JPH033585A - Television telephone set - Google Patents

Abstract

PURPOSE:To attain simultaneous transmission of an audio signal and a picture by outputting 3 periods of signal waveform having a phase and an amplitude corresponding to each picture element, limiting a band of a picture signal modulated to 1/3 and sending the result together with an audio signal. CONSTITUTION:Three periods of signal waveforms of a prescribed frequency having a phase and an amplitude corresponding to each picture element is outputted by a picture modulation section 23 to modulate the picture signal. Thus, the frequency band required for the transmission of the picture signal is decreased to 1/3, and a picture signal whose frequency band is limited to 1/3 by a picture transmission filter 24 is synthesized together with an audio signal whose frequency band is cut off in the picture signal by a transmission filter 27, sent to a telephone line and sent to a receiver side. Thus, the audio signal band is kept wide and the picture signal and the audio signal are sent simultaneously.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Applications] The present invention relates to a video telephone device that transmits and receives images and sounds using a telephone line, and particularly relates to the simultaneous transmission and reception of images and sounds.

[Conventional technology]

Conventionally, images and sounds are transmitted and received using telephone lines, for example, P.
There was a still image video telephone device as shown in 28-P.35. FIG. 6 is a configuration diagram of such a videophone device, in which (1) is the videophone device on the sending side, (2) is the videophone device on the receiving side, and (3) is the videophone device that receives image signals from a television camera, etc. An image sending unit (4) that modulates and sends out an image signal, (4) a control unit that controls sending out an image signal (7) from the image sending unit (3) in response to a transmission trigger (6) from a transmission switch (5), (8) is a transmitting unit that sends out an audio signal (9), and (10) is an audio signal (
(12) is the telephone line (13)
The signals sent to the above image signal (7) and audio signal (9)
An audio/image switching section (engineering section 4) which temporally switches between the telephone line (13) and the receiver section (17) receives the output light of the line signal (15) received from the telephone line (13) and receives the audio signal (16);
An audio/image switching unit (20) controls the audio/image switching unit (14) based on the line signal (15), and an image receiving unit (19) that receives and demodulates the image signal (18). (21) is a transmitter.

In the videophone device having such a configuration, the transmitter section (8) of the videophone device (1) (2) on the image sending side and the image receiving side is
) (21), and the receiver (10) (21)
A telephone call is made by transmitting and receiving voice signals using the .

When transmitting an image signal, the transmission trigger (6) is input to the control unit (4) by pressing the transmission switch (5),
An image signal (7) is output from the image sending section (3). At the same time, the audio/image switching unit (12) is switched to the image signal (7) side, and the image signal is sent out as a line signal (15).

On the receiving side, the control unit (20) identifies the image signal from the line signal (15), and the control signal (22) causes the audio/image switching unit (14) to send the signal to the image receiving unit (19). The received signal, that is, the image signal, is sent to the image receiving unit (
19) and the image signal is demodulated.

Here, modulation and demodulation of image signals by the image sending section (3) and image receiving section (19) will be explained. In this device, an amplitude phase modulation method is used as a modulation method for image signals, and an example in which the pixel has 16 gradations will be described here. FIG. 7 shows this relationship between pixel gradation and output waveform. In other words, two phases with a phase difference of 180" and amplitude values set in 8 stages are prepared for each, and each waveform consisting of each combination is divided into 1 from black to white.
It corresponds to 6 gradation levels. Then, the image signal is modulated by transmitting a waveform signal corresponding to the gradation level of each pixel of the transmitted image at a predetermined carrier frequency. At this time, one pixel gradation level is represented by one cycle of the carrier frequency waveform.

For example, as shown in FIG.
One cycle of waveform with maximum amplitude in phase (hereinafter referred to as S waveform)
corresponds to "white", and each waveform between them corresponds to gray from "black" to "white".

Here, such a phase amplitude modulation method is used as a modulation method for an image signal, and the occupied frequency bands for each of the image signal (7) and the audio signal (9) are determined when the image signal (7) and the audio signal (9) are switched and transmitted and received as described above.

First, the band of the voice signal is equal to the band of the line signal (15) transmitted over the telephone line (13), as shown in FIG. 8(a). That is, the frequency is between the upper limit frequency f2 and the lower limit f1. On the other hand, regarding the band of image signal (7),
The frequency band is thought to be widest when the modulated image signal (7) changes most drastically, that is, when the P waveform and S waveform are alternately repeated as shown in FIG. The distribution of the spectrum when
Shown in Figure (b). As shown in FIG. 8(b), the frequency band of the image signal is such that each pixel is connected to one carrier wave as described above.
If it corresponds to the cycle, the carrier frequency f at the time of modulation
The band has a width of ±fc/2 around c.

[Problem to be solved by the invention]

As mentioned above, in conventional videophone devices, since the frequency bands of the image signal and the audio signal overlap, it is not possible to transmit both signals at the same time, and they must be communicated in a time-sharing manner, so it is not possible to make a voice call. There was a problem in that it was not possible to simultaneously transmit images. Furthermore, if the frequency bands of the audio signal and the image signal are separated and transmitted simultaneously, there is a problem that the reduction in the audio signal band for the frequency band of the image signal is large, making normal telephone communication difficult.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a video telephone device that can transmit images while making a voice call.

[Means to solve the problem]

The videophone device according to the present invention includes an image modulation section that modulates an image signal by outputting three cycles of a signal waveform of a predetermined transmission frequency having a phase and amplitude corresponding to each pixel of a transmitted image; A picture filter that filters the output signal of the image modulation section with a passband width of 173 of the frequency, and a speech filter that filters the audio signal with a band outside the passband of the picture filter as a passband. a transmitting unit that combines the output signal of the voice transmitting filter and the output signal of the picture transmitting filter and transmitting the synthesized signal to the telephone line; an image receiving filter that performs filtering; an image demodulation section that demodulates the output signal of the image receiving filter into an image signal; and a receiver that has the same passband as the transmitting filter and filters the signal received from the telephone line. It is equipped with a filter.

[Effect]

In this invention, the image signal is modulated by outputting three periods of a signal waveform of a predetermined carrier frequency having a phase and amplitude corresponding to each pixel by the image modulation section, so that the frequency required for transmitting the image signal is The image signal whose frequency band is limited to 173 by the transmitting filter is synthesized with the audio signal whose frequency band of the image signal has been cut off by the transmitting filter, and is sent to the telephone line and transmitted to the receiving side. Therefore, the audio signal band is kept wide and the image signal and audio signal are transmitted simultaneously.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
The figure is a configuration diagram of a videophone device according to the present invention.
1) (4) to (6), (8) to (11), (13
) (15), (17), (20) and (21) are similar to the above conventional example. (23) is a signal waveform having a phase and amplitude corresponding to each pixel of the transmitted image, that is, a carrier frequency corresponding to each gradation as shown in FIG.
an image modulation unit that performs amplitude phase modulation of the image signal by successively sending out three cycle signal waveforms; (24)
(25) is an image receiving filter that band-passes the output signal of the image modulation unit (23), (25) is an image-receiving filter that band-passes the signal received from the telephone port A11 (13), and (26)
is an image demodulating section that demodulates the signal output from the image receiving filter (25) into an image signal. Above image feed filter
(24) The passbands of the image receiving filter (25) are both set within the range of fc/6 around the carrier frequency fc in the image modulator (23), so the bandwidth is equal to the carrier frequency fc. The value is 173.

(27) (28) is a transmitter filter that limits the band of the audio signal from the transmitter (8) (21); (29)
(30) is a reception filter that cuts off the band of the signal from the telephone line (13) and outputs it to the reception units (10) and (17). These transmitter filters (27) (28),
The cutoff bands of the reception filters (29) and (30) all match the passband of the picture transmission filter (24). In other words, the image transmission filter (24) passes a band other than the band through which the image signal passes. (31) is a transmitting unit that combines the output signals of the image sending filter (24) and the speaking filter (27) and sends it to the telephone line, and (32) is a speech network that interfaces with the telephone line (13). . In FIG. 1, the transmitting side and the receiving side are shown as separate units connected via a telephone line (13), but FIG. 2 shows a system in which both are combined into one device. In this Figure 2, (33) is an amplifier that adjusts the level of the output of the reception filter (29), and (34)
1 is a speaker, (35) is a microphone, (36) is an amplifier that amplifies the output of this microphone (35), and (37) is an image processing unit that stores and reproduces image signals.

Next, the operation will be explained.

Image modulation is started in the image modulation section (23) by a transmission trigger from the transmission switch (5). As described above, this image signal modulation is such that for each pixel, a signal waveform having a phase and amplitude set corresponding to the gradation level of that pixel is continuously sent for three cycles. . For example, when "black" and "white" are alternately repeated one pixel at a time, the image signal after modulation is a 3-cycle P waveform and a 3-cycle P waveform.
This becomes a signal in which the S waveform of cycles continues alternately. The state of this waveform is shown in FIG. 3, where FIG. 3(a) shows an image signal in the case of the conventional device, and FIG. 3(b) shows an image signal in the case of the apparatus according to the present invention.

The image signal modulated in this way is passed through the image feed filter (24
) and is filtered, and its output is sent to the transmitter (31). The image sending filter (24) is a bandpass filter, and its characteristics are as shown in FIG. 4(a).
It has a characteristic of having a bandwidth of ±fc/6 centered around the carrier frequency fc, that is, a passband width of fc/3 as a whole.

On the other hand, the audio signal from the transmitter (8) is filtered through the transmitter filter.
(27), and its output is sent to the transmitter (31). This transmission filter (27) is a band elimination filter, and its characteristics are as shown in FIG. (2
It has a characteristic of having a pass band other than the pass band of 4).

The image signal and audio signal band-separated in this way are
It is input to the transmitter (31) and synthesized, and the line signal (15
) is transmitted over the telephone line (13). The signal band of this line signal (15) is shown in FIG. 5, and the carrier frequency f
It is shown that an image signal is transmitted in a band of fc/3 centered on c, and an audio signal is transmitted in other bands.

On the receiving side, this line signal (15) is input to a picture receiving filter (25) and a receiving filter (30).

The image receiving filter (25) has the same characteristics as the transmitting side as shown in FIG. The image is sent to the image demodulation section (26). And, contrary to the modulation,
Image demodulation is performed by extracting three consecutive cycles of signal waveforms as gradation information for one pixel.

On the other hand, the reception filter (30) has the characteristics shown in FIG.
7) and the audio is reproduced.

In this way, audio signals and image signals are transmitted simultaneously,
Moreover, the bandwidth of the image signal is 173 in the case of the above conventional device.
Therefore, the band for audio signals is not significantly reduced, and there is little deterioration in audio quality.

If the amount of information that can be sent per unit time, that is, the modulation speed, is increased, the transmission time for a given amount of image signals will be reduced, the band for image signal transmission will be expanded, and the image quality will be improved. As the area becomes narrower, the voice quality deteriorates. On the other hand, if the modulation speed is slowed down, the transmission time for a given amount of image signals will be longer (but the bandwidth required for image signal transmission will be smaller), so the audio signal bandwidth can be wider and the audio quality will be improved. do.

Generally, the carrier frequency fc when using a telephone line is 174
8Hz, but according to the present invention, 1 of the carrier frequency fc
73 is the modulation rate, the bands of each signal are: image signal band 1460-2040 Hz audio signal band 300-14 (i 0 Hz, 2040-3400
1(z). According to this band allocation, there is no major deterioration in both the image quality and the audio 1 quality, and it can be said that it is an optimal allocation.

Note that in the above embodiment, the audio signal is always passed through the transmitting filter.
(27) shows a configuration in which the signal passes through the reception filter (29), but if images are not to be transmitted, the configuration is such that the entire band of the line signal is used for voice signal transmission without passing through each filter. This will improve the audio quality when the image signal is not transmitted.

〔Effect of the invention〕

As described above, according to the present invention, the image signal is modulated by outputting three periods of a signal waveform having a phase and amplitude corresponding to each pixel, and the band of the image signal is increased to 17.
3 and transmitted together with the audio signal with the band for the image signal cut off, it is possible to simultaneously transmit the image signal and the audio signal without significantly reducing the band for the audio signal. This has the effect of providing a videophone device that can simultaneously transmit audio and images without significantly deteriorating audio quality.

[Brief explanation of drawings]

1 and 2 are block diagrams of a video telephone device according to an embodiment of the present invention, FIG. 3 is a waveform diagram showing an example of a modulated image signal waveform in the device, and FIG. 4 is a picture feed filter of this device. FIG. 5 is an explanatory diagram showing the signal band distribution state of the line signal output from this device, FIG. 6 is a configuration diagram of a conventional video telephone device, and FIG. 7 is a characteristic diagram showing the characteristics of the transmitting filter. An explanatory diagram showing the relationship between the gradation level of a pixel and a modulated signal waveform, FIG. 8 is an explanatory diagram showing the bands of audio signals and image signals in the above-mentioned conventional device, and FIG. 9 is an example of the modulated image signal waveform in the above-mentioned conventional device. FIG. In the figure, (4) is a control unit, (8) is a transmitting unit, and (10) is a control unit.
) is the receiver part, (13) is the telephone line, (15) is the line signal, (17) is the receiver part, (20) is the control part, (21) is the receiver part, (23) is the image modulation part, (24 ) is the image sending filter, (25) is the image receiving filter, (26) is the image demodulation section, (
27), (28) are transmitting filters, (29), (30)
(31) is a receiving filter, and (31) is a transmitter. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] An image modulation unit that modulates an image signal by outputting three cycles of a signal waveform of a predetermined carrier frequency having a phase and amplitude corresponding to each pixel of the transmitted image, and a pass band that uses a value of 1/3 of the carrier frequency. A video transmission filter that filters the output signal of the image modulation section as a width, a transmission filter that filters the audio signal using a band other than the passband of the video transmission filter as a passband, and an output signal of the transmission filter. and a transmitter that synthesizes the output signals of the picture sending filter and sends it to the telephone line; and a picture receiving filter that has the same passband as the picture sending filter and filters the signal received from the telephone line; It is characterized by comprising an image demodulation section that demodulates the output signal of the image reception filter into an image signal, and a reception filter that has the same passband as the transmission filter and filters the signal received from the telephone line. videophone device.