JP2511481B2 - Image communication device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image communication apparatus having an encoding unit for highly efficiently encoding a video signal. High-efficiency coding is also called band compression coding, and is typically predictive coding.

[Conventional technology]

Conventionally, this type of image communication device has an encoding unit that encodes a video signal with high efficiency and sends the data to the transmission line at a transmission speed required from the transmission line. The video signal is output by an input device (for example, a video camera or a frame synchronizer). Since the output signal of this input device is output independently of the transmission line clock from the transmission line, the transmission line clock from the transmission line and the output of the input device are generally not synchronized. In terms of image quality, the encoding unit performs encoding with a sampling clock that is synchronized with the output of the input device, so that the sampling clock is asynchronous with the transmission line clock from the transmission line.

[Problems to be solved by the invention]

As described above, in the conventional method, the transmission line clock from the transmission line and the sampling clock are asynchronous. Therefore, in the image communication apparatus, the encoding unit as the transmission unit has a function of transmitting the frequency information of the sampling clock for digitizing the video signal to the decoding unit as the reception unit.
The decoding unit as the receiving unit is required to have a function of reproducing the sampling clock based on the frequency information received from the transmission line. Therefore, the circuit configuration becomes complicated.

An object of the present invention is to provide an image communication device having a simple circuit configuration.

[Means for solving problems]

According to the present invention, a black burst signal generation circuit for generating a black burst signal synchronized with a transmission path clock from a transmission path, and a video signal for outputting a video signal in which a video signal is superimposed in synchronization with the black burst signal. An output unit and a coding unit for high-efficiency coding the video signal with a sampling clock synchronized with a synchronization signal extracted from the video signal and outputting the coded signal to the transmission line at the speed of the transmission line clock. The video signal output by the video signal output means is synchronized with the transmission path clock, and the synchronization signal extracted from the video signal is synchronized with the transmission path clock. A featured image communication device is obtained.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention.
The transmission path clock a from the input terminal 1 is input to the encoding unit 2 and the black burst signal generation circuit 3. The black burst signal generation circuit 3 outputs the black burst signal b synchronized with the transmission path clock a to the television camera 4, and the television camera 4 synchronizes with the input black burst signal b to superimpose the video signal c on the video signal c. Output to the encoding unit 2. The encoding unit 2 encodes the video signal c with high efficiency and sends it to the output terminal 5 at the speed of the transmission path clock a.

Figure 2 shows the transmission line clock, the black burst signal,
And video signals are shown respectively.

FIG. 3 shows the configuration of the encoding unit 2. Video signal c is A /
It is input to the D converter 21 and the sync separator 22, and the sync separator 22 separates the sync signal d from the video signal c and outputs it to the sampling clock generator 23. The sampling clock generator 23 generates a sampling clock e (fundamental frequency is 14.318 MHz) which is in phase with the input synchronizing signal d and outputs it to the A / D converter 21. The A / D converter 21 converts the video signal c into a sampling clock e
Are converted into digital signals by the encoder 24
Output to. The encoder 24 performs high-efficiency coding, temporarily stores it in the buffer memory 25, reads it from the buffer memory 25 at the speed of the transmission path clock a, and sends it to the output terminal 5.

The configuration of the black burst signal generation circuit 3 will be described with reference to FIG. In this embodiment, the value of the transmission line clock a is 6.176 MHz.
It was set to the speed of.

The transmission line clock a is input to the first frequency divider 31 and divided by 779, and the phase comparator 32 is used as a 6.176 / 779 MHz clock signal.
Output to. On the other hand, the clock signal output from the voltage controlled oscillator 34 (same frequency as the sampling clock e in FIG. 3) is input to the second frequency divider 35, frequency-divided by 1806 and the phase comparator 32
Output to. The phase comparator 32 compares the phases of the two clock signals, outputs the phase difference to the low-pass filter 33, removes high-frequency components, and then adds the high-frequency component to the voltage-controlled oscillator 34 so that the oscillation frequency is (6.176 / 779) × Controlled to 1806MHz, second
To the frequency divider 35 and the black burst signal generator 36. The black burst signal generator 36 generates and outputs a black burst signal b synchronized with the transmission path clock a.

In the compounding unit (not shown) as the receiving unit, the 6.176 MHz clock signal extracted from the transmission line is input to the circuit having the same configuration as the black burst signal generation circuit 3 in FIG. A sampling clock synchronized with the transmission line clock is generated.

According to the present embodiment, the sampling clock frequency generated by the black burst signal generation circuit 3 causes a frequency error of 0.56 ppm with respect to the fundamental frequency, but this is not a problem when the frequency tolerance of each constituent device is taken into consideration. .

Further, in this embodiment, the sampling clock e synchronized with the video signal is generated by providing the voltage controlled oscillator (VCO) in the sampling clock generator 23. If incorporated in the generator 23, the voltage controlled oscillator can be omitted and the retracting time by the voltage controlled oscillator can be made zero.

〔The invention's effect〕

As described above, according to the present invention, since the encoding is performed with the sampling clock synchronized with the transmission path clock from the transmission path, the frequency information of the sampling clock, which was necessary for the encoding section as the transmission section, was received. Function to send to the decoding unit as
Since the function of regenerating the sampling clock based on the frequency information received from the transmission line, which is necessary for the decoding unit as the receiving unit, is no longer necessary, the scale of the hardware configuration of the circuit is reduced. Also, image data can be assigned to the time slot assigned to send the frequency information of the sampling clock, and there is an effect that much image information can be transmitted.

[Brief description of drawings]

FIG. 1 is a block diagram of an image communication apparatus according to an embodiment of the present invention, FIG. 2 is a diagram showing waveforms of respective parts of the image communication apparatus of FIG. 1, and FIGS. 3 and 4 are of FIG. 3 is a configuration block diagram of an encoding unit 2 and a black burst signal generation circuit 3. FIG. 1 is an input terminal, 2 is an encoding unit, 3 is a black burst signal generation circuit, 4 is a TV camera, 5 is an output terminal, 21 is an A / D converter, 2
2 is a sync separator, 23 is a sampling clock generator, 24 is an encoder,
25 is a buffer memory, 31 is a first frequency divider, 32 is a phase comparator, 33 is a low-pass filter, 34 is a voltage controlled oscillator, 35 is a second frequency divider, 36 is a black burst signal generator , a is a transmission line clock, b is a black burst signal, c is a video signal, d is a synchronization signal, and e is a sampling clock.

Claims (1)

(57) [Claims] 1. A black burst signal generation circuit for generating a black burst signal synchronized with a transmission path clock from a transmission path, and a video signal output for outputting a video signal in which a video signal is superimposed in synchronization with the black burst signal. Means for high-efficiency encoding the video signal with a sampling clock synchronized with a synchronization signal extracted from the video signal,
An encoding unit for outputting an encoded signal to the transmission line at the speed of the transmission line clock, the video signal output by the video signal output means is synchronized with the transmission line clock, and The image communication device, wherein the synchronization signal extracted from the video signal is synchronized with the transmission path clock.