JPS627293A - Ntsc adaptive type contour extracting filter - Google Patents

Abstract

PURPOSE:To extract a contour signal with high accuracy by directly extracting a contour signal through a sample point as well as an adjacent sample point where the phase of a chrominance subcarrier thereof is the same phase to the phase of the sample point and furthermore extracting the contour signal from the varied direction of a picture. CONSTITUTION:At a time T, it is assumed that the sample value of the sample point P5 is outputted from an A/D converting circuit 2. At the first addition circuit 22a, the output of the A/D converting circuit 2 and the output (P1) of the second delay circuit 20b are added and said output is multiplied by 1/4 at the first a 1/4 multiplying circuit 23a. Then the output of the first line delay circuit 21a is multiplied by 1/2 at a 1/2 multiplying circuit 26 and at the first subtraction circuit 24a, the output of the first 1/4 multiplying circuit 23a is subtracted. The output of the first subtraction circuit 24a is taken by absolute values at the first absolute value circuit 25a and turned into T1. The output of the second subtraction circuit 24b is taken by the absolute value at the absolute value circuit 25b and is turned into T2. Being compared with a comparison circuit 27, T1 and T2 deliver control signals to a switch circuit 28. Said output signal is multiplied by N at a multiplication circuit 29.

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 in various fields for a long time.For example, in television receivers, a method is used to extract a contour signal from a luminance signal and add it to the original luminance signal. The aim is to improve the W accuracy of the image.

NTSC composite video signal S (tl is luminance signal Y
Ttl and the second 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) sin 2πfsct
+ V(t) cos 2 π fsct This type of contour extraction filter, which has been conventionally used, is either an analog type or a digital type. (t), and the separated luminance signal Y (t) is subjected to a horizontal contour extraction filter to obtain a horizontal contour signal, and a vertical contour extraction filter to obtain a vertical contour signal. there were. 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 of the first delay circuit 51 is
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 sampling frequency fs, and the delay time of the first and second delay circuits 51 and 52 is determined by the reciprocal of the sampling frequency fs. It is set to be T.

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, the luminance signal f l) which is the output signal of the YC separation circuit 3
Assuming that f (nT) at a certain time t=nT, 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 outputs 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
It has a structure in which a horizontal contour extraction filter constituted by the above is superimposed, and thereby a vertical contour signal and a horizontal contour signal can be extracted.

[Problem that the invention seeks to solve]

In this way, in the conventional contour extraction filter, since the contour signal is extracted using the luminance signal, the YC separation circuit that separates the composite video signal into the luminance signal and the color signal has a delay of one horizontal scanning time signal. Circuit power (When used, this delay circuit and a delay circuit for delaying one horizontal scanning time signal necessary for contour extraction and filling cannot be shared, resulting in an unavoidable increase in cost.

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 circuit that samples an NTSC composite video signal at a frequency three times or four times the color subcarrier of the NTSC system composite video signal; A delay circuit for simultaneously extracting four adjacent sample points having the same carrier wave phase, and a first circuit that extracts a contour component of the sample point using the sample value of the sample point and the adjacent sample points. a second contour extraction filter; a comparison circuit that detects the direction of change in the image using the sample values of the sample point and the adjacent sample points;
A selection circuit for selecting one of the outputs of the second contour extraction filter is provided.

[Effect]

In this invention, the first . The second filter extracts the contour component of each sample point, and detects the direction of change in the image using the sample values of the sample point and the adjacent sample points, and uses the detection results to detect the direction of change in the image. Select and output one of the outputs of the second filter.

〔Example〕

Hereinafter, embodiments of the present invention will be described 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 terminal for a composite video signal which is an analog signal, 2 is an A/D conversion circuit, and 11 is a contour extraction circuit. 30 is a sampling pulse generation circuit that synchronously oscillates at a frequency fs that is three or four times the color subcarrier frequency fsC of the human-powered composite video signal; 4 is an output terminal;

In the contour extraction filter 11, 20a.

Reference numeral 20b denotes a first . The second delay circuit delays the sampled value series by four sampling periods (4T) when the sampling frequency is 4fsc, and by three sampling periods (3T) when the sampling frequency is 3fsc. zta,
21b delays the sample value series output from the A/D conversion circuit 2 by approximately one horizontal scanning time. This is a second line delay circuit, and when the sampling frequency is 4fsc, the sample value series is delayed by a time equal to 2 sampling periods subtracted from 1 horizontal scanning time, and when the sampling frequency is 3fsc, it is delayed by 1 time from 2 horizontal scanning time. .5 sample period is subtracted from the time delay. Then, as shown in FIG. 3, these delay circuits connect the sample point P3 and four adjacent sample points P1 . P2. P4. P5 can be obtained at the same time. Also, 22 a,
22b is an adder circuit, 23a and 23b are 1/4 coefficient circuits (hereinafter referred to as 174 times circuits) that multiply the input by 1/4, and 24a and 24b are first . second subtraction circuit, 25
a is a first absolute value circuit that takes the absolute value of the output of the first subtraction circuit 24a; 25b is a second absolute value circuit that takes the absolute value of the output of the second subtraction circuit 24b; /2
Multiplying 1/2 times coefficient circuit (hereinafter referred to as 172 times circuit),
27 is a comparison circuit that 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 rapidly changing; 28 is a comparison circuit that detects the direction in which the composite video signal is rapidly changing; Above 1. A sui-no-sen circuit that selects and outputs either one of the outputs of the second subtraction circuits 24a and 24b;
A multiplication circuit 29 adjusts the amplitude of the contour signal output from the switch circuit 28.

Next, the operation will be explained.

The sampling pulse generating circuit 30 outputs a sampling pulse having a frequency fs that is three 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. Thereby, 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 sequence of the NTSC composite video signal sampled using the sampling pulses is arranged as shown in FIG. 3 if attention is paid to the phase of the color signal on the screen. In FIG. 2, line n indicates the n-th horizontal scanning line, and 4f(·) indicates the sample point of the 4fsc system, 3
f(○) indicates a sample point of the 3fsc system, and f indicates a color subcarrier.

・FIG. 3 is a diagram for explaining the operation of this embodiment, and the sample value series shown in FIG. 2 is labeled with symbols. The outline extraction of the sample point P3 in FIG. 3 will be explained using FIG. 1.

At the current time T, the A/D conversion circuit 2 to P5
If the sample value of the sample point is output, then the output of the first delay circuit 20a is the sample value of the sample point P4.The output of the second delay circuit 20b is the sample value of the sample point P1.The output of the first delay circuit 20a is the sample value of the sample point P1. The output of the second line delay circuit 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 addition circuit 22a, the A/D conversion circuit 2
(P5) and the output (P5) of the second delay circuit 20b.
l) and this output is added to the first 1/4 circuit 23a.
is multiplied by 1/4. Next, the first line delay circuit 21
The output of a is multiplied by 1/2 by the 172 multiplier circuit 26, and the output signal of the first 1/4 multiplier circuit 23a is subtracted from the output signal of the 1/2 multiplier circuit 26 in the first subtraction circuit 24a. Therefore, the output signal of the first subtraction circuit 24a is -1/4 (sample value of sample point Pi) + 1/2 (P
The sample value of the sample point P5) - 1/4 (the sample value of the sample point P5). Further, in the second adder circuit 22b, the output (P4) of the first delay circuit 20a and the output (P2) of the second delay circuit 21b are added, and this output is added to the second 1/4 multiplier circuit. 23b multiplies it by 1/4. and the second
In the subtraction circuit 24b, the output signal of the second 1/4 multiplication circuit 23b is subtracted from the output signal of the 1/2 multiplication circuit 26, and therefore the output signal of the second subtraction circuit 24b is -1/2. 4 (sample value of sample point P2) + 1/2
(Sample value of sample point P3) - 1/4 (Sample value of sample point P4).

Furthermore, the output of the first subtraction circuit 24a is applied to a first absolute value circuit 25a, and the absolute value is taken. Therefore, the output signal T1 of the first absolute value circuit 25a is TI=11/4 (sample value at the sample point PI)-1/
2 (sample value of sample point P3) + 1/4 (sample value of sample point P5). In addition, the second subtraction circuit 2
The absolute value of the output signal 4b is taken by a second absolute value circuit 25b. Therefore, the output signal T2 of the second absolute value circuit 25b
is T2-11/4 (sample value of sample point P2)-1/2
(Sample value of sample point P3) + 1/4 (Sample value of sample point P4).

The first absolute value circuit 25a, the second absolute value circuit 25b
The respective output signals TI, T2 are applied to a comparator circuit 27, and the comparator circuit 27 is connected to the output signal TI, T2.

The magnitude of T2 is compared and a control signal is sent to a switch circuit 28, which will be described next. The switch circuit 28 includes the first subtraction circuit 24. a output signal and the second subtraction circuit 24
b is applied, and the comparator circuit 27 adjusts the TI and T2 so that when TI>T2, the output signal of the first subtraction circuit 24a becomes the output of the switch circuit 28, so that T1≦ At T2, a control signal is sent to the switch circuit 28 so that the output signal of the second subtraction circuit 24b becomes the output of the switch circuit 28. The output signal of this switch circuit 28 is applied to a multiplier circuit 29, and the output signal of the switch circuit 28 is multiplied by N times (N: real number).
be done. Although not shown, the multiplier N is controlled from the outside by, for example, a microcomputer.

According to the device of this embodiment, since the contour signal is directly extracted 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. In addition, the direction in which the signal change is large is detected using the values of adjacent sample points, and the pixel signal in the direction in which the change is large is used to calculate the second derivative and extract the contour signal, so the composite video signal is On the other hand, contour signals can be extracted with high precision. Furthermore, in this embodiment, since the adjacent sample points are located at diagonal positions with respect to the target main point, horizontal contour signals, vertical contour signals, and contour signals in diagonal directions can be extracted simultaneously.

Note that it goes without saying that the 1/4 times circuit and the 1/2 times circuit in the above embodiment may be used in other combinations as long as the multiplier for the input signal is in a 1:2 relationship.

〔Effect of the invention〕

As described above, according to the present invention, a contour signal is directly extracted from a composite video signal using a sample point and an adjacent sample point whose color subcarrier is in phase with that of the sample point, and The direction of change in the image is detected using the sample points and the adjacent sample points, and the pixel signals in that direction are used to extract the contour signal, so compared to conventional devices, fewer line delay circuits are required, and accuracy is also improved. This has the effect of extracting a good contour signal.

[Brief explanation of drawings]

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

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, An A/D conversion circuit that samples by frequency, the sample value of the sample point of the digitized composite video signal, and the sample value of the sample point on two scanning lines one scanning line above and below the sample point. a delay circuit for simultaneously extracting sample values of first to fourth adjacent sample points on the screen at the top left, top right, bottom left, and bottom right, which have the same phase of the sample point and the color subcarrier and are closest to the sample point; , the sample point, the first adjacent sample point, and the fourth sample point.
a first contour extraction filter that extracts a contour component of the sample point using the sample values of the sample point adjacent to the sample point; a first contour detection circuit that detects the presence or absence of a contour in the direction in which the three sample points exist, using the sample values of the sample points;
a second contour extraction filter that extracts a contour component of the sample point using the sample values of the sample point adjacent to the sample point; a second contour detection circuit that detects the presence or absence of a contour in the direction in which the three sample points exist using the sample values of the sample points; and a comparison circuit that compares the outputs of the first and second contour detection circuits. , and a selection circuit that selects the output of either the first or second contour extraction filter according to the comparison result of the comparison circuit.