JPS63107282A - Low noise television system - Google Patents

Abstract

PURPOSE:To effectively compress noise while an excessive modulation is prevented by providing a broadcasting, unit with preemphasis circuits for a high frequency component included in a luminance signal and providing a receiver with deemphasis circuits. CONSTITUTION:A matrix circuit 1 separates a luminance signal component Y and a chrominance component C from an image pickup signal incoming to the broadcasting unit. The component Y puts into an LPF 2 and an HPF 3. The preemphasis circuits 4 and 5 process the high frequency component in the luminance signal passing through the HPF 3. The emphasis rate of the circuit 6 is maximum where an input amplitude is minimal, and as the amplitude increases, the rate decreases steadily. Where the input amplitude is maximum, no emphasis takes place. An adder 6 links the high frequency component that the circuit 5 has processed to a low frequency component to attain a luminance signal component Ye. A color encoder 8 links the component Ye to the chrominance component C to attain a broadcasting color television signal. On the other hand the receiver is provided with the deemphasis circuits 14 and 15.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a low-noise television system that improves image quality while suppressing an accompanying increase in noise when transmitting and receiving television broadcast images.

[Conventional technology]

From the broadcast station side, a luminance signal component is transmitted with substantially flat characteristics up to a region exceeding 4 MHz, and a color subcarrier is superimposed at a position of 3.58 MHz. In normal television receivers, in order to prevent problems such as cross color due to insufficient separation of the luminance signal component and color signal component, 2 to 3 MHz is added to the luminance signal component.
Above z, a descending characteristic is provided. In high-resolution receivers, the luminance signal component and color signal component are completely separated by a comb filter, and the luminance signal component is processed with flat characteristics.

[Problem that the invention seeks to solve]

In a high-resolution receiver, the bandwidth of the luminance signal is expanded compared to a normal receiver, so the noise also increases, so an improvement in resolution does not necessarily lead to an improvement in image quality.

As a measure to expand the usable bandwidth of the luminance signal while suppressing noise, it is possible to perform gli-emphasis on the amplitude of the luminance signal on the transmitting side and de-emphasis on the receiving side. If sufficient emphasis is applied, there is a risk that the broadcast radio waves will fall into overmodulation.

The invention aims to provide sufficient emphasis to the luminance signal while avoiding the risk of overmodulation.

[Means for solving problems]

This invention (first invention) is comprised of a broadcaster and a receiver. In a broadcasting device, a luminance signal component of a color video signal obtained by a camera or the like is separated into a high frequency component and a low frequency component at a predetermined frequency f0. A desirable value for fo is around 1 MHz.

This high-frequency component is pre-emphasized according to an emphasis characteristic that is a function of the amplitude of the low-frequency component. A desirable emphasis characteristic is expressed as n==x (1-a) +a, where n is the emphasis rate, X is the maximum emphasis value, a is the amplitude of the low frequency component, and r is the emphasis coefficient. As is clear from this functional expression, the amplitude a of the low frequency component is
When is O, the emphasis rate n becomes the maximum value X, and when the amplitude a of the low frequency component is 1, which is the maximum, the emphasis rate n is lowered to 1Tltc. This pre-emphasized high-frequency component is combined with the above-mentioned low-frequency component, and a color video signal created using this is broadcast.

In the above-mentioned receiver, the luminance signal component in the received color video signal is separated into a high-frequency component and a low-frequency component at the frequency f. This high frequency component is de-emphasized according to the amplitude a of the low frequency component with an emphasis characteristic opposite to that on the broadcasting side, and the processed high frequency component is combined with the above low frequency component and used as a luminance signal for image display. be done.

In addition, in the second invention merged with the first invention,
On the broadcasting device side, the separated high-frequency component of the luminance signal is subjected to a second pre-emphasis in addition to the above-mentioned pre-emphasis (first pre-emphasis). This emphasis characteristic is such that the emphasis rate continuously decreases as the input amplitude increases, and when the input amplitude reaches the maximum value of 1, the emphasis rate becomes equal to 1. It does not matter which one of the first and second pre-emphasis is performed first. Then, on the receiver side, the separated high-frequency component of the luminance signal is subjected to a second de-emphasis in addition to the above-described de-emphasis (first de-emphasis). This de-emphasis characteristic is the exact opposite of the second pre-emphasis characteristic. There is no problem in performing the first and second de-emphasis modes first. One shift of the desirable boundary frequency f0 when carrying out the second invention is 2 to
It is 3MHz.

[For production]

In the first invention, the low frequency component of the luminance signal is broadcast with the same amplitude characteristics and displayed by the receiver, but the high frequency component is subjected to the first pre-emphasis during broadcasting, The signal is then subjected to the first de-emphasis on the receiver to restore its original amplitude characteristics and is then displayed. Therefore,
The amplitude characteristics of the luminance signal component displayed on the receiver are the same as the amplitude characteristics of the night component of the luminance signal supplied to the broadcaster.

The characteristics of the first pre-emphasis in the broadcasting machine are as follows:
It is a function of Since there is no pre-emphasis, the emphasis rate n is 1, in other words, no pre-emphasis is performed. Therefore, while avoiding overmodulation, the desired maximum amount of pre-emphasis is applied, thereby suppressing noise.

The maximum limit of pre-emphasis is determined by the compatibility with which such broadcasts are received by conventional receivers not according to the present invention. The emphasis rate n shows the maximum value X when the low frequency component amplitude a is O. The results of experiments show that when pre-emphasis is performed using an emphasis characteristic such that the maximum value . When the maximum value X was 2 to 3, good images could be obtained even with a normal receiver by softly adjusting the image quality. When the maximum value X exceeds 3, an excess of high-frequency components becomes noticeable in ordinary television receivers. Therefore, by suppressing the maximum value X of the emphasis rate to 3 or less, the present invention can be implemented while maintaining compatibility with ordinary television receivers.

In the second invention, a change in the amplitude characteristic of the luminance signal component due to the second pre-emphasis performed by the broadcaster is returned to the original amplitude characteristic by the second de-emphasis performed by the receiver. The characteristics of the second pre-emphasis in a broadcasting machine are that when the input signal is small, it is greatly emphasized, and as the input signal increases, the emphasis rate decreases continuously, and preferably when the input signal is maximum, it is emphasized. The rate becomes 1. Therefore, when this second pre-emphasis and de-emphasis are carried out simultaneously with the first pre-emphasis and de-emphasis in the invention of il, the diene 2 assist rate n is adjusted to prevent overmodulation according to the first invention. Under these restrictions, it is possible to further increase the emphasis rate when the high-frequency component of the luminance signal is weak, thereby further increasing the noise suppression effect.

Note that when the broadcast according to the second invention is received by a normal television receiver, if the value of the boundary frequency f0 is low, the 1 to 3 MHz region of the luminance signal component will be displayed in an enhanced form, so compatibility is not guaranteed. There is a problem with this.

If the boundary frequency f0 is set to 2 to 3 MHz, it is possible to receive images in the same manner as in the past even with a normal receiver.

〔Example〕

FIG. 1 shows the video signal processing section of the transmitter. An image signal received from a color camera or the like is divided into a luminance signal component Y and a color signal component C in the matrix circuit 1. The luminance signal component Y is filtered by a low-pass filter 2 and a high-pass filter 3 at a frequency f as shown in FIGS. 4 and 5, respectively.
It is separated into a low frequency component and a high frequency component with a border of 0. The boundary frequency f is selected to be 1 MHz when the pre-emphasis circuit 5 described later is not used, and to 2 to 3 MB2 when the pre-emphasis circuit 5 is used.

The high-frequency component of the luminance signal that has passed through the high-pass filter 3 is emphasized in the pre-emphasis circuit 4, and its emphasis characteristic is n=x (1-a
) '+a, and FIG. 6 shows its characteristic diagram. As shown in the same figure, the emphasis coefficient r is appropriately selected around 1, and when r=1, the line becomes a straight line, and when r<1, the line becomes a convex curve. When r>1, the diagram becomes a concave curve.

Figure 3 shows an example of the configuration of the pre-emphasis circuit.
The high-frequency component and the low-frequency component of the luminance signal are supplied to differential amplifiers 41 and 42, respectively, and both amplified outputs are mutually multiplied by a multiplier 43 and appear at an output terminal 44. Terminal 45 is a voltage supply terminal for both amplifiers 41 and 42, and by changing this supply voltage, the maximum value X of the emphasis factor n can be adjusted.
The value of is determined. Note that the circuit shown in Figure 3 is a commercially available I
C (Motorola MCI495L).

The high frequency components that have passed through the pre-emphasis circuit 4 are further processed in the pre-emphasis circuit 5.

The emphasis characteristic of the circuit 5 is as shown by the curve 5a in FIG. 7, and the emphasis rate is maximum when the manual amplitude is small, gradually decreases as the input amplitude increases, and is not emphasized when the input amplitude is maximum.

As mentioned above, in the pre-emphasis circuit 4,
According to the low frequency component amplitude a, the high frequency component assist rate n
Since the value of V varies between 1 and X, the input/output characteristics of the circuit vary between straight lines 4a and 4b shown in FIG. As a result of superimposing the monphasis in the pre-emphasis circuit 5 on this, the relationship between the input of the circuit 4 and the output of the circuit 5 changes between curves 5a and 5b shown in FIG.

The high-frequency component processed by the pre-emphasis circuit 5 is combined with the low-frequency component in an adder 6 to form the broadcasting luminance signal component Ye. In order to align the phases of both signals, the low-frequency component is processed by a delay circuit. 7, there will be a slight delay. The luminance signal component Yθ outputted by the adder 6 is combined with the color signal C in the color encoder 8 to form a broadcasting color television signal. At this time, the color signal C is also passed through a delay circuit 9 for phase adjustment.
There will be a slight delay.

FIG. 2 shows the video signal processing section of the receiver, in which a video signal equal to the output of color encoder 8 is sent to color encoder 1.
1, where the luminance signal component Ye and the color signal component C
This luminance signal component Ye is pre-emphasized by the broadcasting device as described above.

The luminance signal component Ye is filtered through a low-pass filter 12 and a high-pass filter 1.
3 into a low frequency component and a high frequency component with the characteristics shown in FIGS. 4 and 5, respectively. The divided high-frequency components are de-emphasized in the de-emphasis circuit 14 according to the amplitude a of the low-frequency components, but the de-emphasis characteristics are exactly opposite to those of the pre-emphasis circuit 4. Therefore, when the amplitude a of the low frequency component is O, the input/output characteristics become as shown in the straight line 14a shown in FIG. 14b.

The high frequency component de-emphasized in the circuit 14 is
Further de-emphasis is performed in circuit 15Q, but its de-emphasis characteristics are exactly opposite to those of pre-emphasis circuit 5. That is, when emphasis is performed in the pre-emphasis circuit 5 with a characteristic such as 5a shown in FIG. 7, de-emphasis is performed in the de-emphasis circuit 15 with a characteristic such as a curve 15a shown in FIG.

As a result, for example, a signal that has been pre-emphasized with a characteristic as shown in curve 5b in FIG. 7 is de-emphasized as shown in curve 5a in circuit 14, and
5, it is de-emphasized like the straight line 4a,
returned to its original shape.

The high-frequency component processed by the de-emphasis circuit 15 is combined with the low-frequency component in the adder 16 to become a luminance signal component Y. This luminance signal component Y is a luminance signal component generated by matrix 1 in the broadcasting machine. It has the same shape as . The luminance signal component Y is combined with the color signal C separated by the color decoder 11 in the matrix 18, and becomes a video signal for display on the picture tube. Here, the delay circuits 17 and 1 are interposed in the transmission path of the low frequency component and the transmission path of the color signal C.
9 is for compensating for some signal delay occurring within the de-emphasis circuits 14 and 15.

In the above embodiment, the order of the pre-emphasis circuits 4 and 5 may be interchanged, and the order of the de-emphasis circuits 14 and 15 may also be interchanged. In addition, when implementing only the first invention, the pre-emphasis circuit 5
and de-emphasis circuit 15 are omitted.

In the above embodiment, even if the pre-emphasis circuit 5 and the de-emphasis circuit 5 are omitted, the high-frequency components of the luminance signal are emphasized according to the modulation margin determined by the amplitude of the low-frequency components. Noise compression can be effectively performed while preventing overmodulation. In particular, noise often appears in bright forms in images, so if it appears in dark areas of the image, it can be a visual nuisance. is strongly compressed, the visual effect is extremely large.

Moreover, if the maximum value X of the emphasis rate n is selected to be 2 or less, the broadcast can be received as is with a normal receiver, and if the maximum value X is selected between 2 and 3, the image quality can be adjusted with a normal receiver. By selecting software, images can be received without any problems.

Furthermore, when the pre-emphasis circuit 5 and the de-emphasis circuit 15 are added, noise is suppressed from the high-frequency components of the luminance signal by stronger emphasis as the signal becomes weaker, so that the noise suppression effect is further improved. In this case, since a typical receiver is configured such that the luminance signal gradually attenuates from 2 to 3 MHz, the boundary frequency f. 2
If the frequency is selected to be .about.3 MHz, images can be received without being affected by the pre-emphasis W caused by the circuit 5.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to effectively compress noise while preventing overmodulation, and especially when adding the pre-emphasis circuit 5 and the de-emphasis circuit 15, the weaker the signal, the larger the noise. The effect of compressing is added. Moreover, in either case, compatibility with ordinary television receivers can be achieved.

[Brief explanation of the drawing]

The figures show an embodiment of the present invention; FIG. 1 is a block diagram of the video signal processing section of a broadcaster, FIG. 2 is a block diagram of the video signal processing section of a receiver, and FIG. 3 is a pre-emphasis circuit 4.
4 is the characteristic diagram of the low-pass filter 2, FIG. 5 is the characteristic diagram of the high-pass filter 3, FIG. 6 is the characteristic diagram of the pre-emphasis circuit 4, and FIG. 7 is the pre-emphasis characteristic in the broadcasting machine. 8 are de-emphasis characteristic diagrams in the receiver. 2...Low pass filter, 3...High pass filter, 4...
- first pre-emphasis means, 5... second pre-emphasis means, 6... adder (combining means), 12.
...Low pass filter, 13...High pass filter, 14...
・First de-emphasis means, 15... Second de-emphasis means, 16... Adder (combining means), ±
゛. ... Boundary frequency, Y and Ye ... Luminance signal components. Patent applicant: Nippon Television Broadcasting Network Co., Ltd. Agent: Satoshi Shimizu and 2 others April 5th, 4th, Agent Address: Postal Code: 651 5. "Detailed Description of the Invention" column and drawings of the specification subject to amendment. 6 Contents of amendment (1) “Terminal 45 is...
・Correct "supply voltage" to "45 is an adjustment layer that changes the input signal voltage of the amplifier 42." (2) Figure 3 of the drawing is corrected as shown in the attached sheet. Attached document drawing Figure 3 1 copy or more

Claims (2)

[Claims] (1) Consisting of a broadcaster and a receiver, the broadcaster includes means for separating a luminance signal component into a high-frequency component and a low-frequency component at a predetermined frequency, and an amplitude of the high-frequency component and the low-frequency component. Accordingly, a pre-emphasis means that pre-emphasizes a large amount when the amplitude of the low-frequency component is small and pre-emphasizes it small when the amplitude of the low-frequency component is large, and integrates the low-frequency component and the pre-emphasized high-frequency component to produce a brightness signal component for broadcasting. The receiver has a means for separating the received luminance signal component into a high frequency component and a low frequency component with the frequency as a boundary, and a preemphasis means for converting the high frequency component according to the low frequency component. and a synthesizing means for combining the low-frequency component and the de-emphasized high-frequency component to obtain a luminance signal component for image display. Low noise television system. (2) Consisting of a broadcaster and a receiver, the broadcaster includes means for separating a luminance signal component into a high-frequency component and a low-frequency component at a predetermined frequency, and an amplitude of the high-frequency component and the low-frequency component. a first pre-emphasis means which greatly pre-emphasizes when the low-frequency component amplitude is small and performs small pre-emphasis when the low-frequency component amplitude is large; a second pre-emphasis means for pre-emphasizing the component with a characteristic that the emphasis rate of the output amplitude continuously decreases as the input amplitude increases; and the low-frequency component is processed by the first and second pre-emphasis means. and a synthesizing means for obtaining a broadcasting luminance signal component by combining the received luminance signal component with the high frequency component, and the receiver separates the received luminance signal component into a high frequency component and a low frequency component with the frequency as a boundary. a first de-emphasis means for processing the high-frequency component according to the low-frequency component with a de-emphasis characteristic opposite to that of the first pre-emphasis means; a second de-emphasis means that processes the high-frequency components after the de-emphasis with de-emphasis characteristics opposite to those of the second pre-emphasis means; 1. A low-noise television system, comprising a synthesis means for obtaining a luminance signal component for displaying an image by synthesizing the high-frequency components.