JPH0646813B2 - NTSC adaptive contour extraction filter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an NTSC adaptive contour extraction filter for digitally extracting 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 have been proposed from various fields for extracting the contour component from image information.For example, in a television receiver, a contour signal is extracted from a luminance signal and added to the original luminance signal. To improve the sharpness of the image.

The NTSC composite video signal S (t) is a luminance signal Y (t).
And the color subcarrier fsc of the two color difference signals U (t) and V (t)
It is a composite signal with the color signal C (t) which is quadrature-phase modulated at = 3.579545 MHz. That is, S (t) = Y (t) + C (t) = Y (t) + U (t) sin2πfsct + V (t) cos2πfsct Conventional contour extraction filters of this kind are digital even in analog form. Even in the case of the format, for example, the above-mentioned luminance signal Y (t) is separated from the above-mentioned composite video signal S (t), and a horizontal contour extraction filter is applied to the separated luminance signal Y (t) 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 the vertical contour extraction filter will be described 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 of the A / D converter 2 is given from the input terminal 1. The A / D converter 2 converts an analog signal into a digital signal, and a luminance signal color signal separation circuit 3 that separates the converted digital signal into a luminance signal and a color signal.
(Hereinafter referred to as YC separation circuit). YC separation circuit 3
The luminance signal separated by is the horizontal contour extraction filter 8
Given to. The horizontal contour extraction filter 8 is composed of a first delay circuit 51, a second delay circuit 52, a coefficient circuit 6 and an addition circuit 7. 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 described.

The analog composite video signal input to the input terminal 1 is A /
The signal is supplied to the D converter 2 and is converted into a digital composite video signal at the predetermined sampling frequency fs. The digital composite video signal output from the A / D converter 2 is separated into a luminance signal and a chrominance signal by the YC separation circuit 3, and the separated luminance signal is the first delay circuit of the horizontal contour extraction filter 8. It is given to 51 as well as to the adder circuit 7. The output of the first delay circuit 51 is given to the second delay circuit 52 and also to the coefficient circuit 6, and the coefficient circuit 6 causes the first delay circuit 5 to output.
The output signal of 1 is multiplied by "-2". Here, the delay times of the first and second delay circuits 51 and 52 are determined by the reciprocal of the sampling frequency fs, and the A / D conversion circuit 2
Is set to be one sampling interval T of the output digital signal sequence.

In the adder circuit 7, the output of the YC separation circuit 3, the output of the coefficient circuit 6 and the output of the second delay circuit 52 are added. Therefore, assuming that the luminance signal f (t) which is the output signal of the YC separation circuit 3 is f (nT) at a time t = nT, as will be understood from the above description, the output of the addition circuit 7 is , F (nT) −2f {(n-1) T} + f {(n-2) T} is obtained. This is the second-order differential of 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 constituted by the third and fourth delay circuits 53 and 54, the coefficient circuit 6 and the addition circuit 7, and the A / D converter 2
The YC separation circuit 3 is similar to that shown in FIG. The delay times of the third and fourth delay circuits 53 and 54 are configured to be one horizontal scanning time, and the coefficient circuit 6 and the addition circuit 7
Is constructed in the same manner as in FIG. 4, the coefficient circuit 6 multiplies the output of the third delay circuit 53 by "-2", and the adder circuit 7 produces YC.
The output of the separation circuit 3, the output of the coefficient circuit 6 and the output of the fourth delay circuit 54 are added. Therefore, as is clear from the description in FIG. 4, the vertical contour extraction filter shown in FIG. 5 performs the second-order differentiation in the vertical direction on the screen with respect to the luminance signal which is the output signal of the YC separation circuit 3. And then
A vertical high frequency component of the luminance signal, that is, a vertical contour signal is extracted.

FIG. 6 is a diagram showing a conventional contour extraction filter constructed by superposing the horizontal contour extraction filter shown in FIG. 4 and the vertical contour extraction filter shown in FIG. In FIG. 6, a contour extraction filter 10 is a filter for extracting contour signals in the horizontal and vertical directions, and the first and second delay circuits 51 and 52 are the first and second delay circuits described in FIG. The delay circuits 51 and 52 have the same delay time.
The fifth and sixth delay circuits 55 and 56 are configured to have a delay time obtained by subtracting the delay times of the first and second delay circuits 51 and 52 from one horizontal scanning time. Therefore, the total delay time 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 sixth delay circuit 56. The delay time including the delay time of 1 is one horizontal scanning time.

The coefficient circuit 6 is configured to multiply the input signal by "-4", and the adder circuit 7 outputs 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.
Is added to the output of the sixth delay circuit 56. That is, the contour extraction filter 10 is
Vertical contour extraction filter including the delay circuit 55, the first delay circuit 51, the second delay circuit 52, the sixth delay circuit 56, the coefficient circuit 6, and the adder circuit 7, and the first delay circuit 51. , The second delay circuit 52, the coefficient circuit 6, and the horizontal contour extraction filter constituted by the adder circuit 7 are superposed, whereby the vertical contour signal and the horizontal contour signal can be extracted.

[Problems to be solved by the invention]

As described above, since the conventional contour extraction circuit extracts the contour signal using the luminance signal, the YC separation circuit that separates the composite video signal into the luminance signal and the color signal delays one horizontal scanning time signal. When a circuit is used, this delay circuit and the delay circuit for delaying one horizontal scanning time signal necessary for the contour extraction filter cannot be shared, and there is a drawback that an increase in cost cannot be avoided.

The present invention has been made in order to solve the above problems, and by extracting a contour signal directly from a composite video signal, a delay circuit required for a YC separation circuit and a delay circuit required for a contour extraction filter are provided. And an inexpensive contour signal extraction filter that can be shared.

[Means for solving problems]

An adaptive contour extraction filter according to the present invention provides a sampling point of a digital signal obtained by A / D converting a composite video signal of the NTSC system and a sampling point on a scanning line one scanning line with respect to the sampling point. The first and second adjacent sample points having the same phase of the color subcarrier and being closest thereto, and the third and third sample points which are symmetrical with respect to the sample point with respect to the second and first sample points. With respect to the fourth adjacent sample point, a plurality of delay circuits required to extract each sample value of the five sample points at the same timing at the data extraction timing, the sample point, and the first sample point. , A fourth contour extraction filter for extracting contour signals in the first direction in which these three sample points are arranged, using a total of three sample values in consideration of the fourth two adjacent diagonal sample points, Sample points,
A contour signal in the second direction in which these three sample points are arranged is extracted by using three new sample values in consideration of the sample point and the second and third adjacent sample points that are diagonally adjacent to each other. A second contour extraction filter is provided, and the absolute values of the contour signals in the first and second directions are directly compared, and the contour signal having the larger absolute value is output.

[Action]

In the present invention, by using the sample value of the sample point and a plurality of adjacent sample points in the diagonal direction in which the sample point and the color subcarrier obtained on and under one line thereof are in the same phase, The filter extracts the contour components of the sample points, detects the direction of the image change using the sample values of the sample points and the adjacent sample points, and compares the detection results with the absolute values to obtain the first and the first values. Since any one of the outputs of the two filters is selected and outputted, the line delay circuit and the contour extraction filter necessary for the YC separation circuit when considering both the Y / C separation and the contour extraction system are considered. Can be shared with the line delay circuit required for the above, and the line delay circuit can be reduced.

Moreover, since the detection of the image change direction, that is, the selection of the contour signals in the first and second directions is performed by comparing the magnitudes of the contour signals in the first and second directions, the first and second contour signals are detected. The switching signal generating circuit for switching the contour signals in the two directions includes only a comparison circuit that compares the magnitudes of the contour signals in the first and second directions and an absolute value circuit that takes the absolute value of each contour signal in the preceding stage. It can be realized with a simple hardware configuration. Moreover, as described above, the detection of the image change direction is performed by detecting the contour signal itself in the first and second directions.
In other words, not only the difference between the sample values of adjacent sample points but also the magnitude of the signal change amount including the sample value of the sample point concerned is compared, so that there is also an adaptive concept in the form of feeding back the situation of the sample point concerned. With, it is possible to more faithfully perform contour extraction after considering the sample points.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of an NTSC adaptive contour extraction filter according to an embodiment of the present invention. In the figure, 1 is an input end of a composite video signal which is an analog signal, 2 is an A / D conversion circuit, and 11 is contour extraction. A filter, 30 is a sampling pulse generating circuit for synchronously oscillating at a frequency fs which is three times or four times the color subcarrier frequency fsc of the input composite video signal, and 4 is an output terminal.

In the contour extraction filter 11, 20a and 20b are first and second delay circuits that delay the sample value series output from the A / D conversion circuit 2 by one cycle of the color subcarrier,
When the sampling frequency is 4 fsc, the sampled value series is set to 4
The sampling period (4T) is delayed, and in the case of 3fsc, the sampling period is delayed (3T). Reference numerals 21a and 21b denote first and second line delay circuits for delaying the sample value series output from the A / D conversion circuit 2 by about 1 horizontal scanning time. When the sampling frequency is 4 fsc, the sample values are The sequence is delayed by one horizontal scanning time minus two sampling periods, and in the case of 3 fsc, it is 1.5 horizontal scanning times less than 1.5.
It delays the time by subtracting the sample period.
With these delay circuits, as shown in FIG.
The sample point P3 and the color subcarrier have the same phase 4
The adjacent sample points P1, P2, P4 and P5 are simultaneously obtained. Further, 22a and 22b are addition circuits, 23a and 23b are 1/4 multiplication coefficient circuits (hereinafter referred to as 1/4 multiplication circuits) that multiply the input by 1/4, and 24a and 24b.
Is the first and second subtraction circuits, 25a is the first subtraction circuit 24
a first absolute value circuit for taking the absolute value of the output of a, 25b for the second absolute value circuit for taking the absolute value of the output of the second subtraction circuit 24b, and 36 for halving its input by 1/2 A multiplying coefficient circuit (hereinafter referred to as a 1/2 multiplying circuit), 27 compares the outputs of the first and second absolute value circuits 25a and 25b, and detects the direction in which the composite video signal is changing rapidly. Circuit, 28
Depending on the comparison result of the comparison circuit 27,
A switch circuit for selecting and outputting one of the outputs of the subtraction circuits 24a, 24b of
8 is a multiplication circuit for adjusting the amplitude of the contour signal which is the output of 8.

Next, the operation will be described.

The sampling pulse generation circuit 30 outputs a sampling pulse having a frequency fs which is three times or four times the color subcarrier frequency fsc of the composite video signal, and the sampling pulse is applied to the A / D conversion circuit 2. As a result, the A / D conversion circuit 2 converts the analog composite video signal applied to the input terminal 1 into a digital signal. The sampling signal series of the composite video signal of the NTSC system sampled by the sampling pulse has an array as shown in FIG. 3 when attention is paid to the phase of the on-screen color signal. In FIG. 2, line n indicates the nth horizontal scanning line, and 4f () indicates 4fsc system sampling points, 3
f (∘) indicates a sampling point of the 3fsc system. Further, f indicates a color subcarrier.

FIG. 3 is a diagram for explaining the operation of this embodiment, in which symbols are added to the sample value series of FIG. The contour extraction of the sample point P3 in FIG. 3 will be described with reference to FIG.

At a certain time T, the A / D conversion circuits 2 to P5
Suppose that the sample value of the sample point is output from the first delay circuit 20a is the sample value of the sample point of P4. The output of the second delay circuit 20b is the sample value of the sample point of P1. The first line delay circuit. The output of 21a is the sample value of the sample point P3, and the output of the second line delay circuit 21b is the sample value of the sample point P2.

In the first adder circuit 22a, the A / D conversion circuit 2
Output (P5) and the output of the second delay circuit 20b (P5)
1) is added, and the output is the first 1/4 multiplication circuit 23.
It is multiplied by 1/4 with a. Next, the first line delay circuit 2
The output of 1a is multiplied by 1/2 in the 1/2 circuit 26, and the output signal of the first 1/4 circuit 23a is subtracted from the output signal of the 1/2 circuit 26 in the first subtraction circuit 24a. It Therefore, the output signal of the first subtraction circuit 24a is -1/4 (sample value of sample point P1) +1/2 (sample value of sample point P3) -1/4 (sample value of sample point P5) ). In the second adder circuit 22b, the output (P4) of the first delay circuit 20a and the second delay circuit 21 are used.
b output (P2) is added, and this output is the second 1 /
It is multiplied by ¼ by the quadruple circuit 23b. Then, in the second subtraction circuit 24b, the output signal of the second ¼ multiplication circuit 23b is subtracted from the output signal of the ½ multiplication circuit 26. Therefore, the output signal of the second subtraction circuit 24b is -1/4 (sample value of sample point P2) +1/2 (sample value of sample point P3) -1/4 (sample value of sample point P4)

Further, the output of the first subtraction circuit 24a is applied to the first absolute value circuit 25a to take the absolute value. Therefore, the output signal T1 of the first absolute value circuit 25a is T1 = | 1/4 (sample value of sample point P1) -1/2 (sample value of sample point P3) +1/4 (sample value of P5 sample point) Sample value). The absolute value of the output signal of the second subtraction circuit 24b is taken by the second absolute value circuit 25b. Therefore, the output signal T2 of the second absolute value circuit 25b is T2 = | 1/4 (sample value of sample point P2) -1/2 (sample value of sample point P3) +1/4 (sample point P4) Sample value of).

The first absolute value circuit 25a and the second absolute value circuit 25b
The respective output signals T1 and T2 are applied to the comparison circuit 27, which compares the magnitudes of T1 and T2 and sends a control signal to the switch circuit 28 described below. The output signal of the first subtraction circuit 24a and the output signal of the second subtraction circuit 24b are applied to the switch circuit 28. When the T1 and T2 of the comparison circuit 27 are T1> T2, When T1 ≦ T2, the output signal of the second subtraction circuit 24b changes the output signal of the second subtraction circuit 24b so that the output signal of the first subtraction circuit 24a becomes the output of the switch circuit 28.
A control signal is sent to the switch circuit 28 so that the output becomes 8. The output signal of the switch circuit 28 is applied to the multiplication circuit 29, and the output of the switch circuit 28 is multiplied by N (N: real number) in the multiplication circuit 29. Here, the multiplication N is controlled by a microcomputer or the like from the outside, although not shown.

According to the apparatus of this embodiment, since the contour signal is directly extracted from the composite video signal, the number of line delay circuits can be reduced and the cost can be reduced as compared with the conventional apparatus. In addition, the detection of the image change direction, that is, the sampling signal, the first direction in which the first and fourth adjacent sample points are arranged, and the contour signal in the second direction in which the sample point and the second and third adjacent sample points are arranged, Since the selection is performed by comparing the magnitudes of the contour signals themselves in the first and second directions, a switching signal generation circuit for switching the contour signals in the first and second directions is provided. This can be realized by a simple hardware configuration including only the comparison circuit 27 for comparing the magnitudes of the contour signals in the two directions and the absolute value circuits 25a and 25b that take the absolute values of the contour signals in the preceding stage. Moreover, as described above, the detection of the image change direction is performed by detecting the contour signal in the first and second directions, that is, not only the sample value of the adjacent sample point but also the signal change amount including the sample value of the sample point. Since the comparison is performed, the contour extraction at the sample point can be performed more adaptively and faithfully. Further, in the present embodiment, since the adjacent sample points are located obliquely with respect to the sample point of interest, the horizontal contour signal, the vertical contour signal, and the diagonal contour signal can be simultaneously extracted.

It is needless to say that the 1/4 times circuit and the 1/2 times circuit in the above embodiment may be other combinations as long as the multiplier to the input signal has a relationship of 1: 2.

〔The invention's effect〕

As described above, according to the present invention, by the sample point and the first to fourth adjacent sample points around the sample point whose color subcarrier has the same phase as that of the sample point, from the composite video signal. The contour signal is directly extracted, the direction of the image change is detected by the sample point and the adjacent sample point, and the contour signal is extracted by using the pixel signal in that direction. The number of delay circuits is small, and the contour signal can be extracted with high accuracy.

Further, the detection of the image change direction, that is, the contour signal in the first direction in which the sample point and the first and fourth adjacent sample points are arranged and in the second direction in which the sample point and the second and third adjacent sample points are arranged Is selected by comparing the magnitudes of the contour signals themselves in the first and second directions, the switching signal generating circuit for switching the contour signals in the first and second directions is This can be realized by a simple hardware configuration including only a comparison circuit for comparing the magnitudes of the contour signals in the second direction and an absolute value circuit that takes the absolute value of each of the contour signals in the preceding stage, and moreover, the image change direction. Is detected not only by the sample values of adjacent sample points but also by comparing the magnitudes of signal changes including the sample values of the sample points, so contour extraction at the sample points should be performed more faithfully and adaptively. There is an effect that can be.

[Brief description of drawings]

FIG. 1 is a block diagram showing a contour extracting filter according to an embodiment of the present invention, FIGS. 2 and 3 are diagrams showing a sample value series in the filter, and FIG. 4 is a diagram showing a configuration of a conventional horizontal contour extracting filter. FIG. 5 is a diagram showing the configuration of a conventional vertical contour extraction filter, and FIG. 6 is a diagram showing the configuration 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, 20a, 20b, 21a and 21b are delay circuits,
23a, 23b and 26 are coefficient circuits, 22a and 22b are addition circuits, 24a and 24b are subtraction circuits, 25a and 25b are absolute value circuits, 27 is a comparison circuit, 28 is a switch circuit, 1
Reference numeral 1 is a contour extraction filter, and 30 is a pulse generation circuit. The same reference numerals in the drawings indicate the same or corresponding parts.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP 61-35085 (JP, A) JP 61-35086 (JP, A) JP 61-35087 (JP, A) JP 61- 189792 (JP, A) JP 62-7293 (JP, A) JP 59-40788 (JP, A) JP 60-241386 (JP, A)

Claims (1)

[Claims] 1. An NTSC composite video signal is input,
An NTSC adaptive contour extraction filter for extracting a contour component of the composite video signal, comprising: an A / D conversion circuit for sampling the composite video signal at a frequency synchronized with a horizontal scanning frequency; A sample value of a sample point and first and second adjacent sample points that have the same phase of the color subcarrier as the sample point on the scanning line one scanning line with respect to the sample point and are closest to the sample point. , A delay circuit for simultaneously extracting the sample values of the third and fourth sample points that are symmetrical to the second and first sample points with respect to the sample point, and the sample point, The first adjacent sample point, and the fourth
A first contour extraction filter for extracting a contour component in the direction in which the three sample points are arranged in the sample point using the sample values of the adjacent sample points, and the sample point and the second adjacent sample. Point, and the third above
Of the adjacent sample points using the sample values of the adjacent sample points of the second contour extraction filter for extracting the contour component in the direction in which the three sample points are arranged, and the first and second contour extraction filters. NTSC adaptation characterized in that it comprises a comparison circuit for directly comparing outputs and a selection circuit for selecting one of the outputs of the first and second contour extraction filters according to the comparison result of the comparison circuit. Type contour extraction filter.