JPH01220977A - Picture quality automatic control circuit - Google Patents

Abstract

PURPOSE:To obtain the optimum picture quality adjusting state by providing a means eliminating the noise component of an original signal and a means controlling the limiting level of a limiter circuit section in response to the noise level of the noise component. CONSTITUTION:An input video signal at an input terminal 21 is fed to a delay circuit 22 and also fed to a filter 26 with high pass characteristic. The output of the filter 25 is fed to a limiter circuit 27 and a subtractor 28 via a delay circuit 26. The output of the limiter circuit 27 is fed to the subtractor 28 and inputted to an adder 30 as a noise cancel signal. The output of the adder 28 is subject to gain control by a gain control amplifier 29 and fed to the adder 30 as a contour correction signal. Thus, the limiting level or the slice level is made equal to the noise level included in the input video signal to attain proper contour correction in response to the pattern.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention (Field of Industrial Application) The present invention relates to an automatic image quality control circuit that is effective as a video signal processing circuit.

(Prior Art) A video signal processing circuit incorporates an outline correction circuit that enhances the outline of an image and a noise cancellation circuit that reduces noise in the image.

The contour correction circuit performs gain control on a signal around 1 to 2 MIIz, which is most easily perceived as sharpness by the human eye, and controls the apparent sharpness above.

FIG. 7 shows a conventional noise canceling circuit, in which an input video signal a1 is passed through a terminal 1 to a delay circuit 2 and a filter 5.
is supplied to Filter 5 extracts high frequency component b1. The high frequency component b1 includes the high frequency component of the input signal and noise in this region.

The high level of the high frequency component b1 is limited by the limiter circuit 6. The output c1 of the limiter circuit 6 includes some high frequency components of the signal as well as noise. limiter output c
1 is input to the subtracter 3.

It is added as a subtraction element to the video signal delayed by the delay circuit 2. As a result, a video signal d1 with noise canceled is obtained from the output terminal 4.

FIG. 9 shows signal waveforms at each part of the noise canceling circuit. Also'! ? Figures J8 (a) and (b) are characteristic examples of the filter 5. T? The filter with the characteristics shown in Figure 8 (a) is used in video tape recorders that perform noise cancellation only on luminance signals, and the filter with the characteristics shown in Figure 8 (b) is used in video tape recorders that perform noise cancellation on composite video signals. Used in disc players. In the case of a filter with the characteristics shown in FIG. 8(b), the color subcarrier frequency (f
The response near fsc is suppressed in order to prevent noise cancellation near fsc.

FIG. 10 shows an example of the characteristics of a noise canceling circuit using a filter having the characteristics shown in FIG. 8(b).

FIG. 11 shows a conventional contour correction circuit.
The figure shows signal waveforms at various parts of this circuit.

The input video signal a2 at the input terminal 11 is supplied to the delay circuit 12 and also to the filter 15. This filter 15 has the characteristics as shown in FIG. 8, and extracts the high frequency component b2. The high frequency component b2 is obtained by the slice circuit 16
The low level components are removed in the gain control amplifier 17.
The contour correction signal C2 is derived via the contour correction signal C2. This contour correction signal C2 and the video signal delayed by the delay circuit 12 are added by an adder 13, and a contour-corrected video signal d2 can be obtained at the output terminal 14.

Here, the gain of the gain control amplifier 17 can be externally controlled, and the degree of edge enhancement can be adjusted according to the user's preference. Here, in general, for a picture with many high-frequency components and a good S/N, the high-frequency components are emphasized, and for a picture with few high-frequency components and a bad S/N, the high-frequency components are attenuated.

Note that the delay circuits 2 and 12 shown in FIGS. 7 and 11 are for time adjustment necessary when combining a noise canceling signal or a contour correction signal with a video signal.

As described above, the noise cancellation circuit and the contour correction circuit use a limiter circuit and a slice circuit, respectively, to separate noise and signals and high frequency components and signals. Therefore, it is necessary to select an appropriate limiter level and slice level.

For example, if the limiter level of the noise canceling circuit is too large, the amount of cancellation of high-frequency components of the signal will be large, leading to deterioration of the sharpness and resolution of the output video signal. The amount becomes smaller, leading to deterioration of the S/H of the output video signal.

On the other hand, in the contour correction circuit, if the slice level is too large, high-frequency components of low-level signals cannot be extracted, and even if the high-frequency components of the signal are emphasized by image quality adjustment, the low-level signals of the output video signal cannot be extracted. The high range will not be emphasized. On the other hand, if the slice level is too large, some noise components will appear in the slice output, resulting in deterioration of the S/N ratio of the output video signal.

In this way, it is desirable that the limiter level and slice level be exactly equal to the noise level included in the input video signal.

However, due to manufacturing variations in equipment such as video disc players and video tape recorders, or due to
The noise level also varies widely due to manufacturing variations in videotapes and changes over time. Despite this background, the limiter level and slice level of conventional noise cancellation circuits and contour correction circuits are set near the center of the above-mentioned variation range. For this reason, appropriate limiting and slicing could not be obtained due to variations in noise level, and good noise cancellation and contour correction could not be obtained.

Further, although the contour correction circuit adjusts the image quality to the user's preference, it has been impossible to adjust the image quality to the optimum image quality for any picture pattern on the screen.

The optimal image quality depends on the user's preference, but - For images with a lot of high-frequency components, the image quality should be sharp with a slightly inferior S/N ratio, and for images with few high-frequency components, the image quality should be soft and S/N.
This improves N.

(Problems to be Solved by the Invention) Conventional noise canceling circuits and image quality adjustment circuits cannot obtain appropriate effects when the noise level included in the input video signal varies, and may not be able to achieve optimal image quality adjustment depending on the picture on the screen. Conditions change and we are unable to react to them.

Therefore, the present invention has developed an automatic image quality control circuit that can always obtain noise canceling and contour correction effects even when the noise level contained in human video signals varies, and that can obtain the optimal image quality adjustment state even when the picture on the screen changes. The purpose is to provide.

[Structure of the Invention] (Means for Solving the Problems) The present invention sets the limiting level of the noise canceling circuit section and/or the slicing level of the contour correction circuit section in the image quality adjustment circuit to the noise level included in the input video signal. Accordingly, a means is provided for changing the limiting and/or slicing level to an optimum level.

Further, means is provided for obtaining an optimal correction signal by controlling the gain of the output of the slice circuit section according to the level of the signal high-frequency component contained in the input video signal.

(Function) With the above means, the limiting level and/or slice level can be made equal to the noise level included in the input video signal, and optimal limiting and/or h
You can get slice level. Further, even if the picture of the input video signal changes, the gain of the contour correction signal is controlled according to the level of the high frequency component included in the picture, so that optimal contour correction can be obtained according to the picture.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, in which a human input video signal at an input terminal 21 is supplied to a delay circuit 22 and also to a filter 25 with high-pass characteristics. Filter 25
After passing through the delay circuit 26, the output is sent to the limiter circuit 27.
and is supplied to the subtractor 28. The output of the limiter circuit 27 is supplied to a subtracter 28 and also input to an adder 30 as a noise cancellation signal. The output of the adder 28 is gain controlled by a gain control amplifier 29 and input to an adder 30 as a contour correction signal.

As a result, the adder 30 obtains an image quality adjustment signal in which the noise cancellation signal and the contour correction signal are combined.

The image quality adjustment signal is added to the input video signal time-adjusted by the delay circuit 22 in the adder 23. Therefore, an output video signal from which noise has been removed and whose contours have been corrected is obtained at the output terminal 24.

In the above configuration, some of the components are shared by the noise cancellation signal generation section and the contour correction signal generation section.

That is, the output of the limiter circuit 27 can be used as a noise canceling signal. This cancellation signal is further input to the subtracter 28, where it slices the output of the delay circuit 26' and is used to obtain a signal for contour correction. The limiting level of the limiter circuit 27 remains the slice level of the slice section. The contour correction signal is further gain-adjusted by a gain control amplifier 29 to control the degree of contour enhancement.

Next, in this embodiment, a noise detection circuit 41 is provided for detecting the noise level contained in the input video signal using the output of the filter 25.

FIG. 2 shows a specific example of the noise detection circuit 41.

Signal 4a at input terminal 410 is supplied to gate circuit 411. The gate circuit 411 is conductive during the period of the gate pulse 4b from the control terminal 416. Noise detection is performed using a period in which the input video signal is at a constant level, such as a vertical blanking period. The signal waveforms of each part of the circuit shown in FIG. 2 are shown in FIG. 4 and will be explained together with this.

The signal (noise) 4c that has passed through the gate circuit 411 is detected by a double-wave detection circuit 412, and its detection output 4d is supplied to a low-pass filter 413.

The output 4e smoothed by the low-pass filter 413 is supplied to a sample-and-hold circuit 414 and sampled by a sampling pulse 4f. The sampling pulse 4f supplies the gate pulse 4b to one side of the AND circuit 418, and also supplies the gate pulse 4b to one side of the AND circuit 418 via the delay circuit 417.
8.

The noise level detection signal 4g generated by the noise detection circuit 41 is outputted via the output terminal 415 as shown in FIG.
The signal is supplied to a limiting level control terminal of the limiter circuit 27, and also to a slice level control terminal 426 of a high frequency component detection circuit 42, which will be described later.

Due to the action of the noise detection circuit 41 described above, the limiting level is automatically controlled to be equal to the noise level included in the human-powered video signal, so even if the noise level fluctuates, the limiting level can be reliably used for noise cancellation. A signal (an inverted version of the noise component) can be obtained.

This means that the slice level is also appropriate when obtaining a contour correction signal. In other words, only the noise component is removed by the subtracter 28.

Next, in this embodiment, means is provided to control the emphasis level of the contour correction signal according to the picture pattern (frequency) of the input video signal and automatically obtain an emphasis signal of an appropriate level.

That is, the high frequency component detection circuit 42 detects a high frequency component from the output of the filter 25 and supplies the output to the gain control terminal of the gain control amplifier 29 via the adder 43. Adder 43
further provides a user adjusted manual control input from terminal 44 to gain control amplifier 29.

FIG. 3 shows a specific example of the configuration of the high frequency component detection circuit 42.

Further, FIG. 5 is a signal waveform diagram of each part of the circuit of FIG. 3, and will be explained together with the signal waveform diagram.

An output signal 5b obtained by passing the input video signal 5a shown in FIG. 5 through the filter 25 is input to the input terminal 420. This signal 5b is detected by the double wave detection circuit 421 and the detection output 5
It becomes C. This detected output 5c is supplied to a slice circuit composed of a limiter circuit 422 and an adder 423 and is sliced.

This makes it possible to obtain a high frequency component 5d from which noise has been removed, as shown by signals 5c and 5d in FIG. The high-frequency component is smoothed by a low-pass filter 424 and supplied to an output terminal 425 as a control output 5e.

The low-pass filter 424 has a small charging time constant so that it outputs a detection output only at the edge portion of the picture, and outputs a detection output during the period where high-frequency components are continuous in the area. , the discharge time constant is set to a large characteristic. On the other hand, the low-pass filter used in the above-mentioned noise detection circuit section has a cutoff frequency that is sufficiently lower than the cutoff frequency of the high-pass filter characteristic section of the noise canceling section and the contour correction signal filter section. It is set to sufficiently smooth the rectified noise.

As described above, the output of the high-frequency component detection circuit 42 allows the gain of the gain control amplifier 29 to appropriately emphasize the outline according to the picture frequency of the video signal.

Next, the delay circuit 26 shown in FIG. 1 will be explained.

As mentioned above, the low-pass filter 424 is present in the high-frequency component detection circuit 42. For this reason, the detection output lags behind the actual high-frequency components (particularly the edge portions of the picture). Therefore, this delay time is compensated by the delay circuit 26 so that the contour correction signal can be obtained with an appropriate phase.

The configuration and operation of the embodiment shown in FIG. 1 have been described above, and the overall summary is as follows.

(1) Manually detect the noise level in the video signal, and use the detection output to automatically control the respective limiting levels and slice levels of the noise canceling and contour correction signal generating sections to be the same as the noise level.

■, Detects high-frequency components in the input video signal, and uses the detection output to sharpen parts of the input video signal where high-frequency components exist, while softening parts where high-frequency components do not exist. Control signals automatically.

(2) The control (2) above is performed in response to changes in the picture, centering on the desired image quality set by the user.

Note that the delay circuit 22 in FIG. 1 is for time-aligning the signals input to the adder 23.

FIG. 6 shows another embodiment of the present invention, and this embodiment has the following features:
This is an example in which the input terminal of the noise detection circuit 41 is connected to the input terminal 21 of the human input video signal. Since the other parts are the same as those in the embodiment shown in FIG. 1, they are given the same reference numerals and their explanation will be omitted.

In this embodiment as well, the same effects as above can be obtained. The circuits according to each of the above embodiments can be applied to either analog processing or digital processing. Furthermore, it is effective to use an FIR filter as the high-pass filter 25, and ringing components do not occur.

[Effects of the Invention] As explained above, according to the present invention, optimal noise canceling characteristics and image quality adjustment characteristics can be obtained even if the noise level contained in the input video signal varies. Furthermore, when the pattern of the input video signal changes, a sharp image quality can be automatically obtained in the pattern part with many high-frequency components, and a soft image quality can be automatically obtained in the pattern part with few high-frequency components.

[Brief explanation of the drawing]

1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing an example of the noise detection circuit of FIG. 1, and FIG. 3 is a circuit diagram showing an example of the noise detection circuit of FIG.
FIG. 4 is a signal waveform diagram of each part of the circuit of FIG. 2, FIG. 5 is a signal waveform diagram of each part of the circuit of FIG. 3, and FIG. A circuit diagram showing another embodiment, FIG. 7 is a diagram showing a conventional noise canceling circuit, and FIG.
The figure shows an example of the characteristics of the filter in Figure 7, and Figure 9 shows an example of the characteristics of the filter in Figure 7.
10 is a comprehensive characteristic diagram of the circuit in FIG. 7, FIG. 11 is a diagram showing a conventional contour correction circuit,
FIG. 12 is a diagram of signal waveforms at various parts of the circuit of FIG. 11. 22... Delay circuit, 23... Adder, 25... High pass filter, 26... Delay circuit, 27... Limiter circuit, 28... Subtractor, 2... Gain Control amplifier, 30. 43... Adder, 41... Noise detection circuit, 42... High frequency component detection circuit. Applicant's Representative Patent Attorney Takehiko Suzue Figure 2 Figure 4 Figure 5 Figure 6 Figure 9

Claims (4)

[Claims] (1) Extract the high-frequency component of the input original signal through a filter with high-pass characteristics, pass the extracted output to a limiter circuit, and subtract the output of the limiter circuit from the original signal. The method further comprises: means for removing a noise component of the original signal; and means for detecting a noise component of the input original signal or the output of the filter and controlling a limiting level of the limiter circuit section according to the noise level. Features an automatic image quality control circuit. (2) Extracting the high-frequency component of the input original signal through a filter with high-pass characteristics, passing this extracted output through a slice circuit section, and adding the output of this slice circuit section to the original signal. means for adding a contour correction signal to the original signal;
An automatic image quality control circuit comprising means for detecting a noise component of the input original signal or the output of the filter and controlling a slice level of the slice circuit section according to the noise level. (3) Extracting the high-frequency component of the input original signal through a filter with high-pass characteristics, passing this extracted output through a limiter circuit, and subtracting the output of the limiter circuit from the original signal. While removing the noise component of the original signal, the extracted output is passed through a slicing circuit section that subtracts the output from the limiter circuit section, and the output of this slicing circuit section is added to the original signal. The present invention is characterized by comprising means for applying a contour correction signal, and means for detecting a noise component of the input original signal or the output of the filter and controlling the limiting level of the limiter circuit section according to the noise level. Image quality automatic control circuit. (4) The gain of the slice circuit section is configured to be gain controlled by the output of a high frequency component detection circuit that extracts high frequency components from the extracted output of the filter and a manual control input. 3. The automatic image quality control circuit according to item 1 or 2.