JPH0435952B2 - - Google Patents

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 broadcasting station side, the luminance signal component is transmitted with almost flat characteristics up to the region exceeding 4MHz, and the color subcarrier is superimposed at the 3.58MHz position. In ordinary television receivers, the luminance signal component has a descending characteristic above 2 to 3 MHz in order to prevent problems such as cross color due to insufficient separation of the luminance signal component and color signal component. In high-resolution receivers, the luminance signal component and color signal component are completely separated using 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 pre-emphasize the amplitude of the luminance signal on the transmitting side and de-emphasize it on the receiving side. When emphasis is applied, there is a risk that the broadcast radio waves will become overmodulated.

The invention aims to provide sufficient emphasis on 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, the 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 _fO . A desirable value for _fO is around 1MHz. 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 γ is the emphasis coefficient. As is clear from this functional expression, when the amplitude a of the low frequency component is 0, the emphasis rate n becomes the maximum value x, and the amplitude a of the low frequency component
is the maximum of 1, the emphasis rate n is 1
It will be lowered to . 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 with the frequency f _O as a boundary. This high frequency component is
According to the amplitude a of the low frequency component, the high frequency component is de-emphasized with an emphasis characteristic opposite to that on the broadcasting side, and the processed high frequency component is combined with the low frequency component and used as a luminance signal for image display.

Further, in a second invention that is incorporated into the first invention, on the broadcasting device side, the separated luminance signal high frequency component is subjected to a second pre-emphasis in addition to the above-mentioned pre-emphasis (first pre-emphasis). receive. This emphasis characteristic is such that the emphasis rate continuously decreases as the input amplitude increases.
When the input amplitude reaches a maximum value of 1, the emphasis rate is equal to 1. Either of the first and second pre-emphasis may be 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. The first and second day emphasis also
It doesn't matter which one you go first. The desirable value of the boundary frequency f _O when carrying out the second invention is 2 to
It is 3MHz.

[Effect]

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. In the receiver, the signal is subjected to first de-emphasis and restored to its original amplitude characteristics before being displayed. Therefore, the amplitude characteristics of the luminance signal component displayed on the receiver are as follows:
This is the same amplitude characteristic as the luminance signal component supplied to the broadcaster.

As is clear from the above function equation, the characteristics of the first pre-emphasis in a broadcasting device are a function of the amplitude a of the low frequency component, and when the low frequency component amplitude a is small, there is some margin in the modulation degree. Therefore, when the emphasis rate n becomes large and the low frequency component amplitude a reaches the maximum value of 1, the emphasis rate n is 1 because there is no margin at all for the modulation degree, 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 of such broadcasts when received by conventional receivers not according to the invention. The emphasis rate n has a maximum value x when the low frequency component amplitude a is 0.
shows. According to the results of the experiment, the maximum value x is 1.5
When pre-emphasis was performed using an emphasis characteristic of 2 to 2, the image received by a normal receiver turned out to be a fine and desirable image. When the maximum value x is 2 to 3, even with a normal TV receiver, by softly adjusting the image quality,
A good image was obtained. 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, the second invention is performed by a broadcasting machine.
The change in the amplitude characteristic of the luminance signal component due to the pre-emphasis is returned to the original amplitude characteristic by the second de-emphasis performed in 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, the emphasis rate is 1. become. Therefore, when performing the second pre-emphasis and de-emphasis simultaneously with the first pre-emphasis and de-emphasis in the first invention, it is necessary to perform , it is possible to further increase the emphasis rate when the high frequency component of the luminance signal is weak, thereby further increasing the effect of noise suppression.

Note that when the broadcast according to the second invention is received by a normal receiver, if the value of the boundary frequency f _O is low, the 1 to 3 MHz region of the luminance signal component will be displayed in an enhanced form. , there is a problem in terms of compatibility. By setting the boundary frequency f _O to 2 to 3 MHz, it is possible to receive the image in the same manner as before 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 etc. is divided into a luminance signal component Y and a color signal component C in a matrix circuit 1.
It can be divided into The luminance signal component Y is separated by a low-pass filter 2 and a high-pass filter 3 into a low-frequency component and a high-frequency component with the frequency f _O as a boundary, as shown in FIGS. 4 and 5, respectively. boundary frequency f _O
is selected to be 1 MHz when the pre-emphasis circuit 5 described later is not used, and is selected to be 2 to 3 MHz 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 the emphasis characteristic is n=x(1-a)〓+a as described above, as shown in FIG. shows its characteristic diagram. As shown in the figure, the emphasis coefficient γ is appropriately selected around 1, and when γ=1, the diagram becomes a straight line, when γ<1, the diagram becomes a convex curve, and γ >1, the diagram becomes a concave curve.

FIG. 3 shows an example of the configuration of the pre-emphasis circuit 4, in which high-frequency components and low-frequency components of the luminance signal are supplied to differential amplifiers 41 and 42, respectively, and both amplified outputs are mutually multiplied by a multiplier 43. appears at output terminal 44. Reference numeral 45 denotes a regulator that changes the input signal voltage of the amplifier 42, and by changing this, the value of the maximum value x of the emphasis rate n is determined. The circuit shown in Figure 3 uses a commercially available IC (Motorola MC1495L).

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 curve 5a in FIG. 7, and its emphasis rate is maximum when the input 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, the value of the emphasis rate n of the high frequency component changes between 1 and x according to the low frequency component amplitude a, so the input/output characteristics of the circuit are as shown in FIG. Straight line 4a shown in
and 4b. As a result of the emphasis in the pre-emphasis circuit 5 being superimposed 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 a 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. Luminance signal component output by adder 6
Ye is combined with the color signal C in the color encoder 8 to become a broadcasting color television signal. At this time, the color signal C is also combined with the delay circuit 9 for phase adjustment.
There will be a slight delay.

FIG. 2 shows the video signal processing part of the receiver, in which a video signal equal to the output of the color encoder 8 is given to the color decoder 11, where the luminance signal component is
It is separated into Ye and color signal component C, but this luminance signal component Ye is pre-emphasized by the broadcasting device as described above.

The luminance signal component Ye is divided into a low-pass component and a high-frequency component by a low-pass filter 12 and a high-pass filter 13 with characteristics shown in FIGS. 4 and 5, respectively.
The divided high frequency components are sent to de-emphasis circuit 1.
In the pre-emphasis circuit 4, de-emphasis is performed according to the amplitude a of the low-frequency component, but its de-emphasis characteristics are exactly opposite to those of the pre-emphasis circuit 4. Therefore, its input/output characteristics are such that the amplitude a of the low frequency component is 0.
In this case, a straight line 14a shown in FIG. 8 is obtained, but when the amplitude of the low-frequency component is the maximum value 1, a straight line 14b shown in FIG. 8 is obtained.

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

As a result, a signal that has been pre-emphasized with a characteristic such as curve 5b in FIG.
In the circuit 14, it is de-emphasized as shown by the curve 5a, and further in the circuit 15, it is de-emphasized as shown in the straight line 4a, and then 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, but this luminance signal component Y is combined with the luminance signal component generated by the matrix 1 in the broadcasting machine. They have the same shape. 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, a delay circuit 1 interposed in the transmission path of the low frequency component and the transmission path of the color signal C.
7 and 19 are de-emphasis circuits 14 and 1
This is to compensate for some signal delay that occurs within 5.

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

In the above embodiment, the pre-emphasis circuit 5
Even if the de-emphasis circuit 15 is 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, so that noise can be effectively compressed while preventing overmodulation. It can be carried out. In particular, noise often appears in images in a bright form, so if it appears in dark areas of the image, it becomes unsightly. Because of the compression, 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 on a normal receiver, and if the maximum value x is selected to be between 2 and 3, the image quality can be adjusted using 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, the normal receiver is 2~
Since the luminance signal is configured to gradually attenuate from 3MHz onwards, the boundary frequency _fO should be set at 2 to 3MHz.
If this is selected, images can be received almost without being affected by the pre-emphasis by the circuit 5.

〔Effect of the invention〕

As described above, according to the present invention, noise can be effectively compressed while preventing overmodulation.
In particular, when the pre-emphasis circuit 5 and the de-emphasis circuit 15 are added, the weaker the signal, the greater the noise compression effect. Moreover, in either case, compatibility with ordinary television receivers can be achieved.

[Brief explanation of drawings]

The figures show an embodiment of the present invention; FIG. 1 is a block diagram of the video signal processing section of a broadcasting device, FIG. 2 is a block diagram of the video signal processing section of a receiver, and FIG. 3 is a circuit diagram of the pre-emphasis circuit 4. , FIG. 4 is a characteristic diagram of the low-pass filter 2, FIG. 5 is a characteristic diagram of the high-pass filter 3, FIG. 6 is a characteristic diagram of the pre-emphasis circuit 4, FIG. 7 is a characteristic diagram of pre-emphasis in a broadcasting machine, and FIG. 8 is a characteristic diagram of the pre-emphasis circuit 4. is a de-emphasis characteristic diagram 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, 1
5... Second de-emphasis means, 16... Adder (combining means), f _O ... Boundary frequency, Y and Ye
...Brightness signal component.

Claims (1)

[Claims] 1. Consists of a broadcaster and a receiver, and the broadcaster is:
A means for separating a luminance signal component into a high-frequency component and a low-frequency component at a predetermined frequency, and preemphasizing the high-frequency component by a large amount when the low-frequency component amplitude is small according to the amplitude of the low-frequency component. The receiver has a pre-emphasis means for pre-emphasizing to a small value when the received luminance means for separating signal components into high-frequency components and low-frequency components with the frequency as a boundary; de-emphasis means for processing the high-frequency components according to the low-frequency components with de-emphasis characteristics opposite to those of the pre-emphasis means; A low-noise television system characterized by comprising a synthesizing means for synthesizing a low-frequency component and the de-emphasized high-frequency component to obtain a luminance signal component for image display. 2 Consists of a broadcaster and a receiver, and the above broadcaster is:
A means for separating a luminance signal component into a high-frequency component and a low-frequency component at a predetermined frequency, and preemphasizing the high-frequency component by a large amount when the low-frequency component amplitude is small according to the amplitude of the low-frequency component. A first pre-emphasis means that pre-emphasizes the high-frequency components to a small value when a second pre-emphasis means that performs pre-emphasis with a characteristic of decreasing the brightness, and a luminance signal component for broadcasting by combining the low-frequency component and the high-frequency component processed by the first and second pre-emphasis means. and a synthetic means for obtaining
The receiver includes 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 de-emphasis characteristic that is opposite to that of the first pre-emphasis means for converting the high-frequency component to the low-frequency component. a first de-emphasis means that processes the high-frequency components before or after being processed by the first de-emphasis means with a de-emphasis characteristic opposite to that of the second pre-emphasis means; It is characterized by having a second de-emphasis means, and a synthesis means for combining the low-frequency component and the high-frequency component processed by the first and second de-emphasis means to obtain a luminance signal component for image display. Low noise television system.