JPS58179077A - Method for compensating picture deterioration of video signal - Google Patents

Abstract

PURPOSE:To suppress the shading emerging to a reproduced screen, by compensating so as to ensure a slow change of a level between the signal having a certain level and the signal having another level in a video signal. CONSTITUTION:The high band component of a signal (b) extracted out of a delay circuit 3 is eliminated through a low pass filter (LPF) 8, and then the signal (b) is attenuated by an attenuator 9 to be turned into a signal (f'). The signal (f') and a signal (c) extracted through an LPF2 are added together with the same phase by an adder 10 to be turned into a signal (g). The signal (g) is supplied with an adverse phase to an adder 4. Here the signal (g) is subtracted from the signal (a) to obtain only the high band component, and then a signal (h) is obtained with the amplitude limited by a limiter 6. The signal (h) is supplied with an adverse phase to an adder 5, and the signal (h) is subtracted from the signal (a) at an adder 5. Then a reproduced luminance signal (i) from which the noise component is excluded is extracted through an output terminal 7. As a result, the rise of the output (i) becomes slow, and the black shading which is produced at a white part before the edge that especially changes from white to black on a screen can be suppressed. This assures pictures of good quality.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for correcting image deterioration of a video signal, which corrects image deterioration so that the video signal level change between signals becomes gradual, and makes the deteriorated portion less noticeable on the screen. The purpose is to provide a correction method.

Compact magnetic recording and reproducing device for home use! (hereinafter referred to as a VTR) performs various types of signal processing, some of which cause signal degradation.

As an example, a so-called noise reduction circuit is provided in the reproduction system to remove a noise component superimposed on the FM demodulated reproduced luminance signal, and various circuits have been proposed in the past.

FIG. 1 shows a block system diagram 1 of an example of a nine-noise reduction circuit previously proposed by the applicant. In the same figure, the luminance signal a (FIG. 2 (4)) inputted to the input terminal 1, FM demodulated and reproduced 7 including noise components, has a rise time (Q, 5 μsec to 2 μsec) of the low-pass filter 2, which will be described later. ) to Δ
The signal is delayed by a delay circuit 3 having a delay amount of (IH-Δ) (H is one horizontal scanning period). That is, the output of the delay circuit 3 is a signal approximately 1H before the signal a as shown in FIG. C ((0) in FIG. 2) and is supplied to the adder 4 in reverse phase.

The low-pass filter 2 is, for example, a sixth-order Bessel filter having the configuration shown in FIG. 3, its frequency characteristics are as shown in FIG. 4, and its output characteristics are as shown in FIG. 5.

Since a low-pass filter generally has an integral action, the signal C rises with a certain time constant, its waveform is somewhat rounded, and rises with a delay of about 0.5 μsec to 2.0 μθθC with respect to the input signal.

On the other hand, the reproduced luminance signal a is supplied to the adders 4 and 5 in the same phase. In the adder 4, the signal C is subtracted from the signal a to obtain only the high-frequency component, and in the limiter 6, the amplitude of only the large-amplitude signal component, which is the signal component, is limited at the limiter level L, and the small component that is considered to be the noise component is limited in the limiter 6. Only the flea width component is output as shown in FIG.
Since the level signal is subtracted from the signal a, the noise component especially immediately after the rise of the signal a can be reliably separated and extracted.

In the adder 5, the noise component d of the output of the limiter 6 is subtracted from the signal a, and the reproduced luminance signal e is extracted from the output terminal T with the noise component removed as shown in FIG. Note that when subtracting signal C from signal a, signal c
K can completely extract the noise component of this rising part with a certain rising time constant, so some noise remains just before the rising edge of the signal θ during subtraction in the adder 5, but in general The noise immediately before the edge of the VTR raw luminance signal is smaller than that immediately after the edge, and the noise in this part is less noticeable than that immediately after the edge.
Although this cannot be completely removed, there is practically no problem.

Therefore, if we consider the signal deterioration just before this edge, the degree of conspicuousness of this signal deterioration will be determined by the rising edge y of the output e transitioning from the black level to the white level as shown in Figure 2, or similarly from the white level to the white level. It is related to the time constant of the fall of the transition to the black level, and the key to making this signal deterioration less noticeable is to make the rise y or fall time constant as gentle as possible. It is the output C of the reduction filter 2 (Fig. 2(c)) that causes the fall.
) This is because there is a time constant for the rise of ゛, and if this rise is too steep, the white part in front of the edge that changes from white to black, or from gray to gray with higher brightness, may appear on the screen. This causes black areas to appear on the edges, causing the problem of not being able to obtain a high-quality 1-weight.

The present invention solves the above problems, and one embodiment thereof will be described with reference to FIG. 6 and subsequent figures.

FIG. 6 shows a block system diagram 1 in the case where an embodiment of the video signal deterioration correction method according to the present invention is applied to a noise reduction (b) path. Assign the same number. In the figure, 8 is a low-pass filter composed of a capacitor and a resistor, and its delay amount is smaller than that of the low-pass filter 2.

It is set as follows.

The signal outputted from the delay circuit 3 has its high-frequency components removed by a low-pass filter 8 to become a signal f shown by a solid line in FIG. signal f
The signal f° is set at a level of 2° to 5%lii degrees with respect to the level of the signal f° as shown by the broken line in FIG. The signal f' and the signal C ((0) in the figure) taken out from the low-pass filter 2 are supplied in phase to the calculator 10 and added, resulting in a signal 9 shown by a broken line in the figure (C). In this case, since the signal f°, which has a smaller delay than the signal C, is added to the signal C, which has a larger delay than the signal The rise is gradual compared to the rise of the signal.

The signal g is supplied to the adder 4 in reverse phase, where the signal g is subtracted from the signal a to obtain only the high frequency component, and the signal g is supplied to the limiter 6.
Only the large amplitude signal component is amplitude-limited by the limiter level L, and the signal shown in FIG. In the adder 5, the signal a is subtracted from the signal a, and the reproduced luminance signal 1 from which the noise component has been removed is outputted from the output terminal T as shown in FIG. In this case, in the adder 5, the maximum slope until reaching the limiter level L is smaller than the signal C (the rise is gradual compared to the signal). Since the signal g is subtracted from the signal a, the output 1 is The rising edge yl is the rising edge y of the output θ from the circuit shown in FIG. 1, which is configured to subtract using the signal d obtained from the signal C.
It is moderate compared to

That is, in this embodiment, as shown in FIG. 1 (G), instead of attenuating the signal level 11 that causes noise in the Eirin signal itself, the signal level 11 that does not cause noise is changed to the level 1 that causes noise. This is to make the degraded portion less noticeable on the playback screen by making the degree of level change gradual. As a result, the degree of this level change is approximately 4? The black shading that occurs in the white area in front of the edge that changes from self to black can be reduced, resulting in a high-quality image! Obtainable.

In addition, when subtracting the signal h'+2 from the signal a in the adder 5, in addition to setting the level amount of the signal aEl and the signal a to 1:1 (in this case, the noise component is best suppressed), for example, a limiter is used. By attenuating the output l of 6, if these 1 are set to, for example, 1:0.7, the level 11 of the noise component in the signal i is reduced (level 7bl,'), while the noise component remains at levels 1° and 1□. If you do this,
The degree of improvement in the 8M ratio decreases, causing a very slight noise on the entire screen, but since there is little change from level l to rep/l-11', the brightness of the shading on the screen decreases, resulting in a well-balanced image. It can be one person.

Figure 8 shows the method of the present invention! A block system diagram when applied to other noise reduction circuits is shown. In the figure, the same components as in FIG. 6 are given the same numbers.
Delay circuits 11 and 12, attenuators 13 and 14, and an adder 15Y are added to the illustrated circuit.

The signal j shown in FIG. 9 (4) entering the terminal 1 is converted into a signal shown in the figure ω by the delay circuit 3, and the signal j is converted into the signal 1 shown in the same figure (υ) by the low-pass filter 2. On the other hand, the low-pass filter 8 converts the signal m shown in FIG. Similarly to the above case, the signal 1 and the signal m° are added in the same phase to form the signal n shown in FIG.
Here, the signal n is subtracted from the signal j, and the limiter 6 limits the wide imaging width signal component as shown in the figure (
The signal as shown in (g) is output as 0. In the adder 5, the signal 0 is subtracted from the signal j to form a signal p as shown in the figure, which is supplied to the adder 15 in phase.

On the other hand, the signal m from the low-pass filter 8 is supplied to the delay circuit "11,"
The signal ql delayed by 12 and shown in (G) in the same figure, @
CTJ in the same figure after being attenuated by attenuators 13 and 14.
, CL'*r' having a level of about 2% to Tchi with respect to the level of the signal p shown in (J) are supplied to the adder 15iC in opposite phases. In this case, the amount of delay of the delay (b) paths 11 and 12 is set according to the rise time and level of the rise yl of the signal p extracted from the adder 5. In the adder 15, the signal G, + is subtracted from the signal p, thereby attenuating the level of the rising edge yo of the signal p shown in FIG.
The signal B is taken out from the output terminal T.

As mentioned above, in the adder 10, the level! This is a configuration in which the level is gradually increased to make the degraded portion on the screen less noticeable, but the adder 15 is configured to attenuate the level itself to make it less noticeable.

If the signal level of signal p is attenuated in this way, level 1° and level 1. The difference between the brightness of the shaded area at the top of the playback screen becomes smaller! It is possible to reduce the shading, make the shading more noticeable, and obtain even better image quality.

FIG. 10 shows a block system diagram when the method of the present invention is applied to another noise reduction circuit, in which the same components as in FIG. 8 are given the same numbers. This thing is
A signal k as shown in FIG. 8 (to) comes into terminal 1, and is delayed by a delay amount of 33 degrees to obtain a signal j shown in FIG. 8 (4). Filter 2.8
The signal 1, tnY shown in the figure (O), φ] is supplied to
It's something you get.

In this case, a delay filter with a delay amount of 83゛ is used, and the rise time of the low-pass filter 2 is set to t (FIG. 9 (0).
Since the operation and effects of this device can be easily understood from the embodiment shown in FIG. 8, the explanation thereof will be omitted.

Note that, similar to the embodiments shown in the eighth and tenth figures and the embodiment shown in the sixth figure of this book, the subtraction amount i1:o, 7 in the adder 5
It may be set as follows.

In addition, in the embodiments shown in the eighth and tenth figures, in response to the rise of the cutting signal p of the adder 5, in addition to the delay circuits 11 and 12, a further delay circuit jl! Alternatively, if only the delay circuit 11 is sufficient, only this delay circuit may be used.

Further, in each of the embodiments, a filter having an appropriate amount of delay may be used instead of the delay circuit.

In addition, in the embodiments shown in FIG. 8 and $10, the signal m
Signal instead! It may also be supplied to delay circuits 11 and 12.

As mentioned above, the image deterioration correction method of the Eirin signal according to the present invention can improve the image quality of the Eirin signal to a certain level! A noise-free signal and this noise! The level change between the non-containing signal and another noise signal with a level of 3y that continuously passes through the signal is corrected so that it changes gradually with a certain time constant of 1. The brightness changes at the boundary between the two parts are gradual, and this causes noise! It has the advantage that the shading that appears on the reproduced screen can be made less noticeable than when the level change between a signal that does not occur and a signal that generates noise is abrupt, and that the quality of the reproduced image can be improved.

[Brief explanation of the drawing]

Figure wJ1 and Figures 2 (4) to (2) are a block system diagram and a signal waveform diagram for explaining the operation of an example of the noise reduction circuit previously proposed by the applicant, respectively, and Figure 3 is a diagram of the low voltage circuit shown in Figure 1. The specific circuit diagram of the low-pass filter, Figures 4 and 5 are the frequency characteristic diagram and output characteristic diagram of the low-pass filter shown in FA1, respectively, and Figures 6 and W, and Figures 1 (4) to (to) are respectively from this book. An embodiment of the method of the invention> The signal waveform diagrams for explaining the operation of the noise reduction, FIGS. A block system diagram and a signal waveform diagram for explaining its operation. FIG. 10 is a block system diagram when the method of the present invention is applied to another noise reduction circuit. 1... Reproduction luminance signal input terminal, 2, 8... Low pass filter, 3... Delay circuit, 4. S, 10... Adder, 6
...Limiter, T...Output terminal, 9...Attenuator.

Claims (1)

[Claims] An image of a video signal characterized in that the level change between a signal having a certain level in the video signal and a signal having another level Z following the signal is corrected so that it changes gradually with a certain time constant l. Deterioration correction method.