot interference remains in the luminance signal (Y) obtained by subtracting the output of the delay circuit 201 from the output signal of the delay circuit 201.

[0004] This dot disturbance will be described with reference to FIG.
FIG. 13 (a) is a pattern having a red line for one horizontal line at the center of the white screen. Take this pattern with a camera etc. and use NTS
After being extracted as a composite video signal such as a C signal and separated into a luminance signal and a chrominance signal by the Y / C separation circuit shown in FIG. 12, when displayed on the screen of the television receiver, the result is as shown in FIG. 13 (b). . This is because the color signal component remains in the luminance signal (Y) separated by the Y / C separation circuit and is displayed on the screen of the television receiver in the form of dots. In other words, this indicates that the conventional Y / C separation circuit cannot sufficiently separate the luminance signal and the chrominance signal.

The above description will be described more specifically with reference to FIGS. 14 and 15.

FIG. 14 and FIG. 15 schematically show 14 lines of a video signal. The horizontal axis 10 width in the figure indicates one horizontal period,
In the waveform diagram corresponding to the color signal of FIG. 14, ((n +
1) / 2) Includes a sine wave of wavelength (n: integer). This is a simplified representation of the color signal. In the waveform diagram corresponding to the luminance signal in FIG. 15, a sine wave of n wavelengths is included in the width of 10 on the horizontal axis. This is also a simplified representation of the luminance signal. In the figure, H0 is a band-pass filter BPF205.
, H1 indicates the output of the bandpass filter BPF207, and H2 indicates the output of the bandpass filter BPF209. Considering H1 as the current signal, H2 is the past, H0
Is the signal of the future. Focusing on the vertical impulse pattern in the waveform diagram corresponding to the color signal in FIG. 14, when the color signal exists only in H1 (line 13) and when the color signal exists only in H1 (line 14), the median filter 219 Is different from the current H1 signal. Therefore, dot interference (one-line dot interference) appears in the luminance signal (Y) obtained by subtracting the output of the median filter 219 from the input composite video signal.

[0007]

As described above, in the conventional Y / C separation circuit, the current horizontal data of the input composite video signal and the data before and after the m horizontal period (m is NTSC = 1, PAL)
= 2), when the correlation between the current horizontal data and the other two horizontal data is small, one-line dot interference occurs in the separated luminance signal, which hinders the image quality of the television receiver.

According to the present invention, Y /
It is an object to provide a C separation circuit.

[0009]

In a Y / C separation circuit for separating a luminance signal and a chrominance signal from an input composite video signal, the input composite video signal is input, and the past, present, and future of the composite video signal are inputted. A three-line color signal separation circuit that separates a color signal from data of two horizontal lines, a horizontal color signal separation circuit that receives the input composite video signal as input, and separates a high-frequency component of the composite video signal as a color signal; An input composite video signal is input, and the horizontal low-pass signal level of the current line is compared with the horizontal low-pass signal levels of the past and future lines. A vertical impulse detection circuit, which receives the input composite video signal as an input, and wherein the horizontal high band signal level of the current line is a maximum value compared to the horizontal high band signal levels of the past and horizontal lines. A high-level vertical impulse detection circuit for detecting whether or not the minimum value or the minimum value, an OR of an output of the horizontal low-frequency vertical impulse detection circuit, and an output of the horizontal high-range vertical impulse detection circuit Circuit, a selector for selecting an output signal of the three-line color signal separation circuit and an output signal of the horizontal color signal separation circuit according to an output of the OR circuit, and delaying the input composite video signal by a predetermined time. And a subtractor for subtracting the output signal of the selector from the output signal of the delay circuit, and the output signal of the subtractor is a luminance signal.

[0010]

The horizontal low band vertical impulse detection circuit detects whether the horizontal low band level of the current line is the maximum value and the minimum value or not in comparison with the horizontal low band signal levels of the past and future lines. At the same time, the horizontal high band vertical impulse detection circuit detects that the horizontal high band signal level of the current line is
Compared with the horizontal high band signal level of the past and future lines, it detects whether it is the maximum value and the minimum value or not.

The OR circuit performs an OR operation on the outputs of the vertical impulse detection circuits for the horizontal low band and the horizontal high band, and supplies the result to a selector. At least the horizontal low band signal level of the current line is the maximum value and the minimum value compared to the horizontal low band signal levels of the past and future lines, or the horizontal high band signal level of the current line is the horizontal high band signal level of the past and future lines In the case of the maximum value and the minimum value, the selector selects the output signal of the horizontal color signal separation circuit and supplies it to the subtractor.

The horizontal low band signal level of the current line is neither the maximum value nor the minimum value of the horizontal low band signal levels of the past and future lines, and the horizontal high band signal level of the current line is the horizontal level of the past and future lines. If neither the maximum nor the minimum relative to the high-frequency signal level, the selector is 3
Select the output of the line color signal separation circuit.

The subtractor subtracts the output signal of the selector from the output signal of the delay circuit to obtain a luminance signal.

[0014]

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

FIG. 1 shows a first embodiment of a Y / C separation circuit according to the present invention. In FIG. 1, a three-line color signal (C) separation circuit 1 to which an input composite video signal is input outputs a separated color signal (C ′). Horizontal color signal (C) separation circuit 3
Separates a horizontal high-frequency component from the input composite video signal and outputs a color signal (C ″). The selector 11 outputs a three-line color signal separation circuit based on the output of the OR circuit 9 described later. 1 (C ') or horizontal color signal separation circuit 3
Output (C ") of the selected color signal (C").
C) is supplied to one end of the subtractor 15. Further, the input composite video signal is delayed by a predetermined time by the delay circuit 13 and time alignment is performed, and is supplied to the other end of the subtractor 15. Subtractor 15
Subtracts the color signal (CC) output from the selector 11 from the output of the delay circuit 13 to generate a luminance signal (Y). Although the color signal output is not particularly specified, the color signal output of the three-line color signal separation circuit 1 is used as a color signal (C) here. This color signal (C) may be the same signal as the color signal (C '). The horizontal low band vertical impulse detector 5 detects the horizontal low band vertical signal impulse pattern of the input composite video signal from the current horizontal low band signal data of the input composite video signal and the horizontal low band signal data of the upper and lower two lines. Things.
The horizontal high band vertical impulse detector 7 detects a horizontal high band vertical impulse pattern of the input composite video signal from the current horizontal high band signal data of the input composite video signal and the horizontal high band signal data of the upper and lower two lines. It is. The specific circuit will be described later.

FIG. 2 shows a second embodiment of the Y / C separation circuit of the present invention. In the figure, the blocks using the same numbers as those in FIG. The output signal of the selector 11 is converted to a band-pass filter BPF17 for limiting the horizontal band.
, And supplies the color signal (CC) output of the band-pass filter BPF 17 to the subtractor 15. The band-pass filter BPF 17 is inserted so as not to remove the luminance signal oblique characteristic component in the input composite video signal. Thereby, the oblique characteristic component of the separated luminance signal remains without being removed, and so-called image blur is reduced.

FIG. 3 is an explanatory diagram of a vertical impulse pattern. FIG. 3A shows a screen of the television receiver.
In the case where the circles A, B, and C on the lines N-1, N, and N + 1 are the patterns shown in FIGS. 3B and 3C, it is determined that the pattern is a vertical impulse pattern. That is, it is only necessary to detect a case where the level of the current (N) horizontal line signal B is lower than the signals A and C of the horizontal lines N-1 and N + 1 and a case where the level is higher than the levels of A and C. Note that A, B, and C are not the input composite video signal itself, but the low-pass filter L.
This is a signal from which the color subcarrier band has been removed by PF or the like. That is, the fact that the horizontal low-frequency component of the input composite video signal and the color signal in the input composite video signal modulated by the color subcarrier have a strong correlation with the vertical pattern is used. One embodiment that achieves this is shown in FIGS.

FIG. 4 shows another vertical impulse pattern explanatory diagram. G, H, and I in FIG. 4A correspond to A, B, and C in FIG. FIG. 4 (a) shows the three-line color signal separation circuit 1.
When such a signal is input, a color signal as shown in FIG. 4B is output. When this color signal is subtracted from the input composite video signal whose time has been adjusted by delaying it for a predetermined time, FIG.
As shown in (c), dot interference occurs in which a chrominance signal remains in the luminance signal. As shown here, even when the level of the horizontal low band (luminance signal) is the same, dot disturbance occurs when the level of the color signal is an impulse pattern in the vertical direction. Therefore, it is determined that the pattern in FIG. 4A is a horizontal high-frequency vertical impulse pattern.

A specific example of the horizontal high band vertical impulse detector 7 will be described later.

FIG. 5 shows a specific circuit configuration of the first embodiment of the Y / C separation circuit of the present invention. In FIG. 5, an input composite video signal is supplied to band-pass filters BPF25, 49, a low-pass filter LPF41, and a delay circuit 21. The delay signal (S) delayed by one horizontal period by the delay circuit 21 is supplied to the band-pass filters BPF27, 51 and the low-pass filter LPF43. The delay signal (S) is further supplied to the delay circuit 23 to delay one horizontal period. This delay signal is supplied to band-pass filters BPF29 and BPF53 and low-pass filter LPF45.

The band sub-filters BPF 25, 27 and 29 take out the color sub-carrier band of each line. Here, these signals are called H0, H1, and H2, respectively. Hereinafter, H
1 = (= b) is treated as current data. In order to match the color subcarrier phase with H1, the phases of H0 and H2 are inverted by inverter circuits 35 and 37, respectively, to be a and c, respectively. Further, using adders 31 and 33, d = (a
+ B) / 2 and e = (b + c) / 2. These a, b, c, d, and e are converted to a 5-tap median filter 39.
And selects the signal having the third highest signal level among a, b, c, d, and e, and outputs it as a color signal (C).

The low-pass filters LPF41, 43, and 45 extract horizontal low-frequency components (luminance signals) of the composite video signal. Let these be A, B, and C, respectively. The signals A, B, and C are supplied to the vertical impulse detector 47, and the processing described later is performed.

The bandpass filters BPF49, 51, and 53 extract the horizontal high-frequency component (color subcarrier band) of the composite video signal of each line. Here, each of these signals is H
3, H4 (= E) and H5. In order to match the color subcarrier phase with H4, the phases of H3 and H5 are inverted by inverter circuits 55 and 57, respectively, to be D and F, respectively. The signals D, E, and F are supplied to the vertical impulse detector 59, and the processing described later is performed.

The output signals of the vertical impulse detectors 47 and 59 are input to the OR circuit 61, respectively. The selector 63 is controlled by the output of the OR circuit 61, and a 5-tap median
The output (C) of the filter 39 or the band-pass filter BP
F27 output (H1) is selected. The subtractor 65 subtracts the selected color signal (CC) from the delay signal (S) delayed by one horizontal period in the delay circuit 21 to obtain a final luminance signal (Y).
Get.

The vertical impulse detectors 47 and 59 need only detect whether or not the following equation is satisfied, and do not limit the circuit configuration.

(Horizontal low band vertical impulse detector) BA> REF, BC> REF (1) AB> REF, CB> REF (2) (Horizontal high band vertical impulse detector) E -D> REF, EF> REF (3) DE> REF, FE> REF (4) Any of the above conditions (1), (2), (3), and (4) is satisfied At this time, the selector 63 is controlled to make the output (H1) of the band-pass filter BPF27 a color signal (CC). When none of the above conditions (1), (2), (3) and (4) is satisfied, the output (C) of the median filter 39 is used as a color signal (CC). Here, REF is a level set in advance, and is usually a value of several tens of IRE for a signal level of 100 IRE.

FIG. 6 shows a specific example of the circuit configuration of the vertical impulse detector 47. The input signals A, B and C are shown in FIG.
A, B, and C signals in the middle are horizontal low-frequency components of the input composite video signal. BA is subtracted from A, B and C by a subtractor 71.
Thus, BC is realized by the subtractor 73. The absolute values of these two difference signals are obtained by absolute value circuits ABS75 and ABS77. Then, the comparators 79 and 81 compare them with a predetermined comparison level value REF, and determine whether or not the above-mentioned condition is satisfied. Also,
Since this is not enough, the difference signals B-A and B-
Exclusive-C
The logical product of the output of the exclusive NOR circuit 85 and the output of the logical product circuit 83 is obtained by the logical product circuit 87 and is used as a detection output by the NOR circuit 85. The same circuit configuration as that shown in FIG. 6 can be used for the vertical impulse detection circuit 59 shown in FIG. The input signal circuit configuration to the vertical impulse detection circuit 59 is also conceivable as shown in FIG. 7, and FIG. 5 is only an example.

In FIG. 7, the horizontal correlation filters HID91, 93, 95
FIG. 8 shows an example of the circuit configuration of FIG. Output of bandpass filter BPF is input to horizontal correlation filter HMID (J)
Then, it is input to the delay circuit 101 and the 3-tap median filter 105. The delay circuits 101 and 103 delay the signal by a time corresponding to one wavelength of the color subcarrier. The output (K) of the delay circuit 101 is input to the delay circuit 103 and the 3-tap median filter 105. The output (L) of the delay circuit 103 is further input to a 3-tap median filter 105. The three tap median filter 105 selects the second largest signal from the three inputs. Further, signals K and 3
In order to see the output code of the tap median filter 105, it is input to an exclusive NOR circuit 107. An AND circuit 109 controlled by the output of the exclusive NOR circuit 107 outputs a signal K and a 3-tap median signal.
When the output of the filter 107 has a different sign, the reference level is output. With the circuit configuration as described above, the horizontal correlation of the color subcarrier can be obtained, and the band-pass filter BP
The effect of the luminance signal component included in the signal extracted at F can be reduced. The circuit configuration is not limited as long as the circuit removes a luminance signal component included in a signal extracted by the band-pass filter BPF. FIGS. 14 and 15 schematically show the function of the circuit of the above embodiment.
This is shown in FIG. 10 and FIG. In the vertical impulse pattern portion (13th and 14th lines) in the color signal equivalent waveform diagram of FIG.
Line dot interference has been eliminated. By comparing the waveform diagram corresponding to the color signal of FIG. 14 with the waveform diagram corresponding to the color signal of FIG. 10, it can be seen from FIG. 10 that the output Y is improved without one-line dot interference. From the comparison between the waveform diagram corresponding to the luminance signal in FIG. 15 and the waveform diagram corresponding to the luminance signal in FIG. 11, the output of the luminance signal (Y) is the same signal. Therefore, it can be seen that there is no problem even when the input composite video signal is only the luminance signal (Y). FIG. 9 shows a specific circuit configuration of the second embodiment. FIG.
5 is that a band-pass filter BPF 67 is inserted between the selector 63 and the subtractor 65. The color signal (C) for subtraction by this bandpass filter BPF67
As described above, due to the band limitation of C), the oblique characteristic component of the luminance signal in the input composite video signal is not subtracted, so-called image blur does not occur, and the image quality does not deteriorate. 5 and 9, instead of taking out one input of the selector 63 from the band-pass filter BPF27, a separate band-pass filter BPF is provided between the delay circuit 21 and the selector 63. May be.

The same can be said for the PAL system. In the case of the PAL system, the delay time of the delay circuits 21 and 23 is two horizontal periods.

[0030]

As described above, according to the Y / C separation circuit of the present invention, even in the case of a vertical impulse pattern signal, it is possible to separate a luminance signal and a chrominance signal while eliminating one-line dot interference. That is, the image quality of the NTSC system and the PAL system can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of a Y / C separation circuit of the present invention.

FIG. 2 is a diagram showing a second embodiment of the Y / C separation circuit of the present invention.

FIG. 3 is an explanatory diagram of a vertical impulse pattern.

FIG. 4 is an explanatory diagram of another vertical impulse pattern.

FIG. 5 shows a specific circuit configuration of a first embodiment of the Y / C separation circuit of the present invention.

FIG. 6 is a diagram illustrating a specific example of a vertical impulse detection circuit.

FIG. 7 is a diagram illustrating a configuration of an input signal circuit to a vertical impulse detection circuit.

8 is a diagram illustrating an example of a circuit configuration of a horizontal correlation filter HMID in FIG. 7;

FIG. 9 shows a specific circuit configuration of a second embodiment of the Y / C separation circuit of the present invention.

FIG. 10 is a waveform diagram corresponding to a color signal of the present invention.

FIG. 11 is a waveform diagram corresponding to a luminance signal of the present invention.

FIG. 12 is a diagram illustrating a conventional Y / C separation circuit.

FIG. 13 is a diagram illustrating one-line dot disturbance.

FIG. 14 is a waveform diagram corresponding to a conventional color signal.

FIG. 15 is a waveform diagram corresponding to a conventional luminance signal.

[Explanation of symbols]

1 ... 3 line color signal (C) separation circuit, 3 ... horizontal color signal (C) separation circuit, 5 ... horizontal low band vertical impulse detector,
7 ... Horizontal high frequency vertical impulse detector, 9 ... OR circuit,
11 selector, 13 delay circuit, 15 subtractor, 17 bandpass filter BPF, 21, 23 delay circuit, 25, 27, 29 ...
Bandpass filter BPF, 31, 33 ... Adder, 35, 37
... Inverter circuit, 39 ... 5-tap median filter, 41,43,45 ... Low-pass filter LPF, 47 ... Vertical impulse detector, 49,51,53 ... Band-pass filter BPF, 55,57 ... Inverter circuit, 59 ... vertical impulse detector, 61 ... OR circuit, 63 ... selector, 65 ... subtractor, 67
… Bandpass filter BPF, 71, 73… Subtractor, 75,
77: Absolute value circuit ABS, 79, 81: Comparator, 83: AND circuit, 85: Exclusive NOR circuit, 87: AND circuit, 91, 93, 95 ... Horizontal correlation filter HMID, 101, 10
3 ... delay circuit, 105 ... 3-tap median filter,
107: Exclusive NOR circuit, 109: AND circuit.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-278782 (JP, A) JP-A-4-81191 (JP, A) JP-A-6-153223 (JP, A) JP-A-63-1988 209289 (JP, A) JP-A-4-96415 (JP, A) JP-A-6-113324 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04N 9/78

Claims (2)

(57) [Claims] 1. A Y / C separation circuit for separating a luminance signal and a chrominance signal from an input composite video signal, wherein the input composite video signal is inputted, and three horizontal lines of past, present and future of the composite video signal are inputted. A three-line color signal separation circuit that separates a color signal from data; a horizontal color signal separation circuit that receives the input composite video signal as input and separates a high-frequency component of the composite video signal as a color signal; And a horizontal low band vertical impulse detection circuit for detecting whether the horizontal low band signal level of the current line is a maximum value and a minimum value or not, as compared with the horizontal low band signal levels of the past and future lines. Receiving the input composite video signal as input, and determining whether the horizontal high band signal level of the current line is a maximum value and a minimum value compared to the horizontal high band signal levels of the past and future lines. Or a horizontal high band vertical impulse detection circuit for detecting whether or not, an output of the horizontal low band vertical impulse detection circuit, and a logical sum circuit for taking a logical sum of the output of the horizontal high band vertical impulse detection circuit, A selector for selecting an output signal of the three-line color signal separation circuit and an output signal of the horizontal color signal separation circuit according to an output of the OR circuit; and a delay circuit for delaying the input composite video signal by a predetermined time. And a subtractor for subtracting the output signal of the selector from the output signal of the delay circuit, wherein the output signal of the subtractor is a luminance signal. 2. The Y according to claim 1, wherein a band limiting filter is provided between said selector and said subtractor.
/ C separation circuit.