JPS62189880A - Contour emphasizing circuit - Google Patents

Abstract

PURPOSE:To sufficiently suppress noise comparatively high in level by supplying a level controlling signal through a low-pass-filter to a level control circuit forming a level dependent function provided to the contour emphasizing processing. CONSTITUTION:A delay signal Sb inputted to the LPF 30 is inputted to the level controlling circuit 20 to control the gain of a contour emphasizing signal Se taken out by a contour signal extracting part 25. A contour amphasizing signal Sf that is subjected to a gain control corresponding to the magnitude of the level of the low band components of an input video signal Sa, is added with the original signal Sb by an adder 21, and comes to be a contour- emphasized video signal Sg. The original signal Sa passing the LPF 30 turns to be like a signal Sb' which is used in controlling the gain of the signal Se, and the signal Sf is resulted. The signal Sf is added with the original signal Sb to make the signal Sg whose contour is emphasized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to edge enhancement processing of a video signal, and particularly to an edge enhancement circuit suitable for a television camera using a digital video signal processing method.

(Prior Art) A television camera is generally configured as shown in FIG. 5 or 6, for example.

Of these, Fig. 5 first uses an analog signal processing method, in which light from the subject L passes through the lens 2 and then passes through the image pickup tube 3.
The image is formed on the photoelectric conversion surface, converted into an electrical signal, and then
The signal is processed by a preamplifier 5, a process amplifier 6, an edge enhancement circuit 7, a 5YNC (synchronization signal) addition circuit 8, and the like, and output as a video signal.

Next, FIG. 6 shows a digital system, in which the output of the process amplifier 5 is first converted into a digital signal by the A/D converter 10, and then the output of the process amplifier 5 is sequentially converted to a digital signal by the digital process amplifier 1.
1. Digital contour enhancement circuit 1.2) Digital 5YN
The signal is processed by the C addition circuit 13 and converted back to an analog signal by the D/A converter 14 to obtain a video signal.

By the way, as is clear from the above explanation, in such devices, ζ is used as one of the processes to prevent quality deterioration of reproduced images.
Edge enhancement processing is performed, and for this purpose (generally, an edge enhancement circuit is provided).

FIG. 7 shows a conventional example of this edge enhancement circuit.

In FIG. 7, the video signal V, supplied from the input terminal 22 to point a, is delayed by time t6 by delay devices 15 and 16, and is delayed at points b and 0, respectively, by signals 18 V, VC.
becomes. After that, the video signal ■ and the delayed signal vc are added by addition 2x17, and the level is 1/2 times the signal Vd = (V, +V
c)/2. Then, a signal V obtained by subtracting the delayed signal ① from this signal v4 by the subtracter 19 is obtained at point e.

Therefore, an example of these signals is shown in Fig. 8, where the signal V is called an edge emphasis signal, and if this signal V is added to the delayed signal II, the signal V shown in Fig. 8 is obtained. As shown, a video signal with a contoured shape can be obtained at point g.

By the way, although this Figure 8 shows the waveform in an ideal state with no noise, in reality 1; the mixing of noise into the video signal is unavoidable, and for this reason, as described above. Simply convert the contour-enhanced video signal v8 into a delayed signal V.
, the noise is also emphasized and S/
A problem arises in that N deteriorates.

Therefore, in general, the contour fI signal V is not added as is, but its level is controlled according to the level of the original video signal before being added.
It has a so-called level dependent function, and in the example shown in FIG. 7, this appears in the form of the addition of a level control circuit 20. The addition of this level and dependent function means that even if the noise is at the same level, the effect will be different when it appears in the bright areas of the reproduced image and when it appears in the dark areas, and the effect will be different when it appears in the dark areas compared to the dark areas. This takes advantage of the human visual characteristic that noise in bright areas is less noticeable.

Returning to FIG. 7, the contour emphasis signal ■ appears at point e. is input to the level control circuit 20. On the other hand, this level control circuit 20 receives a delayed signal V from point b of the contour signal extraction section 25.
1 is also input, and the level of the contour emphasis signal V is controlled according to the level of this signal vb. In this way, the gain is controlled according to the level of the delayed signal ■, and the signal appearing at point f is supplied as an edge emphasis signal to the adder 21, where it is added to the delayed signal ■, and the signal appearing at point f is It is designed to obtain a video signal (2) in which edges are sufficiently emphasized while suppressing an increase in noise.

Figure 9 shows a video signal ■ containing noise. This is an operation example when the same aVNa is input to the point e of the contour signal extraction unit 25.
The signal (il shown in FIG.
. Contour-enhanced video signal 8. Contour-enhanced video signal that suppresses increase in noise in dark areas of the reproduced image plane because it is added to the delayed signal. will be obtained.

Note that related to the above conventional example, for example, "Journal of Television Society, January 1982 issue, Vo'i, 36
, No., IJ, pages 30 and below.

[Problem that the invention seeks to solve]

However, in the conventional example described above, there is a problem in that the function of suppressing the increase of relatively large level noise among the noise mixed in the video signal cannot be sufficiently obtained.

In other words, as mentioned above, the noise dependent function is intended to alleviate the weakness of edge enhancement, which is that it also emphasizes noise and causes a decrease in S/N, so that the decrease in resolution is not as noticeable. Instead, edge enhancement is not performed much in the dark areas of the image plane, which are sensitive to noise, and for this reason, the level of the edge enhancement signal is controlled according to the level of the video signal. If the response speed of this level control is too fast, the level control will respond to a relatively large level of noise mixed into the video signal, and the contour of the large level will be strong against this noise! The Pl signal appears, greatly emphasizing the noise, and as a result, for noise that is larger than it is, it remains at an even larger, outsized level, causing an unnatural phenomenon in which white granular noise appears in the dark areas of the image. This will affect the image quality.

Note that in the conventional example described above, the level control circuit 20 that can continuously control the gain is used, and the contour node! P! Change the signal level to i! !
However, in popular television cameras, etc., instead of using a circuit that continuously controls the gain as described above, the gain is controlled according to the level of the video signal.
In some cases, a level control circuit is used that operates in an on/off manner, with a finite gain above a predetermined level and zero gain below it. The operation of is explained in Fig. 11.
During the period TN during which the noise of the video signal a exceeds the predetermined level VL&, the gain is finite (for example, gain -1, 0)
In other periods, the gain is zero, and as a result, the contour-enhanced signal shown in figure f is added to the original video signal a, using the contour-extracted signal e, to obtain the signal shown in figure g. Become.

Therefore, in the case of such a system, the signal g in FIG.
As is clear from the waveform, the level of noise below medium level does not change at all, while the level of high-level noise is sufficiently emphasized and becomes extremely high-level noise.
The noise state becomes an unnatural noise distribution state consisting of only medium-level or lower noise and extra-large-level noise derived from large-level noise, and an abnormal noise state in which large grains of noise appear conspicuously on the image plane. I end up.

The purpose of the present invention is to address the problems of the prior art mentioned above,
It is an object of the present invention to provide an edge enhancement circuit that can sufficiently suppress deterioration of image quality in this respect without causing an unnatural noise state even through edge enhancement processing.

(Means for solving the rJ1B point) The above problem can be solved by supplying a level control signal to the level control circuit in the level dependent function provided to the contour enhancement process via a low-pass filter.

[For production]

Large-level noise includes high-frequency components in the changing part, but this is blocked by the low-pass filter and the response speed of level control is suppressed, so the contour enhancement function does not work even for large-level noise. This can prevent level noise from being emphasized.

〔Example〕

Hereinafter, the outline enhancement circuit according to the present invention will be described in detail with reference to the illustrated embodiment.

FIG. 1 shows an embodiment of the present invention. In the figure, 30 is a low pass filter (hereinafter referred to as LPF), and the other parts are the same as the conventional example shown in FIG.

The LPF 30 is a delay device in the contour signal extraction section 25 -15
is inserted into the path for supplying the delayed signal S, which is the output of
, are prevented from being supplied as the level control input of the level control circuit 20.

Next, the operation of this embodiment will be explained.

The delay signal Sb input to the LPF 30 has its high level Sb'
is output as The signal Sh' thus removed from the high frequency base 4 is input to the level control circuit 20, which controls the gain of the contour emphasis signal S extracted by the contour signal extraction section 25.

Then, the contour Pi-key ε signal Sf, which has received the gain sub-gate according to the level of the low-frequency component of the input video signal S1, is added to the original signal S in an adder 21, resulting in a contour-enhanced image. The signal becomes S.

Next, the operation at this time will be explained using the waveform diagram in FIG. FIG. 2 shows a case where the input video signal S is a signal containing only noise, and the signal S includes a part of it that contains high-level noise.

When the signal S is input to the contour signal extracting section 25, the contour I ε extracting section 25 outputs a contour emphasis signal S from this signal S. Further, the signal Sh, which is a delayed signal of the original input video signal S, which is outputted at the same time, becomes like the signals S and I because the high frequency component is removed by the LPF 30. Then, the gain of the contour emphasis signal S is controlled by this signal sb', resulting in a signal St, which is added to a signal S having the same waveform as the original input video signal S, to produce a tiii contour-emphasized video signal S. , is obtained. As is clear from this figure, by providing the LPF 30, the signal s
, (-sb) contains a large level of noise,
Noise generally has a steep waveform and contains many high frequency components, so this is removed by I, P F 30, and the level control signal sb' shows almost no level change due to noise, resulting in contour enhancement. Signal sr also shows almost no level change due to noise.

According to this embodiment, only large-level noise is enhanced, and there is no risk of an unnatural image, and it is possible to obtain a signal sg that is approximately equal to the input signal.

Next, an example of operation in the case of a signal including a video portion is shown in FIG.

The original signal Sa that has passed through the LPF 30 becomes a signal Sb', and the contour emphasis signal whose gain is controlled by No. 13 Sb' becomes a signal S, which is added to the original signal S. The contour-enhanced signal is as shown by signal S, and no particular problem arises due to the provision of the LPF 30.

In the above embodiment, the operation of each part is ideal, and no signal delay occurs (excluding delay!:!15 and 16).
It was explained as a thing. However, in reality, signal delays occur in each part, so each part requires a delaV line or a delaV line to match the signal timing.
Shift registers and the like are required, but the description of these settings has been omitted because those related to the above technology can easily perform them.

Next, a configuration example of one embodiment of the digital LPF is shown in FIG.
D noise flip known as L3374 etc.
Flop and adder ・45.48 has product name H
It can be easily constructed by using TTL elements known as D74LS2B3 and the like. It goes without saying that when delaying is performed using a D-type flip-flop, etc. in this way, it is necessary to input a clock pulse related to the conversion rate of the A/D converter used for digital conversion. Nor.

〔Effect of the invention〕

As explained above, according to the present invention, a low frequency 1fll filter is applied to the level control signal for the level dependent function! This configuration effectively suppresses high-level noise from being particularly emphasized and gives unnatural image quality, and fully addresses the problems of conventional technology, making it particularly suitable for digital video cameras. etc., it is possible to sufficiently improve the resolution while minimizing the increase in noise.
It is possible to easily provide an edge enhancement circuit that can take full advantage of the features of the dependent method.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of an edge enhancement circuit according to the present invention, FIGS. 2 and 3 are waveform diagrams for explaining its operation, and FIG. 4 is an embodiment of a digital low-pass filter. 5 is a block diagram showing an example of an analog television camera, and FIG. 6 is a block diagram showing an example of a digital television camera.
FIG. 7 is a block diagram showing a conventional example of an edge enhancement circuit;
9 and 9 are waveform diagrams for explaining the contour enhancement operation,
FIGS. 10 and 11 are waveform diagrams for explaining the problems of the conventional example. 15.16...Delay device, 17.21...Adder, 1
8... Level converter, 19... Castle calculator, 20...
Level control circuit, 22... input terminal, 24... output terminal, 25... contour signal extraction section, 3°O... low pass filter (LPF). Agent: Patent Attorney Takeshi Kenji Department

Claims (3)

[Claims] (1) A contour signal extraction circuit that extracts a contour emphasis signal from an input video signal, and a level control circuit that controls the level of the contour emphasis signal according to the level of the input video signal, the output of the level control circuit In an edge enhancement circuit that performs edge enhancement by adding an edge enhancement signal obtained from the image signal to the video signal, a reduced pass filter is provided at the control input of the level control circuit, and the input image is processed through the reduced pass filter. An edge enhancement circuit characterized in that the signal is input to a control input of the level control circuit. (2) The edge enhancement circuit according to claim 1, wherein the input video signal is a digital signal and is configured to perform edge enhancement processing digitally. (3) In claim 2, the reduced pass filter includes first and second delay circuits connected in series with respect to an input signal, and an output signal of the second delay circuit and the input signal. and a second adder that adds the output signal of the first adder and the output signal of the first delay circuit at predetermined levels, respectively. A contour enhancement circuit characterized by: