JPS6240900B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of transmitting a sub-scanning line density control signal in a facsimile apparatus.

In order to perform facsimile transmission more efficiently and in a shorter time, a sub-scanning line density control signal is sent together with the image signal for each scanning line or when converting a line containing information to a line not containing information, and is transmitted in the sub-scanning direction. There is a method of changing the line density according to the image signal, and this method has been implemented in both digital facsimile devices and analog facsimile devices, but analog facsimile devices will be described here.

That is, information (black signals) does not necessarily exist in all scanned lines of a transmission document, and there are blank spaces between lines of text, and there are large characters and small characters. Therefore, if small characters are scanned closely, large characters are scanned coarsely, and margins between lines are skipped, the overall transmission time will be shortened and the quality of the transmitted copy will not be compromised too much. Never. Therefore, the sending side scans and discriminates the transmitted document line by line, changes the reading speed itself, and sends a control signal indicating what linear density the receiving side should record. If recording is performed based on such a control signal, the transmission time can be shortened.

By the way, in order to shorten the transmission time, it is necessary to solve the problems of when to transmit the control signal and how to reliably transmit and receive the control signal. Therefore, the object of the present invention is to
It is an object of the present invention to provide a method for reliably transmitting and receiving a control signal for changing the linear density on the receiving side in accordance with an image signal obtained by scanning the linear density in the sub-scanning direction on the transmitting side.

In the present invention, first, the transmitter transmits the signal for controlling the linear density on the receiving side during the phase signal time between the image signal of one line and the image signal of the next line. suggest.

In facsimile transmission, as shown in Fig. 1, there is a phase signal time interval t2 between one line of image signal t1 and the next line of image signal t1, and one line of image signal including this time interval t2 is transmitted. If the time required for transmission is to=t1+t2, t2/to is
Approximately 0.06 is common, and International
Telegram, Telegaph and Telephone
This value is also stated in Recommendation T.3 for G equipment of the Consultative Committee (hereinafter referred to as CCITT).
It is set as 0.04 to 0.06. By the way, to=
At a transmission speed of 100 ms, that is, when the drum rotation speed is about 600 rpm, if the control signal transmission time is set to t2 only,
It is easy to make errors in determining the signal.

For example, in CCITT/G mode, the modulation method is
AM-PM-VSB, cylinder rotation speed is 360 rpm with white feed
(6rps), to = 1/6 second = 166.6ms t2 = 0.04to ~ 0.06to = 6.66 ~ 9.99ms, and if you try to detect it using an analog method such as a filter on the receiving side, there will be a problem with the response speed of the filter. It is difficult to reliably detect the control signal at time t2. Furthermore, with the same modulation method as above,
At 600 rpm (10 rps), to = 1/10 seconds = 100 ms t2 = 4 to 6 ms, which makes it even more difficult.

Therefore, it is clear that the control signal can be transmitted and received more reliably by making the width of t2 two to three times as long and reducing the image signal transmission time t1 to some extent. Therefore, in the present invention, the above-mentioned time t2 is further utilized as a time for transmitting the control signal, and the image signal transmitting time is compressed to make the time t2 longer than usual, thereby improving the reliability of control signal transmission and reception. .

In the above example, actually increase the frequency of the image signal by 5%.
In other words, t2=0.05to is doubled and t2=
If 0.1to, the image signal sending time t1 is t1=
The time was reduced from 0.95to to t1 = 0.90to, but the deterioration in image quality was only about 5%, making it possible to more reliably improve the transmission and reception of control signals without significantly affecting image quality. .

Furthermore, in the CCITT/G mode described above, when the modulation method is AM-PM-VSB, synchronous detection is required. In synchronous detection, it is necessary to accurately capture the zero-crossing point of the input signal, and for this purpose, a phase difference detector (Phase
Detector) and low pass filter (Low Pass
Filter) and voltage controlled oscillator (Voltage Controlled
A phase-locked loop circuit (Phase-Locked Loop Circuit) is used. As is well known, this phase-locked loop circuit operates to follow the frequency and phase of the voltage controlled oscillator with the carrier wave transmitted during the time t2 as a target. Therefore, according to the present invention, if only the control signal having a frequency other than the carrier wave is transmitted during time t2 and the carrier wave is not transmitted, the phase-locked loop circuit (PLL) loses its target and goes out of the lock state. Deterioration of image quality occurs. For this reason, it is desirable to maintain the locked state by leaving the carrier wave at the same time when transmitting the control signal. Therefore, the present invention further proposes that the carrier wave component remains at the time t2 when the control signal is sent out to prevent synchronization of the receiving side phase-locked loop (PLL).

FIG. 2 shows the transmission waveform of normal white feed, and when there is a carrier, it corresponds to white or a phase signal, and when there is no carrier, it corresponds to black. In FIG. 2, a black line is sent out as an image signal, and carrier 1 is sent out as a phase signal. This second
The figure does not describe the sending of control signals. In FIG. 3, the control signal 2 of the invention is sent out during the phase signal period. Furthermore, the phase signal indicated by 3 remains without being completely removed. Although signals 2 and 3 are drawn separately due to difficulty in illustration, they are actually combined.

The method of the present invention proposed above can be easily implemented by preparing a known common sense circuit.

An example of an apparatus for carrying out the invention is shown in FIG.

The transmission document D is scanned by the scanner 4, and the switch 9 is switched by a known computer or other control circuit 8 for each scanned line, so that the shift register 5 or 6 is scanned.
An image signal for one line is stored in memory. That is, in FIG. 4, since the shift register 5 is being read out, the image signal is input to the shift register 6. On the other hand, the image signal for each line, that is, the image signal input to the shift register 6, is input to the line density determination circuit 7. This line density determination circuit 7 half-discriminates whether black information exists in one scanned line, and the determination result is input to the control circuit 8 and stored in memory. This determination result is sent to the receiving side as a control signal after the readout of the shift register 5 is completed, and according to the control signal, the shift is made at a short time when there is no black information, and a long time when there is black information. The image signal is read from the register 6. For this reason, the control circuit 8, in accordance with the discrimination information of the density of the linear density,
The clock 11 or 12 is controlled to change the frequency, set the readout time of the shift register 5 or 6, and switch 10 to output a predetermined image signal via the modulation circuit 13. Further, after one line of image signals is read out from the shift register 5 within a predetermined time, the next one line of image signals is transmitted from the shift register 6, that is, during time t2 in FIG. On the receiving side, a control signal indicating at what linear density recording is to be performed is sent. Therefore, in order to send out a control signal, the control circuit 8 turns off the switch 14 and turns on the switch 15, and transmits the carrier wave 18 having an amplitude determined by the voltage +VC divided by the resistors R1 and R2 to the modulation circuit. It outputs f1 via 13. Further, the control signal generation circuit 16 outputs a line density control signal f2 according to the determined line density of one line. These outputs f1 and f2 are combined by an adder circuit 17 and output as a combined waveform to the receiving side. As a result, a carrier wave whose amplitude is suppressed by resistors R1 and R2 will be present in the output signal. Of course, it is also possible to set the resistor R2 to 0 in the above circuit, but it must be taken into consideration that the combined waveform of the carrier frequency and the control signal will become large, which may adversely affect the telephone line. Also, resistance R2
As mentioned above, it is undesirable to set the control signal to zero and send out only the control signal without the presence of any carrier wave in a modulation system that requires a phase synchronization circuit.

As described above, in the present invention, the phase signal transmission time between the image signal of one line and the image signal of the next line is lengthened to the extent that the image signal does not deteriorate, and the sub-scanning line density control signal is transmitted throughout the period. Since the control signal that changes the linear density in the sub-scanning direction according to the image signal can be reliably transmitted and received, the carrier wave remains even while the control signal is being transmitted, so the phase synchronization of the receiver can be improved. The circuit can maintain a locked state and has the advantage of being able to send and receive image signals in good condition.

Although the present invention has been illustrated and described with reference to more preferred embodiments, it should be understood that improvements and changes that can be easily made by those having ordinary knowledge in this field do not depart from the spirit of the present invention. be. Therefore, the invention is not limited to the particular embodiments shown and described above.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing control signal sending time, Figure 2 is an explanatory diagram showing the control signal sending time.
3 is a diagram showing a normal carrier waveform, FIG. 3 is a diagram showing a waveform component when sending a control signal, and FIG. 4 is a circuit diagram showing an example of implementing the method of the present invention. t1...One line of image signal, t2...Time interval between one line of image signal and the next one line of image signal, to...Time required to transmit one line of image signal, 2... ...control signal, 3...residual component of carrier.

Claims (1)

[Claims] The phase signal transmission period between the image signal of one line and the image signal of the next line is lengthened to the extent that the image signal does not deteriorate, and the sub-scanning line density of each line is increased throughout the above-mentioned transmission period. A control signal transmission method in a facsimile machine, characterized in that control signals are transmitted respectively, and a carrier wave component is left at the time of transmitting the control signal, and the carrier wave component is transmitted as a composite waveform with the control signal. 2. The method according to claim 1, wherein the range in which the image signal is not degraded is to compress the image signal transmission period by 5%.