JPH02285779A - Contour correction device - Google Patents

Abstract

PURPOSE:To avoid unbalance to a contour signal by attenuating the frequency band in the oblique direction in the case of a color signal with remarkable cross color so as to eliminate the cross color and switching a contour signal without attenuating the frequency band in the oblique direction of the contour signal in the case of a color signal whose cross color is not eminent. CONSTITUTION:An original signal comprising a luminance signal or a signal similar to the luminance signal is retarded by 1H delay circuits 8, 9, 10 and a 1H delay signal f1H delayed by one horizontal scanning time and a 2H delay signal f2H delayed further from the signal f1H are obtained respectively by the circuits 9, 10. Moreover, an enhancer circuit obtains a vertical contour signal through a vertical contour signal forming circuit 18 based on the original signal and the 1H and 2H signals f1H, f2H. Furthermore, band limit is applied to the contour signal at an LPF 17 and a horizontal contour signal is obtained by a processing horizontal contour signal forming circuit 19 with LPF 18, 26 and a selector 27 or the like. The vertical and horizontal contour signals are added by an adder 20, a signal with a prescribed frequency characteristic is formed and a signal with contour correction is obtained from an adder 21.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a contour corrector for improving the image quality of television signals and the like.

2. Description of the Related Art A conventional camera configuration including a contour corrector includes, for example, the configuration shown in FIG.

In FIG. 8, 1 is a process circuit that includes a clamp circuit, a γ circuit, etc., 2 and 3 are IJ-Fuchs circuits that produce the Q signal, (1) signal, and 4 is a matrix circuit that produces the luminance signal Y. In addition, 5 and 6 are loaf size filters (LP
F). ? , 8. 9. 10 is a 1H (horizontal scanning time) delay circuit (1HDL), 11 is the original signal,
12 is an enhancer circuit that creates horizontal and vertical contour signals from the 1H delayed signal and the 28 delayed signal; 12 is a coring circuit that reduces the noise component of the contour signal; and 13 is a contour signal generator for combining the 1H delayed signal and the contour signal. 14 is an adder, and 15 is an encoder.

Figure 9 shows the operation of the contour corrector included in this camera configuration.
This will be explained using FIG.

FIGS. 9(a) to 9(e) are waveforms of each portion of FIGS. 8(a) to (e). However, there is no delay time for the contour signal, and the coring circuit 12 also sets the coring level to zero. 9th
The waveforms in figures (a), (b), and (c) are the original signal faH(t), the 1H delayed signal f1H(t), and
The 2H delayed signal r2H(t) shows the level change of the luminance signal in the vertical direction. By operating the three signals in the enhancer circuit 11, a contour signal as shown in FIG. 9(d) is obtained. (In this example, 2 f 1
H(t)−(fiu+(t)+f2)+(t
)) is calculated. ) Furthermore, the contour signal is
It passes through the coring circuit 12 and is added to the delay time compensated signal of the 1H delayed signal f1H(t) in the adder 14 (in this example, the delay time compensation is set to zero), and is added to the signal whose delay time has been compensated for by the adder 14 (in this example, the delay time compensation is set to zero).
The contour-corrected signal shown in e) is obtained. This contour-corrected luminance signal and the Q from the low-pass filters 5 and 6
The signals 1 and 2 are input to the encoder 15, and an NTSC signal with improved frequency characteristics is obtained. This is because the frequency characteristics of the circuit generating the contour signal exhibit the characteristics of a bypass filter, as shown in FIG. 10(a). Since the actual television system uses 2:1 interlace scanning, the signal is boosted so that it reaches a peak at half the frequency of the scanning line. Horizontal contour correction is also performed on the same principle. If a tH delay circuit is used instead of each 1H delay circuit in FIG. 8, the frequency to be boosted will be as shown in FIG. 10(b). To boost both horizontal and vertical frequencies, three signals f0H(t) are input to the enhancer circuit 11 of FIG.

Calculation is performed by dividing each of r tH(t) and r 2t+(t ) so that a desired frequency is boosted.

In this way, contour correction is performed two-dimensionally.

11 is a diagram showing an example of the internal configuration of the enhancer circuit 11 shown in FIG. 8, in which 16 is the original signal f0H(t),
a vertical contour signal forming circuit that forms a vertical contour signal from the delayed signal f1H(t) and the 2H delayed signal f2H(1);
17 is a horizontal low-pass filter, 18 is the original signal fs
n(t), 1H delayed signal f+o(t).

a vertical low-pass filter that adds the 2H delayed signal rt14(t), 19 a horizontal contour signal forming circuit that forms a horizontal contour signal, 20 an adder that adds horizontal and vertical contour signals, 21 a delay circuit, This is an adder that adds the 1H delayed signal f +u(t ) time-adjusted by the DL 13 and the contour signal.

Since the contour signal forming circuit is a bypass filter, it also emphasizes high-frequency noise components. Therefore, when extracting the horizontal and vertical contour signals, the low and s11 filters 17 and 18 perform band limitation in the respective orthogonal directions. This reduces high-frequency noise components. Horizontal through a low pass filter.

The frequency characteristics of the vertical contour signal are shown in FIG. 12(a).

The characteristics shown in (b) are shown in Figure 12 (C) when the two are combined.
As shown in (the size of the arrow indicates the size of the boost amount), it has a characteristic that does not emphasize frequencies in the diagonal direction. In the figure, the boost frequencies of the horizontal and vertical contour signals are fH and fV, respectively, and the band-limiting frequencies of the low-pass filters 17 and 18 are also fH and fV. After the horizontal and vertical contour signals are added in the adder 20, the adder 21 adds the D
In step L13, the time-adjusted luminance signal and the contour signal that does not emphasize frequencies in the diagonal direction are added to obtain a contour-corrected luminance signal. Further, FIG. 12(d) shows the frequency characteristics when no low-pass filter is applied in the horizontal and vertical directions, but in this case, as can be seen from the figure, frequencies in diagonal directions are emphasized. Here, a horizontal low-pass filter of 3.58 m is applied to the vertical contour signal.
If we use a filter that reduces the frequency around hZ, and a vertical low-pass filter mixed with the horizontal contour signal that removes the frequency of the 525/4 line, it will drop the frequency around the color subcarrier band, and if we control high-frequency noise, At the same time, the high range (vertical 525/4 lines, horizontal 3.
The so-called cross color, in which a luminance signal in a frequency band around 58 MHz (frequency band around 58 MHz) is mixed into a color signal and flickers, is particularly noticeable in hues with high visibility, such as red.

Furthermore, in order to eliminate the influence of this cross color, the present applicant has proposed a contour corrector (Japanese Patent Application No. 107942/1981) for the purpose of removing cross color.

Its configuration is as shown in Figure 13, where 22 is vertical.

Two-dimensional bandpass filter (BP) that performs horizontal band limitation
F), 23 is a gain control circuit, 24 is a subtracter,
Reference numeral 25 denotes a delay circuit for time adjustment, and the other components are the same as in the conventional example.

Using the same signals as the original signal f@II(t)-1H delayed signal f1H(t) and 2H delayed signal f2□(1) for creating the contour signal, a two-dimensional band pass filter (BPF) 22
The species fraction band (vertical 52
5/4 line, horizontal 3.58MHz)
4. Extract two-dimensionally as shown in Fig. 4 (a), and subtracter 2
4 is subtracted from the 1H delayed signal f 1H(t ) whose contour is emphasized. (Figure 14 (b)) Therefore, when horizontal and vertical contour signals similar to those in Figures 12 (a) and (b) are added to the signal from which the cross color component has been removed, the influence of the cross color is almost eliminated. It is possible to produce up to 78 high-resolution images with no color flickering. As mentioned above, the contour corrector, which removes cross color components from the main signal to which the contour signal is added and provides a calm, high-quality image, is suitable for high-performance professional television cameras. It is very effective.

Problems to be Solved by the Invention However, with the above configuration, even if it is possible to remove cross colors and obtain a calm image, the diagonal components of the original luminance signal (vertical 525/4. horizontal 3.58 MHz) Nearby frequency bands) are filtered out by a two-dimensional bandpass filter, and the contour signal does not boost the band, resulting in a decrease in resolution in diagonal directions. this is,
For example, when capturing an image of a circular object, the diagonal contour signal becomes thicker than the horizontal and vertical contour signals, resulting in an unbalanced feeling and a decrease in quality. This is a major problem for the cameras that are in demand. On the other hand, in order to increase the resolution in the diagonal direction, if the horizontal contour signal is created from only the 1H delayed signal without limiting the vertical band, there is a problem that the effect of the two-dimensional bandpass filter is lost and cross color becomes noticeable. Ta.

In view of this, an object of the present invention is to provide a contour corrector that can remove cross colors without causing a decrease in resolution in diagonal directions, and can obtain visually calm and high-quality images.

Means for Solving the Problems In order to solve the above problems, the present invention delays the original signal rsn(t) consisting of a luminance signal or a signal similar to a luminance signal by 1H (one horizontal scanning time) to obtain a 1H delayed signal f, □(
1) and a first 1H delay circuit that obtains the 1H delay signal r.
+o(t) is further delayed by 1H to obtain a 2H delayed signal r2H(
t), and a second 1H delay circuit that obtains the original signal faH(
t), a 1H delayed signal f1H(t), and a vertical contour signal forming circuit that obtains a vertical contour signal from the 2H delayed signal r2H(t); a low-pass filter that applies a band limit to the vertical contour signal; The 1H delayed signal f, □(1) is used as an input signal, and the original signal f is used as a second input signal.
QH(t) or 2H delayed signal f2H(t) and 1
The sum signal of the H delayed signal r+o(t) is added to the original signal r@te(t) and the 1H delayed signal f as a third input signal.
A sum signal of 1H(t) and 2H delayed signal ralI(t) is input, and the first . a selection circuit for selecting any one of the second and third input signals, a horizontal contour signal forming circuit for forming a horizontal contour signal from the output signal of the selection circuit, and a color signal for a color signal of an arbitrary axis; The color signal level difference detection circuit detects a level difference at the boundary between the color signal level difference detection circuit and the output signal of the color signal level difference detection circuit to control the frequency characteristics of the selection circuit and the low-pass filter.

Operation The present invention has the above-mentioned configuration, and when a color signal in which the cross color stands out, especially red, the cross color is removed by lowering the frequency band in the diagonal direction of the contour signal and the signal to which the contour signal is added. In the case of an inconspicuous color signal, the contour signal is switched so as not to drop the frequency band in the diagonal direction of the contour signal, and the horizontal and
Unbalance with respect to vertical contour signals can be eliminated.

Embodiment FIG. 1 shows the configuration of a contour corrector according to an embodiment of the present invention. In FIG. 1, 8. 9. 10 is a 1H delay circuit,
16 is a vertical contour signal forming circuit, 17° 18.28 is a low pass filter, 19 is a horizontal contour signal forming circuit, 20.2
1 is an adder, 22 is a two-dimensional band pass filter, 23 is a gain control circuit, 24 is a subtracter, 25.29 is a delay line for timing adjustment, and 28 is a color signal level difference detection circuit. FIG. 2 is a block diagram showing an example of the internal structure of the color signal level difference detection circuit, and 30 is τ, (1
31 is a subtracter, and 32 is an absolute value circuit. In FIG. 1, the same parts as in the conventional example shown in FIG. 8 are given the same numbers.

The operation of the contour corrector configured as above will be explained using FIGS. 3 to 7.

FIGS. 3(a) and 3(b) are diagrams showing the frequency characteristics of the LPFs 2B and 18, which are obtained from the following characteristic equations, respectively.

(The gain is normalized.) LPF28: CO8 (f*π/f8) LPF18:
C082 (f*π/f-) where f is the frequency, π is pi, and fa is the sampling frequency, and since f11=525/2 line, the band limit frequency is 525/4 line.

Therefore, the vertical band limit of the horizontal contour signal is LPF
Since the value is maximum at 18, frequency components in the diagonal direction are also significantly dropped.

In addition, in Fig. 4 (a), (b), and (c), the boost frequency of the horizontal and vertical contour signals is 5.0 MHz, respectively.
z.

525/4 line vertical low pass filter L
The band limit frequency of PF18.26 is 525/4 line,
The band limit frequency of the horizontal low-pass filter 17 is 3.
．． This figure shows a frequency characteristic diagram of the contour signal in the case of 58 MHz, and (a) and (b) + (C) in the figure are respectively selected by the selection circuit 27 (a).

This corresponds to cases (b) and (c). From the same figure L
When PF18.2B is selected, the diagonal direction (horizontal 3.
It can be seen that the frequency of 58MHz (vertical 535/4 line) is dropped.

Now, Figure 5 (a), (b), (c), (
c 1 ), (c 2 ) are each part (a) in Figure 1,
The frequency characteristic diagrams of (b), (c), (d), and (e) are shown (the selection of the selection circuit 27 is C). The 1HDL luminance signal serving as the main signal is input to the subtracter 24 after being delayed by a delay line DL25 for an appropriate time. Also, as in the conventional example shown in Fig. 13, 2
The dimension BPF 22 contains the original signal fs)l(t), the 1H delayed signal f1H(t), and the 2H delayed signal fs)I(t).
is input and the horizontal value is 3.58 as shown in Figure 14(a).
MHz, a frequency centered on the vertical 525/4 line is extracted, and the gain is set to an appropriate value by the gain control circuit 23. This gain-controlled signal is subtracted from the 1HDL luminance signal by the subtracter 24, resulting in frequency characteristics as shown in FIG. 5(a) (FIG. 14(b)) (however, the original signal faH(t) Brightness signal is horizontal 5.0M
Hz.

The characteristics are almost flat up to frequencies above the vertical 525/4 line. ).

On the other hand, the contour signal is processed by the vertical contour signal forming circuit 16 into an original signal faH(t) and a 1H delayed signal f1H(t).
.

A vertical contour signal that boosts the 525/4 line is obtained from the 2H delayed signal r2)I(t) signal. Furthermore, this signal is band-limited in the horizontal direction by a low-pass filter LPF17 (band-limiting frequency is 3.58 MHz).

). In addition, the horizontal contour signal is a 1H delayed signal f+)l(t)
or the original signal f'aH(t) (or the 2H delayed signal r2H(t)) and the 1H delayed signal f1□(t
') or original signal fai+(t), 1H delayed signal f1H(t).

One of the low-pass filter signals generated from the 2H delayed signal f2H(t) is selected by the selection circuit 27, and a horizontal contour signal is obtained by the horizontal contour signal forming circuit 19 based on the selected signal. (The vertical band limit of the low-pass filters 18 and 26 is 525/4 lines.) Here, C is selected by the selection circuit 27.

The above horizontal and vertical contour signals are added by an adder 20,
A signal with the frequency characteristic shown in FIG. 5(b) is obtained, and this signal is further added to the signal in FIG. 5(a) by an adder 21,
A contour-corrected signal shown in FIG. 5(C) is obtained. In this case, due to the selection of C by the selection circuit 27 and the effect of the two-dimensional BPF 22, the diagonal band is 3.58M horizontally.
Hz, the frequency band of vertical 525/4 lines has been dropped. Here, the selection circuit 27 selects, for example, al
If it is set to b, the result will be as shown in Fig. 5 (d) and (e), and the diagonal frequency band will not drop as compared to the case of select C (
or emphasized) characteristics are obtained.

In this embodiment, the selection of the selection circuit 27 is controlled by a color signal of an arbitrary axis, for example, a ■ signal. (The low-pass filter 17 is not controlled.) This will be explained below using FIGS. 6(a) to 6(d). Figure 6 (
a) to (d) are signal waveforms of each part (a) to (d) in FIG. ■If the signal changes as shown in FIG. 6(a), the output of the delay circuit τHDL30 becomes as shown in FIG. 6(b), and the difference between the two signals is output from the subtracter 31 and
It will look like figure (C). Further, in the absolute value circuit 32, as shown in FIG.
Obtain the output shown in d). This output is input to the selection circuit 27 via the delay circuit 29, and t4. Select a for section t2
, select b is selected for the t1 interval, select C is selected for the t3 interval, and so on. As a result, the frequency characteristic of the contour-corrected luminance signal becomes as shown in FIG. 5(e): (2) When the level change of the signal is small (SL1 or less), select a is selected. In addition, ■The level change of the signal is moderate (SLI
~5L2), select b is selected, and the result is as shown in FIG. 5(d). Furthermore, when the level change of the I signal is large (SL2
The above) becomes select C, as shown in FIG. 5(c).

(SLI and SL2 are the selection threshold levels.) In this way, the larger the change in the I signal, the higher the diagonal frequency band (horizontal 3.58 MHz, vertical 5
25/4 line), and avoid dropping it when it is small. Therefore, at boundaries where visual sensitivity is high and color level differences are large, by lowering the characteristics of the frequency band of the luminance signal, it is possible to reduce the cross color caused by the mixing of the high-frequency luminance signal into the color signal, thereby reducing the noticeable color, In particular, flickering in colors such as red can be reduced, and images with visually calmer color reproduction can be obtained.

Further, FIG. 7 is a diagram showing the frequency characteristics of the low-pass filter 17. By fixing the characteristics of the horizontal contour signal to, for example, select C, and changing the characteristics of the vertical contour signal to characteristics a, b, and c in FIG. Emphasis and attenuation can be controlled.

As described above, according to this embodiment, the frequency band in the diagonal direction (horizontal 3.58 MHz, vertical 525/4 line vicinity) can be controlled by the level difference of color signals. It is possible to not emphasize the frequency band of the signal, but to emphasize it when the signal is inconspicuous.

It goes without saying that both horizontal and vertical contour signals may be controlled at the same time.

Comparison of signal levels, selection of signals, and switching of filter characteristics can be easily performed by using, for example, a digital circuit. Further, in the present embodiment, the delay circuit 30 of the color signal level difference detection circuit 28 has a delay of one pixel scanning time, but it may be a delay circuit with any delay time that does not interfere with detection. Although a signal from the (RY) axis is used, a signal from the (RY) axis or the like may also be used. It goes without saying that similar processing can also be performed in the vertical direction by detecting level differences in color signals.

DETAILED DESCRIPTION OF THE INVENTION According to the present invention, the low-pass filters applied to the horizontal and vertical contour signals with equal polarization in the vertical and horizontal directions, respectively, are switched depending on the level difference of the color signals, so that, for example, cross-color If the signal is noticeable,
Diagonal band (horizontal 3.5
8MHz, vertical 525/4 lines) frequency is suppressed to suppress color flickering, and in the case of inconspicuous cross-color signals, it is emphasized to increase resolution in diagonal directions. This prevents deterioration in quality due to the resolution in the direction being lower than that in the horizontal and vertical directions, and it is possible to obtain high-quality images that are visually lower.
Its practical effects are great.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a contour corrector according to an embodiment of the present invention, FIG. 2 is a block diagram of the color signal level difference detection circuit 28 of FIG. 1, and FIG. 3 is a frequency diagram of the LPF2E3.18 of FIG. Figure 4 is a frequency characteristic diagram of the contour signal, Figure 5 is a frequency characteristic diagram of the signals at each part in Figure 1, Figure 6 is a signal waveform diagram at each part in Figure 2, and Figure 7 is a diagram of the signal waveforms at each part in Figure 1. The frequency characteristic diagram of the LPF 17 shown in Fig. 8 is a block diagram of a conventional contour corrector,
Figure 9 is a signal waveform diagram of each part of Figure 8, Figure 10 is vertical,
FIG. 11 is a block diagram of the enhancer circuit 11 of FIG. 8, and FIG. 12 is a two-dimensional characteristic diagram of horizontal and vertical contour signals. 16... Vertical contour signal forming circuit, 17... Horizontal low-pass filter, 18.26... Vertical low-pass filter, 19... Horizontal contour signal forming circuit, 20.21... Adder, 22 ...Two-dimensional band pass filter, 23... Gain control circuit, 24... Subtractor, 25.29... Delay line, 27... Selection circuit, 28... Color signal level difference detection circuit . Name of agent: Patent attorney Shigetaka Awano Baka 1 No. 4
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Claims (1)

[Scope of Claims] A first 1H delay circuit that obtains a 1H delayed signal f_1_H(t) by delaying an original signal f_0_H(t) consisting of a luminance signal or a signal similar to the luminance signal by 1H (one horizontal scanning time); a second 1H delay circuit that further delays the 1H delayed signal f_1_H(t) by 1H to obtain a 2H delayed signal f_2_H(t); and the original signal f_0_H(t) and the 1H delayed signal f_1_.
a vertical contour signal forming circuit that obtains a vertical contour signal based on H(t) and the 2H delayed signal f_2_H(t); a low-pass filter that applies a band limit to the vertical contour signal; The 1H delayed signal f_1_H(t
) is the original signal f_0_H(t
) or the sum signal of the 2H delayed signal f_2_H(t) and the 1H delayed signal f_1_H(t) is used as the third input signal to input the original signal f_0_H(t) and the 1H delayed signal f_1_
a selection circuit which receives the addition signal of H(t) and the 2H delay signal f_2_H(t) and selects one of the first, second, and third input signals; and an output signal of the selection circuit. a horizontal contour signal forming circuit for forming a horizontal contour signal; a color signal level difference detection circuit for detecting a level difference at a color boundary for a color signal of an arbitrary axis; A contour corrector comprising a selection circuit and a frequency characteristic of the low-pass filter.