JPH067685B2 - Y / C separation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention relates to a Y / C separation circuit in a color television receiver (from an input composite video signal to a luminance signal, that is, a Y signal.
Circuit for separating and outputting signals and color signals, that is, C signals)
More specifically, the present invention relates to such a Y / C separation circuit that enables accurate Y / C separation in the contour portion of the pattern of the display image to improve the resolution of the display image.

[Background of the Invention]

Conventionally, in an NTSC color television signal, in order to achieve band compression, a carrier color signal (C) is interpolated and multiplexed in a gap between spectra in a high frequency part of a luminance signal (Y) on the principle of frequency interleaving. ing. Therefore, it is necessary for the receiver to perform Y / C separation in the received color television signal, and as a method therefor, a Y / C separation method or a 1H delay line (where H is 1 horizontal) is used by a low-pass filter and a band-pass filter. There is a method using a comb filter using (indicating a scanning period) (see, for example, a discussion on the comb filter for high quality color TV images in the National Conference of the Institute of Electronics, Communication, 1984, No. 1367).

In the case of the former method, since the high frequency component of Y is missing, the resolution deteriorates, which is not preferable in terms of performance.

FIG. 5 is a block diagram showing the latter method, that is, a conventional Y / C separation circuit using a comb filter.

In the figure, 1 is a composite video signal (composite video signal) input terminal, 2 and 3 are 1H delay lines, and 4 to 6 respectively.
Are multipliers (weighting circuits), 7 is an adder, 8 is a band pass filter (BPF), 9 is a subtractor, 10 is a C signal output terminal, and 11 is a Y signal output terminal.

In this Y / C separation circuit using a comb filter, basically, the displayed images are correlated in the vertical direction, and N
In the TSC system, the carrier color signal has its phase inverted for each line (horizontal scanning line), and this is utilized to perform Y / C separation.

FIG. 5A is a waveform diagram showing signal waveforms of respective portions of the circuit of FIG.

The circuit operation will be described with reference to FIGS. 5 and 5A. When the signal of the (l + 1) th line of the composite video signal input from the terminal 1 is on the output side of the 1H delay line 3, the signal of the 1st line is on the output side of the 1H delay line 2 (the input of the 1H delay line 3 Signal on the (l-1) th line is the 1H delay line 2
On the input side of.

In FIG. 5A, the signal waveform of each line (the carrier color signal frequency-multiplexed with the luminance signal, in other words, the waveform of the video signal itself, is emphasized for easy understanding of the color signal portion. The waveform of the carrier color signal is inverted every line.

Next, in FIG. 5A, (B), the signal of each line is multiplied by the multiplier 4
The waveforms obtained by loading -1/4, 1/2, and -1/4 times respectively are shown by ~ 6 (It should be understood that the negative signal when loading means phase inversion) Good).

Next, after adding the outputs of the multipliers 4 to 6 by the adder 7, and passing the band-pass filter 8 to remove the DC component, the C signal in the video signal of the (l) line is changed to the fifth signal.
It can be extracted as shown in FIG. on the other hand,
The subtractor 9 is a circuit for removing the extracted C signal from the video signal of the (l) th line, and as a result, as shown in FIG. 5A (D), only the Y signal is obtained at its output. You can

As described above, Y by the conventional comb filter is used.
-The C separation circuit has upper and lower lines (scan lines) on the screen.
Since the correlation between the two is used, there is no problem with vertical lines running in the vertical direction, but when the contour part is composed of horizontal lines and diagonal lines, sufficient separation performance cannot be obtained at the contour part. There was a problem. This will be described below with reference to FIGS. 6 and 6A.

FIG. 6 is a diagram showing a contour portion composed of horizontal lines,
As indicated by the dotted line S, it is assumed that the color changes between the (l) line and the (l + 1) line to form the contour portion.
Therefore, the phase of the carrier color signal should originally be in the opposite phase between the (l) line and the (l + 1) line, but in this case, they are in phase and in a complementary color relationship.

As a result, the C signal and the Y signal in the video signal of the (l) th line are separated through a process exactly the same as that described with reference to FIG. 5A. In the case of, it becomes 1/2, and the remaining 1/2 leaks into the Y signal. This is what is called dot interference.

FIG. 6A is a diagram showing a contour portion formed by diagonal lines. In FIG. 6A, it is assumed that the phase of the carrier color signal is changed and the color is changed in the dotted line portion S to constitute the contour portion. . In this case, too, the faithful reproduction (separation) at the contour portion of the C signal becomes impossible due to the completely same process as in the case of FIG.
The signal will be mixed.

As described above, Y / C by the conventional comb filter
In the separation circuit, there is a problem that Y / C separation becomes incomplete at a contour portion formed by horizontal lines and diagonal lines, dot interference occurs, and the resolution of a display image deteriorates.

[Object of the Invention]

The object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, and to perform Y / C separation on a television screen not only in vertical lines but also in contours formed by horizontal lines and diagonal lines. It is to provide a C separation circuit.

[Outline of Invention]

In order to achieve the above object, in the present invention, a means for determining a pattern on a display screen, that is, a contour is provided, and Y / C separation is performed by using signals of a plurality of lines extending over both regions having the determined contour as a boundary. When it is necessary to perform the calculation for, Y / C separation is performed using signals of a plurality of lines that have a strong mutual correlation in one of the regions bounded by the contour, and the result is applied to the line. It is characterized by being used.

Example of Invention

 Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention.

In the figure, the same symbols as those in FIG. 5 indicate the same things. In addition, in the figure, 2a to 2d are 1H delay lines, 4a to 4h are multipliers (weighting circuits), 12a to 12b are inverting circuits (inverters), 13a to 13c are subtraction and absolute value circuits, respectively. Is a minimum value selection circuit, and 15 is a switch.

The circuit configuration shown in FIG. 1 looks complicated at first glance, but it is easy to understand if the following is considered.

That is, the 1H delay lines 2a and 2b and the multipliers 4d and 4e,
4f and the adder 7c constitute a first comb-shaped filter, and similarly the 1H delay lines 2b and 2c and the multipliers 4a and 4 are used.
b, 4c and the adder 7a constitute a second comb-shaped filter, and similarly the 1H delay lines 2c, 2d and the multiplier 4f,
It is considered that 4g, 4h and the adder 7b constitute a third comb-shaped filter. The output of the first comb-shaped filter (output of the adder 7c) and the output of the third comb-shaped filter (output of the adder 7b) are respectively inverted.
The output of the second comb filter (the output of the adder 7a) is led directly to the switch 15 via b and 12a.

On the other hand, the input a of the 1H delay line 2a and the output c of the 1H delay line 2b are guided to the subtraction and absolute value conversion circuit 13a, where the absolute value | Ia | of the difference between them is calculated and the minimum value selection circuit 14 Sent to. Similarly, the inputs B and 1 of the 1H delay line 2b
The output D of the H delay line 2c is the subtraction and absolute value conversion circuit 13b.
, And the absolute value | Roni | of both is calculated there and sent to the minimum value selection circuit 14. Similarly, 1
The input C of the H delay line 2c and the output E of the 1H delay 2d are guided to a subtraction / absolute value conversion circuit 13c, where an absolute value | ha | of the difference between them is calculated and sent to the minimum value selection circuit 14.

The minimum value selection circuit 14 compares the three input values, that is, | Iha |, | Roney |, ||
It is determined which is the minimum value, and the determination output is sent to the switch 15.

The switch 15 selects the output of the inverting circuit 12b if the discriminant output given from the minimum value selection circuit 14 is | I ||, and the output of the adder 7a if | Roni |
If e, then the output of the inverting circuit 12a is selected.

The output selected by the switch 15 passes through the band pass filter 8 and then appears at the output terminal 10 as a C signal. On the other hand, the subtractor 9 subtracts the c signal from the signal C (video signal) fetched from the input side of the 1H delay line 2c to obtain the Y signal and output it to the terminal 11.

The above is the outline of the embodiment and the configuration and operation shown in FIG. 1, and the circuit operation will be described in detail below with reference to FIGS. 2 and 3 as well.

FIG. 2 is an operation waveform diagram of each part in the circuit of FIG. As shown in FIG. 2, from the (1-2) line,
It is assumed that the video signal up to the (l + 2) line has a contour indicated by a dotted line S, and that the color and the luminance change with the contour position as a boundary. In addition, black circles indicate sample points.

Now, consider separating the C signal and the Y signal from the video signal C on the (l) line. From the (l-2) line to (l +
2) If the signals up to the line are a to h, there is a delay time difference of 1H between them, so that they can be obtained simultaneously from the respective outputs of the 1H delay lines 2a to 2d in FIG.

The subtraction / absolute value conversion circuits 13a to 13c respectively obtain | Iha |, | Roni |, and | Har | as described above. Since the outline exists in the dotted line portion S, the (l-2) line to the (l) line are in the same region (first region) having the same color and luminance, while the (l + 1) line to the (l + 2) line. ) The line forms a second area which, for example in the case of color, differs in color from the first area. Therefore, although the luminance signals of the signals a and c and b and c are almost the same, the phases of the color subcarriers are inverted.

Therefore, the signals a and c have almost the same luminance signal and color subcarrier. Therefore, | i-ha | takes a value close to 0 (it becomes 0 if the brightness of a and c are exactly the same). Next, when | Roni | and | Ha-ho | are calculated, the signals Ro and Ha belong to the first region, while the signals D and Ha belong to the other second region. Has a positive value.

The minimum value selection circuit 14 includes a subtraction and absolute value conversion circuit 13a.
.About.13c, that is, the minimum value of the values | I ||||||||||||| To the output from the adder 7a via the inverting circuit 12b, the output from the adder 7a if | Loni | is minimum, and the output from the adder 7b via the inverting circuit 12a if | harho | is minimum. The switch 15 is controlled so as to select each.

In this case, | Iha | is the minimum, so the output of the adder 7c is selected via the inverting circuit 12b. Adder 7c
As described above, since the multipliers 4d to 4f and the IH delay lines 2a and 2b constitute a conventional 2H type comb filter, as described above with reference to FIG. In exactly the same manner, the C signal having a certain small DC value of the video signal of the (l-1) line is output (no DC if the luminances of the signals a and b are the same). This is shown as [b, c] in FIG.

The inverting circuit 12b inverts this and passes the inverted output to the band pass filter 8 to remove the direct current component,
As shown in [C], C in the video signal of line (l)
You can get a signal.

The method for obtaining the Y signal is exactly the same as that in the conventional example, that is, from the video signal on the (l) line to the C on the (l) line.
It is obtained by subtracting the signal by the subtractor 9.

As described above, according to the present embodiment, the contour formed of the horizontal lines is correctly separated, although the Y / C separation was not complete as shown in FIG. 6 in the related art.

Next, it will be described with reference to FIG. 3 that the Y / C separation can be correctly performed even in the contour portion composed of diagonal lines. Similarly to FIG. 2, a to h are video signals from line (l-2) to line (l + 2), and black circles A _{1 to} A _{5 and the} like indicate sample points. In addition, it is assumed that the color and the brightness are changed on the left and right of the diagonal dotted line S. Here, it is considered to separate the C signal and the Y signal included in the video signal C of the (l) line.

First, at sample point 1, since A _{1 to} A ₁ are all in the same area, | A ₁ -C ₁ |, | B ₁ -D ₁ |, |
Each of C ₁ -E ₁ | is a value close to 0. For this reason,
The minimum value selection circuit 14 is uncertain which of the above three is the minimum value due to the mixing of noise, but the result is the same regardless of which of the three is determined as the minimum value.

In other words, when | A ₁ -C ₁ | is minimized, inversion of B ₁ is performed in the same manner as in FIG. 2, and when | B ₁ -D ₁ | is minimized, 1H delay lines 2b and 2c are used. When C ₁ , | C ₁ -E ₁ | is minimized as the output of the comb filter to be performed, the inverse of the output D ₁ of the comb filter constituted by the 1H delay lines 2c and 2d is output. , Both are equal to C ₁ .

In the sample points _{2, |} A 2 -C 2 _| and _| B 2 -D
₂ | is a value close to 0 for both, while | C ₂ −E ₂
| Takes a positive value because C ₂ belongs to the first area and E ₂ belongs to the second area. Minimum line selection circuit 14 is therefore _| A ₂ -C 2 _| or _| B 2 _-D 2 _|
Is selected as the minimum value, the switch 15 outputs B ₂ in the case of the former and C ₂ in the case of the latter, and in either case, it becomes equal to C ₂ .

Next, for sample point 3, | A ₃ −C ₃ |
_{Although, | B 3 -D 3 |,} | C 3 -E 3 | takes a positive value for the same reason. Therefore, the inversion of B ₃ is caused by the switch 15
, Which is equal to C ₃ .

For sample point 4, | C ₄ −E ₄ | is 0, so switch 15 outputs the inverse of D ₄ , which is equal to C ₄ .

Finally, for sample point 5, | B ₅ −D ₅ |, | C ₅
Although −E ₅ | takes a value close to 0, in the former case, C ₅ is output, and in the latter case, the inversion of D ₅ is output, and both are equal to C ₅ .

In this way, the C signal contained therein can be correctly extracted from the video signal of the (l) line. If the subtracted corrector subtracts the extracted correct C signal from the video signal of the (l) line, the correct Y signal can be obtained.

It should be noted that the band-pass filter 8 is not always necessary because the C signal does not include direct current as long as it is the same video signal belonging to the same region, as is already clear. It can be used properly according to the purpose.

Next, a specific circuit configuration of the minimum value selection circuit 14 will be described.

FIG. 4 is a diagram showing a minimum value selection circuit. In FIG. 4, 16 to 18 are input terminals for comparison data, which are judged by mutually comparing which is the minimum value, 19 and 20 are comparators, Reference numerals 21 to 24 are AND circuits, 25 to 27 are OR circuits, and 28 to 30 are output terminals showing which of the minimum values is X, Y or Z, respectively.

The correspondence relationship with the minimum value selection circuit 14 in FIG. 1 is as follows: | ha | is X, | Roni | is Y, | Loho | is Z, and the control output terminal to the switch 15 is shown. Is 28-30
Equivalent to.

Next, the circuit operation will be described. First, the input data X and Y are compared in magnitude. X and Y are input to the comparator 19. The comparator 19 checks the magnitude relationship between X and Y, and the terminals (X <Y), (X = Y), (X
The H level is output to any one of <Y). Therefore, if X <Y or X = Y, it is necessary to compare X and Z and select the smaller one in the next step, so OR
The AND circuit 21 is opened via the circuit 25,
The data X is sent to the comparator 20 through the OR circuit 26. The comparator 20 compares X and Z, and if X> Z, the terminal 30 is set to the H level to indicate that Z is the minimum value. Further, if X ≦ Z, A is output via the OR circuit 27.
The ND circuit 23 is opened, and the terminal 28 is set to the H level to show that X is the minimum value.

On the other hand, also in the case of X> Y, in the above description,
If X and Y are exchanged and considered, the same operation is performed, and it can be shown that Y takes the minimum value.

〔The invention's effect〕

As described above, according to the present invention, accurate Y / C separation from a video signal at a contour position composed of a horizontal line and a diagonal line, which is difficult with a conventional Y / C separation circuit using a comb filter, is performed. Therefore, it is possible to significantly suppress dot interference and cross-color interference, which are problems in conventional television receivers, and it is possible to improve the resolution of a display image, that is, improve the image quality.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG.
FIG. 3 is an operation waveform diagram of each part for showing the circuit operation of the embodiment shown in FIG. 1, FIG. 4 is a circuit diagram showing a concrete example of the minimum value selection circuit in FIG. 1, and FIG. A block diagram showing a conventional Y / C separation circuit using a filter,
FIG. 5A is a waveform diagram showing the waveform of each part signal in FIG. 5, and FIG. 6 is an explanatory diagram showing problems in the conventional Y / C separation circuit when the contour part is constituted by horizontal lines,
FIG. A is an explanatory view showing the same problem when the contour portion is formed by diagonal lines. Explanation of symbols 2a to 2d ... 1H delay line, 4a to 4h ... Multiplier, 7a to
7c ... Adder, 8 ... Bandpass filter, 9 ... Subtractor, 1
2a, 12b ... Inversion circuit, 13a-13c ... Subtraction and absolute value conversion circuit, 14 ... Minimum value selection circuit, 15 ... Switch

Claims (1)

[Claims] 1. A Y / C separation circuit which receives a television signal and separates and outputs a luminance signal (hereinafter abbreviated as Y signal) and a color signal (hereinafter abbreviated as C signal) from the inputted television signal. In the above, the first to fourth 1H delay lines (where H represents one horizontal scanning period) are cascade-connected with the input terminal of the television signal as an input side, and the input side of the first delay line is connected to the first side. After the respective signals extracted respectively from the output side of the first delay line (that is, the input side of the second delay line) and the output side of the second delay line are passed through the respective weighting circuits, the first addition circuit A first rectangular filter for adding and outputting, an input side of the second delay line, an output side of the second delay line (that is, an input side of the third delay line), and an output of the third delay line. After the respective signals extracted from the side and the Second and outputting the added by the addition circuit
A comb filter, and each of the input side of the third delay line, the output side of the third delay line (that is, the input side of the fourth delay line), and the output side of the fourth delay line. A third addition circuit that outputs the signals after passing through the respective weighting circuits
A comb-shaped filter, and a first for detecting a level difference between respective signals extracted from the input side of the first delay line and the output side of the second delay line.
Of the third delay line, a second detection circuit for detecting the level difference between the signals respectively extracted from the input side of the second delay line and the output side of the third delay line, The third detection circuit for detecting the level difference between the respective signals extracted from the input side and the output side of the fourth delay line, and the minimum of the detection outputs from the first to third detection circuits A minimum value selection circuit for selecting one of the outputs of the first to third detection circuits in the minimum value selection circuit, and the first to third comb shapes according to which of the outputs of the first to third detection circuits is selected as the minimum value. Selection switch means for selecting an output from any one of the filters, and means for separating the Y signal and the C signal from the input television signal by using the output signal selected by the selection switch means. Y and C minutes characterized by being made Isolated circuit.