JPH0451674A - Video signal dc component reproducing device - Google Patents

Abstract

PURPOSE:To obtain a video signal with a correct DC component with few errors by removing the error of the DC component of the video signal clamped once from the video signal with no DC component by a clamp circuit by using an error detection circuit and an error subtraction circuit. CONSTITUTION:The subject device is constituted of the clamp circuit 30 to keep the DC component of the video signal at reference potential by a clamp pulse generated from a synchronizing signal in the inputted video signal, a quantizer 24 to quantize the clamped video signal, the error detection circuit 26 to compare a reference level and the DC component of the quantized video signal, and the error subtraction circuit 27 to remove a detected error value from the quantized video signal. Then, the error of the DC component of the video signal clamped once from the video signal with no DC component by the clamp circuit 30 is removed by the error detection circuit 26 and the error subtraction circuit 27. Thus, the video signal with the correct DC component with few errors can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a video signal DC component reproducing device for providing a constant DC component to a video signal that does not have a DC component in video signal equipment.

2. Description of the Related Art In recent years, video signal equipment has increasingly been used to quantize video signals and handle them as digital signals. When a video signal is quantized for recording, transmission, etc., high-efficiency encoding of the video signal is performed in order to efficiently record, transmit, etc. the video signal having a huge amount of information.

In high-efficiency encoding, the horizontal blanking period of a video signal may be deleted to compress the amount of information.

In such a case, a technique is required to reproduce a video signal having an accurate DC component with few errors from a video signal having no DC component.

An example of application of a conventional video signal DC component reproducing device to an HDTV transmission device will be described below with reference to the drawings.

FIG. 3 is a block diagram of an example of application to an HDTV transmission device using a conventional DC component regenerator, and FIG.
C) is a signal waveform diagram showing the operation. In Fig. 3, 1 is an amplifier, 2 is a clamp pulse generation circuit, 3 is a capacitance, 4 is a resistor, 5 is a switch, 4 and 6 are amplifiers, 7 is a reference potential generation circuit, 8 is a quantizer, and 9 is a horizontal block. A ranking period removal circuit, 10 an encoding device, 11 a transmitter of the transmission device, 12 a receiver of the transmission device, 13 a decoding device, 14 a horizontal blanking period synthesis circuit, and 15 a dequantizer. , 16 surrounded by dotted lines is a conventional DC component regenerator.

The operation of an example of application of the conventional video signal DC component reproducing device configured as described above to an HDTV transmission device will be described below.

First, the input HDTV signal that does not have a DC component is
It passes through amplifier 1 and is amplified. The amplified HDTV signal is divided into two parts, one of which is input to the capacitance 3 as it is, and the other is input to the clamp pulse generation circuit 2.
A ramp pulse like signal B in FIG. 4 is generated. When a clamp pulse is generated, switch 5 is closed only during the clamp pulse period in signal B of FIG. 5, and capacitance 3 is charged through resistor 4. By charging the quivacitance 3, the potential at point A becomes the reference potential ■. Fixed.

The HDTV signal at point A looks like signal A in FIG. The HDTV signal with a fixed DC level is processed by a quantizer 8.
After being inputted to and subjected to A/D conversion, it is inputted to a horizontal blanking period removal circuit 9, and after the horizontal blanking period is removed, it is inputted to an encoding device 10. The output signal of the encoding device flo, which encodes only the video signal period in the HDTV signal, is input to the transmitter 11 of the transmission device. transmitted by the transmitting device to the transmitting device receiver 12. The encoded HDTV signal is input to a decoding device 13 and decoded, and then input to a synchronization signal synthesis circuit 14 to synthesize a horizontal blanking period signal. The HDTV signal with the horizontal blanking period combined is D/A converted by the inverse quantizer 15 and reproduced into an analog 1 (DTV signal). (See "Television Textbook 2" edited by the Japan Broadcasting Corporation, published by the Japan Broadcasting Publishing Association, pages 135-135).

Problem to be Solved by the Invention However, in the above configuration, since the charging current of the capacitance 3 has a characteristic determined by the resistance 4 and the capacitance 3, the capacitance 3 cannot be completely charged during the clamp pulse period. This is represented by the length of the arrow in the signal A diagram in FIG. DC component error occurs. If the signal with this error is quantized, the horizontal blanking period is removed, and only the video signal period is encoded, the video signal period of the HDTV signal with the DC level error will be encoded as is. the encoded IID
The reproduced HDTV signal obtained by decoding the TV HDTV signal, combining the horizontal blanking period signals with a constant DC level, and dequantizing it will look like signal C in Figure 4, which is indicated by the arrow in the figure. Such a DC component error of ΔV occurs during the video signal period.

Once the error occurs, it cannot be removed again, and if the above-described processing is repeated, the error components will be accumulated one after another.

As described above, when the conventional DC component regeneration circuit is used, it is not possible to reproduce a complete DC component with few errors. In particular, when used for high-efficiency encoding in which the horizontal blanking period is removed, there is a problem in that the error component cannot be removed again.

In view of the above-mentioned problems, the present invention is a video signal DC component reproducing device that can remove errors in the DC component of the video signal that remain even after the video signal is clamped, and can stably reproduce a video signal with an accurate DC component. It provides:

Means for Solving the Problems In order to solve the above problems, the video signal DC component reproducing device of the present invention generates a clamp pulse from the synchronization signal in the input video signal, and uses the clamp pulse to reproduce the video signal. A clamp circuit that keeps the DC component at a reference potential, a quantizer that quantizes the clamped video signal,
It is comprised of an error detection circuit that detects an error that compares the DC component of the quantized video signal with a reference level, and an error subtraction circuit that removes the detected error value from the quantized video signal. This is a feature.

As described above, the present invention eliminates the error by using the error detection circuit and the error subtraction circuit to remove the DC component error of the video signal that has been clamped by the clamp circuit from the video signal that does not have a DC component. It is possible to realize a video signal with less accurate DC components.

In addition, if high-efficiency encoding is performed to remove the horizontal blanking period from the obtained video signal having accurate DC components with little error, the code for the video signal period in the video signal having accurate DC components is Even if they are combined and the horizontal blanking period is combined, a video signal with an accurate DC component can be reproduced, and it can be applied to accurate transmission and recording of video signals.

Embodiment Hereinafter, a video signal DC component reproducing apparatus according to an embodiment of the present invention will be described with reference to the drawings. First, FIG. 1 shows a block diagram of a DC component regeneration circuit in an embodiment of the present invention. FIGS. 2(a) to 2(e) are signal waveform diagrams showing the operation of a video signal DC component reproducing apparatus according to an embodiment of the present invention. In FIG. 1, 17 is an amplifier, 18 is a clamp pulse generation circuit, 19 is a capacitance, 20 is a resistor, 21 is a switch, 22 is an amplifier, 23 is a reference potential generation circuit, 24 is a quantizer, and 25 is a reference level generation circuit. ,2
6 is an error detection circuit, 27 is an error subtraction circuit, 28 is an error holding circuit, and the part surrounded by the dotted line 30 is a clamp circuit.
This is the same as a conventional video signal DC component reproducing device.

The operation of the video signal DC component reproducing apparatus configured as described above will be described below with reference to FIGS. 1 and 2.

Assume that the video signal to be handled is an HDTV signal.

The input HDTV signal does not have a DC component.

After the 1 (DTV signal) is amplified by the amplifier 17, it is divided into two parts, one of which is directly input to the capacitance 19, and the other is input to the clamp pulse generation circuit 18.The output signal of the clamp pulse generation circuit 18 is , as shown in Figure 4 E.The switch 21 is closed only during the clamp pulse period in Figure 4 E, and the reference potential v0 generated from the reference potential generation circuit is connected to the resistor 20.Switch 21 is closed, the capacitance 19 becomes the resistance 20
B in Figure 1 is charged by the charging current flowing through the
The potential at the point approaches the reference potential V0. However, since the potential at point B has a time constant determined by the values of capacitance 19 and resistance 20, the potential at point B is completely equal to the reference potential V during the clamp pulse period. cannot match. The HDTV signal waveform diagram at point B is shown in the second diagram.
It is shown like a figure number. The part of the HDTV signal where the signal is clamped is the part where there is no signal between the synchronization signal and the video signal indicated by the arrow in the figure, and has a DC component error represented by the length of the arrow. The above is the same as the conventional example.

The clamped 1 (DTV signal) is input to an amplifier 22, amplified again, and then input to a quantizer 24 where it is quantized.The quantized HDTV signal is divided into two parts, one of which has an error One signal is input to the detection circuit 26, and the other is input to the error subtraction circuit 27.

The reference level signal outputted from the reference level generating circuit 25 is input to the error detection circuit 26, and is compared with the quantized HDTV signal. The clamp pulse, which is the output of the clamp pulse generation circuit 18, is generated by the delay element 29.
The signal is input to the error detection circuit 25 through the. The timing at which the clamp pulse is input to the error detection circuit 25 is adjusted to match the timing at which the clamped portion of the quantized HDTV signal is input from the quantizer 25 to the error detection circuit 26. .

The output signal of the error detection circuit 26 is the difference between the quantized value of the clamped portion of the HDTV signal and the quantized value of the reference potential, that is, the error value of the DC component of the HDTV signal is determined by the period of the clamp pulse. Output. The output signal of the error detection circuit is as shown in Figure 4, symbol F.

By manually inputting the output signal of the error detection circuit 26 to the error holding circuit 28, a signal as shown in figure 4 symbol 6 is output. The signal G is a quantized error value generated in the period of the clamp pulse, which is held for a period of one thousand hours and output. The signal G is input to the error subtraction circuit 27, and the quantizer 2
The quantized [D
By subtracting from the TV signal, a quantized HDTV signal from which error values have been removed is output from the error subtraction circuit 27.

When the output signal of the error subtraction circuit 27 is subjected to inverse quantization,
Accurate HD with little error in the DC component of the signal
It becomes a TV signal. Further, since the output signal of the error subtraction circuit 27 does not have an error in the DC component, after removing the horizontal blanking period, only the video signal period is encoded and transmitted, and then decoded to the reference potential V. Even if a horizontal blanking period with a DC component fixed to is synthesized and dequantized, an accurate HDTV signal with little error in the DC component can be reproduced.

Effects of the Invention As described above, the present invention uses an error detection circuit and an error subtraction circuit to remove the error in the DC component of a video signal once clamped by a clamp circuit from a video signal that does not have a DC component. It is possible to realize a video signal having accurate DC components with less noise.

In addition, if high-efficiency encoding is performed to remove the horizontal blanking period from the obtained video signal having accurate DC components with little error, the code for the video signal period in the video signal having accurate DC components is Even if it is decoded and the horizontal blanking period is combined, a video signal with accurate DC components can be reproduced, and it can be applied to accurate transmission and recording of video signals. As mentioned above, its industrial value is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a video signal DC component reproducing device according to an embodiment of the present invention, FIG. 2 is a signal waveform diagram showing the operation of the video signal DC component reproducing device according to an embodiment of the present invention, and FIG. 3 is a block diagram of a video signal DC component reproducing device according to an embodiment of the present invention. I (IIT) using a conventional video signal DC component reproducing device
The fourth block diagram of an application example to an I/transmission device is a signal waveform diagram showing the operation of an application example to an HDTV transmission device using a conventional video signal DC component reproducing device. 1...Amplifier, 2...Clamp pulse generation circuit, 3...Capacitance, 4...
...Resistor, 5...Switch, 6...Amplifier, 7...Reference potential generation circuit, 8...
・Quantizer, 9...Horizontal blanking period separation circuit, 10...Encoding device, 11...
Transmission device transmitter, 12...Transmission device receiver, 1
3...Decoding device, I4...Horizontal blanking synthesis circuit, 15...Dequantizer, 16
...... Conventional video signal flow component reproducing device, 17.
...Amplifier, 18...Clamp pulse generation circuit, 19...Capacitance, 20...
...Resistance, 21...Switch, 22...
...Amplifier, 23...Reference potential generation circuit, 24
...Quantizer, 25...Reference level generation circuit, 26...Error detection circuit, 27...
...Error subtraction circuit, 28...Error holding circuit, 2
9... Delay element, 30... Clamp circuit.

Claims (1)

[Claims] A clamp circuit generates a clamp pulse from a periodic signal in an input video signal that does not have a DC component, and uses the clamp pulse to maintain the DC component of the video signal at a reference potential, and quantizes the clamped video signal. a quantizer; an error detection circuit that detects an error by comparing a DC component of the quantized video signal with a reference level; and an error subtraction circuit that removes the detected error value from the quantized video signal. A video signal DC component reproducing device comprising: