JPH04265092A - Luminance signal/chrominance signal separating circuit - Google Patents

Abstract

PURPOSE:To prevent appearance of dots in the center line even at the time when upper and lower lines are colored but the center line is achromatic. CONSTITUTION:Outputs of BPFs 4 and 6 constituting a horizontal filter and the inverted signal of a BPF 5 are given to a state detecting circuit 21. This circuit 21 subjects signals of upper and lower lines from BPFs 4 and 6 and the signal of the center line from the BPF 5 to subtraction to obtain differences D1 and D2. When detecting it by signs of differences D1 and D2 that upper and lower lines are colored but the center line is achromatic, the circuit 21 selectively outputs an inverted signal (n) of the BPF 5 to a selector 22 as the chrominance signal output. This chrominance signal is given to an adder 16, and dots do not appear in the luminance signal from the adder 16.

Description

[Detailed description of the invention]

[Object of the invention]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a luminance signal/chrominance signal separation circuit for color television receivers and the like.

0002

2. Description of the Related Art FIG. 2 is a block diagram showing a conventional luminance signal/chrominance signal separation circuit. The composite video signal introduced into the input terminal 1 is delayed by 1H (H is a horizontal period) in the 1H delay circuit 2, and is further delayed by 1H in the 1H delay circuit 3.
delay. In this way, the current signal a, the 1H delayed signal b, and the 2H delayed signal c are applied to the BPFs 4, 5, and 6, respectively. BPF4, 5, and 6 are frequency bands near the color subcarrier frequency (
3.58MHz band) signal components are passed through. BPF
Signals d and f that have passed through BPF 5 are applied to amplifiers 11 and 12, respectively, and the polarity of signal e that has passed through BPF 5 is inverted by an inverting amplifier 7. These amplifiers 11 and inverting amplifiers 7
and the output signals m, n, o of the amplifier 12 are given to the intermediate value detection circuit 10.

The intermediate value detection circuit 10 detects signals m, n,
Detect the intermediate value of o. These signals m, n, and o have the same phase for carrier color signal components in the same horizontal period. Therefore, the intermediate value detection circuit 10 outputs the intermediate value signal h containing the carrier color signal component. Further, the intermediate value detection circuit 10 outputs an intermediate value signal h that includes a luminance signal component only during a period in which each of the signals m, n, and o includes a luminance signal component.

[0004] Signals m and n are introduced into an adder 8 and added,
The added signal g is output to the intermediate value detection circuit 15 via the amplifier 13 with a gain of 1/2. Moreover, the signals n and o are sent to the adder 9
The adder 9 outputs the addition signal i to the intermediate value detection circuit 15 via the amplifier 14 with a gain of 1/2. The intermediate value detection circuit 15 also has the same configuration as the intermediate value detection circuit 10,
The intermediate value detection circuit 15 detects the intermediate value of the intermediate value signal h from the intermediate value detection circuit 10 and the addition signals g and i. signal n
Since the luminance signal components of the signals m, n, and o in the same horizontal period have opposite phases, the added signal g in the period in which the luminance signals are included in all of the signals m, n, and o does not include the luminance signal component. Not yet. Similarly, the addition signal i for this period also does not include a luminance signal component. Therefore, the luminance signal component of the intermediate value signal h is deleted by the intermediate value detection circuit 15, and the intermediate value signal j derived from the intermediate value detection circuit 15 to the output terminal 18 is
This becomes a carrier color signal that does not include a luminance signal component.

The adder 16 adds the intermediate value signal j and the output of the 1H delay circuit 2. Since the phases of both carrier color signals are opposite to each other, the output signal l from the adder 16 does not include the carrier color signal component. As a result, output terminal 1
7, a luminance signal l is derived. In this way, the luminance signal and the color signal can be reliably separated, and a picture with relatively high resolution can be obtained even in the vertical direction.

Further, the circuit shown in FIG. 2 will be explained separately into the operations of the horizontal filter and the vertical filter. Horizontal filter is BPF
4, 5, and 6, and the horizontal color signal component of the input composite video signal is first extracted by this horizontal filter. On the other hand, a 3-line dynamic comb filter (hereinafter referred to as DCF) circuit is used as the vertical filter. The DCF circuit is 1H in Figure 2.
It is constituted by delay circuits 2 and 3 and a portion 19 shown by a dashed-dotted line. After extracting the horizontal color signal component by the horizontal filter, the vertical color signal component j is extracted by the DCF circuit.
Extract. Next, the luminance signal l is obtained by subtracting the color signal j thus obtained from the input composite video signal. Note that the center frequency (fsc) of the color signal is given by the following equation (1) in two-dimensional frequency display.

μ=3.58MHz, ν=525/4cpH
(1) However, μ is the horizontal frequency and ν is the vertical frequency.

By adopting a DCF circuit as a vertical filter, it is possible to change the color signal from the color bar part of the standard color bar signal to the YIQ part (I don't know what it stands for) in the part of the picture where the color signal changes in the vertical direction. It is possible to reduce dot interference occurring in the changing portion. In this way, the accuracy of separating luminance signals and color signals (hereinafter referred to as Y/C separation) in vertical uncorrelated parts is improved compared to the case of using a comb filter that utilizes the correlation between two horizontal lines. be able to.

However, if only the center line of the three consecutive lines does not contain a color signal, there is a problem in that a dot will appear on the center line. This problem will be explained with reference to Tables 1 and 2 below. Table 1 shows the normalized color signal amplitude at each sampling point obtained by sampling the color signal at a sampling frequency of 2 fsc.

0010

[Table 1]

[0011]

0012

[Table 2]

[0013]

Since the color signal frequency is sufficiently higher than the horizontal frequency, all normalized color signal amplitudes can be considered to be 1. Further, as shown in Table 1, the phase of the color signal is inverted around 1H.

[0015] Now, let us convert the calculation mid(A, B, C) into A, B
, C, the output h of the intermediate value detection circuit 10 can be expressed by the following formula (2): h=mid(m,n,o)...(2) Intermediate value detection circuit The color signal j from 15 can be expressed by the following equation (3).

j=mid(h, (m+n)/2, (n+o)/2)
(3) By applying this equation (3) to Table 1 above, the color signal j when the color signal is input is determined. The signal n is an inversion of the 1H delayed signal e in Table 1, and the same output as the current signal is obtained from the intermediate value detection circuit 10, and the same output as the current signal is obtained from the intermediate value detection circuit 15. A color signal j is obtained.

On the other hand, it is assumed that a composite video signal is inputted through the input terminal 1, like a picture of a blind, in which the center line of three consecutive lines is black and the lines above and below it are colored. Table 2 above shows the signals d, e, f, j, l of each part in this case sampled at a sampling frequency of 2 fsc and the amplitudes normalized.

Current signal a, 1H delay signal b and 2H delay signal c from input terminal 1 and 1H delay circuits 2 and 3 are respectively B
Bandwidth is limited by PF4, 5, and 6. This results in
The central line signal that does not contain color components, i.e., BP
The normalized amplitude of the 1H delayed signal e from F5 is 0 as shown in Table 2. The signals of the upper and lower lines, i.e., BP
The current signal d and the 2H delayed signal f from F4, 6 are alternately repeated with the same phase and normalized amplitude of 1 and -1, as shown in Table 2.

These signals d, e, f are sent to amplifiers 11, 1
2 and the inverting amplifier 7 to the intermediate value detection circuit 10 to perform the calculation of the above equation (2). Then, the above formula (3)
By performing the calculation shown in Table 2, the color signal j shown in Table 2 is obtained.
get. As shown in Table 2, the color signal j from the intermediate value detection circuit 15 has a normalized amplitude of -0.5 and 0.5 repeated. This color signal j is applied to an adder 16 and subtracted from the output of the 1H delay circuit 2, that is, the black signal of the center line. Therefore, as shown in Table 2, the center line luminance signal l appearing at the output terminal 17 has a normalized amplitude of 0.5, -
0.5 repetitions.

[0020] As described above, when the input video signal of the center line does not contain a color component and the lines above and below it contain color signal components, there is a problem that dots occur on the center line. was there.

[0021]

As described above, in the conventional luminance signal/chrominance signal separation circuit described above, when the center line is colorless and the lines above and below it are colored,
There was a problem that dots appeared on the center line.

The present invention has been made in view of this problem, and even if the center line is colorless and the lines above and below it are colored, the luminance signal and the color signal are reliably separated and the center line is colorless. An object of the present invention is to provide a luminance signal/color signal separation circuit that can prevent dots from appearing on lines.

[Configuration of the invention]

[Means for Solving the Problems] A luminance signal/color signal separation circuit according to claim 1 of the present invention separates color signal components from an input composite video signal by using at least one of a horizontal filter and a vertical filter. In a luminance signal/chrominance signal separation circuit that obtains a luminance signal using a chrominance signal component, a state detection means for detecting a state of change in three consecutive lines of signals that have passed through the horizontal filter and outputting a detection result; The luminance signal/color according to claim 2 of the present invention includes a selector that is controlled based on the detection result and selectively outputs one of the output of the vertical filter and the output of the horizontal filter. In the signal separation circuit, the state detecting means calculates first and second differences between the signals of the upper and lower lines and the signal of the center line among the three consecutive lines of signals that have passed through the horizontal filter, respectively. The luminance signal/chrominance signal separation circuit according to claim 3 of the present invention is characterized in that the selector is controlled based on the sign of the first and second difference, and the state detection means Of the three consecutive lines of signals that have passed through the horizontal filter, first and second ratios of the signals of the upper and lower lines and the signal of the center line are respectively determined, and the first and second ratios and the predetermined value are calculated. The present invention is characterized in that the selector is controlled based on the comparison.

[0024]

In the present invention, the state detection means detects the direction of change in three consecutive lines of signals that have passed through the horizontal filter. When the state detection means detects from the direction of the detected change that the upper and lower lines of the three consecutive lines are colored and the center line is colorless, it controls the selector to output the output of the horizontal filter as a color signal. Output. This prevents dots from occurring in the luminance signal component due to vertical filter processing.

[0025]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a luminance signal/chrominance signal separation circuit according to the present invention. In FIG. 1, the same components as in FIG. 2 are given the same reference numerals.

A composite video signal is input to the input terminal 1. This composite video signal is processed by BPF4 and 1H.
Supplied to delay circuit 2. The 1H delay circuit 2 delays the composite video signal by 1H and supplies it to the BPF 5, the 1H delay circuit 3, and the adder 16. The 1H delay circuit 3 delays the signal from the 1H delay circuit 2 by 1H and supplies it to the BPF 6. B.P.
F4, 5, and 6 all have a pass band in the frequency band (3.58 MHz band) near the color subcarrier frequency, and the carrier color signal and 3.58 MHz of the introduced composite video signal.
MHz band luminance signals are passed through.

Output signals d, e, and f of the BPFs 4, 5, and 6 are outputted via an amplifier 11, an inverting amplifier 7, and an amplifier 12, respectively. The output signals m and n of the amplifier 11 and the inverting amplifier 7 are applied to the adder 8, and the output signals m and n of the inverting amplifier 7 and the amplifier 12
The respective output signals n and o are given to an adder 9. Adders 8, 9
adds the input signals and supplies the result to the intermediate value detection circuit 15 via amplifiers 13 and 14, each with a gain of 1/2. Further, the signals m, n, and o are also applied to the intermediate value detection circuit 10, and the output of the intermediate value detection circuit 10 is applied to the intermediate value detection circuit 15. The intermediate value detection circuits 10 and 15 are calculated using the above equations (2) and (3), respectively.
) to obtain the intermediate value of the input signal, and obtain the color signal j from the intermediate value detection circuit 15.

In this embodiment, the signals m, n, and o are also applied to the state detection circuit 21, and the signal n is applied to the selector 2.
It is also given to 2. The selector 22 is controlled by the state detection circuit 21 to selectively output either the color signal j or the signal n from the intermediate value detection circuit 15 to the adder 16 and the output terminal 18. The state detection circuit 21 detects the state of change in the signals m, n, and o and controls the selector 22. That is, the state detection circuit 21 calculates (m−n)
=D1 and (n-o)=D2, if D1 and D2 have opposite signs, that is, D1 >0 and D2 <0, or D1 <0 and D2 >
0 and the absolute values of D1 and D2 are greater than or equal to a certain value k, that is, |D1 |>k and |D2 |>k
In this case, the selector 22 selects the signal n, and in other cases, the selector 22 selects the signal j. The adder 16 connects the output of the selector 22 and the 1H delay circuit 2.
The luminance signal is outputted to the output terminal 17 by adding the output of the luminance signal.

Next, the operation of the luminance signal/chrominance signal separation circuit configured as described above will be explained with reference to Table 3.

Now, input terminal 1 and 1H delay circuits 2 and 3
Signals a and b input to BPFs 4, 5 and 6 respectively via
, c include color signal components. In this case, as shown in Table 1 above, the output e of the BPF 5 is inverted in phase with the outputs d and f of the BPFs 4 and 6, and the outputs m and o of the amplifiers 11 and 12 and the inverting amplifier 7 are inverted.
, n are all in phase. Therefore, D1 and D2 are 0 at all timings. In this case, the state detection circuit 21 causes the selector 22 to output the color signal j from the intermediate value detection circuit 15.

Here, it is assumed that a composite video signal is input to the input terminal 1, in which the center line of three consecutive lines is colorless and the upper and lower lines are colored. Table 3 below shows the signals of each part in this case, sampled and normalized at a sampling frequency of 2 fsc. Note that the selector 22 can also be a mix circuit that changes the mixing ratio according to the magnitudes of D1 and D2.

[0032]

[Table 3]

[0033]

As shown in Table 3 above, the outputs d and f of the upper and lower lines from the BPFs 4 and 6 are in phase, and the absolute values of their normalized amplitudes are approximately 1. Also, BPF5
The output e of the center line from is 0. therefore,
Difference D1 between the output m of the amplifier 11 and the output n of the inverting amplifier 7
is a repetition of -1 and 1, and the output n of the inverting amplifier 7
The difference D2 between the output o of the amplifier 12 and the output o of the amplifier 12 is a repetition of 1 and -1. Since the signal n is 0 and the signals m and o are in phase with each other, D1 and D2 have opposite signs at all sampling points, as shown in Table 3. In this case,
The state detection circuit 21 determines that a video signal in which the upper and lower lines are colored and the center line is colorless is input, and causes the selector 22 to selectively output the signal n.

In this way, the selector 22 outputs the signal n to the output terminal 18 and the adder 16. As shown in Table 3, since the output of the selector 22 (signal n) in this case does not include a color signal component, the adder 16 outputs the output of the 1H delay circuit 2, that is, the luminance signal of the center line. Output the components as they are. That is, no dots are generated in the luminance signal of the output terminal 17.

In this way, in this embodiment, the BPF
Find the differences D1 and D2 between the outputs d and f of BPF 5 and the inverted output of the output e of BPF5, and if the differences D1 and D2 have opposite signs, the upper and lower lines of the three consecutive lines are colored. Judging that the center line is colorless, B
The inverted signal n of PF5 is output as a color signal output. This makes it possible to prevent dots from appearing in the luminance signal from the adder 16.

In addition to the above conditions, the state detection circuit 21 also determines m/n=Dr1, o/n=Dr2, and calculates Dr1,
It may be determined whether the above condition is satisfied only when Dr2 is larger than the predetermined value K. In this case, even if the BPF 5 outputs a luminance signal component in the 3.58 MHz band, reliable determination is possible. Furthermore, in this case, if the level of the signal n is extremely small, D
Since r1 and Dr2 become extremely large, the signal n
It is desirable that the process be performed only when the value is equal to or higher than a predetermined level.

[0038]

As explained above, according to the present invention, even when the center line is colorless and the lines above and below it are colored, it is possible to prevent dots from forming on the center line. have

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a luminance signal/chrominance signal separation circuit according to the present invention.

FIG. 2 is a block diagram showing a conventional luminance signal/chrominance signal separation circuit.

[Explanation of symbols]

4,5,6...BPF 16... Adder 21...State detection circuit 22...Selector

Claims (3)

[Claims] 1. A luminance signal/chrominance signal separation circuit which separates a color signal component from an input composite video signal by at least one of a horizontal and vertical filter and obtains a luminance signal by using the separated color signal component. a state detection means for detecting the state of change in the three consecutive lines of signals that have passed through the horizontal filter and outputting a detection result;
A luminance signal/chrominance signal separation circuit comprising means for outputting a color signal from the output of the vertical filter and the output of the horizontal filter based on the detection result of the state detection means. 2. The state detecting means calculates first and second differences between the signals of the upper and lower lines and the signal of the center line among the three consecutive lines of signals that have passed through the horizontal filter; The luminance signal/chrominance signal separation circuit according to claim 1, wherein the selector is controlled based on the first and second differences. 3. The state detecting means calculates first and second ratios of the signals of the upper and lower lines and the signal of the center line among the three consecutive lines of signals that have passed through the horizontal filter, respectively. 2. The luminance signal/chrominance signal separation circuit according to claim 1, wherein the selector is controlled based on a comparison between the first and second ratios and a predetermined value.