JPH03120963A - Contour correction device - Google Patents

Abstract

PURPOSE:To clip a noise component emphasized by adaptive emphasis by setting larger coring level to a luminance signal whose dark level is deeper. CONSTITUTION:An input and output characteristic of a data conversion circuit 14 is shown in figure (i). That is, the input level is converted into an output level in such a way that when the input level is M1 or below (corresponding to a luminance signal level with no adaptive emphasis applied thereto), an output signal level of an inverting amplifier 13 at a time t1 is 0, when the input level is from M1 to MAX (corresponding to a luminance signal level with adaptive emphasis applied thereto), an output signal level of an inverting amplifier 13 at a time t1 is increased monotonously, and when the input level is MAX, the output data is a maximum level of CL1. When a signal shown in figure (d) is inputted to the data conversion circuit 14 having the input and output characteristic, a coring level data shown in figure (f) is obtained. The coring level data is. employed for the coring circuit 11, which controls adaptively the coring level inversely to the level increase/decrease of the luminance signal. Thus, noise increased with adaptive emphasis is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is directed to EDTV (E-xt), which is a next generation television system.
ended l1eflnition Te1evis
This invention relates to a contour corrector for improving the sharpness of images suitable for the Z.

2. Description of the Related Art A conventional contour corrector has a configuration as shown in FIG. 5, for example. In FIG. 5, 1 is an input terminal into which a luminance signal is input, 2 is a contour signal forming circuit that generates horizontal and vertical contour signals, and 3 is a level circuit that adjusts the amplitude of the contour signal according to the level of the input luminance signal. A pendent circuit, 4 a noise slice circuit, 5 an adder for adding a luminance signal and a contour signal, 6.7 a delay line for timing adjustment, and 8 an output terminal.

The operation of the contour corrector configured as described above is shown in FIGS.
This will be explained using FIG.

FIG. 6 is a block diagram showing the internal configuration of the contour signal forming circuit 2 shown in FIG. The amplifier 18 is an adder. To explain the operation of each part,
In the vertical contour signal section, the luminance signal shown in FIG. 7(a) is
If input in V (1 field) period, each IH
The output of the delay circuit 15 becomes the signals shown in FIGS.
By adding , the vertical contour signal shown in FIG. 7(d) is obtained. Similarly, in the horizontal contour signal section, if the luminance signal shown in FIG. 7(e) is input during the IH period, the output of the time delay circuit 16 is as shown in FIG.
), (g), and by adding the output signals of each amplifier 17 by each adder 18, the signal shown in FIG.
The horizontal contour signal shown in h) is obtained. The horizontal contour signal and vertical contour signal obtained in this way are added to the adder 1.
By adding 8, a two-dimensional contour signal is obtained. The frequency characteristics of the horizontal and vertical contour signal parts are as follows:
The results are as shown in Figures 8(a) and (b), respectively.

The contour signal generated by the contour signal forming circuit 2 as described above passes through a level dependent circuit 3 and further a noise slice circuit 4, and an adder 5 generates an IH delay luminance signal which is time-adjusted by a delay line 6.7. A contour-corrected luminance signal is obtained from the output terminal 8.

The level dependent circuit 3 is, for example, shown in FIGS.
), when the input luminance signal is a staircase wave shown in FIG. 9(a), a contour signal as shown in FIG. 9(b) is obtained from the contour signal forming circuit 2. Gain control is performed as shown in FIG. 9(C). This is because the contour signal forming circuit 2 also amplifies high-frequency noise using a so-called bypass filter, so in order to reduce noise in dark areas, the gain of the contour signal is controlled according to the level of the luminance signal.

Further, the noise slice circuit 4 is shown in FIG. 10(a).

As shown in (b), high-frequency noise appearing in flat areas of the signal (with little change in brightness and darkness) is sliced and removed by edge enhancement.

In this way, the level debendente circuit 3. The noise slice circuit 4 prevents the S/N ratio from deteriorating by emphasizing the outline. A good luminance signal with a poor S/N ratio is obtained from the output terminal 8.

In the above method, the contour signal is created from the luminance signal, but another method is to create the contour signal from only the green signal and convert this signal to R(
Out-of-green (red), G (green), and B (blue) are mixed in each process amplifier.
There is a system (for example, "Contour Compensator for Plumbicon Color Cameras" by Hiroshi Marubayashi et al., August 28, 1972, material of the 14th Television System Circuit Research Committee). The rOUTOF GREENJ method is a cash register Ron.

Due to the circuit scale, it is often used in cameras that use image pickup tubes.

On the other hand, in recent years, BTA (Broadcas
ting Te-chnology As5ociat
The next generation television system (EDTV system), which is being studied and promoted by ION Broadcasting Technology Association Japan, is one of the items to improve image quality in the current television system. Improvement of the phenomenon of deterioration of brightness details (sharpness) in dark areas of images due to increase in gamma value due to high brightness of the tube and leakage light (S
There is l).

As a technique for realizing Sl, there is a so-called adaptive emphasis, in which a compensation circuit compensates for the high frequency components of the luminance signal on the transmitting side so that the detail components (high frequency components) increase in darker areas.

FIG. 11 is a block diagram of a configuration example of an adaptive emphasis circuit.

In FIG. 11, 19 is an input terminal into which a luminance signal is input, 20 is an emphasis circuit that generates a compensation signal from the input luminance signal, 21 is a low-pass filter, 22 is an inverting amplifier,
23 is a fixed attenuator, 24 is a multiplier, 25 is an adder, 26
is the output terminal.

Further, FIG. 12 shows a frequency characteristic diagram (emphasis curve) of the emphasis circuit 2o.

The operation of the Sl compensation circuit configured as described above is explained in the first
This will be explained using FIGS. 3(a) to 3(d).

If the luminance signal is input as shown in FIG. 13(a), the output of the low-pass filter 21 will be as shown in FIG. 13(b), and the output of the inverting amplifier 22 will be as shown in FIG. 13(C). It becomes like this. This output is attenuated at a constant rate by a fixed attenuator 23, and multiplied by a compensation signal from an emphasis circuit 20 and a multiplier 24, resulting in 8 signals each as shown in FIG. 13(d).

The amount of compensation is controlled according to the level amount of T7J. In other words, in this adaptive emphasis circuit, the amplitude of the emphasized signal is determined by the signal (signal information representing the brightness and darkness of the image) obtained by the low-pass filter 21.
It increases and decreases monotonically in the opposite direction of the change.

The amount of compensation is based on the emphasis curve obtained using a time constant of 100 nsec, and when the amplitude of the low frequency component of the luminance signal is 0%, the maximum is 3 dB at 4 MHz!
It is recommended to set the minimum value to 1 dB, maximum 2 dB and minimum 1 dB at 2 MHz, and set it to O dB when the amplitude of the low frequency component is 100%.

The adaptive emphasis circuit as described above compensates for the deterioration of details in dark areas of an image, and provides an image with sharper sense in dark areas than before.

Problems to be Solved by the Invention However, with the configuration of the adaptive emphasis circuit as described above, it is possible to obtain sharpness in the dark areas of the image, and to de-emphasize the luminance signal on the receiver side, it is possible to reduce S in the transmission system. Even if an improvement in the S/N ratio is obtained, the result is nothing more than emphasizing high-frequency components in the dark areas of the image, and conventional contour correctors are required to suppress the deterioration of the S/N ratio in the dark areas of the image by This is contradictory to the so-called level-dependent system, in which the gain of high frequency components is controlled according to the level of the luminance signal, and the gain is reduced in dark areas.In the camera output signal, the S/N in dark areas is There is a problem that the ratio deteriorates. For example, the luminance signal in FIG. 14(a) is compensated as shown in FIG. 14(b).

In view of the above, an object of the present invention is to provide a contour corrector that suppresses an increase in circuit scale and does not cause deterioration of the S/N ratio even if an adaptive emphasis operation compatible with next-generation TV systems is incorporated. .

Means for Solving the Problems In order to achieve the above object, the present invention provides first and second contour signals that form desired first and second contour signals from a luminance signal or a signal similar to a luminance signal. a second contour signal forming circuit; a low-pass filter that receives the luminance signal or a signal similar to the luminance signal and limits the band to a predetermined frequency; and an inverting amplifier circuit that inverts and amplifies the output signal of the low-pass filter. and a gain control circuit that receives the second contour signal and controls the gain of the second contour signal using the output signal of the inverting amplifier circuit, and controls the noise level of the output signal of the gain control circuit to a coring level. a coring circuit that clips the coring circuit, an adder circuit that adds the output signal of the coring circuit and the first contour signal, and converts the output signal of the low-pass filter or the output signal of the inverting amplifier circuit; The contour corrector includes a data conversion circuit that outputs coring level data to the coring circuit, and controls the coring level according to an output signal of the low-pass filter or an output signal of the inverting amplifier circuit. .

Effect The present invention has the above-described configuration, and uses the same signal as the signal that controls the adaptive emphasis effect (the inverted signal of the luminance signal that has been low-pass filtered) or its inverted signal (the inverted signal of the luminance signal that has been low-pass filtered). control the coring level. and,
This is controlled by using a data conversion circuit to set a large coring level for dark areas of the luminance signal, thereby clipping the noise component emphasized by adaptive emphasis.

Embodiment FIG. 1 is a block diagram showing the configuration of a contour corrector according to a first embodiment of the present invention.

In FIG. 1, 1 is an input terminal into which a luminance signal is input;
2 is a first contour signal forming circuit that generates a first contour signal that is a horizontal and vertical contour signal; 3 is a level dependent circuit; 4 is a noise slice circuit; 5 is an adder; 8 is an output terminal; 9 1 is a second contour signal forming circuit that generates a second contour signal that is a contour signal for adaptive emphasis; 10 is a gain control circuit that controls the gain of the second contour signal; 11 is a noise of the second contour signal; 12 is a low-pass filter, 13 is an inverting amplifier, and 14 is a data conversion circuit that creates coring level data from the output of the inverting amplifier 13.

Each circuit of this embodiment is constructed of a digital circuit, and components 1 to 5 and 8 are the same as those of the conventional example shown in FIG.

The reason why there are two contour signal forming circuits, a first contour signal forming circuit 2 and a second contour signal forming circuit 9, in this embodiment is that the first contour signal is generated to increase the sharpness of a normal image. 1st
The emphasis frequency of the contour signal forming circuit 2 for adaptive emphasis differs depending on the user's preference, but the emphasis frequency of the second contour signal forming circuit 9 that creates the second contour signal for adaptive emphasis depends on the S/N ratio. For reasons of appearance, for example, it is recommended that the maximum frequency be 4 MHz as explained in the conventional example, and this is to show that the emphasis frequencies of the two contour signal forming circuits are different. However, in the following explanation, for convenience of explanation, it is assumed that the emphasis frequencies of the two contour signals described above are almost the same, and that similar contour signals are generated due to the same level change of the luminance signal. The operation of the contour corrector of the embodiment will be explained using FIGS. 2(a) to 2(f).

Figures 2 (a) to (h) are the parts (a) to (h) of Figure 1.
) is a signal waveform diagram. Further, FIG. 2(i) is an input/output characteristic diagram of the data conversion circuit 14. Note that the adaptive emphasis is assumed to act on the luminance signal level below time 1+.

In FIG. 1, if a luminance signal varying in the horizontal direction as shown in FIG. 2(a) is input to the input terminal 1, the first contour signal forming circuit 2 The level dependent circuit 3 compresses the amplitude of the first contour signal generated by the first contour signal corresponding to the low level portion of the luminance signal. In addition, noise components in low-level areas, that is, dark areas, are also suppressed. Furthermore, the noise slicing circuit 4 detects flat parts of the signal (parts with little change in brightness and darkness).
The noise component superimposed on the image is sliced to obtain the contour signal shown in FIG. 2(b).

Also, a second contour signal forming circuit 9. Gain control circuit 10. The low-pass filter 121 and the inverting amplifier 13 constitute a circuit that has the same effect as the adaptive emphasis circuit shown in FIG. 11 described in the conventional example. In other words,
It is converted by the low-pass filter 12 into a luminance signal as shown in FIG. 2(C), and this signal is converted into the control signal shown in FIG. 2(d) by the inverting amplifier 13. On the other hand, the second contour signal forming circuit 9 generates a second contour signal which is a compensation signal having a desired emphasis characteristic.

By appropriately controlling the gain of this second contour signal using the output signal (d) of the inverting amplifier 13 in the gain control circuit 10, the gain shown in FIG.
A contour signal as shown in is obtained. If this contour signal is added to the luminance signal, the sharpness in dark areas will increase and the purpose of adaptive emphasis will be achieved, but as shown in Figure 2(e), noise will also be emphasized and the S/N ratio will deteriorate. do.

In this embodiment, the input/output characteristics of the data conversion circuit 14 are as shown in FIG. 2(i). In other words, when the input level is at time t1, the output signal level of the inverting amplifier 13 below M1 (corresponding to the luminance level at which adaptive emphasis does not act) is O, and from M1 to MAX (corresponding to the luminance signal level at which adaptive emphasis acts) (correspondence) increases monotonically and is converted into data up to the maximum level of CL1.

Therefore, when the signal shown in FIG. 2(d) is input to the data conversion circuit 14 having this input/output characteristic, the signal shown in FIG.
) Coring level data as shown in Figure 2 is obtained. This coring level data is used by the coring circuit 11.

The coring circuit has a different name from the conventional noise slicing circuit, but its operation9 is exactly the same; it clips the ± (plus or minus) signal level set by the coring level. It is a circuit. Therefore,
The contour signal shown in FIG. 2(e) input to the coring circuit 11 has a coring level (isometrically as shown by the dotted line in FIG. 2(e)) with the characteristic shown in FIG. 2(f). It is clipped at a maximum level value of ±CL1 by the characteristic), and as shown in Figure 2 (
The contour signal shown in g) from which noise components have been removed is obtained.

In other words, just as adaptive emphasis causes the contour signal to increase monotonically in opposition to changes in brightness, the coring level also increases monotonically in opposition to changes in brightness, and is increased by adaptive emphasis. Noise components are removed.

The contour signal for adaptive emphasis with this noise component removed (Fig. 2 (g)) and the conventional contour signal (Fig. 2 (g))
b)) are added by the adder 5, and the contour signal shown in FIG. 2(h) is obtained from the output terminal 8.

As described above, with the contour corrector of this embodiment, it is possible to obtain a contour signal which has an adaptive emphasis effect and whose S/N ratio does not deteriorate.

FIG. 3 is a block diagram showing the configuration of a contour corrector according to a second embodiment of the present invention. As in the first embodiment, each circuit is composed of a digital circuit.

In FIG. 3, 1 is an input terminal into which a luminance signal is input;
2 is a first contour signal forming circuit that generates a first contour signal which is a horizontal and vertical contour signal; 3 is a level dependent circuit; 5 is an adder; 8 is an output terminal; 9 is a circuit for adaptive emphasis. 10 is a gain control circuit for controlling the gain of the second contour signal; 11 is a coring circuit for clipping noise in the contour signal; 12 is a coring circuit for clipping noise in the contour signal; A low-pass filter, 13 an inverting amplifier, and 14 a data conversion circuit that creates coring level data from the output of the inverting amplifier.

The difference from the first embodiment is that the coring circuit 11 is placed after the adder 5 in FIG. 1, thereby eliminating the need for the noise slicing circuit 4. The emphasis frequency of the contour signal is almost the same as in the first embodiment.

The operation of the contour corrector of the second embodiment configured as described above is illustrated in FIGS.
This will be explained using Figures (a) to (e).

Figures 4 (a) to (d) represent the respective parts (a) to (d) of Figure 3.
) is a signal waveform diagram. Further, FIG. 4(e) is an input/output characteristic diagram of the data conversion circuit 14.

Assuming that the luminance signal of the horizontal direction change shown in FIG. 2(a) is input to the input terminal 1 as in the embodiment of FIG.
A first contour signal is formed by the contour signal forming circuit 2, and a contour signal shown in FIG. 4(a) is obtained by the level dependent circuit 3. In this case, since the contour signal corresponding to the low level part (dark part) of the luminance signal is compressed, the noise component to be superimposed is the noise component to be superimposed on the contour signal corresponding to the high level part (bright part) of the luminance signal. It is comparatively suppressed.

On the other hand, as explained in the first embodiment, the gain control circuit 10 obtains the contour signal for adaptive emphasis shown in FIG. 2(e). This contour signal and the contour signal shown in FIG. 4(a) are added by an adder 5, and the contour signal shown in FIG.
The contour signal shown in b) is obtained. The noise superimposed on the added contour signal differs in magnitude between the contour signals corresponding to the bright and dark portions of the luminance signal, depending on the gain setting of the gain control circuit 1o. In this example, the noise component superimposed on the contour signal corresponding to the dark part of the luminance signal is larger than the noise component superimposed on the contour signal corresponding to the bright part.

Here, the input/output characteristics of the data conversion circuit 14 are shown in FIG.
). The difference from the input/output characteristics of the data conversion circuit 14 (FIG. 2(i)) in the case of the first embodiment is that when the input level is below M1, Cl3 is at a constant level, and M
The characteristic is that it increases monotonically from l to MAX, and is converted into data up to a maximum of L2. That is, at a luminance signal level where adaptive emphasis does not act, Cl3 is constant, and at a luminance signal level where adaptive emphasis acts, Cl3 monotonically increases as the emphasis increases.

The data conversion circuit 14 having this input/output characteristic is shown in FIG.
When the signal shown in d) is input, coring level data in which the dark part of the luminance signal is large as shown in FIG. 4(C) is obtained, and this coring level data is
The characteristics are changed depending on the ratio of the level of noise superimposed on the contour signal corresponding to the bright portion and dark portion of the luminance signal described above.

Therefore, the contour signal shown in FIG. 4(b) in the coring circuit 11 has a coring level (maximum ±C) shown in FIG.
By isometrically clipping at L2 (characteristics like the dotted line shown in FIG. 4(b)), as in the first embodiment,
Not only can noise be removed by the adaptive emphasis effect, but also noise caused by a normal contour signal to which the adaptive emphasis is not applied can be removed, and a contour signal as shown in FIG. 4(d) can be obtained from the output terminal 8.

As described above, in the second embodiment, it is possible to eliminate the noise slice circuit, provide an adaptive emphasis effect, and obtain a contour signal with no deterioration in the S/N ratio.

The first point explained above. In the second embodiment, the case where the luminance signal changes only in the horizontal direction has been described, but it goes without saying that the same explanation can be made even if vertical changes are considered.

Note that processes such as contour signal formation, data conversion, and clipping are areas that digital circuits are good at; It goes without saying that the second embodiment is easy to construct.

Also, 1st. In the second embodiment, the input of the data conversion circuit 14 is not the output of the inverting amplifier 13 but the low-pass filter 1.
It goes without saying that even if the output of No. 2 is used, similar effects can be obtained by changing its conversion characteristics.

Alternatively, the first contour signal forming circuit 2 and the second contour signal forming circuit 9 may be constructed from the same contour signal forming circuit, and output two systems of contour signals having desired emphasis frequencies. Needless to say.

Furthermore, a second contour signal forming circuit 9. forms a second contour signal for adaptive emphasis. It goes without saying that the frequency characteristics of the low-pass filter 12 may be appropriate characteristics other than those recommended by the BTA, and this will not affect the achievement of the objective of the present invention in any way.

DETAILED DESCRIPTION OF THE INVENTION As described in detail, according to the present invention, it is possible to obtain an adaptive emphasis effect, and also to adaptively control the coring level of the coring circuit inversely to the increase/decrease in the level of the m-degree signal. , it is possible to remove increasing noise by adaptive emphasis, and it is possible to perform contour correction with a good S/N ratio suitable for next-generation TV systems, and its practical effects are great.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a contour corrector according to a first embodiment of the present invention, and FIGS. 2(a) to (h) are signals of each part (a) to (h) of the first embodiment. Waveform diagram, Figure 2 (i)
is an input/output characteristic diagram of the data conversion circuit 14 in the first embodiment, FIG. 3 is a block diagram showing the configuration of the contour corrector in the second embodiment of the present invention, and FIGS. 4(a) to (d) ) is the second
FIG. 4(e) is an input/output characteristic diagram of the data conversion circuit 14 in the second embodiment, and FIG. 5 is a diagram of the conventional contour corrector. FIG. 6 is a block diagram showing an example of the structure of a contour signal contour signal forming fascis circuit in a conventional contour corrector.
FIG. 2 is a waveform diagram showing 2. 1... Input terminal, 2... Contour signal forming circuit a1
3... Level dependent circuit, 4... Noise slice circuit, 5... Adder, 8... Output terminal, 9... Contour signal forming circuit, 10...
Gain control circuit, 11... Coring circuit, 12... Low pass filter, 13...
Inverting amplifier, 14...data conversion circuit.

Claims (2)

[Claims] (1) first and second contour signal forming circuits that form desired first and second contour signals from a luminance signal or a signal similar to the luminance signal; and a low-pass filter that receives the input and limits the band to a predetermined frequency; an inverting amplifier circuit that inverts and amplifies the output signal of the low-pass filter; and an output signal of the inverting amplifier circuit that receives the second contour signal as an input. a gain control circuit that controls the gain of the second contour signal by a coring level; a coring circuit that clips the noise level of the output signal of the gain control circuit at a coring level; and a data conversion circuit that converts the output signal of the low-pass filter or the output signal of the inverting amplifier circuit and outputs it to the coring circuit as coring level data, A contour corrector characterized in that the coring level is controlled according to the output signal of the low-pass filter or the output signal of the inverting amplifier circuit. (2) first and second contour signal forming circuits that form desired first and second contour signals from a brightness signal or a signal similar to the brightness signal; a low-pass filter that receives the input and limits the band to a predetermined frequency; an inverting amplifier circuit that inverts and amplifies the output signal of the low-pass filter; and an output signal of the inverting amplifier circuit that receives the second contour signal as an input. a gain control circuit that controls the gain of the second contour signal by a gain control circuit; an adder circuit that adds the output signal of the gain control circuit and the first contour signal; a coring circuit that clips at a ring level; and a data conversion circuit that converts the output signal of the low-pass filter or the output signal of the inverting amplifier circuit and outputs it to the coring circuit as coring level data, A contour corrector characterized in that the coring level is controlled according to an output signal of a low-pass filter or an output signal of the inverting amplifier circuit.