GB1570914A

GB1570914A - Method and apparatus for bandwidth compression

Info

Publication number: GB1570914A
Application number: GB280177A
Authority: GB
Original assignee: Mita Industrial Co Ltd
Current assignee: Kyocera Mita Industrial Co Ltd
Priority date: 1976-01-24
Filing date: 1977-01-24
Publication date: 1980-07-09
Also published as: FR2339304B1; JPS5290216A; DE2702746B2; DE2702746A1; DE2702746C3; FR2339304A1

Description

(54) METHOD AND APPARATUS FOR BANDWIDTH COMPRESSION (71) We, MITA INDUSTRIAL COM PANY, a Japanese company, of 5, Miyabayashi-cho, Higashi-ku, Osaka City, Osaka Prefecture, Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a method and apparatus for bandwidth compression in an electric image transmission system and more particularly to a method of coding for use in the transmission and reception of an image signal obtained by scanning a twodimensional image. One example of such a transmission system is facsimile transmission.

There has been proposed a method of collectively coding a plurality of images by utilizing two-dimensional correlation in both the horizontal and the vertical directions of scanning, since a high compression rate cannot be obtained with one-dimensional correlation of an image. In such method, the bandwidth compression is achieved by detecting a black and white mode between a predetermined number of adjacent picture elements, giving a code to each mode, measuring the run length of each mode, and coding the run length.

When employing such a system, however, a plurality of scanning lines are collectively coded, so that if a signal error is generated during a scanning line, an image reproduced in said scanning line after generation of the error becomes distorted. In fact, the reproduced image due to the scanning line where an error occurs is all white or is the same as that immediately before the scanning line.

When a plurality of scanning lines are reproduced, a considerably distorted image is obtained, and further since a plurality of scanning lines are collectively transmitted, it is necessary to detect the mode (black or white) of picture elements occupying corresponding positions in the collectively transmitted lines, and to detect when a transition to the next mode occurs, to allot a transition code thereto, and to run length code the mode. In practice, the run length code of each mode is comparatively short, so that mode transitions occur frequently. Hence, if a transition code is allotted to each mode and a code expressing the run length is given, redundancy is inevitably increased, and as a result, the apparatus becomes very complicated and expensive.

The present invention seeks to eliminate these defects of the above method.

According to one aspect of the present invention there is provided a method of reducing or compressing band width of an image signal to be transmitted, said method comprising the steps of scanning an image to be transmitted to produce an image signal containing a plurality of scanning lines, each line being divided into a plurality of picture elements representative of either a black or a white area of the image, converting that part of the signal representative of each picture element into a logic 0 or logic 1 in accordance with whether that picture element is black or white, logically combining the logic 0 or the logic 1 signal corresponding to each picture element on one scanning line with that corresponding to a respective one of each picture element on at least one other scanning line to form a resultant logic 1 signal or logic 0 signal, the resultant logic signals constituting a signal train having logic 0 sections and logic 1 sections, and coding said logic signal train for transmission.

According to a further aspect of the invention there is provided a transmitting apparatus for carrying out the method of this invention, said apparatus comprising means for scanning an image to be transmitted to produce an image signal containing a plurality of scanning lines, each line being divided into a plurality of picture elements represen tative of either a black or a white area of the image, means for converting that part of the signal representative of each picture element into a logic 0 or logic 1 in accordance with whether that picture element is black or white, delay means for delaying the logic signal representing a first of said scanning lines for at least one line period, and a logic circuit for receiving and carrying out a logic operation on the logic 0 or logic 1 signal corresponding to each picture element on said first scanning line and that corresponding to a respective one of each picture element on at least one other scanning line to form a resultant logic 1 signal or logic 0 signal, the resultant logic signals constituting a signal train having logic 0 sections and logic 1 sections, and means for coding said logic signal train for transmission.

In a still further aspect, the invention provides a receiving apparatus comprising means for decoding the signal transmitted by the transmitting apparatus according to said further aspect of this invention, and scanning means for reproducing the transmitted image.

In order that the invention may be better understood, an embodiment thereof will now be described by way of example only and with reference to the accompanying drawings in which: Figure 1 is a diagram showing the principle of the coding method utilized for transmission and reception of an image signal according to the present invention; Figure 2 is a table showing one example of run length coding for use in the method shown in Figure 1; Figure 3 is a block diagram showing one embodiment of a transmitting apparatus for generating and transmitting signals by the coding method according to the present invention; and Figure 4 is a block diagram showing one embodiment of a receiving apparatus for decoding the signal coded by the method according to the present invention.

Referring now to Figure 1, there is shown a diagram illustrating the coding system for reducing the bandwidth of an image signal.

Two scanning lines to be transmitted are shown in Figure 1(a). Each line is divided into a plurality of picture elements, each of which may be either black or white. The picture elements A, C, G and I in the first (upper) scanning line and the picture elements D, F and J the second (lower) scanning line are black, while the remaining picture elements are white.

When such picture elements are transmitted, each picture element on each scanning line is converted into a logic 0 or 1 bit according to whether it is black or white (logic 1 for black, logic 0 for white), the logic bits of each scanning line making up a "new" signal, as shown in Figure 1(b). Also the logic signals corresponding to the two picture elements at the same position on the first and second scanning line are subjected to the logical OR operation to form an "OR" signal shown in Figure 1(c) comprising alternate sections of logic 1 and logic 0. In other words, adjacent white picture elements (logic 0) result in a logic 0 signal, whilst all the remaining combinations result in a logic 1 signal.

The section of the OR signal comprising logic 0 is run length-coded, i.e. the section is given a code indicative of the number of logic bits in the section. On example of such a code is shown in Figure 2, in which for each "runlength" (RL), i.e. the number of bits in the section, a binary code is allotted. The right hand column of the table gives the resultant word length, after coding, from which it will be seen that, for large run lengths, a considerable compression occurs. Inspection of Figure 2 will reveal that, if the first bit of the code is 0, the word length necessary for expressing the run length is the next two bits (3 bits in all), and if the first two bits are 10, the word length is the next 4 bits (6 bits in all) and so on. Thus the logic 0 section is defined and the run length is merely binary coded as a numerical number, as shown in Figure 1(d).

Turning now to the section of the OR signal comprising logic 1, the length of this is not certain and even if the raw signal is transmitted, the end of the section cannot be determined. Therefore, referring to Figure 1(a), the picture elements A to F are transmitted sequentially in the order AB CD EF and in the form of the raw signal, i.e. 10 11 01. During this section, the OR signal is permanently at logic 1, so that either or both of B or A, C or D, E or F is a black element, so that, if a signal produced by dividing every 2 bits is observed, it is found that 00 (i.e. logic 0 twice) never occurs. Thus, in order to show the end of the section containing the raw signal, an end signal comprising 00 is added at the end as shown in Figure 1(d). In order to be effective, the number of logic 0's in the end signal must be equal to the number of scanning lines to be collectively transmitted.

The reception side thus examines every 2 bits of the raw signal section and understands that the raw signal section is finished when an end signal "00" is received, and because the run length code and a raw signal are transmitted alternately, further understands that the following bits represent the coded run length of the white mode.

Figure 3 is a block diagram showing one embodiment of a transmitter for generating signals in accordance with the above described coding system. The transmitter comprises a scanning section 1 for obtaining the information shown in Figures 1(a) and l(b) by scanning the image to be transmitted and by sampling and quantising it. Reference 2 is a memory circuit for storing the information contained in the first scanning line shown in Figures 1(a) and 1(b). The memory circuit 2 uses a shift register for reading out one bit of the information contained in the next scanning line is read in. The output from the memory circuit 2 is passed to one input of an OR circuit 3 which is operable to generate the OR signal shown in Figure 1(c) by successively applying a logic OR operation to the logic signal corresponding to a picture element in one scanning line and a correspondingly positioned picture element in the next scanning line. The output from the OR circuit 3 is passed to a discriminator circuit 4 for generating an output signal indicative of whether the output signal of the OR circuit 3 is logic 0 or logic 1. Reference 5 is a mode transition detecting circuit for comparing the code of the output signal of the OR circuit 3 when the output signal discriminates whether the 0 section or the 1 section with the code of the output signal of the OR circuit 3 corresponding to the prior section and by detecting whether the coincidence signal or the mode transition is generated. Reference 6 is a counter and run length coding circuit for counting the number of pulses when one pulse is transmitted in logic 0 section of the output signal of the OR circuit for run length-coding. Numeral 7 is a second memory circuit for storing the information contained in the picture element at the present scanning position in the logic 1 section of the output signal of the OR circuit 3 and the information contained in the picture element at the same position as tlhat of the first scanning line in the predetermined order.

If the output of the mode transition detecting circuit 5 does not detect any mode transition, each circuit 6 or 7 performs the above described action, but when a mode transition is detected, for example when the mode changes from the logic 1 section to the logic 0 section of the output signal of OR circuit 3, the counter circuit 6 codes the counted run length by means of the code shown in Figure 2 and transmits it to a second OR circuit 8.

Thereafter, the counter circuit 6 is reset to await the next logic 0 section.

The memory circuit 7 stores the information contained in two picture elements respectively positioned in the first and second scanning lines. When the mode transition signal is generated due to a change from the logic 0 section of the output signal of the OR circuit 3 to the logic 1 section, the memory circuit 7 passes the stored information in the logic 1 section of the output signal of OR circuit 3 to the second OR circuit 8 and further passes an appropriate end signal when all the information stored has been passed to the OR circuit 8. Then, the memory circuit 7 is cleared to await the next logic 1 section. On the other hand, the counter circuit 6 receives one pulse corresponding to the logic 1 section of the OR signal 0 and counts 1. The OR circuit 8 passes the information from the counter circuit 6 or the memory circuit 7 to a buffer memory circuit 9. In the buffer memory circuit 9, a signal once transmitted from the OR circuit 8 is stored prior to transmitting the information to a transmission line 10 at a certain transmission speed.

Figure 4 is a block diagram showing one embodiment of a receiver for decoding signals coded by the method of the invention.

The receiver comprises a discriminator circuit 11 for discriminating whether the received signal is to be supplied to a decoding circuit 12 or to a deserializer circuit 13. If the received signal is in the logic 0 section of the OR signal, it is supplied to the decoding circuit 12, while if the received signal is in the logic 1 section of the OR signal, it is transmitted to the deserializer circuit 13. The decoding circuit 12 decodes the logic 0 section of the received signal back to its original run length. When the logic 0 section of the OR signal is ended, an "end" signal is supplied to the discriminator circuit 11, and the following section of the received signal, being a logic 1 section of the OR signal, is supplied to the deserializer circuit 13. The output signal of decoder circuit 12 is also supplied to one input of an OR circuit 15.

The deserializer circuit 13 receives and stores the logic 1 section of the OR signal, and then receives the end signal indicative of the number of collectively transmitted scanning lines, thereby enabling the logic 1 section to be released from store, and a seriesparallel conversion to be effected on it. The parallel output from the deserialiser circuit 13 is passed to an OR circuit 14 which discriminates between a raw signal or an end signal by carrying out a logical OR operation on the converted signal. If the signal is a raw signal, the raw signal is reconverted back from parallel to series mode and is supplied to the other input of the OR circuit 15 in the form of a signal having the same time series as that of the originally received signal.

When the end signal is detected, it is transmitted to the discriminater circuit 11 to cause the following section of the received signal, being a logic 0 section, to be supplied to the decoding circuit 12, as described above, the output of the OR circuit 15 is passed to a buffer memory circuit 16. The buffer memory circuit 16 stores the signal passed to it.

Finally, the output of the memory circuit 16 is passed to a scanning section 17 which forms a receiving image by scanning.

As described above there is employed a system in which each picture element on at least two scanning lines to be collectively transmitted is logically operated to form logic 0 sections and logic 1 sections, the logic 0 section being run length coded to ensure a large compression rate, and the logic 1 section being converted into a raw signal continued in the optionally selected order at the same position as in the original signal and an end signal having the same number as that of the scanning lines to be collectively transmitted. As a result about 60% of the transmitted signal is raw signal, so that allowance of any transmission error is high (even if a coded error is generated during transmission, if the error is a transmission error in a section of raw signals, only one picture element is mistaken from white to black or black to white without any influence upon a reproduced image, so that the system is very resistant to transmission errors), and the raw signal is transmitted in its original form so that there is no need to detect the mode and the like, and as a result, the apparatus can be simplified and made cheap.

In the above, the collective transmission of two picture elements on two scanning lines is described. However, it will be appreciated that the number of scanning lines can be made more than two lines and the present invention can be applied to the collective transmission of each picture element of each line.

Further, it is possible to carry out a logical NOR operation on the scanning lines rather than, as described above, a logical OR operation. Thus, conversion to a raw signal shown in Figure l(d) can be 01 11 10 00. In addition, the run length coding of the logic 0 section of the OR signal is not limited to a code table of two bit group, as shown in Figure 2, but any coding system can be employed.

There has thus been described a method of reducing band width of image signal in which transmission time is shortened by making a band compression rate as large as possible.

WHAT WE CLAIM IS: 1. A method of reducing or compressing band width of an image signal to be transmitted, said method comprising the steps of scanning an image to be transmitted to produce an image signal containing a plurality of scanning lines, each line being divided into a plurality of picture elements representative of either a black or a white area of the image, converting that part of the signal representative of each picture element into a logic 0 or logic 1 in accordance with whether that picture element is black or white, logically combining the logic 0 or the logic 1 signal corresponding to each picture element on one scanning line with that corresponding to a respective one of each picture element on at least one other scanning line to form a resultant logic 1 signal or logic 0 signal, the resultant logic signals constituting a signal train having logic 0 sections and logic 1 sections, and coding said logic signal train for transmission.

2. A method as claimed in claim 1, wherein the coding step comprises run length-coding one of said sections and converting the other section into a signal containing a series of logic bits in any selected order at the same position as in the image signal and into an end signal positioned at the end of the series of logic bits for indicating the termination of the section.

3. A method as claimed in claim 2, wherein said end signal consists of a binary signal having the same number of bits as the number of said scanning lines.

4. A method as claimed in any one of the preceding claims, wherein said step of logically combining the logic 0 or logic 1 signals on the different scanning lines comprises a logical OR operation.

5. A method as claimed in any one of claims l to 3, wherein said step of logically combining comprises a logical NOR operation.

6. A method of reducing or compressing band width substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.

7. A transmitting apparatus for carrying out the method claimed in any one of the preceding claims, said apparatus comprising means for scanning an image to be transmitted to produce an image signal containing a plurality of scanning lines, each line being divided into a plurality of picture elements representative of either a black or a white area of the image, means for converting that part of the signal representative of each picture element into a logic 0 or logic 1 in accordance with whether that picture element is black or white, delay means for delaying the logic signal representing a first of said scanning lines for at least one line period, and a logic circuit for receiving and carrying out a logic operation on the logic 0 or logic 1 signal corresponding to each picture element on said first scanning line and that corresponding to a respective one of each picture element on at least one other scanning line to form a resultant logic 1 signal or logic 0 signal, the resultant logic signals constituting a signal train having logic 0 sections and logic 1 sections, and means for coding said logic signal train for transmission.

8. A transmitting apparatus substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.

9. A receiving apparatus comprising means for decoding the signal transmitting apparatus as claimed in claim 7 or claim 8, and scanning means for reproducing the transmitted image.

10. A receiving apparatus substantially as hereinbefore described with reference to Figure 4 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

0 section being run length coded to ensure a large compression rate, and the logic 1 section being converted into a raw signal continued in the optionally selected order at the same position as in the original signal and an end signal having the same number as that of the scanning lines to be collectively transmitted. As a result about 60% of the transmitted signal is raw signal, so that allowance of any transmission error is high (even if a coded error is generated during transmission, if the error is a transmission error in a section of raw signals, only one picture element is mistaken from white to black or black to white without any influence upon a reproduced image, so that the system is very resistant to transmission errors), and the raw signal is transmitted in its original form so that there is no need to detect the mode and the like, and as a result, the apparatus can be simplified and made cheap.

In the above, the collective transmission of two picture elements on two scanning lines is described. However, it will be appreciated that the number of scanning lines can be made more than two lines and the present invention can be applied to the collective transmission of each picture element of each line.

Further, it is possible to carry out a logical NOR operation on the scanning lines rather than, as described above, a logical OR operation. Thus, conversion to a raw signal shown in Figure l(d) can be 01 11 10 00. In addition, the run length coding of the logic 0 section of the OR signal is not limited to a code table of two bit group, as shown in Figure 2, but any coding system can be employed.

There has thus been described a method of reducing band width of image signal in which transmission time is shortened by making a band compression rate as large as possible.

WHAT WE CLAIM IS: 1. A method of reducing or compressing band width of an image signal to be transmitted, said method comprising the steps of scanning an image to be transmitted to produce an image signal containing a plurality of scanning lines, each line being divided into a plurality of picture elements representative of either a black or a white area of the image, converting that part of the signal representative of each picture element into a logic 0 or logic 1 in accordance with whether that picture element is black or white, logically combining the logic 0 or the logic 1 signal corresponding to each picture element on one scanning line with that corresponding to a respective one of each picture element on at least one other scanning line to form a resultant logic 1 signal or logic 0 signal, the resultant logic signals constituting a signal train having logic 0 sections and logic 1 sections, and coding said logic signal train for transmission.
2. A method as claimed in claim 1, wherein the coding step comprises run length-coding one of said sections and converting the other section into a signal containing a series of logic bits in any selected order at the same position as in the image signal and into an end signal positioned at the end of the series of logic bits for indicating the termination of the section.
3. A method as claimed in claim 2, wherein said end signal consists of a binary signal having the same number of bits as the number of said scanning lines.
4. A method as claimed in any one of the preceding claims, wherein said step of logically combining the logic 0 or logic 1 signals on the different scanning lines comprises a logical OR operation.
5. A method as claimed in any one of claims l to 3, wherein said step of logically combining comprises a logical NOR operation.
6. A method of reducing or compressing band width substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.
7. A transmitting apparatus for carrying out the method claimed in any one of the preceding claims, said apparatus comprising means for scanning an image to be transmitted to produce an image signal containing a plurality of scanning lines, each line being divided into a plurality of picture elements representative of either a black or a white area of the image, means for converting that part of the signal representative of each picture element into a logic 0 or logic 1 in accordance with whether that picture element is black or white, delay means for delaying the logic signal representing a first of said scanning lines for at least one line period, and a logic circuit for receiving and carrying out a logic operation on the logic 0 or logic 1 signal corresponding to each picture element on said first scanning line and that corresponding to a respective one of each picture element on at least one other scanning line to form a resultant logic 1 signal or logic 0 signal, the resultant logic signals constituting a signal train having logic 0 sections and logic 1 sections, and means for coding said logic signal train for transmission.
8. A transmitting apparatus substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.
9. A receiving apparatus comprising means for decoding the signal transmitting apparatus as claimed in claim 7 or claim 8, and scanning means for reproducing the transmitted image.
10. A receiving apparatus substantially as hereinbefore described with reference to Figure 4 of the accompanying drawings.