JPH0591479A - Luminance processing circuit for video tape recorder reproducing device - Google Patents

Abstract

PURPOSE:To improve resolution by expanding only the intermediate level of a synchronization amplification luminance signal obtained by expanding the horizontal synchronization signal and black signal of a luminance signal whose pedestal level is fixed constant and compressing the white signal of the luminance signal so as to improve a white level and reduce a black level. CONSTITUTION:A pedestal clamping circuit 13 inputs a horizontal gate signal HG and a vertical synchronization signal VSYN and outputs a luminance signal Y2' obtained by fixing the pedestal level of an input luminance signal Y2 to a constant level. A synchronization amplification circuit 14 outputs a synchronization luminance signal Y3 obtained by expands the horizontal synchronization signal and black signal of the signal Y2' and compressing the white signal of the signal Y2', and an amplifier 15 complifies a signal Y3 and outputs a signal Y3'. A polygonal line conversion circuit 16 converts the white level to a higher level and the black level to a lower level by expanding only the intermediate level of the signal Y3'. Thus, the nominal resolution can be improved in simple circuit construction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a luminance processing circuit for a video tape recorder reproducing apparatus.

[0002]

2. Description of the Related Art FIG. 7 is a block diagram showing a conventional video tape recorder reproducing apparatus.

In FIG. 7, a modulated video signal is reproduced by a video head 1 from a recorded tape. The reproduced modulated video signal is amplified by the amplifier circuit 2 and input to the equalizer circuit 3.

In the equalizer circuit 3, the frequency characteristic of the reproduced modulated video signal is adjusted so that the frequency characteristic has a predetermined value regardless of the type of tape. For this adjustment, for example, a plurality of equalizer circuits having different frequency characteristics are provided,
Select an appropriate equalizer circuit according to the type of tape,
This can be done by processing the modulated video signal with the equalizer circuit.

The modulated video signal output from the equalizer circuit 3 is input to a high pass filter (HPF) 4 and a low pass filter (LPF) 7.

The modulated video signal output from the high pass filter 4 is demodulated by the demodulation circuit 5 into a luminance signal, which is processed by the luminance processing circuit 6.

The modulated video signal input to the low pass filter 7 is filtered by the filter 7 to be demodulated into a color signal, which is processed by the color processing circuit 8.

The luminance signal output from the luminance processing circuit 6 and the color signal output from the color processing circuit 8 are added by the adding circuit 9 and output as a reproduced video signal.

By the way, conventionally, there has been a demand for improving the resolution of the above video tape recorder reproducing apparatus. In order to meet such demands, in a conventional video tape recorder playback device, a plurality of types of equalizer circuits having different frequency characteristics are provided, an appropriate equalizer circuit is selected according to the type of tape, and an equalizer circuit filter is also selected. By doing so, the apparent resolution was improved.

As another method, a picture control circuit is provided in the luminance processing circuit 6, and the picture control circuit adjusts the frequency characteristic of the reproduced luminance signal so that the edge of the image is emphasized. Was trying to improve the resolution of.

[0011]

However, in the method of providing a plurality of types of equalizer circuits having different frequency characteristics, selecting an appropriate equalizer circuit according to the type of tape, and further selecting the equalizer circuit filter, the circuit configuration is However, there is a problem in that the circuit becomes complicated due to the large number of components, the cost of designing and manufacturing increases, and the reliability decreases.

Further, in the method of adjusting the frequency characteristic of the reproduced luminance signal so that the edge of the image is emphasized by the picture control circuit provided in the luminance processing circuit 6, the frequency characteristic of the luminance signal is changed. Therefore, there are problems such as ringing of the luminance signal and increase of noise in the high frequency range.

The present invention has been made in consideration of the above circumstances. An object of the present invention is to improve apparent resolution with a simple circuit configuration in a luminance processing circuit and to cause ringing in the circuit. It is an object of the present invention to provide a luminance processing circuit of a video tape recorder reproducing device which does not increase the high frequency noise.

[0014]

In order to achieve the above object, the present invention provides a luminance processing circuit of a video tape recorder reproducing apparatus for processing a luminance signal of a video signal reproduced and demodulated from a magnetic tape. A pedestal clamp circuit that fixes the level to a constant level, a sync amplifier circuit that obtains a sync amplified brightness signal by expanding the horizontal synchronizing signal and the black signal of the brightness signal that fixes the pedestal level to a constant level, and compressing the white signal, A polygonal line conversion circuit that expands only the middle level of the sync amplified luminance signal to make the white level higher and the black level lower is provided.

[0015]

In the luminance processing circuit of the video tape recorder reproducing apparatus according to the present invention, as shown in FIGS. 1 and 2, the luminance signal Y1 of the reproduced and demodulated video signal has its waveform improved by the de-emphasis circuit 11. It becomes Y2 and is input to the pedestal clamp circuit 13.

The luminance signal Y2 is supplied to the pedestal clamp circuit 1
At 3, the pedestal level is fixed to a constant level and output as a luminance signal Y2 '. The luminance signal Y2 'has its horizontal synchronizing signal and black signal expanded and its white signal compressed by the sync amplifier circuit 14. Therefore, the amplification factor of the horizontal synchronizing signal becomes a very large value as compared with the amplification factor of the white signal. By such processing, the luminance signal Y2 'becomes the sync amplified luminance signal Y3.

The sync amplified luminance signal Y3 is amplified by the amplifier circuit 15 and then input to the broken line conversion circuit 16 as a luminance signal Y3 '. In the polygonal line conversion circuit 15, the luminance signal Y3 '
The middle level is stretched. As a result, the white level becomes a higher level and the black level becomes a lower level, so that a luminance signal with a sharp effect and thus an apparently improved resolution can be obtained.

[0018]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a luminance processing circuit of a video tape recorder reproducing apparatus according to the present invention. The reproduced and demodulated luminance signal Y1 is input to the de-emphasis circuit 11. Since the luminance signal Y1 is pre-emphasized in the recording system (not shown),
The signal has a waveform as shown in (a), and overshoot or undershoot occurs at the edge portion of the signal. The de-emphasis circuit 11 is processed so that the overshoot or undershoot does not occur.

The luminance signal shown in FIGS. 2 (a) to 2 (d) is a luminance signal for a 1H period and is composed of a horizontal synchronizing signal HS and a monochrome signal YS.

The luminance signal Y2 output from the de-emphasis circuit 11 is shown in FIG. 2 (b). The luminance signal Y2 having the improved waveform at the edge portion is input to the pedestal clamp circuit 13 via the buffer 12.

The pedestal clamp circuit 13 inputs the horizontal gate signal HG and the vertical synchronizing signal VSYN, fixes the pedestal level of the luminance signal Y2 to a constant level, and outputs it as the luminance signal Y2 'to the sync amplifier circuit 14.

The sync amplifier circuit 14 has a larger amplification degree as the black level (low level) of the video signal and a smaller amplification degree as the white level (high level), that is, the horizontal synchronizing signal and the black signal are expanded. , The white signal is compressed, so that the amplification factor of the horizontal synchronizing signal is very large as compared with the amplification factor of the white signal. By such processing, the luminance signal Y2 'becomes the sync amplified luminance signal Y3 in which the horizontal synchronizing signal is expanded. This is shown in FIG.

FIG. 3 is a characteristic diagram showing the characteristics of the sync amplifier circuit 14, in which the input luminance signal is shown below the characteristic curve Sa and the output luminance signal is shown to the left thereof. The input luminance signal is shown in Fig. 2.
The luminance signal Y2 'shown in (b), and the output luminance signal is the luminance signal Y3 shown in FIG. 2 (c). A method of setting the characteristic curve Sa shown in FIG. 3 will be described later.

With the characteristic curve Sa shown in FIG. 3, the signal of FIG. 2C in which the portion of the horizontal synchronizing signal HS is expanded and the white signal portion is compressed, that is, the output luminance signal Y3 is obtained.

A brightness signal Y3 'obtained by amplifying the brightness signal Y3 by the amplifier circuit 15 is input to the polygonal line conversion circuit 16. The polygonal line conversion circuit 16 processes the input luminance signal Y3 'and outputs the luminance signal Y4 shown in FIG.

The characteristic curve Sb of the polygonal line conversion circuit 16 is shown in FIG. The input luminance signal is shown below the characteristic curve Sb in FIG. 4, and the output luminance signal is shown to the left. The input luminance signal is shown in FIG.
The luminance signal Y3 ′ shown in (c) is an amplified luminance signal Y3 ′, and the output luminance signal is the luminance signal Y shown in FIG. 2 (d).
It is 4.

With the characteristic curve Sb shown in FIG. 4, the luminance signal Y in which the horizontal synchronizing signal portion is expanded and the white signal portion is compressed
In 3 ', the horizontal sync signal amplitude and the black-and-white signal amplitude are both normal values (values shown in FIG. 2B), but the intermediate level of the black-and-white signal is the expanded luminance signal Y4.

Therefore, the white signal portion is at a higher level (whiter) (lower level because it is a negative polarity signal in FIG. 4).
And the black part becomes a lower level (blacker). As a result, the black and white glue is effective, and the apparent resolution is improved. A method of setting the characteristic curve Sb of FIG. 4 will be described later.

Since the luminance signal Y4 thus obtained is a negative polarity signal, it is inverted and amplified to be a positive polarity luminance signal Y5.

The luminance signal Y5 is output to the outside via the switch circuit 18 and the buffer 19. Switch circuit 18
Selects either of the luminance signals Y2 and Y5, that is, the luminance signal to be output to the outside is the luminance signal Y5 processed so as to increase the apparent resolution, or the luminance signal not processed at all. The signal Y2 is selected.

The switch circuit 18 may be switched manually or automatically by a microcomputer. In the automatic mode, for example, the high frequency components of the video signal are extracted,
It may be determined whether to output the luminance signal Y2 or Y5 depending on the level.

Next, a method of setting the characteristic curve Sa (FIG. 3) in the sync amplifier circuit 14 will be described. A differential amplifier circuit which is an example of the sink amplifier circuit 14 is shown in FIG. In FIG. 5, reference numerals 20 and 21 denote pair transistors forming a differential amplifier circuit, and a luminance signal Y2 'is input to an input terminal 22.
Is input, and the luminance signal Y3 is output from the output terminal 23. The terminal 24 is a power supply terminal and is supplied with, for example, 5V. Each resistance value is an example, and these values need to be changed according to the characteristic values of the transistors 20 and 21.

Transistor 2 of such a differential amplifier circuit
The bias of 0 is determined by the base potential V0 of the transistor 21, and the base potential V0 determines the relative positional relationship between the characteristic curve Sa shown in FIG. 3 and the input luminance signal. That is, the input luminance signal can be moved in the left-right direction (the direction of the luminance signal level) with respect to the characteristic curve Sa, so that the portion of the horizontal synchronizing signal HS and the black signal portion are expanded. The waveform of the output luminance signal Y3 can be determined.

Of course, if the value of the fixed level of the pedestal clamp circuit 13 is different, the value of the base potential V0 needs to be changed according to the level value. The curve shape of the characteristic curve Sa itself is determined by the bias of the transistor 20, saturation characteristics, and the like. Next, a method of setting the characteristic curve Sb (FIG. 4) in the polygonal line conversion circuit 16 will be described. An example of the broken line conversion circuit 16 is shown in FIG. In FIG. 6, the luminance signal Y3 'input to the input terminal 25 has the DC component removed by the capacitor C1 and then the transistor 2
It is amplified by 6 and output as a luminance signal Y3 ″ to the emitter of the transistor 26.

Depending on the level of the luminance signal Y3 ", the diode D1, D2, D3 or D4 conducts. When the luminance signal Y3" is low level, only the diode D4 conducts and Y3 "exceeds a certain level. Then, the diode D4 is non-conducting and the diodes D1 to D3 are conducting.Even above the certain level, the conduction resistance of the diodes D1 to D3 is different depending on the level.

As described above, the conduction, non-conduction, or conduction resistance of each diode differs depending on the level of the luminance signal Y3 ", and therefore the value of the load resistance seen from the emitter of the transistor 26 differs, and is output to the output terminal 28. The level of the luminance signal Y4 is different.

Therefore, by adjusting the values of the cathode side potentials V1, V2, V3 of the diodes D1, D2, D3, the anode side potential V4 of the diode D4, and the respective resistance values,
The characteristic curve Sb as shown in FIG. 4 can be obtained. The potential V3 is determined by the base potential of the transistor 27, that is, the base bias resistance. Each resistance value in FIG. 6 is an example, and these values need to be changed according to the characteristic value of each active element.

[0039]

As described above, according to the present invention, by expanding the middle level of the luminance signal, the white level becomes more white,
Since the black level is set to be blacker, the black-and-white sharpening is effective, and the apparent resolution can be improved with a simple circuit configuration.

Since the frequency characteristic is not changed, ringing does not occur and high frequency noise does not increase.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a waveform diagram showing signal waveforms of respective parts of the apparatus of FIG.

FIG. 3 is a characteristic diagram showing a characteristic curve in a sync amplifier circuit that constitutes the device of FIG.

FIG. 4 is a characteristic diagram showing a characteristic curve in a broken line conversion circuit which constitutes the device of FIG.

5 is a circuit diagram showing in detail a sync amplifier circuit that constitutes the device of FIG.

FIG. 6 is a circuit diagram showing in detail a polygonal line conversion circuit which constitutes the device of FIG.

FIG. 7 is a block diagram showing a conventional video tape recorder reproducing apparatus.

[Explanation of symbols]

 13 Pedestal clamp circuit 14 Sink amplifier circuit 16 Broken line conversion circuit

Claims (1)

[Claims] 1. A brightness processing circuit of a video tape recorder reproducing apparatus for processing a brightness signal of a video signal reproduced and demodulated from a magnetic tape, and a pedestal clamp circuit for fixing the pedestal level of the brightness signal to a constant level, and the pedestal level. The horizontal sync signal and the black signal of the luminance signal, which is fixed to a constant level, are expanded and the white signal is compressed to obtain the sync amplified luminance signal. A brightness processing circuit for a video tape recorder reproducing apparatus, comprising: a polygonal line conversion circuit for changing a level to a higher level and a black level to a lower level.