JPS6240899B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a facsimile transmission system using a 3-level AM system or a 2-phase AM-PM system, and is particularly equipped with white feed and black feed functions, and both functions are controlled according to the state of the image signal. This invention relates to a switchable facsimile transmission system.

There are two types of facsimile transmission systems in which the reception detection waveform is a three-level signal: the three-level AM system and the two-phase AM-
There is a PM method. The ternary AM method is a method in which the binary image signal shown in FIG. 1a is converted into ternary signals as shown in FIG. On the other hand, two-phase AM-
The PM method is a method that changes the carrier phase by π for each black signal or white signal, and uses both amplitude modulation and phase modulation.

By the way, in these transmission methods, since most of the surface of the document to be sent in a facsimile is usually "white" and some thin "black" lines are included, the image signal is transmitted using so-called "white feed". Often transmitted.
White feed means that the black signal is always at the "0" level, and the polarity of the white signal alternately changes to + and -, as shown in Figure 1b. In a conventional manner, this is achieved by inverting the original signal and then applying the ternary AM or two-phase AM-PM described above. As is well known, in this white feed, it is possible to reproduce the "black" thin line, which is the information to be transmitted, without being lost due to the band limitation of the transmission path. In addition, two-phase
The AM-PM method and the carrier-suppressed ternary AM method (which is equivalent to the two-phase AM-PM method) also have advantages such as easy extraction of carrier waves for demodulation for coherent detection.

However, it is clear that white feeding is completely disadvantageous when the transmitted document is a negative image or is mostly "black". That is, in this case, the "white" thin line that is information tends to disappear due to band limitation, and it becomes difficult to extract a carrier wave for demodulation in the case of coherent detection. Therefore, in such a case, as shown in Figure 1c, the white signal of the received detection waveform is always at the "0" level, and the black signal is a "black feed" in which the polarity alternately changes to + and -. ” is desirable.

The present invention has been made in view of the above circumstances.
When transmitting an image signal using the value AM method or the two-phase AM-PM method, it is possible to switch between white feed operation and black feed operation depending on whether there are many white signals or many black signals in the image signal. By making it easy for the receiving side to determine whether it is a forward or black feed, there is less loss of information due to band limitation, and even when no carrier is sent out, it is possible to extract carrier waves for demodulation for synchronous detection. The purpose of the present invention is to provide a facsimile transmission system that can facilitate the transmission of information.

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

FIG. 2 is a block diagram of a facsimile device showing an embodiment in which the present invention is applied to a ternary AM system, where A is the transmitting side and B is the receiving side. At the sending side A , 1
is a photoelectric conversion unit that scans the surface of a document and obtains a binary image signal of high level (hereinafter referred to as "H" level) for black areas and low level (hereinafter referred to as "L" level) for white areas. 2 is an inverter that inverts this image signal, and 3 is a switch that selectively takes out the image signal inverted by the inverter 2 and the image signal that is not inverted.The image signal selected by this switch 3 is a binary/3-value signal. After being converted into a ternary signal by the value conversion circuit 4, it is sent to a modulation circuit 5 and a transmission bandpass filter 6.
(for example, a VSB filter) and sent to the transmission line 7. The modulation circuit 5 performs AM modulation on the carrier wave of frequency c, which is the output of the sine wave oscillation circuit 8, using the output of the binary/ternary conversion circuit 4.

Here, the switch 3 is normally switched to the upper side, and the image signal inverted by the inverter 2 is supplied to the binary/ternary value conversion circuit 4, so that white feeding is performed. If the document has many black parts, by switching the switch 3 to the lower side, the image signal from the photoelectric conversion section 1 is supplied to the binary/three-value conversion circuit 4 as it is, so it is possible to perform black feeding. can. In this case, it is necessary to send to the receiving side a discrimination signal indicating whether it is white feed or black feed, that is, information indicating whether the image signal is inverted or not. In this embodiment, two types of activation signals having different frequencies are used as this discrimination signal. That is, in facsimile, normally the transmitting side A transmits a carrier wave of frequency c from the oscillation circuit 8 for a certain period of time to start the receiving side B , but in this embodiment, the sine-shaped oscillation circuit 9 of frequency c' and the oscillation circuit are separately transmitted. By providing a switch 10 linked to the switch 3 for selectively taking out the outputs of 8 and 9, a start signal of frequency c is sent out for white feed, and a start signal of frequency c' is sent out for black feed. to be sent.

Next, the receiving side B will be explained. 11 is a reception bandpass filter, the output of which is sent to the demodulation circuit 12
is led to the ternary/binary conversion circuit 13 via the third
As shown in FIG. 4 and FIG. 4, the signal is converted from three values to two values by zero cross detection, and is also applied to the tuning circuits 14 and 15 of tuning frequencies c and c'.
The outputs of the tuning circuits 14 and 15 are combined by a NOR circuit 16 and guided to a start-up control circuit (not shown), and the output of the tuning circuit 15 is further applied to a set terminal S of a flip-flop circuit 17. The flip-flop circuit 17 is provided to be reset by the transmission end signal, and its Q output is applied to the NAND circuit 18 together with the output of the ternary/binary conversion circuit 13, and the output is the output of the ternary/binary conversion circuit 13. is applied to the NAND circuit 20 together with a signal inverted by the inverter 19. And NAND circuits 19, 20
The output is led to the recording section 22 via the NOR circuit 21.

3 and 4 are waveform diagrams of various parts on the receiving side B. FIG. 3 is an example of white feed, and FIG. 4 is an example of black feed. In FIGS. 3 and 4, a is the demodulation circuit 12, b is the ternary/binary conversion circuit 13, c is the NAND circuit 20, and d is the NAND circuit 1.
8 and e indicate each output waveform of the NOR circuit 21. That is, in the case of white feed, since no output is generated in the tuning circuit 15, the Q output of the flip-flop circuit 17 is kept at the "L" level and the output is kept at the "H" level. Therefore, the output of the NAND circuit 18 is always at the "H" level, but the output of the NAND circuit 20 is a "black" and "L" level signal.
A “black” and “H” level signal is supplied from the NOR circuit 21 to the recording unit 22 . On the other hand, in the case of black feed, the flip-flop circuit 17 is set by the output of the tuning circuit 15, and its Q output becomes "H" level and its output becomes "L" level, so conversely, the output of the NAND circuit 20 is always " Since a "black" and "L" level signal is obtained at the output of the NAND circuit 18, a "black" and "H" level signal is similarly supplied to the recording section 22 from the NOR circuit 21. That will happen.

In this way, according to the present invention, both the white feed and black feed functions are provided on the sending side, and when the original has a lot of white parts as usual, the white feed is performed, and when the original has many black parts like a negative image, the white feed is performed. Since black feed can be performed when there are many white areas, fine black lines in the document surface with many white areas or thin white lines in the original with many black areas can be moved as shown in Figures 3a and 4a, respectively. Since the signal is located at the center level of the ternary signal of the detected waveform on the receiving side, it will not disappear even if the band is limited and can be reproduced without fail. Furthermore, even in transmission systems that do not send carrier waves from the transmitting side, there is no possibility that the signal does not exist for a long period of time, for example, one scanning period.
It has the advantage that it can be extracted relatively easily without using complicated circuits such as lock loops. In addition, by switching the frequency of the activation signal transmitted at the start of transmission, the receiving side can determine whether to send white or black.
Not only can the transmission cost be saved compared to a method of transmitting a dedicated discrimination signal, but also the processing corresponding to white feed and black feed can be performed immediately after receiving the start signal, and the recording operation can be started.

[Brief explanation of the drawing]

FIG. 1 is a waveform diagram of an image signal for explaining white feed and black feed in facsimile transmission, FIG. 2 is a circuit configuration diagram of a facsimile transmission and reception device according to an embodiment of the present invention, and FIGS. The figure is a waveform diagram of each part for explaining the operation of FIG. 2. A : Sending side, B : Receiving side, 3, 10: White feed/black feed selection switch.

Claims (1)

[Claims] 1. By performing binary-to-ternary conversion of a binary black-and-white image signal on the receiving side using a three-value AM method or a two-phase AM-PM method, one signal of the black-and-white image signal is at zero level and the other is at zero level. After converting the signal into a 3-value signal whose polarity changes alternately between positive and negative, this 3-value signal is transmitted via a transmission line with a band-limiting effect, and on the receiving side, the received detected waveform is converted into 3-value signals by zero-cross detection. - In a facsimile transmission method in which the black and white binary image signal is restored by performing binary conversion, the sending side includes means for inverting the black and white binary image signal, and an image signal inverted by the means and an inverter. and a selection means for selectively extracting the image signal that is not converted, and the means converts the selected image signal into two values and three values and transmits it, and also indicates whether or not this image signal is an inverted image signal. means for transmitting discrimination information and inverting the binary signal obtained by the ternary-to-binary conversion to the receiving side; and selectively selecting the inverted signal and the non-inverted signal by this means based on the information. 1. A facsimile transmission system comprising means for obtaining a restored black and white binary image signal. 2. The discrimination information is an activation signal that is transmitted at different frequencies depending on whether the selection means takes out an inverted image signal or a non-inverted image signal. 1
Facsimile transmission method described in section.