System for coding information change picture elements in facsimile signal

Abstract

A system for coding information change picture elements in a facsimile signal, which is employed for coding the address of each information change picture element assuming information different from that of an immediately preceding picture element on each scanning line. A distance between the information change picture element and a final reference information change picture element selected from the information change picture elements of an immediately preceding scanning line and, if necessary, said scanning line is encoded in a manner to minimize the number of bits of each code word.

Description

FIELD OF THE INVENTION

This invention relates to a coding system employed for efficient transmission or storage of a facsimile signal.

BRIEF DESCRIPTION OF THE PRIOR ART

Conventional coding method of the type are (1) a runlength coding method, in which signals of every scanning line are converted into a time-serial signal and then run lengths of successive white picture elements and of successive black picture elements are encoded in sequence and transmitted, and (2) a system, in which signals of a plurality of scanning lines are subjected to batch processing and then encoded and transmitted. In the method (1), however, the address of a picture element whose information has changed from white to black or vice versa (which picture element will hereinafter be referred to as the information change picture element) with respect to the state of an immediately preceding picture element, is encoded by the use of a distance between this picture element and an immediately preceding information change picture element on the same scanning line, but this system (1) does not ever utilize such property that a picture signal has close correlation in a vertical direction, and hence is not sufficient in its band compression effect. The method (2) is more excellent in the band compression effect than the abovesaid method (1 ) but is defective in that it generally requires a large memory capacity and is inevitably complicated in construction.

BRIEF SUMMARY OF THE INVENTION

An object of this invention 7A 3A are modified as shown in FIG. 7B to be employed in the modified embodiment shown in FIG. 3B. In this modified circuit, an output terminal 911 is added and connected from the output of the subtractor 906 to the input of the flip flop circuit 10001. The output pulse of the subtractor 906 is employed as described above to read out the run information on the reference scanning line from the memory 802. In other words, an output pulse is applied to the flip flop circuit 10001 at each renewal instant of the run information of the registor 905.

With reference to FIG. 8, an example of the encoder 14 comprises input terminals 1400 and 1401 for receiving the outputs of the comparator 12, input terminals 1402 and 1403 for receiving the outputs of the comparator 13, an input terminal 1404 for receiving the output of the comparator 16, a NOT circuit 1405, gates 1406 and 1407, and an OR circuit 1408. Moreover, a counter 1409 is set to the output contents of the OR circuit 1408 and generates an output pulse when the contents thereof become zero. The output pulse of the counter 1409 is applied to a NOT circuit 1410, which generates output pulses in case of no pulse from the counter 1409, to reduce by one the contents of the counter 1409. The example further comprises a gate 1411, a pulse generator 1412 for generating one pulse in response to the state "1" of its input from the counter 1409, an OR circuit 1413, a NOT circuit 1414, AND circuits 1415 and 1416, a register 1417 for storing the outputs of the AND circuits 1415 and 1416, the OR circuit 1408 and the gate 1411, and an output terminal 1418.

In operation, a pulse is obtained at the input terminal 1404 as described with reference to FIG. 6B when the distance d₀ between the information change picture elements P₁ and P₂ is less than the predetermined number L, so that the gate 1406 is opened to apply the contents from the input terminal 1401 to the OR circuit 1408. In this case, the contents from the input terminal 1401 the indicate smaller one of the absolute values of the distances d₁ and d₃ shown in FIG. 1. However, in a case where the distance d₀ is larger than the number L, the gate 1407 is opened since no pulse is applied to the input terminal 1404, so that the contents from the input terminal 1403 indicative of the smaller one of the absolute values of the distances d₁ and d₂ are applied to the OR circuit 1408. The sign bit of the input contents of the OR circuit 1408 is applied to the register 1417, while the absolute value of the input contents of the OR circuit 1408 is applied to the counter 1409 to set the counting state thereof to the absolute value. The circuits 1409, 1410, 1411, 1412 and 1413 provide variable length code words shown in Table 3.

TABLE 3
______________________________________
Length    Variable length code words
______________________________________
0          0
1         10
2         110
3         1110
4         11110
:         :
:         :
n         11 . . . 110
______________________________________

The number of "1" of the variable length code words corresponds to the number indicative of the length. If zero is set to the counter 1409, a pulse is applied to the NOT circuit 1410 while the pulse generator 1412 generates one pulse. Since the gate 1411 is opened as a result of this operation, the output state "0" of the NOT circuit 1410 is applied to the register 1417 through the gate 1411. If one of other values other than zero is set to the counter 1409, these circuits operate as follows. The counter 1409 generates its output pulse only when the counting state therof becomes zero. The counting state of the counter 1409 is reduced by one in response to the output pulse of the NOT circuit 1410 when the counting state of the counter 1409 is not zero. As a result of this operation, a number of pulses corresponding to the value, which is set to the counter 1409, are obtained at the output of the NOT circuit 1410. In this case, since the gate 1411 is opened in response to the output pulses of the NOT circuit 1410 or the one pulse from the pulse generator 1412 when the counting state of the counter 1409 becomes zero, a pulse of state "0" and at least one pulse of state "1" corresponding to the set number in the counter 1409. As mentioned above, the variable length code words shown in Table 3 are obtained. The circuits 1414, 1415 and 1416 select a desired one of the distances d₁, d₂ and d₃ to apply the desired one to the register 1417 under conditions: which distances d₁ or d₃ has a smaller absolute value than the other, which distances d₁ or d₂ has a smaller absolute value than the other; and whether or not the distance d_o is larger than the number L. In a case where the distance d_o is equal or smaller than the number L, an output pulse is received from the input terminal 1404. In a case where the absolute value of the distance d₁ is equal or larger than the absolute value of the distance d₃, an output is received from the input terminal 1400. Accordingly, outputs of the AND circuits 1415 and 1416 assume the states "1" and "0" respectively. In a case where the absolute value of the distance d₁ is smaller than the absolute value of the distance d₃, outputs of the AND circuits 1416 and 1417 assume zero since no pulse is received from the input terminal 1400. If the distance d_o is larger than the number L, no pulse is received from the input terminal 1404. In a case where the absolute value of the distance d₁ is equal or larger than the absolute value of the distance d₂, an output pulse is obtained from the input terminal 1402. Accordingly, outputs of the AND circuits 1415 and 1416 assumes the states "0" and "1" respectively. In a case where the absolute value of the distance d₁ is smaller than the absolute value of the distance d₂, the outputs of the AND circuit assume zero.

With reference to FIG. 9, an example of the decision circuit 19 and 21 comprises an input terminal 1900 from the counter 18 or 20, a register 1901 for temporarily storing the contents from the input terminal 1900, a register 1902 for storing a predetermined number, a subtractor 1903 for subtracting the contents of the register 1902 from the contents of the register 1901 to produce an output pulse when the subtracted result assumes zero, and an output terminal 1904 for supplying the outpur pulse of the subtractor 1903 to the counter 20 and other circuits. In operation of the decision circuit 19, the number of picture elements included in one scanning line is stored in the register 1902. Since the number of picture elements from the left end of a scanning line including the instant scanning picture element to the instant scanning picture element is applied from the input terminal 1900, the subtractor 1903 generates an output pulse at the output terminal 1904 in response to coincidence of the contents of the registers 1901 and 1902 when the scanning reaches the right most picture element of each scanning line. In operation of the decision circuit 21, the number of spaces of scanning lines is stored in the register 1902 to set the reference information to the predetermined pattern, while the number of scanning lines from a scanning line, to which the reference information is set to the predetermined pattern, is stored in the register 1901. Accordingly, an output pulse is obtained from the subtractor 1903 for the number of scanning lines stored in the register 1902.

With reference to FIG. 10, an example of the encoder 27 shown in FIG. 4 comprises an input terminal 2700 connected to the input information memory 26, an output terminal 2701 connected to the input information memory 26, gates 2702, 2703, 2704 and 2705 for selectively passing the information from the input terminal 2700, registers 2706 and 2707 temporarily storing the respective outputs of the gates 2702 and 2703, NOT circuits 2708 and 2709, AND circuits 2710, 2711 and 2712, a counter 2713 reset to the state "0" by an output pulse of a below mentioned AND circuit 2721 for counting the output pulses of a below mentioned AND circuit 2723, a subtractor 2714 for subtracting by "1" from the counted result of the counter 2713, a register 2715 for storing the outputs of the gate 2704 and the subtractor 2714, a scale-of-4 counter 2716, NOT circuits 2717 and 2718, AND circuits 2719, 2720 and 2721, an OR circuit 2722, an AND circuit 2723, a NOT circuit 2724, an AND circuit 2725, an OR circuit 2726 for providing output pulses applied to the binary counter 2716, an OR circuit 2727, and output terminals 2728, 2729, 2730 and 2731 connected to the circuits 32, 33, 34 and 35 respectively.

In operation, the decoder 27 reads out for one bit the information stored in the input information memory 26 and sends out the variable length code word of the readout information after decoding. In this case, information indicative of which one of th the picture elements P₁, P₂ and P₃ is the reference information change picture element is sent out through the terminals 2728, 2729 and 2730, while relative distance information of a coded information change picture element with respect to the reference information change picture element. The input code work applied through the input terminal 2700 comprises two initial bits indicative of which one of the information change picture elements P₁, P₂ and P₃ is selected as the reference information change picture element, a next bit indicative of a sign of the coded distance, and a remainder of one bit indicative of the absolute value of the coded distance as shown in Table 3. The scale-of-4 counter 2716 is reset to the state "00" at the initial condition, so that the AND circuit 2719 generates an output pulse by the outputs of the NOT circuit 2717 and 2718 to open the gate 2702 so as to store the input code word from the input terminal 2700 to the register 2706. In this case, since the output pulse of the AND circuit 2719 is applied to the scale-of-4-1 counter 2716 through the OR circuits 2722 and 2726, the contents of the counter 2716 are counted up to the state "01". Moreover, the output pulse of the OR circuit 2726 is applied to the memory 26 through the OR circuit 2727 and the output terminal 2701 to read out one bit from the memory 26, so that the read out one bit is then applied to the input terminal 2700. At this time, since the AND circuit 2720 generates an output, the gate 2703 is opened to pass a second bit of the input code word to the register 2707. As mentioned above, the stored bits in the registers 2706 and 2707 respectively indicate which one of the picture elements P₁, P₂ and P₃ is the reference information change picture element. An output pulse is obtained at the output terminal 2728, 2729 or 2730 through the NOT circuits 2708 and 2709 and the AND circuits 2710, 2711 and 2712 in accordance with the reference picture element of the picture elements P₁, P₂ and P₃ respectively. The output pulse of the AND circuit 2720 is also applied to the counter 2716 through the OR circuit 2722 and 2726 and to the memory 26 as mentioned above. Accordingly, the counter 2716 is counted up to the state "10", while a next bit is read out from the memory 26. In this case, since the gate 2704 is opened by the output pulse of the AND gate 2721, the third bit of the input code word is stored in the register 2715 as the sign of the coded distance. In response to the output pulse of the AND circuit 2721, the counter 2713 is reset to zero, while the counter 2716 is counted up to the state "11". In this case, since the gate 2705 is opened by the output pulse of the AND circuit 2723, the fourth bit of the input code word is applied to the NOT circuit 2724. If the fourth bit is the state "1", since the AND circuit 2725 generates no output pulse, the contents of the counter 2716 are not changed and the opened state of the gate 2705 continues. The output pulse of the AND circuit 2723 is counted by the counter 2713. When the output of the gate 2705 becomes the state "0", since the AND circuit 2725 generates an output pulse, the counter 2716 is counted up to the state "00". In this case, the contents of the counter 2713 which indicates one plus the number of continuous bits "1" of the input code word are applied to the subtractor 2714 to subtract one bit therefrom. Accordingly, the number of continuous bits "1" of the input code word is stored in the register 2715. As mentioned above, decoding of the variable length code words shown in Table 3 is performed. After the resetting of the counter 2716 to the state "00", the above mentioned operations are repeated.

With reference to FIG. 11, an example of the reference information memory 28 comprises an input terminal 2800 for receiving the output of the restoring circuit 35 which is the absolute address information of the coded information change picture element, an input terminal for receiving the output of the decision circuit 39 which is information indicative of setting of the reference information to a predetermined pattern, a register 2802 for storing a predetermined number corresponding to the number of picture elements included in a scanning line, a subtractor 2803 for subtracting the contents of the register 2802 from the input information of the input terminal 2800 to provide a pulse in response to the zero of the subtracted result thereof. In other words, the subtractor 2803 generates the pulses in response to completion of the decoding of each scanning line. The example further comprises a memory 2804 for storing the absolute address of the information change picture element on the instant scanning line, a read-write circuit 2805 for the memory 2804, a memory 2806 for storing the absolute address of the information change picture element on the reference scanning line, a read-write circuit 2807 for the memory 2806, and a register 2808 for temporarily storing the information of the input terminal 2800. A subtractor 2809 is provided for subtracting the absolute address of the information change picture element in the memory 2806 from the contents of the register 2808. If the subtracted result is minus or zero, the subtractor 2809 sends our a pulse to the read write circuit 2807 to read out the absolute address of a next information change picture element. The above operations are repeated until a pulse subtracted result is obtained. In case of obtaining the plus subtracted result from the subtractor 2809, a next information change picture element is once more read out from the memory 2806. The example moreover comprises a gate 2810, a delay circuit 2811, a gate 2812, and output terminals 2813, 2814 and 2815 for respectively connected to the registers 29, 30 and 31.

In operation, absolute address information of a decoded information change picture element is applied from the input terminal 2800 and stored in the memory 2804 and the register 2808. If this information change picture element is the right most picture element, this right most picture element is detected by the subtractor 2803 so that the contents of the memory 2804 are transferred to the memory 2806 to be ready for decoding a next scanning line. When a pulse is applied to the input terminal at this time, the contents of the memory 2806 are set to a predetermined pattern as shown in FIG. 2. the absolute address information of an information change picture element stored in the register 2808 becomes a reference information change picture element (P₁ in FIG. 1) employed at the decoding of a next information change picture element and is then send out to the output terminal 3813 2813. Other reference information change picture elements (P₂, P₃ in FIG. 1) are read out from the memory 2806 as described below. If the absolute address of an information change picture element of the memory 2806 is read out, the read out absolute address is compared with the contents (P₁ in FIG. 1) of the register 2808 at the subtractor 2809. If the contents of the register 2808 are larger than the read out absolute address in a case where the picture element P₁ is positioned at the right hand of the information change picture element, the absolute address of a next information change picture element is read out. After repeating the above operations, if the read out absolute address from the memory 2806 is larger than the contents of the register 2808, this information change picture element becomes a second reference picture element (P₂ in FIG. 1) so that a pulse is applied to the gate 2810 to send out the absolute address to the output terminal 2814. In this case, the absolute address of a next information change picture element is further read out from the memory 2806 and sent out, through the gate 2812, to the output terminal 2815 as a third reference information change picture element (P₃ in FIG. 1).

With reference to FIG. 12, an example of the restoring circuit 35 comprises input terminals 3500, 3501 and 3502 for respectively receiving the outputs of the gates 32, 33 and 34, an input terminal 3503 for receiving the output of the decoder 27, an OR circuit 3504, and adder 3505, a delay circuit 3506, and a register 3507, a subtractor 3508 for subtracting the contents of the register 3507 from the adder 3505. A counter 3509 is initially set to the output value of the subtractor 3508 and generates one pulse when the set value is not zero. The one pulse reduces the counting state of the counter 3509 by one. The example further comprises a NOT circuit 3510, a flip flop circuit 3511 reversing its state for each input pulse thereof, a gate 3512, an output terminal connected to the reference information memory 28 and the error detector 37, and an output terminal connected to the output terminal memory 36.

In operation, since the input terminals 3500, 3501 and 3502 receive respective outputs of the gates 32, 33 and 34, the output of the OR circuit 3504 becomes the absolute address of the reference information change picture element. On the other hand, the coded distance information is applied through the input terminal 3503, so that the output of the adder 3505 becomes the absolute address of the decoded information change picture element. This information picture element becomes a reference information change picture element at the decoding of a next information picture element and is sent out through the output terminal 3513 to the reference information memory 28 and then to the subtractor 3508 and the delay circuit 3506. Since the absolute address of an information change picture element immediately preceding the information change picture element obtained at the adder 3505 is stored in the register 3507, the subtracted result of the subtractor 3508 becomes a distance between the questioned information change picture elements, that is, a run length, which is set to the counter 3509. This counter 3509 generates one pulse at the counting states except the zero state and counts down by one in response to the one pulse. The gage 3512 is opened by the one pulse, so that the output value of the flip flop circuit 3511 is sent out to the output terminal 3514 by a number equal to the run length. When the counting state of the counter 3509 assumes zero, the output pulse of the counter 3519 is stopped so that the output value of the flip flop circuit 3511 is reversed. Accordingly, the output value of the flip flop circuit 3511 assumes that state "1" and "0" in response to black and white of the run, respectively.

With reference to FIG. 13, an example of the error detector 37 comprises an input terminal 3700 connected to the output of the input information memory 26, gates 3701 and 3702, a flip flop circuit 3703, a register 3704, a coincidence circuit 3705 for generating a pulse in a case where the state of the flip flop circuit 3703 coindides with the contents of the register 3704, a NOT circuit 3706, an input terminal 3707 connected to the output of the restoring circuit 35, a register 3708 for storing a predetermined number corresponding to the number of picture element on each scanning line, a subtractor 3709 for generating a pulse in response to its zero state by subtracting the information of the input terminal 3707 from the contents of the register 3708, a NOT circuit 3710, and an output for sending out a pulse in case of detecting an error.

In operation, this error detector 37 performs parity check (i.e. odd parity). In this case, it is assumed that an error detecting bit is added to the last code word of each scanning line. The absolute address of a decoded information change picture element applied through the input terminal 3700 is subtracted at the subtractor 3709 from the contents of the register 3709, so that a pulse is obtained from the subtractor 3709 at the completion of decoding of each scanning line information. In response to this pulse, the gate 3702 is opened so that the parity check bit included in the input code word is stored in the register 3704. On the other hand, the remainder of the input code word other than the parity check bit is applied to the flip flop circuit 3703 through a gate 3701, so that the flip flop circuit 3703 counts the number of "1" in the input code word. In a case where the contents of the register 3704 coincides with the state of the flip flop circuit 3703 at the completion of the decoding of each scanning line, no error is decided so that the coincidence circuit 3704 generates a pulse while no pulse is obtained at the output terminal 3711. If the contents of the flip flop circuit 3703 and the register 3704 do not coincide with each other, a pulse indicative of error detection is obtained at the output terminal 3711.

As has been described in detail in the foregoing, the method of this invention is proposed under a principle in that the address information of each information change picture element is encoded by encoding the distance between the information change picture element and that considered to have the closest correlation to the former. The distribution of this distance is over one-sided to 0 and ±1 in practice, so that this information has a very small amount of information. Accordingly, this invention greatly reduces the number of bits to be sent out and enables marked reduction of the band with respect to the band-time integral, and hence can be practised with; such relatively simple circuitry as shown in the examples.

Claims

1. A system for coding information change picture elements in a facsimile signal, comprising:

input terminal means for receiving the facsimile signal;

first encoder means connected to said input terminal means for encoding the absolute address of each information change picture element, having a state different from that of an immediately preceding picture element on each scanning line, in the facsimile signal in such a manner that a distance between the information change picture element and a reference information change picture element selected from information change picture elements of at least an immediately preceding scanning line is encoded by a minimum number of bits of each code word in the order of occurrence of all the information change picture elements;

detector means connected to said input terminal means for generating a detection output signal when no information change picture element is included in an instant scanning line of the facsimile signal;

second encoder means connected to said input terminal means and said detector means for encoding the run length of the scanning line of the facsimile signal in response to said detection output signal; and

output means connected to said first encoder means and said second encoder means for obtaining a coded output pulse train from outputs of said first

encoder means and said second encoder means.

2. A system for coding information change picture elements in a facsimile signal comprising:

input terminal means for receiving the facsimile signal;

first encoder means connected to said input terminal means for encoding the absolute address of each information change picture element, having a state different from that of an immediately preceding picture element on each scanning line, in the facsimile signal in such a manner that a distance between each information change picture element and a reference information change picture element selected from information change picture elements of at least an immediately preceding scanning line is encoded by a minimum number of bits of each code word in the order of occurrence of all the information change picture elements, said first encoder means comprising first reference means for selecting, as a first reference information change picture element, an information change picture element immediately preceding an instant information change picture element to be coded on the same scanning line as the instant information change picture element, second reference means for selecting, as a second reference information change picture element, a first information change picture element having the same information change direction as the instant information change picture element and positioned to the right of said first reference information change picture element on a scanning line immediately preceding the instant scanning line, reference detection means connected to said first reference means and said second reference means for providing a final reference information change picture element by selecting a nearer one of the first reference information change picture element and the second reference information change picture element to the instant information change picture element to be coded, and encoder means for encoding the number of picture elements from said final reference information change picture element to the instant information change picture element to be coded;

detector means connected to said input terminal means for generating a detection output signal when no information change picture element is included in an instant scanning line of the facsimile signal;

second encoder means connected to said input terminal means and said detector means for encoding the run length of the scanning line of the facsimile signal in response to said detection output signal; and

output means connected to said first encoder means and said second encoder means for obtaining a coded output pulse train from outputs of said first

encoder means and said second encoder means.

3. A system for coding information change picture elements in a facsimile signal comprising:

input terminal means for receiving the facsimile signal;

first encoder means connected to said input terminal means for encoding the absolute address of each information change picture element, having a state different from that of an immediately preceding picture element on each scanning line, in the facsimile signal in such a manner that a distance between each information change picture element and a reference information change picture element selected from information change picture elements of at least an immediately preceding scanning line is encoded by a minimum number of bits of each code word in the order of occurrence of all the information change picture elements;

detector means connected to said input terminal means for generating a detection output signal when no information change picture element is included in an instant scanning line of the facsimile signal;

second encoder means connected to said input terminal means and said detector means for encoding the run length of the scanning line of the facsimilie signal in response to said detection output signal;

gate means connected to said input terminal means, first encoder means and said second encoder means for forcibly gating the facsimile signal to said second encoder means for every predetermined number of scanning lines; and

output means connected to said first encoder means and said second encoder means for obtaining a coded output pulse train from outputs of said first encoder means and said second encoder means.

4. A system for encoding information change picture elements in a facsimile signal comprising:

input terminal means for receiving the facsimile signal;

first encoder means connected to said input terminal means for encoding the absolute address of each information change picture element, having a state different from that of an immediately preceding picture element on each scanning line, in the facsimile signal in such a manner that a distance between each information change picture element and a reference information change picture element selected from information change picture elements of at least an immediately preceding scanning line is encoded by a minimum number of bits of each code word in the order of occurrence of all the information change picture elements; said first encoder means comprising, first reference means for selecting, as a first reference information change picture element, an information change picture element immediately preceding an instant information change picture element to be coded on the same scanning line as the instant information change picture element, second reference means for selecting, as a second reference information change picture element, a first information change picture element positioned to the right of said first reference information change picture element on a scanning line immediately preceding the instant scanning line, third reference means for selecting, as a third reference information change picture element, a first information change picture element position to the right of said second reference information change picture element on a scanning line immediately preceding the instant scanning line, reference detection means connected to said first reference means, said second reference means and said third reference means for providing a final reference information change picture element by selecting a nearer one of the first reference information picture element and the second information picture element to the instant information change picture element to be coded in a case where a reference distance between the first reference picture element and the second reference picture element is greater than a predetermined value or by selecting a nearer one of the first reference information picture element and the third reference picture element ot the instant information change picture element in a case where said reference distance is smaller than said predetermined value, and encoder means for encoding the number of picture elements from said final reference information change picture element to the instant information change picture element;

detector means connected to said input terminal means for generating a detection output signal when no information change picture element is included in an instant line of the facsimile signal;

second encoder means connected to said output terminal means and said detector means for encoding the run length of the scanning line of the facsimile signal in response to said detection output signal; and

output means connected to said first encoder means and said second encoder means for obtaining a coded output pulse train from outputs of said first encoder means and said second encoder means.

5. A system for coding information change picture elements in a facsimile signal according to claim 4, further comprising: gate means connected to said input teminal means, first encoder means and said second encoder means for forcibly gating the facsimile signal to said second encoder means for every predetermined number of scanning lines.

6. A system for coding information change picture elements in a facsimile signal according to claim 2, further comprising: gate means connected to said input terminal means, first encoder means and said second encoder means for forcibly gating the facsimile signal to said second encoder means for every

predetermined number of scanning lines. 7. A system for coding information change picture elements in a facsimile signal, comprising:

input terminal means for receiving the facsimile signal;

encoder means connected to said input terminal means for encoding the absolute address of each information change picture element, having a state different from that of an immediately preceding picture element on each scanning line, in the facsimile signal in such a manner that a distance between the information change picture element and a reference information change picture element selected from information change picture elements of an immediately preceding scanning line and the scanning line to be coded is encoded by a minimum number of bits of each code word in the order of occurrence of all the information change picture elements; and

output means connected to said encoder means for obtaining a coded output pulse train from the output of said encoder means. 8. A system for coding information change picture elements in a facsimile signal comprising:

input terminal means for receiving the facsimile signal;

encoder means connected to said input terminal means for encoding the absolute address of each information change picture element, having a state different from that of an immediately preceding picture element on each scanning line, in the facsimile signal in such a manner that a distance between each information change picture element and a reference information change picture element selected from information change picture elements of an immediately preceding scanning line and the scanning line to be coded is encoded by a minimum number of bits of each code word in the order of occurrence of all the information change picture elements, said encoder means comprising first reference means for selecting, as a first reference information change picture element, an information change picture element immediately preceding an instant information change picture element to be coded on the same scanning line as the instant information change picture element, second reference means for selecting, as a second reference information change picture element, a first information change picture element having the same information change direction as the instant information change picture element and positioned to the right of said first reference information change picture element on a scanning line immediately preceding the instant scanning line, reference detection means connected to said first reference means and said second reference means for providing a final reference information change picture element by selecting a nearer one of the first reference information change picture element and the second reference information change picture element to the instant information change picture element to be coded, and means for encoding the number of picture elements from said final reference information change picture element to the instant information change picture element to be coded; and

output means connected to said encoder means for obtaining a coded output

pulse train from the output of said encoder means. 9. A system for coding information change picture elements in a facsimile signal comprising:

input terminal means for receiving the facsimile signal;

first encoder means connected to said input terminal means for encoding the absolute address of each information change picture element, having a state different from that of an immediately preceding picture element on each scanning line, in the facsimile signal in such a manner that a distance between each information change picture element and a reference information change picture element selected from information change picture elements of an immediately preceding scanning line and the scanning line to be coded is encoded by a minimum number of bits of each code word in the order of occurrence of all the information change picture elements;

second encoder means connected to said input terminal means for encoding each run length of the scanning line of the facsimile signal;

gate means connected to said input terminal means, first encoder means and said second encoder means for forcibly gating the facsimile signal to said second encoder means for every predetermined number of scanning lines; and

output means connected to said first encoder means and said second encoder means of obtaining a coded output pulse train from outputs of said first encoder means and said second encoder means. 10. A system for encoding information change picture elements in a facsimile signal comprising;

input terminal means for receiving the facsimile signal;

encoder means connected to said input terminal means for encoding the absolute address of each information change picture element, having a state different from that of an immediately preceding picture element on each scanning line, in the facsimile signal in such a manner that a distance between each information change picture element and a reference information change picture element selected from information change picture elements of an immediately preceding scanning line and the scanning line to be coded is encoded by a minimum number of bits of each code word in the order of occurrence of all the information change picture elements; said encoder means comprising, first reference means for selecting, as a first reference information change picture element, an information change picture element immediately preceding an instant information change picture element to be coded on the same scanning line as the instant information change picture element, second reference means for selecting, as a second reference information change picture element, a first information change picture element positioned to the right of said first reference information change picture element on a scanning line immediately preceding the instant scanning line, third reference means for selecting, as a third reference information change picture element, a first information change picture element positioned to the right of said second reference information change picture element on a scanning line immediately preceding the instant scanning line, reference detection means connected to said first reference means, said second reference means and said third reference means for providing a final reference information change picture element by selecting a nearer one of the first reference information picture element and the second information picture element to the instant information change picture element to be coded in a case where a reference distance between the first reference picture element and the second reference picture element is greater than a predetermined value or by selecting a nearer one of the first reference information picture element and the third reference picture element of the instant information change picture element in a case where said reference distance is smaller than said predetermined value, and means for encoding the number of picture elements from said final reference information change picture element to the instant information change picture element; and

output means connected to said encoder means for obtaining a coded output pulse train from the output of said encoder means. 11. A system for coding information change picture elements in a facsimile signal according to claim 10, further comprising: auxiliary encoder means connected to said input terminal means for encoding each run length on the scanning line of the facsimile signal; and

gate means connected to said input terminal means, said encoder means and said auxiliary encoder means for forcibly gating the facsimile signal to said auxiliary encoder means for every predetermined number of scanning lines. 12. A system for coding information change picture elements in a facsimile signal according to claim 8, further comprising:

auxiliary encoder means connected to said input terminal means for encoding each run length on the scanning line of the facsimile signal; and

gate means connected to said input terminal means, said encoder means and said auxiliary encoder means for forcibly gating the facsimile signal to said auxiliary encoder means for every predetermined number of scanning lines.