Information transmission method and apparatus

Abstract: In an information transmission method and apparatus, information is transmitted in units of a block including information codes and error-correcting check codes, and the transmission speed is switched by changing the number of blocks to be transmitted per unit time without changing the amount of information of the information codes and the amount of information of the error-correcting check codes within each block.

Description: This invention relates to an information transmission method and apparatus, and more particularly, to an information transmission method and apparatus in which the transmission speed of information can be switched. FIG. 4 is a diagram schematically illustrating transmitted information whose amount per unit time T (seconds) (the data rate) equals N (bits). In FIG. 4, a hatched portion 11 represents check codes for error correction. FIG. 4 illustrates a case in which the redundancy for the total amount of information N (bits) including an information-code portion 12 equals m, and the following amount of check codes per unit time T (seconds) equals mN (bits). A case will now be considered in which the amount of information to be transmitted per unit time T (seconds) (transmission speed) is changed to kN (bits). FIG. 5 is a diagram schematically illustrating information to be transmitted per unit time in such a case. If it is assumed that the redundancy m is not changed for the purpose of not changing the error correction capability, the amount of check codes per unit time T (seconds) becomes kmN (bits), as shown in FIG. 5. In the above-described transmission format, therefore, the amount, of check codes per unit time T (seconds) following the information codes is changed if the transmission speed is changed. Hence, it is necessary to change the form of the error-correcting code so as to be suitable for the amount of check codes. This results in providing different forms of error-correcting codes for different transmission speeds, causing difficulty in circuit design and an increase of the size of the hardware. The above-described approach also has the problem that even though the redundancy is not changed, the correction capability may change when different error-correcting codes are used in accordance with the form of the error-correcting code. Such a conventional method of transmitting data is disclosed in JP-A-2123831 and EP-A-0271866. An article entitled "HDTV Transmission System and Coding Method in an ATM Network" (in Signal Processing of HDTV II., Proceedings of the Third International Workshop on HDTV, September 1989, pages 561-568, Kishimoto et al) discloses an image transmission system in which image data is quantized and variable length encoded. The encoded data is then divided into blocks of fixed length and error correction codes are added to the blocks to form blocks of fixed length. The fixed length blocks are transmitted using ATM asynchronous transfer mode (ATM) and the number of fixed length blocks transmitted per second can be varied thus varying the data transmission speed. According to one aspect the present invention provides an image transmission apparatus for transmitting image data at one of a plurality of transmission speeds, the apparatus comprising: a) encoding means for variable length encoding image data to generate encoded image data; b) dividing means for dividing the encoded image data into a plurality of blocks of encoded image data, each block of encoded image data having a fixed number of codes; c) error-correcting encoding means for forming a fixed number of error-correcting check codes for each block of encoded image data processed by said dividing means; d) formation means for forming fixed-length blocks of data, each fixed length block including a said block of encoded image data produced by said dividing means and the error-correcting check codes formed for the block of encoded image data by said error-correcting encoding means; e) output means for outputting the fixed-length blocks of data formed by said formation means; and f) outputting control means for controlling the number of fixed length blocks of data output per unit time by said output means in accordance with the transmission speed without changing the number of error correcting check codes or the number of codes of the encoded image data in each block; characterized in that said encoding means includes encoding control means for controlling the amount of encoded image data of a picture frame of the image data to be constant. According to a second aspect the present invention provides a method of transmitting image data at one of a plurality of transmission speeds, the method comprising: a) forming encoded image data by variable length encoding image data; b) dividing the encoded image data into a plurality of blocks of encoded image data, each block of encoded image data having a fixed number of codes; c) forming a fixed number of error correcting check codes for each block of encoded image data; d) forming fixed length blocks of data, each fixed length block including a said block of encoded image data produced by the dividing step and the error correcting check codes formed for the block of encoded image data; e) outputting the fixed length blocks of data; and f) controlling the number of fixed length blocks of data output per unit time in accordance with the transmission speed without changing the number of error correcting check codes or the number of codes of the encoded image data in each block; characterized in that the step of forming encoded image data includes controlling the amount of encoded image data of a picture frame of the image data to be constant. Embodiments of the present invention will now be described with reference to the accompanying drawings, in which: FIG. 1 is a block diagram showing the schematic configuration of an image transmission apparatus according to an embodiment of the present invention; FIG. 2 is a diagram schematically illustrating an information-code string to be transmitted per unit time in a first mode in the image transmission apparatus shown in FIG.1; FIG. 3 is a diagram schematically illustrating an information-code string to be transmitted per unit time in a second mode in the image transmission apparatus shown in FIG.1; FIG. 4 is a diagram schematically illustrating conventional information to be transmitted per unit time; and FIG. 5 is schematically illustrating conventional information to be transmitted per unit time at a transmission speed different from that shown in FIG. 4. A preferred embodiment of the present invention will now be explained in detail with reference to the drawings. FIG. 1 is a block diagram showing the schematic configuration of an image transmission apparatus to which the present invention is applied. In FIG. 1, there is shown an input terminal 101 for image signals. An image signal input from the input terminal 101 is supplied to a quantization circuit 102. The quantization circuit 102 performs quantization in accordance with a quantization coefficient determined by transmission-speed information input from a transmission clock signal generation circuit 105 and information relating to the amount of encoded data input from a variable-length encoding circuit 103, so that the amount of data which are finally output is constant in units of each picture frame. The variable-length encoding circuit 103 performs variable-length encoding of information output from the quantization circuit 102 and supplies the encoded information to a data adding or synthesis circuit 106, and also outputs the information to the quantization circuit 102 for determining the quantization coefficient in accordance with the amount of data of the encoded information. The data synthesis circuit 106 divides the image information subjected to variable-length encoding into respective blocks for every predetermined amount of codes. An error-correcting code generation circuit 104 generates check codes and adds the generated check codes to each of the above-described blocks. Each block to which the check codes are added will be hereinafter termed a small block. The transmission clock signal generation circuit 105 supplies the data synthesis circuit 106 with a transmission clock signal whose frequency is switched in accordance with the transmission speed. The data synthesis circuit 106 changes the number of small blocks to be transmitted per unit time so that the desired transmission speed can be obtained in accordance with the transmission clock signal. It is thereby possible to supply a code string at the desired transmission speed to an output terminal 107. FIG. 2 is a diagram schematically illustrating an information-code string to be transmitted in a unit time T (seconds) in a first mode in the image transmission apparatus shown in FIG. 1. In FIG. 2, reference numeral 1 indicates the total amount N (bits) of codes to be transmitted in the unit time T (seconds). The encoded image information is divided into n portions (2a - 2n shown in FIG. 2), one for each small block containing the predetermined amount of information codes. The total amount of codes in each of the divided small blocks equals N/n (bits). Check codes 3a - 3n for error correction whose amount is defined by a predetermined redundancy m are added to the respective small blocks. The amount of check codes in each small block equals mN/n (bits). FIG. 3 is a diagram schematically illustrating an information-code string to be transmitted per unit time T (seconds) in a second mode in the image transmission apparatus shown in FIG. 1, when the amount of codes to be transmitted per unit time T (seconds) is assumed to be kN (bits). In FIG. 3, reference numeral 4 indicates the total amount kN (bits) of codes to be transmitted in unit time T (seconds). The encoded image information is divided into x (= nk) portions (2a - 2x shown in FIG. 3), one for each small block containing the predetermined amount of information code. Also, the amount of check codes 3a - 3n in each small block is mN/n (bits). Thus, the amount of image information and the amount of information of check codes in each of the x divided small blocks are the same as in the first mode. The total amount of codes in each small block therefore equals N/n (bits). The desired transmission speed can be obtained by arranging that the value nk be an integer. Accordingly, by making the value n as large as possible, the degree of freedom increases for the value k. Consequently, the value k is not necessarily an integer. That is, if the number of different transmission speeds which can be used is small, the amount of codes may be determined so that the total amount of codes to be transmitted becomes an integer multiple of the amount of codes in each block. As is apparent from the foregoing explanation, in the information transmission method and the information transmission apparatus of the present invention, while transmission at different speeds can be performed, the amount of information of information codes and the amount of information of check codes for error correction within a block do not change. Hence, the error correction capability does not have to change in any way even if the transmission speed is changed, and thus the problem in the prior art that the error correction capability changes when the transmission speed is changed is overcome. In addition, the size of the hardware does not increase since exactly the same error processing can be performed for different transmission speeds. The present invention can be executed in various other forms without departing from the scope of the invention. For example, although in FIGS. 2 and 3 illustrating the above-described embodiment, encoded image information and check codes for error correction are alternately arranged, the object of the present invention may, of course, be achieved no matter how they are arranged in the information transmission string, provided that all information in the information transmission strings 1 and 4 in FIGS. 2 and 3, respectively, can be transmitted in a unit time T (seconds). In other words, the foregoing description of the embodiment has been given for illustrative purposes only and not to be construed as imposing any limitation in every aspect. The scope of the invention is, therefore, to be determined by reference to the following claims and is not limited by the text of the specification, and alterations may be made within the scope of the appended claims.

Claims: An image transmission apparatus for transmitting image data at one of a plurality of transmission speeds, the apparatus comprising: a) encoding means (102,103) for variable length encoding image data to generate encoded image data; b) dividing means (106) for dividing the encoded image data into a plurality of blocks of encoded image data, each block of encoded image data having a fixed number of codes; c) error-correcting encoding means (104) for forming a fixed number of error-correcting check codes for each block of encoded image data processed by said dividing means (106); d) formation means (106) for forming fixed-length blocks of data, each fixed length block including a said block of encoded image data produced by said dividing means (106) and the error-correcting check codes formed for the block of encoded image data by said error-correcting encoding means (104); e) output means (107) for outputting the fixed-length blocks of data formed by said formation means (106); and f) outputting control means (105) for controlling the number of fixed length blocks of data output per unit time by said output means (107) in accordance with the transmission speed without changing the number of error correcting check codes or the number of codes of the encoded image data in each block; characterized in that said encoding means (102,103) includes encoding control means (102) for controlling the amount of encoded image data of a picture frame of the image data to be constant. An apparatus according to claim 1, wherein said encoding control means (102) comprises quantizing means for quantizing the image data. An apparatus according to claim 2, wherein said quantizing means (102) is adapted to determine a quantization coefficient for use in the quantization so as to fix the number of codes of the encoded image data in a picture frame of the image data. A method of transmitting image data at one of a plurality of transmission speeds, the method comprising: a) forming encoded image data by variable length encoding image data; b) dividing the encoded image data into a plurality of blocks of encoded image data, each block of encoded image data having a fixed number of codes; c) forming a fixed number of error correcting check codes for each block of encoded image data; d) forming fixed length blocks of data, each fixed length block including a said block of encoded image data produced by the dividing step and the error correcting check codes formed for the block of encoded image data; e) outputting the fixed length blocks of data; and f) controlling the number of fixed length blocks of data output per unit time in accordance with the transmission speed without changing the number of error correcting check codes or the number of codes of the encoded image data in each block; characterized in that the step of forming encoded image data includes controlling the amount of encoded image data of a picture frame of the image data to be constant. A method according to claim 4 wherein the image data is quantized during the encoding step. A method according to claim 5 wherein a quantization coefficient used during the quantization is determined so as to fix the number of codes of the encoded image data in a picture frame of the image data.

Inventors: TAKIZAWA HIROSHI, TAKIZAWA, HIROSHI, Takizawa, Hiroshi, c/o Canon Kabushiki Kaisha
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1992
Main classification: H04N1
IPC codes: G06T9, H04N1, H04N7, H04L1