JPH078048B2 - YC separation circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a YC separation circuit for separating a Y _C (luminance) signal and a C _C (carrying color) signal from a composite video signal in a VTR or the like.

2. Description of the Related Art FIG. 3 shows a block diagram of an example of a conventional YC separation circuit.
In the figure, a composite video signal (for example, a color bar signal) that has entered the terminal 1 is passed through the bandpass filter 2 and a filter circuit 3 to be described later to be a C _C signal, which is taken out from the terminal 4, while the Δt delay circuit 5 , 1H delay circuit 6 and is supplied to an adder 7 where it is added to the C _C signal and taken out from a terminal 8 as a Y _C signal. This YC separation circuit uses vertical correlation of video signals. Conventionally, a comb filter using vertical correlation has two lines (current line information and 1H
This is done with past line information), but this is predicted with 3 lines (current line information, 1H past line information, and 1H future line information).

Here, in the filter circuit 3, the input signal is C (future), the output of the 1H delay circuit 9 is B (current), and the 1H delay circuit 10
If the output of A is set to A (past), the information of the above three lines can be obtained by the signals A, B, and C. In FIG. 3, reference numerals 11, 12, and 13 are high-potential detection circuits (hereinafter referred to as MAX), which are configured as shown in FIG. 4 (A) and output the higher potential of two inputs. To do. Reference numerals 14, 15 and 16 are low potential output circuits (hereinafter referred to as MIN), which are configured as shown in FIG. 4 (B).
It outputs the lower potential of the inputs.

Now, for example, looking at the video signal of the NTSC system in the vertical direction of the screen, and selecting and classifying 3 lines, it is roughly the 5th.
There are three patterns shown in FIGS. The figure (A) is a flat pattern, the figure (B) is a step pattern, and the figure (C) is a pulse pattern. Where n
Is one point (present) of an arbitrary raster, (n-1) is a point on one line of the arbitrary raster (past), and (n + 1) is a point on one line of the arbitrary raster (future). For example, considering a C _C signal, the frequency f _{SC of the} subcarrier is f _SC =
Since (455/2) f _H (f _H is the horizontal scanning frequency), it can be said that when there is vertical correlation, it is a pattern that alternates line by line, that is, a pulse pattern (FIG. 5C). This pulse pattern is a pattern that cannot be obtained by the conventional two-line type.

FIG. 6 shows a diagram for explaining the basic operation of the filter circuit 3 in FIG. For example, MAX11 outputs the larger potential of signals A and B, MAX12 outputs the larger potential of signals A and B, and MIN14 outputs the output of MAX11 and MAX12. The electric potential X ₍₊₎ of the smaller one is output, and X ₍₊₎ = MIN (M
AX (C, B), MAX (B, A)). Similarly, MIN1
5 outputs the smaller potential of signals A and B, MIN16 outputs the smaller potential of signals B and C, and MAX13 outputs MI.
It outputs the larger potential X _(-) of the output of N15 and the output of MIN16, and is written as X _(-) = MAX (MIN (C, B), MIN (B, A)). Signals X ₍₊₎ and X _(-) are added by adder 17, and 1/2 circuit 1
At 8 the level is halved and C _C = 1/2 (X ₍₊₎ + X _(-) ). Since this circuit is configured to obtain the C _C signal first, the calculation is performed using a signal obtained by inverting the signal of the current line.

In this case, the transfer function of the filter circuit 3 is 1/2 (B + MID
(A, B, C)). Where MID (A, B, C) is the signal
It is a function that outputs the second highest data for the three inputs of A, B, and C. Therefore, the C _C signal as shown is obtained for the four patterns shown in FIG.

The conventional circuit shown in FIG. 3 displays the image of vertical stripes by repeating black and white such as the multi-burst shown in FIG. 7 (A), as shown in FIG. 7 (B). However, there is a problem that cross color and blurring of Y _C signal occur. That is, when there is a vertical stripe below B as shown in FIG. 7 (A), the information of the upper 3 lines is A = 0, B = C = 1 as shown in FIG. 8 (A), Since B is inverted to produce the C _C signal, A = 0, B = −1, C = 1 as shown in FIG. 8 (B). Therefore, transfer function = 1/2
(-B + A) / 2 = 1/2 is taken out from (B + MID (A, B, C)) as a C _C signal, and there is a problem that a part that should not be originally colored is colored (cross color). there were. On the other hand, the Y _C signal has an amplitude of 1/2, such as Y _C = 1- (1/2) = 1/2.
Then, there was a problem of blurring.

Therefore, the present applicant has proposed a patent application of the same date (invention title “YC separation circuit”) in order to solve the above problems. As shown in FIG. 9, this is the information of the past line and the information of the future line. When the same code is used, the one having the larger absolute value is output, and when the different code is used, the algebraic sum thereof is output. Circuit (1H delay circuit 9,10, MAX20,21, MIN22,23, adder 24)
And the information of the output of the first arithmetic circuit and the current line,
The second arithmetic circuit (MAX25, 28, MIN26, 27, MIN26, 27,
And a third arithmetic circuit (subtractor 3) that obtains a color signal by subtracting the output of the second arithmetic circuit from the information of the current line.
0) and.

Here, in the circuit shown in FIG. 9, “0” and “1” for each of the signals V ₁ , V ₂ and V ₃ from each pattern shown in FIG.
The possible patterns of combinations of "-1" and the signals F _G ,
Figure 2 shows the relationship with Y _H , C _C , and Y _C.

For example, in the pulse pattern as shown in column * _{1 in} Fig. 10.
When V ₁ = 1, V ₂ = 0, V ₃ = 1 (Past, present, and future line information changes in the order of 1,0,1 because the C signal does not currently exist. It is generally desirable that the signal C _C output zero), and in the conventional circuit shown in FIG. 3, the signal C _C becomes 1/2 and cross color occurs, but In the circuit shown in the figure, there is no zero and no cross color occurs. Also, as shown in column * _{2 of} Fig. 10, when V ₁ = V ₃ = 0, V ₂ = 1 in the pulse pattern (past, present, and future line information changes in the order of 0,1,0 It is common to assume that the C signal is present, and the signal C _C is 1
Is output), the signal C _C becomes 1/2 and blurs in the conventional circuit shown in FIG. 3, but becomes 1 in the circuit shown in FIG. 9 and no blur occurs. .

Also, as shown in column * _{3 of} Fig. 10, V ₁
= 0, V ₂ = V ₃ = 1 and as shown in column * ₁ , when V ₁ = V ₂ = 1 and V ₃ = 0 in the step pattern (both are signals like multi-burst, It is desirable that the signal C _C output zero). In the conventional circuit, the signal C _C becomes 1/2 and cross color occurs, but in the circuit shown in FIG. 9, it becomes zero and cross color does not occur. . On the other hand, since the signal Y _C can also be set to 1 for 1/2 of the conventional circuit, no blur occurs.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention By the way, in the circuit shown in FIG. 9, in the case of an image having no vertical correlation, a C signal output is a signal obtained by passing a bandpass filter and a Y signal output is obtained by passing a bandstop filter. , And the bandwidth in this case is determined by the band of the bandpass filter 2. On the other hand, in the case of images with vertical correlation,
Both the C signal output and the Y signal output are responses obtained by passing through the comb filter, and the bandwidth in this case is also determined by the band of the band filter 2. As described above, the bandwidth of the separated C signal and Y signal depends on the band of the bandpass filter 2 regardless of whether there is vertical correlation or not.

However, in the circuit shown in FIG. 9, when the band width of the bandpass filter 2 for obtaining the C signal is set to be relatively wide, cross luminance (color boundary of the color bars of a color bar) is generated in an image having vertical correlation. However, the frequency characteristics of the C signal are good, but a random pattern without vertical correlation (such as the normal outdoor scenery) (the C signal level is the same as that of a color bar). However, there is a problem that the screen is blurred. On the contrary, if the band width of the band-pass filter 2 is set to be relatively narrow, blur does not occur in the image having no vertical correlation, but cross luminance occurs in the image having vertical correlation and the C signal There was a problem that the frequency characteristics deteriorate.

Therefore, in order to solve this problem, the present applicant previously proposed Patent Application (2) (the title of the invention "video signal processing circuit") on October 21, 1987. As shown in FIG. 11, this product separates a composite video signal with a broadband filter 50 to obtain a color signal, and a 1H delay circuit 51, MAX52 to 55, MIN56
Up to 59, adders 60 to 63, subtractor 64, delay circuit 66, and narrow band filter 65 detect from the output of the wide band filter 50 whether or not there is vertical correlation with the color signal, respectively. When there is a correlation, the color signal is taken out as it is in a wide band characteristic, and when there is no vertical correlation, it is taken out as a narrow band characteristic in the color signal.

Therefore, as shown in FIG. 12, when there is vertical correlation of color signals like a color bar, the broadband C comb signal C _W is 1, the Y _H signal is 0, and therefore the signal C _N is 0, C _W is extracted as a broadband C signal (* _n ). On the other hand, when there is no vertical correlation of color signals in a fine pattern such as an ordinary outdoor landscape, the broadband C comb signal C _W is 0 and the Y _H signal is also 0. Therefore, the signal C _N is 1 and the signal C is _N is extracted as a narrow band C signal (* ₁₂ ). In this way, optimum band characteristics can be obtained for each of the presence and absence of vertical correlation.

The present invention combines the circuit shown in FIG. 11 and the circuit shown in FIG. 9, and particularly when displaying vertical striped multibursts by repeating black and white, cross color or
There is no blur of Y _C signal, and when displaying a pulse pattern, there is no cross color or blur in C _C signal,
Further, it is possible to obtain the optimum band characteristic for each of the presence or absence of the vertical correlation of the color signal, which makes it possible to improve the cross-luminance in the color bar and the frequency characteristic of the color signal when there is the vertical correlation. , If there is no vertical correlation, there will be no blurring in a fine pattern, and there will be little cross color YC
The purpose is to provide a separation circuit.

Means for Solving the Problems In FIG. 1, a wide band filter 50, 1H delay circuits 9 and 10,
The MAX20,21, MIN22,23, and adder 24 output the information of the past line and the information of the future line. The one with the larger absolute value when the same sign is output, and the algebraic sum thereof is output when the different code is used. The arithmetic circuits, MAX25, 28, MIN26, 27, and adder 29 are the information of the output of the first arithmetic circuit and the current line. When the sign is the same, the absolute value is smaller, and when the sign is different, the reference potential is respectively. The second arithmetic circuit for outputting, the subtractor 30 subtracts the output of the second arithmetic circuit from the information of the current line to obtain a color signal, the third arithmetic circuit, MAX68,71, MIN69,70, adder 22 The fourth arithmetic circuit that detects a signal having a strong vertical correlation by using each information of the past line, the present line, and the future line, the subtractor 67, the narrow band filter 65, and the adder 63 are output from the output signal of the third arithmetic circuit. A signal obtained by subtracting the output signal of the fourth arithmetic circuit and passing it through a narrow band filter and the output of the fourth arithmetic circuit It added the door,
It is one embodiment of each of the fifth arithmetic circuits taken out as color signal outputs.

Operation In the above first arithmetic circuit, from the output of the wide band filter, the information of the past line and the information of the future line, the one with a larger absolute value when the same sign is output, and the algebraic sum thereof is output when the different sign (signal F _G) and, in the second arithmetic circuit, with the output and the information of the current line of the first arithmetic circuit, when the absolute values are different smaller absolute value, respectively output (signal reference potential when different signs Y _H ), and in the third arithmetic circuit, subtracts the output of the second arithmetic circuit from the information of the current line to obtain a color signal C _C ′, and in the fourth arithmetic circuit, the past line and the present line. And a signal having a strong vertical correlation (signal C _P ) is detected by using each information of the future line, and in the fifth arithmetic circuit, from the output signal of the third arithmetic circuit to the output signal of the fourth arithmetic circuit. And pass it through a narrow band filter Signal (signal C _G), adds the output C _P of the fourth arithmetic circuit, taking as a color signal output.

Especially when V ₁ = V ₃ = 1 and V ₂ = 0 in the pulse pattern,
C _C can be zero, no cross color is generated, and
When V ₁ = V ₃ = 0 and V ₂ = 1 the signal C _C can be set to 1, and no blurring will occur. Furthermore, in the flat pattern, V ₁ = 0, V ₂ ＝
When 1, V ₃ = 1 and in the step pattern V ₁ = V ₂ = 1,
When V ₃ = 0, the signal C _C can be made zero, and cross color and blurring of the Y _C signal do not occur at the upper and lower ends of the image.

Furthermore, with or without vertical correlation of color signals, it is possible to obtain optimum band characteristics for each, and when there is vertical correlation, cross luminance in color burst and frequency characteristics of color signals can be improved, On the other hand, when there is no vertical correlation, blurring does not occur in a fine pattern, and cross color is small.

Embodiment FIG. 1 shows a block diagram of an embodiment of the circuit of the present invention. In FIG. 1, the same parts as those of FIGS. Is omitted. In the figure, parts other than the part surrounded by the broken line are substantially the same as those in FIG.

In FIG. 1, the signal V ₁ and the signal V ₃ are taken out by the MAX 20 having the higher potential and compared with zero by the MAX 21 and the one having the higher potential is taken out. On the other hand, the signals V ₁ and V ₃ are
The one with the lower potential is taken out at MIN22, compared with zero at MIN23, and the one with the lower potential is taken out. The output signal of MIN23 and the output signal of MAX21 are added by the adder 24 to form a signal F _G.

That is, the signal F _G is the information of the past line and the information of the future line. To be

Further, the signal V ₂ and the signal F _G are taken out by the MAX 25 having the higher potential, compared with zero by the MIN 26 and taken out by the lower potential. On the other hand, the signal V ₂ and the signal F _G are taken out at the lower potential at the MIN 27, compared with zero at the MAX 28 and taken out at the higher potential. MAX28 output signal and MIN
The output signal of 26 is added by an adder 29 to form a signal Y _H.

That is, the signal Y _H is the information of the output and the subtraction line of the first arithmetic circuit. The second arithmetic operation outputs the reference voltage (zero) having the smaller absolute value when the same sign and the different sign. Obtained in the circuit.

The signal V ₂ is subtracted from the signal Y _H by the subtractor 30 and is supplied to the subtractor 67 as a C _C ′ signal. On the other hand, signals V ₁ , V ₂ and V ₃ are
8 、 MIN69, the highest potential and the lowest potential are extracted respectively, the output of MAX68 is compared with zero in MIN70 and the lower potential is extracted, and the output of MIN68 is compared with zero in MAX71. And the higher potential is taken out. The output of the MIN70 and the output of the MAX71 are added by the adder 72 and supplied to the subtractor 67 and the Δt ₂ delay circuit 66 as a signal C _P.

The output of the subtractor 67 is passed through the narrow band filter 65 to form the signal C _G (vertical transient chroma signal), and the adder 63
Is added to the output of the delay circuit 66 and is taken out as C _C from the output terminal 4. On the other hand, the composite video signal input to the terminal 1 is delayed by the total delay time of the wide band filter 50 and the narrow band filter 65 (Δt ₁ + Δt ₂ ), a delay circuit 73, a 1H delay circuit 6, and a subtracter 31. Supplied to C _C
The signal is subtracted and taken out from the output terminal 8 as a Y _C signal.

Here, the output signal C _P (wide band C comb signal) of the adder 72, the signal F _G , the signal Y _H , the output signal C _C ′ of the subtractor 30, and the output of the narrow band filter 65 obtained through the wide band filter 50. Signal C _G ,
The truth value for each potential V ₁ , V ₂ , V ₃ of the signal Y _C is as shown in FIG.

In particular, in the case of an image having a vertical correlation of C signal such as a color bar (* _{5 in} FIG. 2), the signals V ₁ and V ₃ are “−1”, and the signal V ₂ is “1”, The output signal C _P of the adder 72 is “1”,
The output signal Y _H of the adder 29 becomes “0”. Therefore, the subtractor
The output C _C ′ of 30 becomes “1”, the output of the subtractor 67 becomes “0”, and the signal C _G becomes “0”. "1" of signal C _P is adder 63
Through is taken out from the terminal 4 as a wide band C _C No. _{(1 (W)).} The output "1" of the delay circuit 6 is subtracted from the C _C signal "1" by the subtracter 31 and is taken out from the terminal 8 as a "0" Y _C signal.

On the other hand, in the case of a random image with no vertical correlation to the C signal (* ₆ to * _{10 in} Fig. 2), as in normal outdoor scenery, each signal
V _{1 to} V ₃ are as shown in FIG. 2, and the output signal of the adder 72
C _P becomes “0”, and the output signal Y _H of the adder 29 becomes “0”. Therefore, the output C _C ′ of the subtractor 30 is “1”, the output of the subtractor 67 is “1”, and the narrow band filter 65 outputs the narrow band of “1”.
C Extracted as _C signal (1 _(N) ). Since the signal C _P is “0”, the narrow band C _C signal is taken out from the adder 63 as it is, and taken out from the terminal 4. Output "1" of delay circuit 6
Is subtracted from the C _C signal by "1" in the subtracter 31, and is taken out from the terminal 8 as a Y signal of "0".

In this way, as a band-pass filter for the C signal, it becomes a wide-band filter when there is vertical correlation, and a wide-band C signal output can be obtained. Therefore, the cross-luminance in the color bar and the frequency characteristic of the C signal are improved. On the other hand, when there is no vertical correlation, a narrow band filter can be used to obtain a narrow band C signal, so that blurring in a fine pattern does not occur and cross color is small. That is,
The optimum band characteristic can be obtained for each of the presence and absence of vertical correlation.

In the case of PAL system, 2H delay circuit can be used instead of 1H delay circuit.

EFFECTS OF THE INVENTION According to the present invention, in particular, when displaying vertical striped multi-burst by repeating black and white (step pattern), cross color and blurring of Y _C signal are generated at the upper and lower ends of the screen as in the conventional circuit. In addition, when displaying a pulse pattern, there is no cross color in the C _C signal or blurring of the Y _C signal, and moreover, the optimum band characteristics are obtained depending on the presence or absence of vertical correlation of the color signals. This makes it possible to improve the cross-luminance in the color bar and the frequency characteristics of the color signal when there is vertical correlation, while on the other hand, when there is no vertical correlation, blurring does not occur in fine patterns. , You can get a high quality screen.

[Brief description of drawings]

1 is a block diagram of an embodiment of the circuit of the present invention, FIG. 2 is a diagram of signals obtained by the circuit of the present invention, FIG. 3 is a block diagram of a conventional circuit, FIG. 4 is a circuit of a MAX circuit and a MIN circuit. FIG. 5 is a diagram showing a pattern obtained by the 3-line method, FIG. 6 is a diagram explaining a C _C signal obtained by a comb filter circuit of a conventional circuit, and FIG. 7 is a diagram showing a multiburst image, FIG. 8 is a multi-burst pattern obtained by a conventional circuit, FIG.
The figure is a block diagram of a circuit proposed by the applicant on the same date,
FIG. 10 is a signal diagram obtained by the circuit shown in FIG. 9, FIG. 11 is a block diagram of the circuit previously proposed by the applicant, and FIG.
FIG. 12 is a diagram of signals obtained by the circuit shown in FIG. 11. 1 ... Composite video signal input terminal, 4 ... Color signal output terminal, 6, 9, 10 ... 1H delay circuit, 8 ... Luminance signal output terminal, 20, 2
1,25,28,68,71 ... High potential detection circuit (MAX), 22,23,26,27,
69, 70 ... Low potential detection circuit (MIN), 24, 29, 63, 72 ... Adder, 30, 31, 67 ... Subtractor, 50 ... Wide band filter, 65 ... Narrow band filter, 66, 73 ... Delay circuit.

Claims (1)

[Claims] 1. A filter for extracting a color signal having a small amount of unnecessary signal components by further calculating a color signal extracted from a composite video signal by a wideband filter using information of three lines of a past line, a present line and a future line. In the YC separation circuit provided with a circuit, from the output of the wide band filter, the information of the past line and the information of the future line, the one with the larger absolute value when the same sign is added, and the algebraic sum thereof when the different sign is used. Of the first arithmetic circuit that outputs the above, and the information of the output of the first arithmetic circuit and the current line, the one with the smaller absolute value when the same sign is output, and the reference potential is output when the different sign is output. A second arithmetic circuit; a third arithmetic circuit that obtains a color signal by subtracting the output of the second arithmetic circuit from the information of the current line; the past line, the present line, and A fourth arithmetic circuit that detects a signal having a strong vertical correlation by using each information of the incoming line, and subtracts the output signal of the fourth arithmetic circuit from the output signal of the third arithmetic circuit, and narrows this band. A YC separation circuit comprising a fifth arithmetic circuit for adding a signal obtained through a filter and an output of the fourth arithmetic circuit to obtain a color signal output.