JPH02214284A - Still picture communication equipment - Google Patents

Abstract

PURPOSE:To prevent phase shift and picture element deviation of a received picture due to interruption of reception with simple circuit constitution by devising the equipment such that a demodulation means is operated in the same timing as that before interruption even when the interruption of reception is caused. CONSTITUTION:When a modulation wave received at picture reception is interruption, a phase synchronizing circuit 30 outputs a signal of an indefinite frequency different from that of a conventional equipment to a synchronizing control circuit 32. When the synchronizing control circuit 32, however, detects the interruption of a received modulation wave, the signal is switched to an output synchronously with the phase synchronizing signal before the detection of interruption and the synchronizing signal in the same timing as that before interruption is fed to a demodulation circuit 28. When a received wave is detected again, the synchronizing control circuit 32 supplies the output of the phase synchronizing circuit 30 as it is or a signal synchronously with the output of the phase synchronizing circuit 30 to the demodulation circuit 28. Thus, even in the case of reception interruption due to line disconnection phase shift and picture element deviation of the received picture are prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a still image communication device, and more particularly, to a still image communication device that transmits and receives audio and still images via an analog telephone line.

[Prior Art] A still image video telephone is well known as an example of the above-mentioned device. The communication method for still image videophones has been standardized as the TTC standard, and according to this, communication control signals and image signals are modulated using a carrier wave amplitude phase modulation method of 1,747.82 Hz and transmitted over an analog line. do.

In the conventional example, when receiving such a modulated wave, the received modulated wave is input to a demodulation circuit 40 and a phase synchronization circuit 42 as shown in FIG. was formed, and the demodulation circuit 40 demodulated the received wave using the synchronization signal. FIG. 3 shows the relationship between the amplitude phase modulation image brightness signal and the carrier wave according to the TTC standard.

[Problems to be Solved by the Invention] In the above-mentioned conventional example, if the received wave is partially interrupted, the phase synchronization will be lost, and the phase of the received image may be reversed and the position of the image on the display screen may be shifted. there were. Such interruptions can occur, for example, when switching relay stations in a mobile phone.

Therefore, it is an object of the present invention to provide a still image communication device that does not cause such inconveniences.

[Means for Solving the Problems] A still image communication device according to the present invention detects the presence or absence of a received image signal modulated wave, and when a received wave is present, outputs a phase synchronized signal that is phase synchronized with the received wave. However, when the received wave is interrupted, a synchronizing signal forming means outputs a signal with the same timing as the phase synchronizing signal output before the interruption, and a demodulating means demodulating the received wave according to the output of the synchronizing signal forming means. It is characterized by comprising the following.

[Operation] With the above means, even if reception is interrupted, the demodulation means continues to operate at the same timing as before the interruption, and when reception is resumed, demodulation can be continued without causing phase shift or pixel shift.

[Example] Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention. However, since the audio processing part is well known and is not directly related to the present invention, only the image processing related part is shown.

In FIG. 1, 10 is an image input device that converts an optical image into an electrical image signal, 12 is an A/D converter that digitizes an analog image signal, 14 is an image memory that temporarily stores digital image signals, and 16 is an image input device that converts an optical image into an electrical image signal. An image memory control circuit controls writing and reading of the memory 14, 18 is a D/A converter that converts digital image signals into analogs, and 20 is an image display device that converts electrical image signals into optical images. 2
2 is a central control circuit that controls the entire system, and 24 is a modulation circuit that modulates a voice band carrier wave with a digital image signal to be transmitted and a communication control signal.

26 is a network control circuit that controls connection with the public telephone line;
8 is a received wave from the telephone line (specifically, the network control circuit 26
30 is a phase synchronization circuit that forms a synchronization signal that is phase-synchronized with the received wave; 32 is a demodulation circuit that demodulates the modulated wave from
When there is a received wave, the phase synchronization signal output from the phase synchronization circuit 30 is directly transmitted to the central control circuit 22 and the demodulation circuit 28.
This is a synchronization control circuit that supplies the demodulation circuit 28 and the central control circuit 22 with a signal synchronized with the phase synchronization signal that had been supplied from the phase synchronization circuit 30 when the received wave is interrupted. Such a synchronization control circuit 32, for example, uses a PLL circuit to form a signal synchronized with the phase synchronization signal output from the phase synchronization circuit 30 as an output signal to the demodulation circuit 28, and uses a detection circuit to detect the presence or absence of a received wave. This can be realized by controlling the opening/closing of the loop of the PLL circuit based on the detection result.

The operation shown in FIG. 1 will be briefly explained. The optical image of the user is converted into an electrical signal by the image input device 10 and converted into a digital image signal by the A/D converter 12 under the control of the central control circuit 22 . This digital image signal is written into the image memory 14 by the image memory control circuit 16 which receives a write command from the central control circuit 22.

When transmitting the image signal written in the image memory 14 in this manner, the central control circuit 22 first supplies the modulation circuit 24 with a communication control signal for establishing communication. The modulation circuit 24 amplitude-phase modulates the voice band carrier wave with the communication control signal, and the modulated wave is sent to the public telephone line via the network control circuit 26. Once the communication path is established, central control circuit 22 sends a read command to image memory control circuit 16 to read the digital image signal from image memory 14 and apply it to modulation circuit 24 . The modulation circuit 24 amplitude-phase modulates the carrier wave with the digital image signal. The modulated wave output from the modulation circuit 24 is sent out to an analog public telephone line via the network control circuit 26, and sent to a similar video telephone at the destination.

On the other hand, when receiving the above modulated wave, the network control circuit 26 first applies the modulated wave of the received communication control signal to the demodulation circuit 28, the phase synchronization circuit 30, and the synchronization control circuit 32. The phase synchronization circuit 30 forms a phase synchronization signal synchronized with the modulated wave of the communication control signal, and the phase synchronization signal is applied to the demodulation circuit 28 via the synchronization control circuit 32. The demodulation circuit 28 demodulates the modulated wave of the communication control signal using this phase synchronization signal and outputs it to the central control circuit 22. The central control circuit 22 enters the image reception mode by this communication control signal and prepares to receive image signals.

The modulated wave of the image signal is similarly demodulated by the demodulation circuit 28 and applied to the central control circuit 22. The central control circuit 22 sends a write command to the image memory control circuit 16 to cause the digital image signal from the demodulation circuit 28 to be written into the image memory 14 . The received image thus stored in the image memory 14 is displayed as an image on the image display device 20, as described above.

When the modulated wave to be received is interrupted during image reception, the phase synchronization circuit 30 outputs a signal with an undefined frequency to the synchronization control circuit 32, unlike in the past. However, when the synchronization control circuit 32 detects an interruption in the received modulated wave, it switches to outputting a signal synchronized with the phase synchronization signal before the interruption was detected, and supplies the demodulation circuit 28 with a synchronization signal at the same timing as before the interruption. When the received wave is detected again, the synchronization control circuit 32 supplies the output of the phase synchronization circuit 30 as is or a signal synchronized with the output of the phase synchronization circuit 30 to the demodulation circuit 28 . Thereby, even if reception is interrupted due to line interruption or the like, phase shift and pixel shift of the received image can be prevented.

In order to display the received image on the image display device 20, the central control circuit 22 applies a read command to the image memory control circuit 16 to read the digital image signal from the image memory 14. This digital image signal is sent to the D/A converter 18
is converted into an analog signal and supplied to the image display device 20. The image display device is, for example, a CRT or a liquid crystal device, and allows an image of the other party to be viewed. During this image display operation, normal voice communication is possible, and the central control circuit 22
switches from image reception mode to voice communication mode.

In the above embodiment, in order to facilitate comparison with the conventional example,
Although the output of the phase-locked circuit 30 having the same configuration as the conventional example is controlled by the synchronous control circuit 32, it is of course possible to realize the functions of the phase-locked circuit 30 and the functions of the synchronous control circuit 32 in one circuit. Needless to say.

[Effects of the Invention] As can be easily understood from the above description, according to the present invention, phase shift and pixel shift of a received image due to interruption of reception can be prevented with a simple circuit configuration.

[Brief explanation of the drawing]

Figure 1 is a block diagram of the configuration of an embodiment of the present invention, Figure 2 is a block diagram of the configuration of a conventional example, and Figure 3 is a diagram of the relationship between the luminance signal and carrier wave in the amplitude phase modulation method of the TTC standard. be. 10: Image human power device 12: A/D converter 14:
Image memory 16 Two image memory control circuits 18: D/
A converter 20: Image display device 22: Central control circuit
24: Modulation circuit 26: Network control circuit 28 2 Demodulation circuit 3
0: Phase synchronization circuit 32: Synchronization control circuit Fig. 1 Fig. 2

Claims (1)

[Claims] This is a still image communication device that can freely send and receive still images.It detects the presence or absence of a received image signal modulated wave, and when a received wave is present, outputs a phase synchronization signal that is phase-synchronized with the received wave. and a demodulating means for demodulating the received wave according to the output of the synchronizing signal forming means. A still image communication device characterized by.