JPS627292A - Pal adaptive type contour extracting filter - Google Patents

Abstract

PURPOSE:To extract a contour signal with high accuracy by using a sample point as well as an adjacent picture element where the phase of a chrominance subcarrier is an inverse phase to the sample point and also extracting the contour signal so as to seek high frequency component of signal value series in the direction of larger signal variation. CONSTITUTION:At a time T, it is assumed that the sample value of the sample point P5 is outputted from an A/D converter 2. At the first addition circuit 221, the output (P4) of the first delay circuit 201 and the output (P2) of the fourth delay circuit 22 are added. At the second addition circuit 222, the output of the A/D converter 2 and the output (P1) of the second delay circuit 202 are added. At the first subtraction circuit 241, the output of the first addition circuit 221 is subtracted by the output of the second addition circuit 222 and the output of the first subtraction circuit 241 are multiplied by 1/4 at 1/4 multiplying circuit 23. If a luminance signal varies only in a vertical direction in a sampled screen and no color changes in both horizontal and vertical directions, a chrominance signal component contained in the first term of the output signal of 1/4 multiplying circuit 23 is canceled by the second term and the contour components in the vertical direction for the luminance signals are extracted.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a PAL adaptive contour extraction filter that digitally extracts a contour signal from a PAL 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. This aims to improve the sharpness of the image.

The PAL system composite video signal S (tl is the luminance signal Y (
1) and the color signal C(t) which is quadrature two-phase modulated with the color subcarrier f s c =4.43361875MHz of the two color difference signals U (tl and V (t). In other words, S(t) −Y(t) + C(t)
=Y(t)+U(t) 5in2 rc f sc
t±V(t) cos2 rc f sc However,
The sign of V (t) is switched between + and - for each scanning line.

Conventionally used contour extraction filters of this kind, whether in analog or digital format, are used to extract the luminance signal Y from the composite video signal S(t).
(t), and this separated luminance signal Y (t)
In contrast, it has been common to use a horizontal contour extraction filter to obtain a horizontal contour signal, and a vertical contour extraction filter to obtain a vertical contour signal. 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 (t
) is 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 (
(n2)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 closing 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 fifth delay circuit 55 are one horizontal scanning time. The delay time including the 56 delay times 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:

[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 a PAL-based composite video signal using a sampling pulse four times as large as the color subcarrier and converting it into a digital signal, a delay means, and a signal change a two-dimensional filter consisting of an amount detecting means and an adaptive high frequency component extracting means, and the color subcarrier phase is opposite to that of the sample point of the digital signal, and the color subcarrier phase is opposite to that of the sample point of the digital signal, and 2
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 direction in which the signal change is large is detected by using the sampling point and neighboring pixel signals whose color subcarriers are in opposite phases to the sampling point, and the high frequency of the signal value series in the direction in which the signal change is large is detected. Since the contour signal is extracted by determining the components, it is possible to precisely extract the contour signal from the composite video signal 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.

This A/D converter 2 is supplied with a sampling pulse having a frequency fs that is four times the color subcarrier frequency Esc of the composite video signal from the pulse generator 30, and the 88 A/D converter 2 receives this sampling pulse. 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 circuits 201, 202, and third delay circuits 201-202; a fourth delay circuit 21.22, a first delay circuit 21.22;
The second addition circuits 221 and 222, the 1/4 multiplication circuit 23, the first to third subtraction circuits 241 to 243, and the first to third subtraction circuits 241 to 243. Second
It is composed of absolute value circuits 251 and 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 that is the output of the A/D converter 2 by a time obtained by subtracting two sample periods from two horizontal scanning times. 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 2
01 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 second delay circuit 202. . The first 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 1/4. The doubling circuit 29 multiplies the output of the third delay circuit 21 by 1/2. Further, the second and third subtraction circuits 242 and 243 respectively
゜Doubling circuit 2 from the outputs of the second adder circuits 221 and 222
It is configured to subtract the output of 9.

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 a PAL system composite video signal sampled by sampling pulses;
The figure is a diagram for explaining the specific operation of an embodiment of the present invention, and the illustration is reversed in FIG. 2.

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 at point P1 and the sample value at 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 adder circuit 222 is subtracted from the output (P2+P4) of the first adder circuit 221, and in the 1/4 times circuit 23, this first subtracter 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: 1/4 (sample value of sample point P1) -1/4 (sample value of sample point P5) +1/4 (sample value of sample point P2) +1 /4 (sample value of sample point P4) ...(1), which can also be written as follows.

[-1/4 (11 points P1 to pot (+1/2 of Rin point P3 example pot (-1/4σ sample 1 of main point P5)] -[-1/43 zero point P2 (c) +1/2 [shares] Main point P3 (2) Lunar surface -1/4 (IRE point P 461
) Ko ・ (1') The first term in this (1°) equation (
The first term [in square brackets] represents the second-order differential in the vertical direction of the image, and the second term (inside the second bracket) similarly represents the second-order differential 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 contour component in the vertical direction with respect to the luminance signal can be extracted. Also, the brightness 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, when 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 (1°). 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·P
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 becomes Tl-1 (sample value of sample point P1) -2 (sample value of sample point P3) + (sample value of sample point P5) i. 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 (1) of sample point P3) + (sample value of sample point P4) 1.

The first absolute value circuit 251 described above. Second absolute straight circuit 2
52 respective output signals Tl, T2L, the comparison circuit 26
The comparison circuit 26 compares their sizes, and a control signal is sent to the 7th year inversion circuit 27 in accordance with the comparison result. The output signal of the first subtraction circuit 241 is given to the 7th o'clock inversion circuit 27, and the output signal of the first subtraction circuit 241 is given to the comparator circuit 2.
6 is the output signal Tl.

When T2 is Tl>72, the output signal of the sign inversion circuit 27 becomes the output signal of the first subtraction circuit 241.
When , the output of the sign inverting circuit 27 is the first subtracting circuit 24
A control signal is sent to the sign inverting circuit 27 so that the sign of the output signal 1 is inverted. The output signal of this sign inverting circuit 27 is given to a multiplier circuit 28, and the output signal of the sign inverting circuit 27 is multiplied by N times (
N: real number). Here, the multiplier N is not shown (1 is
For example, it is externally controlled by a microcomputer or the like.

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. Further, in this embodiment, since sample points having opposite color subcarrier phases are located above, below, and to the left and right of the target main point, the horizontal contour signal and the vertical contour signal can be extracted at the same time.

〔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 direct extraction is performed, fewer line delay circuits are required than in conventional devices, and contour signals can be extracted with high accuracy from 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 a PAL adaptive contour extraction filter according to an embodiment of the present invention, and FIGS. 2 and 3 show a sampling signal sequence of a PAL 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, 201.2 (12 is a delay circuit, 2
3.29 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, 2
41 to 243 are subtraction circuits, 251 and 252 are absolute value circuits, and 11 is a contour extraction filter.

Claims (1)

[Claims] (1) A PAL adaptive contour extraction filter that receives a PAL-based composite video signal as input and extracts the contour components of the composite video signal, wherein the composite video signal is processed at a sampling frequency that is four times the color subcarrier of the composite video signal. 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 two horizontal scanning lines 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. P characterized by
AL adaptive contour extraction filter.