JPS627294A - Ntsc adaptive type contour extracting filter - Google Patents

Abstract

PURPOSE:To extract an contour signal with high accuracy by detecting the direction of larger signal variation by using an adjacent picture element signal where the phase of chrominance subcarrier is an inverse phase and directly extracting the contour signal in the direction of the larger signal variation. CONSTITUTION:At a time T, if it is assumed that the sample value of sample point P5 is outputted from an A/D converter 2, the sample values of sample points P4, P1 and P2 are outputted from delay circuits 201, 202 and 22 respectively. At an addition circuit 221, outputs of the delay circuits 201 and 22 are added and at an addition circuit 222, the output of the A/D converter 2 and addition circuit 222 are added. At a subtraction circuit 241, the output of the addition circuit 221 is subtracted from the output of the addition circuit 222 and is multiplied by 1/4 at a 1/4 multiplying circuit 23. If a luminance signal varies only in a vertical direction in a sampled screen and no colors change in both horizontal and vertical directions, the first term of the output of the 1/4 circuit 23 comes to the sum of components of the contour of the luminance signals' as well as a chrominance signal and the second term comes to the chrominance signal component.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an NTSC adaptive contour extraction filter that digitally extracts a contour signal from an NTSC composite video signal in which a luminance signal and a chrominance signal are frequency multiplexed. .

[Conventional technology]

Various methods for extracting contour components from image information have been proposed since ancient times.For example, in television receivers, a contour signal is extracted from a luminance signal and this is added to the original luminance signal. This aims to improve the sharpness of the image.

The composite video signal S (t) of the NTSC system is a luminance signal Y
(t) and two color difference signals U (t) and V (t)
It is a composite signal with the color signal C(t) which is quadrature two-phase modulated with the color subcarrier f s c =3.579545 MHz. That is, S (t) = Y (t) + C(t
)=Y(t)+U(t) 5in2 tt f sc
tl V (t) cos 'lπfsct Conventionally, this type of contour extraction filter, whether in analog or digital format, extracts from the composite video signal S (t) described above to the luminance signal Y ( t)
This separated luminance signal Y (for tl,
Generally, a horizontal contour signal is obtained by a horizontal contour extraction filter, and a vertical contour signal is obtained by a vertical contour extraction filter. The horizontal contour extraction filter and vertical contour extraction filter will be explained below.

FIG. 4 is a diagram showing an example of a conventional digital horizontal contour extraction filter. In FIG. 4, an analog composite video signal is applied to an A/D converter 2 from an input terminal 1. The A/D converter 2 converts an analog signal into a digital signal, and passes the converted digital signal to a luminance signal/chrominance signal separation circuit 3 (hereinafter referred to as YC separation circuit) that separates the converted digital signal into a luminance signal and a chrominance signal. give. The luminance signal separated by the YC separation circuit 3 is given to a horizontal contour extraction filter 8. This horizontal contour extraction filter 8 includes a first delay circuit 51, a second delay circuit 52, a coefficient circuit 6, and an adder circuit 7.
It consists of The contour signal extracted from the horizontal contour extraction filter 8 is output to the output terminal 4.

Next, the operation of the horizontal contour extraction filter shown in FIG. 4 will be explained.

The analog composite video signal input to input terminal 1 is A/
The signal is applied to a D converter 2, where it is converted into a digital composite video signal at a predetermined sampling frequency fs. The digital composite video signal output from the A/D converter 2 is separated into a luminance signal and a color signal by the YC separation circuit 3, and the separated luminance signal is sent to the first delay circuit of the horizontal contour extraction filter 8. 51 and also to the adder circuit 7. The output cover of the first delay circuit 51
is applied to the second delay circuit 52 and the coefficient circuit 6
This coefficient circuit 6 multiplies the output signal of the first delay circuit 51 by -2.

Here, the delay time of the first and second delay circuits 51 and 52 is determined by the reciprocal of the sample frequency fs, and one sample of the digital signal series output from the A/D conversion circuit 2 is determined by the reciprocal of the sample frequency fs. The interval is set to be T.

In the adder circuit 7, the output of the VC separation circuit 3, the output of the coefficient circuit 6, and the output of the second delay circuit 52 are added. Therefore, the luminance signal f (t
) is f (nT) at a certain time t-n'l', as understood from the above explanation, the output of the adder circuit 7 is f(nT) -2f ((n-1) T ) +f ((
n-2) T) is obtained. This is the luminance signal f
(t) in the horizontal direction on the screen, and therefore, the horizontal high frequency component of the luminance signal, that is, the horizontal contour signal is extracted.

FIG. 5 is a diagram showing an example of a conventional digital vertical contour extraction filter. In FIG. 5, the vertical contour extraction filter 9 is the third. It is composed of a fourth delay circuit 53, 54, a coefficient circuit 6, and an adder circuit 7, and the A/D converter 2
The YC separation circuit 3 is similar to that shown in FIG. Third
．． The delay time of the fourth delay circuits 53 and 54 is configured to be one horizontal scanning time, the coefficient circuit 6 and the addition circuit 7 are configured in the same manner as in the case of FIG. The output of the circuit 53 is multiplied by -2, and the adder circuit 7 combines the output of the YC separation circuit 3, the output of the coefficient circuit 6, and the fourth delay circuit 5.
Add the output of 4. Therefore, as is clear from the explanation in FIG. 4, the vertical contour extraction filter shown in FIG. Therefore, the vertical high-frequency component of the luminance signal, that is, the vertical contour signal is extracted.

FIG. 6 is a diagram showing a conventional contour extraction filter constructed by superimposing the horizontal contour extraction filter shown in FIG. 4 and the vertical contour extraction filter shown in FIG. 5. In FIG. 6, a contour extraction filter 10 is a filter that extracts contour signals in the horizontal and vertical directions. The second delay circuits 51 and 52 are the same as the first delay circuits 51 and 52 described in FIG. It has the same delay time as the second delay circuits 51 and 52.

Also, 5th. The sixth delay circuits 55 and 56 operate from one horizontal scanning time to the first. The delay time is obtained by subtracting the delay time of the second delay circuits 51 and 52. Therefore, the delay time that is the sum of the delay time of the first delay circuit 51 and the delay time of the fifth delay circuit 55 is one horizontal scanning time, and the delay time of the second delay circuit 52 and the delay time of the sixth delay circuit 56 is one horizontal scanning time. The delay time including the delay time is one horizontal scanning time.

The coefficient circuit 6 is configured to multiply the input signal by "-4", and the adder circuit 7 receives the output of the YC separation circuit 3, the output of the fifth delay circuit 55, the output of the coefficient circuit 6, and the second delay circuit 52. The output of the sixth delay circuit 56 is added to the output of the sixth delay circuit 56. That is, the contour extraction filter 10 includes the fifth delay circuit 55, the first delay circuit 51. Second delay circuit 5
2. Sixth delay circuit 56. Coefficient circuit 6. and addition circuit 7
a vertical contour extraction filter, and a first delay circuit 51. Second delay circuit 52. Coefficient circuit 6 and addition circuit 7
The vertical contour signal and the vertical contour signal can be extracted using this configuration.

[Problem that the invention seeks to solve]

In this way, the conventional contour extraction circuit extracts the contour signal using the luminance signal, so the YC separation circuit that separates the composite video signal into the luminance signal and color signal has a delay of one horizontal scanning time signal. When a circuit is used, this delay circuit cannot be used in common with a delay circuit for delaying one horizontal scanning time signal necessary for the contour extraction filter, which has the disadvantage that an increase in cost is unavoidable.

This invention was made to solve the above-mentioned problems, and by directly extracting a contour signal from a composite video signal, the delay circuit necessary for the YC separation circuit and the delay circuit necessary for the contour extraction filter can be combined. This provides an inexpensive contour signal extraction filter that can be used in common.

[Means for solving problems]

The adaptive contour extraction filter according to the present invention includes an A/D conversion means for sampling an NTSC system composite video signal at a sampling frequency four times as high as a color subcarrier and converting it into a digital signal, a delay means, and a signal change amount. A two-dimensional filter consisting of a detection means and an adaptive high-frequency component extraction means is provided, and the color subcarrier phase is opposite to the sample point of the digital signal, and the color subcarrier phase is opposite to the sample point of the digital signal, and the color subcarrier phase is opposite to the sample point of the digital signal, The upper and lower sample points on the horizontal scanning line are used, and the two sample points on the left and right of the horizontal scanning line are used, and the sample values of these sample points are used to generate a composite video signal. This method detects the direction in which the signal is rapidly changing, and extracts the contour component in the direction in which the signal is rapidly changing.

[Effect]

In this invention, the sampling point and neighboring pixel signals whose color subcarrier phases are opposite to those of the sampling point are used to detect the direction in which the signal change is large, and to flatten the signal value series in the direction in which the signal change is large. Since the contour signal is extracted by determining the frequency components, it is possible to extract the contour signal from the composite video signal with high accuracy using fewer line delay circuits than in the past.

〔Example〕

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

FIG. 1 is a schematic block diagram showing an embodiment of the present invention. In the figure, 1 is an input terminal, and this input terminal 1
A composite video signal is applied to the A/D converter 2 via the A/D converter 2.

The A/D converter 2 is supplied with a sampling pulse having a frequency fs four times the color subcarrier frequency fsc of the composite video signal from the pulse generator 30, and the A/D converter 2 receives the sampling pulse from the pulse generator 30. The composite video signal is converted into a digital signal according to the following, and this is applied to the contour extraction filter 11. The contour extraction filter 11 includes the first . Second delay circuit 201゜"202
and 1 3rd. a fourth delay circuit 21.22, a first delay circuit 21.22; The second adder circuits 221 and 222, the 1/4 times circuit 23, and the first
- third subtraction circuits 241 to 243; It is composed of a second absolute value circuit 251, 252, a comparison circuit 26, a sign inversion circuit 27, a multiplication circuit 28, and a doubling circuit 29.

1 above. The second delay circuits 201 and 202 delay the sample value series output from the A/D converter 2 by a time equal to one horizontal scanning time minus two sample periods. Third. The fourth delay circuits 21 and 22 delay the sample value series output from the A/D converter 2 by two sample periods. The first adder circuit 221 is the first delay circuit 20
1 and the output of the third delay circuit 22, and the second addition circuit 222 adds the output of the A/D converter 2 and the output of the third delay circuit 22.
The output of the delay circuit 202 is added to the output of the delay circuit 202. 1st
The subtraction circuit 241 is a circuit that subtracts the output signal of the second addition circuit 222 from the output signal of the first addition circuit 221. The 1/4 multiplier circuit 23 is configured to multiply the output of the first subtraction circuit 241 by 174 times. The doubling circuit 29 is the third
The output of the delay circuit 21 is multiplied by 1/2. Further, the second and third subtraction circuits 242 and 243 are connected to the doubling circuit 29 from the outputs of the first and second addition circuits 221 and 222, respectively.
is configured to subtract the output of

Further, the first absolute value circuit 251 calculates the absolute value of the output of the subtraction circuit 243, and the second absolute value circuit 252
is used to find the absolute value of the output of the subtraction circuit 242. The sign inversion circuit 27 inverts the sign of the output of the 1/4 multiplier circuit 23 in accordance with the comparison output of the comparison circuit 26.

FIG. 2 is a diagram showing a sampling signal sequence of an NTSC composite video signal sampled by sampling pulses, and FIG. 3 is a diagram for explaining the specific operation of an embodiment of the present invention. FIG. 2 shows that the phases are reversed.

Next, with reference to FIGS. 1 to 3, a specific operation of an embodiment of the present invention will be described.

First, outline extraction of the sample point P3 shown in FIG. 3 will be explained. Now, suppose that the A/D converter 2 outputs the sample value of the sample point P5 at a certain time T, the first delay circuit 201 outputs the sample value of the sample point P4, and the second delay circuit 202 outputs the sample value of the sample point P5. The sample value of the sample point P1 and the sample value of the sample point P2 are output from the fourth delay circuit 22, respectively. Then, in the first adder circuit 221, the output (P4) of the first delay circuit 201 and the fourth delay circuit 2
2 output (P2) is added, and the second addition circuit 222
Then, the output (P5) of the A/D converter 2 and the second delay circuit 2
02 output (Pl) is added, and the first subtraction circuit 24
1, the output (P1+P5) of the second addition circuit 222 is subtracted from the output (P2+P4) of the first addition circuit 221, and in the 174 times circuit 23, this first subtraction circuit 24
The output of 1 (P2+P4-PI-P5) is multiplied by 1/4. Therefore, the output signal of this 1/4 multiplication circuit 23 is: 11/4 (sample value of sample point P1) 11/4 (sample value of sample point P5) +1/4 (sample value of sample point P2) +1 /4 (sample value of sample point P4) ...(1)
This can also be written as:

[-1/4 (2) Zero point P1 wheel + 1/2 G zero point P
3 books (Nao-1/4 @E point P 5 (7) 11 books (1
1D] - [-1/4 @ 1 point of zero point P2 + 1/2G l sectional surface of main point P3 - 1/4 L material of m point P4 ■] ...
(1”) □The first term (inside the first []) in this equation (1”) represents the second-order differential in the vertical direction of the image, and the second term (inside the second []) similarly It represents the second derivative in the horizontal direction.

Therefore, if the luminance signal changes only in the vertical direction on the sampled screen, and the color does not change in both the horizontal and vertical directions, the first term in the above equation will be the sum of the contour component of the luminance signal and the color signal component. , the second term becomes the color signal component.

Therefore, according to the above equation (1''), the color signal component included in the first term is canceled by the second term, and the vertical contour component with respect to the luminance signal can be extracted.Also, the luminance changes only in the horizontal direction. , horizontal.

If the color does not change in both vertical directions, the first term in equation (1') becomes the color signal component, and the second term becomes the sum of the contour component of the luminance signal and the color signal component. Therefore, by changing the sign of equation (1'), the horizontal contour component for the luminance signal can be extracted in the same manner as described above. Here, if the color signal changes spatially, the color signal component in the first term of equation (1) and the color signal component in the second term do not exactly match, so it is given by equation (l). Although some color signal components leak in the contour compensation signal, there is no practical problem.

Next, control of the above-mentioned sign inversion will be explained.

At time T, the output of the third delay circuit 21 is at the sample point P
3, and this signal is doubled by the doubling circuit 29 and outputted to the second .3 sample value. It is supplied to a third subtraction circuit 242, 243. The output (P1+P5) of the second addition circuit 222 is given to the other input of the third subtraction circuit 243, and the output of the doubling circuit 29 (2・P5) is supplied from the output of the second addition circuit 222.
The result obtained by subtracting 3) is sent to the first absolute value circuit 251.
The absolute value is taken. Therefore, the first absolute value circuit 251
The output signal T1 is as follows: T1=1 (sample value of sample point P1) -2 (sample value of sample point P3) + (sample value of sample point P5) 1. Further, the output (P2+P4) of the first addition circuit 221 is given to the other input of the second subtraction circuit 242,
The absolute value of the result obtained by subtracting the output (2·P3) of the doubling circuit 29 from the output of the first adder circuit 221 is taken by the second absolute value circuit 252. Therefore, the output signal T2 of the second absolute value circuit 252 becomes T2-1 (sample value of sample point P2) -2 (sample value of sample point P3) + (sample value of sample point P4) 1.

The first absolute value circuit 251 described above. Second absolute value circuit 25
2 respective output signals T1. T2 is applied to a comparator circuit 26, which compares their magnitudes,
A control signal is sent to the sign inversion circuit 27 in accordance with the comparison result. The sign inversion circuit 27 includes a first subtraction circuit 24
1 output signal is given, and the comparator circuit 26 outputs an output signal such that when the output signal TIT2 is Tl>T2, the output of the sign inversion circuit 27 becomes the output signal of the first subtraction circuit 241, and when TI<72. sends a control signal to the sign inverting circuit 27 so that the output of the sign inverting circuit 27 becomes a signal with the sign of the output signal of the first subtracting circuit 241 inverted. The output signal of the sign inversion circuit 27 is then given to the multiplication circuit 28, and the output signal of the sign inversion circuit 27 is multiplied by N times (N;
real number). Although not shown, the multiplier N is controlled from the outside by, for example, a microcomputer.

According to this embodiment, since the contour signal is extracted directly from the composite video signal, the number of line delay circuits can be reduced compared to the conventional device, and the cost can be reduced. Further, since the contour signal in the direction in which the signal change is large is extracted using the values of adjacent sample points, the contour signal can be extracted with high accuracy from the composite video signal. Furthermore, in this embodiment, 1. Since sample points with opposite color subcarrier phases are located above, below, and to the left and right of the target point,
Horizontal contour signals and vertical contour signals can be extracted simultaneously.

〔Effect of the invention〕

As described above, according to the present invention, the direction in which the signal change is large is detected using neighboring pixel signals whose color subcarriers have opposite phases, and the contour signal in the direction in which the signal change is large is extracted from the composite video signal. Since the direct extraction is performed, the number of line delay circuits is reduced compared to the conventional device, and there is also an effect that the contour signal can be extracted with high precision (contour signal extraction) for composite video signals.

Furthermore, since sample points with opposite color subcarrier phases are located above, below, and to the left and right of the target main point, there is an effect that horizontal contour signals and vertical contour signals can be extracted at the same time.

[Brief explanation of drawings]

FIG. 1 is a schematic block diagram of an NTSC adaptive contour extraction filter according to an embodiment of the present invention, and FIGS. 2 and 3 show a sampling signal sequence of an NTSC composite video signal sampled by a sampling pulse. 4 is a schematic block diagram of a conventional horizontal contour extraction filter, FIG. 5 is a schematic block diagram of a conventional vertical contour filter, and FIG. 6 is a schematic block diagram of a conventional contour extraction filter. In the figure, 1 is an input terminal, 2 is an A/D converter, 4 is an output terminal, 21.22, 201.202 are delay circuits, 23
．． 29 is a coefficient circuit, 26 is a comparison circuit, 27 is a sign inversion circuit, 28 is a multiplication circuit, 221°222 is an addition circuit, 24
1 to 243 are subtraction circuits, 251.252 are absolute value circuits,
11 is a contour extraction filter.

Claims (1)

[Claims] (1) An NTSC adaptive contour extraction filter that receives an NTSC system composite video signal as input and extracts contour components of the composite video signal, the composite video signal being processed at a sampling frequency four times as high as its color subcarrier. A/D that samples and converts it into a digital signal
a conversion means, the sampling point of the digital signal, and upper and lower sampling points whose color subcarrier phase is opposite to that of the sampling point, and which are located one horizontal scanning line above and below from the sampling point on the screen; and a delay means for simultaneously extracting the sample values of left and right sample points located two sample points to the left and right of the sample point on the same horizontal scanning line as the sample point, and the sample points above and below the sample point. Vertical signal change amount detection means for detecting the amount of change in the signal in the vertical direction on the screen from the sample value of the point; and means for detecting the amount of change in the signal in the horizontal direction on the screen from the sample values of the sample point and the left and right sample points. horizontal direction signal change amount detection means; and adaptive high frequency component extraction means that compares the change amount of the signal in the horizontal direction and the vertical direction and extracts the high frequency component of the signal sequence in the direction where the change amount is large. N characterized by
TSC adaptive contour extraction filter.