AU655800B2 - Systems for encoding and decoding data in machine readable graphic form - Google Patents

Description

S F Ref: 206398 AUSTRALIA 0 PATENTS ACT 199" V COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

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Name and Address of Applicant: Actual Inventor(s): Address for Service: Invention Title: Symbol Technologies, Inc.

116 Wilbur Place Bohemia New York 11716 UNITED STATES OF AMERICA Ynjiun P. Wang Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia Systems for Encoding and Decoding Data in Machine Readable Graphic Form The following statement is a full description of this invention, including the best method of performing it known to me/us:- 5845/4 BACKGROUND OF THE INVENTION SThe present invention generally relates to the representation of data in machine readable form, and more particularly to a method and apparatus for encoding and decoding data into a twodimensional graphic image, such as the two-dimensional bar code PDF417, that can be automatically machine read to obtain the encoded data in both open and closed systems.

In today's high-technology world, more and more operations are being automatically performed by machines and systems. This io ever-increasing drive for automation has resulted in a demand for new techniques for encoding data into machine readable form for o.

automatic entry into the various systems and machinery. The data entry may be for such uses as data transmission, operating various machine functions or the identification of persons or items. The various media that carry the data for automatic entry include punch cards, magnetic tapes and discs and magnetic stripes on cards such as credit cards and badges. The systems utilizing the above carriers are in "closed" systems, the read function is performed within an apparatus or housing and the reading element

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2 is in contact or in near-contact with the carrier means during the reading operation.

One method for representing data in a machine readable form is to encode the data into a pattern of indicia having parts of different light reflectivity, for example, bar code symbols. A bar code symbol is a pattern comprised of a series of bars of various widths and spaced apart from one another by spaces of various widths, the bars and spaces having different light reflective properties. The bars represent strings of binary ones fy to and the spaces represent strings of binary zeros. Generally, the bars and spaces can be no smaller than a specified minimum width which is called a "module" or "unit." The bars and spaces are multiples of this module size or minimum width.

Bar code symbols are typically priLted directly on the object Is or on labels that are attached to the object. The bar code symbols are read by optical techniques, such as scanning laser beams or CCD cameras, and the resulting electrical signals are decoded into data representative of the symbol for further processing. Bar code reading systems are known as "open" systems 20 in that the carrier while being read is not sealed, but is read from a distance and without being in physical contact with the o scanner.

The conventional bar code described above is "onedimensional" in that the information encoded therein is *iirepresented by the width of the bars and spaces, which extend in a r. single dimension. Thus, a bar code of a supermarket item, for example, consists of a string of eleven digits which represent an 3 identifying number, but not a description of the item. The remainder of the relevant information, such as the price, name of the product, manufacturer, weight, inventory data, and expiration date, must be obtained from a database using the identification number. Similarly, data encoded onto other media such as credit card magnetic stripes is composed of one or more "one-dimensional" tracks of encoded data.

The use of bar code symbols and magnetically encoded data has found wide acceptance in almost every type of industry. However, the one-dimensional nature of the encoded data limits the amount of information that can be encoded and hence use has been generally restricted to simple digital representations.

There is an increasing need, however, for a system to encode data in machine readable form that allows for an increase in the amount of data encoded into a given space that can be quickly and easily decoded for further processing. In particular, there is a desire to create "portable data files" which provide more than an identification number which is then used as an index to reference a database. The "portabie data file" approach is well-suited to 1Oapplications where it is impractical to store item information in a database or where the database is not readily accessible when and where the bar code is read. For example, information such as the contents of a shipping manifest or an equipment maintenance history could be carried directly on the object without requiring i access to a remote database. Similarly, a hospital could use portable, data files to put more medical information on patient identification bracelets. In a manufacturing environment, 4 portable data files could be used to keep production records or even to provide instructions to control machine operations.

Ideally, such portable data files could contain up to several hundred or more characters in a relatively small area, but still be read from a distance by a hand-held laser scanner.

One approach for increasing the information in machinereadable symbols is to reduce the height of the bar codes and stack the bar codes one on top of each other to create a "stacked" or "two-dimensional" bar code. A major problem in reading twoi o dimensional symbols, however, is the loss of vertical synchroniztwion. As shown in Figure 1A, if the data rows are too short or the scan line intersects the row at a large angle, the scan lines will not coincide with the horizontal lines of the pattern. The height of the rows can be increased as shown in t Figure 1B, but this causes an obvious reduction of information density.

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A proposed solution to the vertical synchronization problem is to include both row identifiers and local row discriminators in the two-dimensional bar code symbol in order to distinguish S.ao between the rows. One such two-dimensional bar code with row s ee 0 identifiers and local row discriminators is PDF417, which was developed by Symbol Technologies, Inc. A more complete 5 3 7 g- description of PDF417 is contained in U.S. Patent S:aia- mu. 07-'461 ,881, filed January 5, 1990, and assigned to the 2 same assignee as the present invention, which is hereby incorporated by reference.

5 j f3; Even if the symbol is constructed so that the rows can be distinguished from one another, however, there remains the problem of how to decode such a symbol efficiently.

In particular, it is not enough for a decoding method or apparatus to simply recognise that a scan line crossed a row boundary.

SUMMARY OF THE INVENTION According to the invention there is provided a system for representing and recognising data in the form of a machine readable two-dimensional bar code structure comprising: encoding means including: entering means for entering data in said encoding means; processing means for encoding said data into a two-dimensional bar code structure, said bar code structure including a plurality of ordered, adjacent rows of codewords of bar-coded information, each of said codewords representing at least one information-bearing character; and recognition means including: scanning means for scanning an image of the two-dimensional bar code structure and for converting the codewords into electrical signals representative of the information-bearing characters; and decoding means for decoding the electrical signals into output signals 20 representative of said data.

x [N:\libe]00108:rhk -7- The invention also provides an encoding apparatus for use in a system for secure transmission of data, the apparatus comprising: means for entering data; means for encrypting at least some of said data using an encryption algorithm based upon an encryption key; and means for representing said encrypted data in the form of a two-dimensional bar code structure, said bar code structure including a plurality of ordered, adjacent rows of codewords of bar-coded information, each of said codewords representing at least one information-bearing character.

The invention also provides a decoding apparatus for use in a system for secure transmission of data by a two-dimensional bar code structure, said bar code structure including a plurality of ordered, adjacent rows of codewords of bar-coded information, each of said codewords representing at least one information-bearing character, the apparatus comprising: means for scanning the two-dimensional bar code structure and converting the codewords into output signals representative of said information-bearing characters, and ~means for decrypting at least some of said information bearing characters using a decryption algorithm based upon an encryption key.

*lo* *a ]0 lN:\l1e00108:rhk -8- The invention also provides a facsimile communications system for transmitting a document to a destination comprising: means for entering transmission infonnation including a destination telephone number; means for converting said transmission information into a two-dimensional bar code representation; means for affixing said two-dimensional bar code representation of said transmission information, including thedestination telephone number, to said document; means for scanning said document, including said two-dimensional bar code representation fixed thereto, and for p'oducing signals representing said transmission information; and means for transmitting said document to said destination in accordance with said signals representing said transmission information, including the destination telephone number, wherein said two-dimensional bar code representation includes a plurality of ordered, adjacent rows of codewords of bar coded information, each of said codewords representing at least one information-bearing character.

go *ft o* *o *o~o [N:\libe]00108:rhk -9- The invention also provides a method of operating a facsimile communications system for transmitting a document to a destination, comp.ising the steps of: entering transmission information including a destination telephone number on a keyboard; converting said transmission information into a two-dimensional bar code representation; affixing said two-dimensional bar code representation of said transmission information, including the destination telephone number, to said document; scanning said document, including said two-dimensional bar code representation affixed thereto, and producing signals representing said transmission information; and transmitting said document to said destination in accordance with said signals representing said transmission information, including the destination telephone number, wherein said two-dimensional bar code representation includes a plurality of ordered, adjacent rows of codewords of bar-coded information, each of said codewords representing at least one information-bearing character.

e e 9 [N:\libe]00108:rhk The invention also provides an apparatus for decoding a two-dimensional bar code symbol, the bar code symbol including a plurality of ordered, adjacent rows of codewords of bar-coded information from a set of codewords, ths, set of codewords being partitioned into at least three mutually exclusive clusters, each row in the symbol having at least one row indicator codewords and containing only codewords from a cluster different from the codewords in an adjacent row, comprising: means for scanning the two-dimensional bar code symbol to produce scan lines of data representing the bar-coded information in the codewords of the symbol; means for decoding a scan line of data into a vector of codeword values corresponding to the codewords that were scanned, at least one of the codeword values being for a row indicator codeword; means for assigning a row number to each of the codeword values in the vector based on the value of the row indicator codeword and the cluster of the codeword; and means for filling in a codeword matrix with the codeword values in the vector according to their assigned row numbers.

ea *to [N\libe]00108:rhk 4 1 '1 -11 A laser light beam can be scanned across the indicia in a raster pattern for reading and decoding two-dimensional graphic codes. Optical scanners suitable for reading two-dimensional patterns are disclosed in European Patent Application Nos.

89116393.3 and 90104029.5 (published under nos. 0,384,955 and 0,385,478 respectively), which are incorporated herein by reference.

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention, by way of example only.

BRIEF DESCRIPTION OF THE DRAWINGS Figures 1A and 1B are diagrams illustrating the intersection of scan lines with the rows of a two-dimensional bar code symbol; Figure 2 is a diagram illustrating one example of a codeword in PDF417; Figure 3 is a diagram illustrating the overall structure of a PDF417 symbol; Figure 4 is a table listing the number of error correction codewords for a given security level in PDF417; Figure 5 is a block diagram of the system of the present invention; Figure 6 is a perspective view of an encoding means of the system of the present invention; Figure 7 is a perspective view of a recognition means of the system of the present invention; **5

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*of o** [N:libe]00108:rhk Figure 8 is a perspective view of a data entry device and reader in which a key may be entered for encrypting and decrypting data; Figure 9 is a perspective view of a facsimile machine incorporating the recognition means of the present invention; Figure 10 is a schematic diagram of another embodiment of recognition means for scanning and decoding a two-dimensional bar code symbol;' Figure 11 is a schematic block diagram of an embodiment of 0O the hardware apparatus of a low-level decoder for decoding a twodimensional bar code symbol; Figure 12 is a flow diagram of the steps performed by the low-level decoder for decoding a two-dimensional bar code symbol; Figure 13 is a flow diagram of the steps performed by the i low-level decoder for determining the dimensions and security Slevel of the symbol being scanned; Figure 14 is a flow diagram of the steps performed by the low-level decoder for searching a scan line of data for a start or a stop pattern; o* i20 Figure 15 is a diagram illustrating the various width *a measurements that are used for the "t-sequence" of a codeword; e

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Figure 16 is a flow diagram of the steps performed by the low-level decoder for decoding a scan line of data into a vector of codeword values and their cluster numbers; 2T" Figures 17A, 17B, and 17C are diagrams showing an example of a codeword vector; 12 Figure 18 is a flow diagram of the steps performed by the low-level decoder for decoding an individual codeword value and its cluster number from the scan line data; and Figures 19A and 19B together are a flow diagram of the steps performed by the lo,-level decoder in order to update the codeword matrix using the codeword vector.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the presently preferred embodiments of the invention, examples of which are S ,o illustrated in the accompanying drawings.

Code PDF417 Before discussing the method and apparatus of the invention for encoding and decoding data in machine readable graphic form, such as the two-dimensional bar code PDF417, it is important to understand the structure olE the two-dimensioral bar code symbol itself.

Each PDF417 symbol is composed of a stack of rows of barcoded information. Each row in the symbol consists of a start pattern, several symbol characters called "codewords," and a stop pattern. A codeword is the basic unit for encoding a value zrepresenting, or associated with, certain numbers, letters, or other ,symbols. Collectively, the codewords in each row form data Scolumns.

Both the number of rows and the number of data columns of the PDF417 symbol are variable. The symboYi must have at least three 13 -rows and may have up to ninety rows. Likewise, within each row, the number of codewords or data columns can vary from three to thirty.

Each PDF417 codeword consists of seventeen modules or units.

There are four bars and four spaces in each codeword. Individual bars or spaces can vary in width from one to siz modules, but the combined total per codeword is always seventeen modules. Thus, each codeword can be defined by an eight-digit sequence, which represents the four sets of alternating bar and space widths owithin the codeword. This is called the "X-sequence" of the codeword and may be represented by the sequence XO,X, .X 7 For example, for an X-sequence of "51111125", the first element is five modules wide, followed by five elements one module wide, one element two modules wide, and the last element five modules wide.

6This example is illustrated in Figure 2.

The set of possible codewords is further partitioned into three mutually exclusive subsets called "clusters." In the PDF417 symbol, each row uses only one of the three clusters to encode data, and each cluster repeats sequentially every third row.

2oB ecause any two adjacent rows use different clusters, the decoder is able to discriminate between codewords from different rows within the same scan line.

The cluster number of a codeword may be determined from its X-sequence using the following formula: u 2- cluster number (X X 2 X X 6 mod 9 14 where "mod 9" is the remainder after division by nine. Referring to the codeword in Figure 2, the cluster number is calculated as follows: cluster number (5 1 1 2) mod 9 3 To minimize error probabilities, PDF417 uses only three clusters, even though nine are mathematically possible. Thus, each row uses only one of the three clusters 0, 3, or 6, to encode data, with the same cluster repeating sequentially every third row. Row 0 codewords, for example, use cluster 0, row 1 uss io cluster 3, and row 2 uses cluster 6, etc. In general, the cluster number may be determined from the row number as follows: cluster number ((row number) mod 3) 3 There are 929 codeword values defined in PDF417. These 1I values are 0 through 928 Each cluster presents the 929 available i values with distinct bar-space patterns so that one cluster cannot be confused with another.

o** Figure 3 is a block diagram showing the overall structure of a PDF417 symbol. Each row of the symbol consists of a start pattern, a left row indicator codeword data codewords d i or 26 error detection/correction codewords Ci, a right row indicator codeword and a stop pattern. The minimum number of codewords in a row'is three, including the left row indicator codeword, at least one data codeword, and the right row indicator codeword.

15 .1 13~ Y .The right and left row indicator codewords, which are discussed further below, help synchronize the structure of the symbol.

The start and stop patterns identify where each row of the symbol begins and ends. PDF417 uses unique start and stop patterns. The start pattern, or left side of each row, has the unique pattern, or X-sequence, of "81111113". The stop pattern, or right side of each row, has the unique X-sequence of "711311121".

Every symbol contains one codeword (the first data codeword 0 oin row 0) indicating the total number of codewords within the symbol, and at least two error-detection codewords C 0 and C 1 These two error-detection codewords together form a checksum which is two codewords long.

A PDF417 symbol can also encode data with error correction 1 capability. The level of error correction capability, called the *4 "security level," is selected by the user and ranges from 0 to 8.

SThis means, for example, that at level 6, a total of 126 codewords can be either missing or destroyed and the entire symbol can be read and decoded. Figure 5 is, a table showing the relatioiiship m e 2 obetween the security level of the PDF417 symbol and the number of error correction codewords C..

In addition to correcting for missing or destroyed data (known as "erasures"), PDF417 can also recover from misdecodes of codewords. Since it requires two codewords to recover from a zmisdecode, one to detect the error and one to correct it, a given security level can support half the number of misdecodes that it can of undecoded codewords.

16 S 'The row indicator codewords in a PDF417 symbol contain several key components: row number, number of rows, number of data columns, and security level. Not every row indicator contains every component, however. The information is spread over Sseveral rows, and the pattern repeats itself every three rows.

The pattern for encoding the information in the row indicator codewords can be illustrated as follows: Row 0: LO (row of rows) RO (row of columns) S Row 1: L 1 (row security level) R1 (row of rows) 0 Row 2: L 2 (row of columns) R 2 (row security level) Row 3: L 3 '.row of rows) R 3 (row of columns) etc.

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In other words, the left row indicator codeword LO for the first row 0 contains the row number and the total number of rows in 15 the symbol. The right row indicator codeword R 0 for row 0 contains the row number and the number of data columns in the symbol, and so on. Encoding data into a PDF417 symbol is typically a two-step process. First, data is converted into codeword values of 0 to 20928, which represent the data. This is known as "high-level encoding." The va$s are then physically represented by particular bar-space patterns, which is known as "low-level encoding." 17 Encoding/Decoding System Referring now to Figures 5-7 in the drawings, Figure 5 is a block diagram of the system 10 of the present invention for representing and recognizing data in machine readable graphic Simage form. System 10 includes an encoding means generally indicated by the reference numeral 12 and a recognition means generally indicated by the reference numeral 14. Encoding means 12 produces a carrier means 16 containing at least a twodimensional pattern of graphic indicia 18. Carrier means 16 may to also contain human readable data 20. The two-dimensional pattern of graphic indicia on carrier means 1i is recognized by recognition means 14 to produce output signals representative of the data encoded into the pattern 18.

see: Data to be transferred onto carrier means 16 is entered by :lentering means 22 into the encoding means 12. The data entered by entering means 22 may be both the data to be encoded into the twodimensional pattern of graphic indicia and the data to appear on carrier means 16 in human readable form. Processing means 24 encodes the set of data to appear in pattern 18 into a two- S"2odimensional pattern praphic indicia and generates transfer S drive signals for controlling the transfer of the indicia onto the I* carrier means 16. Transferring means 26 transfers an image oc the two-dimensional pattern of graphic indicia onto carrier means 16 S in response to the transfer drive signals. If human readable data :lis also to be transferred onto carrier 16, the processing means 24 generates a second set of transfer drive signals for controlling the transfer of the human readable data onto carrier 16. A 18 portion or all of the data to be encoded and the human readable data may be transferred from a storage memory in processing means 24 or other computer files rather than being entered by means 22.

The carrier means 18 shown in Figures 5, 6, and 7 is represented as being in the form of a card approximately the size of a credit card. This type of card is illustrative only as the carrier means 18 may be made of any material on which graphic indicia may be transferred to, such as paper, etc.

Recognition means 14 includes converting means 28 that loconverts the image on carrier means 16 into electrical signals S representati of the graphic indicia. Decoding means 30 decodes the electrical sign&is into decoder output signals indicated at 32 that are representative of the data encoded into the pattern 18.

Figure 6 is a perspective view of one embodiment of encoding &tmeans 12. In this embodiment, the entering means 22 of Figure is shown in form of a keyboard 32 for entering alphanumeric and graphic data into the encoding means 12. The embodiment of Figure 6 is illustrative only as entering means 22 may take forms other than a keyboard such as an optical scanning means for scanning 2odata directly from documents for entry into the encoding means 12.

Entering means 22 may also be in the form of various card readers in which magnetically encoded information is scanned and converted into electrical signals representative of the data.

4 Referring again to Figure 6, the processing means 24 of l. Fi;.re 5 is shownrin the form of a processor and display unit 34.

SThe data entered by keyboard 32 is transmitted to the processor and display unit 34 for storage and processing. In addition to 19 Sentering data. the keyboard 32 is also used for entering control commands to effect operation of the processor unit 34.

The data entered by keyboard 32 is displayed on display screen 36 and upon entry of a proper control command, is also Sstored in memory. The data to be encoded into the pattern of graphic indicia is stored in a first memory, in processor 34 and the data, if any, to be transferred in human readable form is stored in a second memory. Alternatively, the data may be stored in a separate portion of a single memory. Upon the appropriate o control command from keyboard 32, the processor unit 34 encodes the d~ta in the first memory into a two-dimensional pattern of graphic indicia and generates first transfer drive signals representative of the data stored in the first memory. The 9* processor unit 34 also generates second transfer drive signals S representative of the data stored in the second memory.

e The processor unit 34 is shown in Figure 6 as being coupled to a printer 38. The printer 38 is one form of the transferring means 26 of Figure 5. Printer 38 transfers an image of the two- S dimensional pattern of graphic indicia on carrier means 18 in l* o aresponse to the first transfer drive signals and prints the second S set of data in human readable form onto carrier means 18 in *e response to the second transfer drive signals. In one embodiment, the printer 38 prints the two-dimensional pattern in the form of graphic indicia having different areas of light reflectivity, such 1( as the two-dimensional bar code described above. Printer 38 may c take other forms such as a means for printing the two-dimensional pattern of graphic indicia with magnetic-ink. In such a device, 20 magnetic indicia are deposited on the carrier material in a twodimensional pattern that may be recognized by magnetic-ink recognition sensors.

Turning now to Figure 7, the recognition means 14 includes a card reader 40 which contains the converting means 28 and the S decoding means 30 of igure 5. The converting means 28 may be a bar code reader such as those disclosed in U.S. Patent Application Serial Nos. 317,433 and 317,533, assigned to the same assignee as the present invention and incorporated herein by reference. The S to readers disclosed in the above patent applications are open system(L) devices designed to read an optically encoded two-dimensional bar code and to convert the light reflected from the pattern into electrical signals representative of the graphic indicia.

The card reader 40 may also comprise a magnetic-ink 0O e recognition device for reading and decoding magnetically encoded eggs data. These closed system devices include a magnetic read head that senses the change in reluctance associated with the presence of the magnetic-ink. The use of appropriate converting means that corresponds to the particular data encoding technology employed is 0 contemplated by the present invention.

S"The decoding means 30 decodes the electrical signals into e g.

output signals representative of the data encoded onto carrier means 18. The decoder output signals are outputted from the recognition unit 40 to various output means 42. Figure 7 depicts z,2two examples of output devices, one being a display unit 44 and the other a printer 46. Display unit 44 may be any suitable display such as liquid crystal display or a CRT. The printer 46 -21 may be any print device such as a dot matrix printer, laser printer, etc.

Theasystem of the present invention maximizes the use of available space for encrypting data. The density of the encoded Sdata is such that for a two-dimensional bar code s mbol, a minimum of about 1600 characters can be encoded into a space of approximately 5" x In addition to being compact in size, the system provides for high secIrity in the transmission of information. For example, a sensitive message may be encoded onto S lo a document also containing non-sensitive material. This document, the same as any document, can be copied, transmitted by facsimile, etc., but only those with a recognition means of the present q invention will be able to "read" the sensitive portion. The carrier means, being a single sheet of paper or a plastic credit ie card type of card, is an inexpensive read-only-memory structure that facilitates data communication.

In another embodiment, the data may be encoded using a keyed eS encryption algorithm that may be accessed only by an encryption 0 key. As shown in Figure 8, the data entry means 47 contains the 9okeyed algorithm and upon entry of the key 49, the data will be encoded into a two-dimensional graphic pattern in a unique configuration. The unique configuration can only be read by a .reader 48 having the algorithm and only upon entry of the key 49 into the reader. Thus, a high degree of security may be provided with the'keyed encryption embodiment.

In addition, the recognition unit 40 may also transmit the S" output signals to a central processing unit locally or remotely, 22 *by for example a modem, for further use or processing by the CPU.

In this embodiment, the data encoded onto the carrier means 18 may be control data in the form of machine operating instructions for controlling a robotic system or to a security identification system for performing such functions as unlocking doors. In connection with the use of the present invention in a robotic system, it is contemplated that the two-dimensional graphic pattern containing the control data be placed or printed directly onto a machine part or part holder. A scanner coupled to the machine tool reeds the pattern and transmits the decoded instruction to the control computer which in turn controls the machining of the part in accordance with the control program.

Another example of the use of the present invention includes a microwave food container where the two-dimensional graphic pattern i5 contains instructions automatically entering the recommended cooking sequence. A further use may be in connection with placing on roadway signs two-dimen.ional patterns containing geographic location information that may be read by a scanner in passing vehicles for use with onboard computers.

lo The present invention further contemplates the use of the 0 system of the present invention to encode control data containing machine operating instructions onto the carrier means in the form, of machine readable graphic indicia that may be inserted into the machine to effect operation of the machine. Figure 9 is an example of a facsimile machine 50 in which a document 52 containing human readable data 54 and a two-dimensional pattern of graphic machine readable indicia 56. The document 52 is inserted 23 into the facsimile machine 50 the same as documents are normally inserted for transmission. The machine 50 contains a converting means for converting the two-dimensional image into electrical signals and a decoding means for decoding the signals into output signals operative to actuate the facsimile machine 50. The pattern 56 may contain such information as the phone number of the intended recipient of the memo 54 and the appropriate instructions for automatically entering the phone number and actuating the transmission process. Thus, where numerous messages are faxed to So a particular recipient, a supply of paper containing the phone number of the recipient encoded in the two-dimensional graphic indicia machine readable format may be maintained by the sender.

The transmission of messages to that recipient will be facilitated by placing the message onto the pre-encoded paper and simply 1inserting the paper into the facsimile machine. In addition to simplifying and speeding the transmission process, the possibility of sending highly sensitive information to an incorrect party will also be eliminated.

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24 Scanning/Decoding Apparatus Referring now to Figure 10, there is illustrated a further embodiment of the recognition means 14 for scanning and decoding graphic indicia in machine readable form, where that graphic S indicia is in the form of a two-dimensional bar code symbol such as PDF417. As shown in Figure 10, the recognition means 14 includes a host computeo 112, which may be a personal computer, a low-level decoder 114, and a hand-held laser scanner 116. Scanner 116 uses a laser light beam 118 to scan a two-dimensional bar code o symbol 120 in a raster pattern while a trigger 122 is pulled. A laser scanner suitable for scanning a two-dimensional bar code symbol is disclosed in U.S. Patent Application No. 07/317,433, filed March 1, 1989, and assigned to the same assignee as the present invention, which is hereby incorporated by reference.

Electrical signals from laser scanner 114 are transmitted to *soc low-level decoder 114 where they are decoded into a ?atrix of codeword values corresponding to the rows and columns of the twodimensional bar code symbol. As explained in further detail below, low-level decoder 114 may be embodied in a computer programnJ.

.0 operating on a micro-computer separate from the host computer.

9 The low-level decoder is connected to the host computer by a e standard interface, such as an RS-232 interface, for transmitting the codeword values after they are decoded. Alternatively, the low-level decoder 114 may be embodied entirely in hardware, or a lcombination of a hardware and software, which is physically located in.either the scanner itself or the host computer.

a 25 The matrix of codeword values from low-level decoder 114 is decoded into usable data by, high-level decoder, which may be embodied as a separate computer program operating on the host computer 112. For example, PDF417 has three predefined modes and nine reserved modes. The predefined modes are Binary, EXC, and Numeric. In the Binary mode, each codeword can encode 1.2 bytes.

In the EXC mode, the alphanumeric data can be encoded in double density two characters per code word), and in Numeric mode, the numeric data can be packed in almost triple density.

loTherefore, the high-level decoder in host computer 112 will further decode the codeword values (0-928) from low-level decoder 114, depending on the mode, to obtain the actual data embodied in the symbol. The decoded data from the high-level decoder may then be used by a user application program also operating on the host computer 112.

e**e* Low-Level Decoder Figure 11 is a schematic block diagram of one embodiment of the hardware apparatus of low-level decoder 114 shown in Figure In this embod)iment, the low-level decoder is primarily embodied in a computer program which is executed by a microcomputer separate from the host computer.

As shown in Figure 11, the low-level decoder includes a scanner interface 130 which receives the electrical signals from the scanner. The electrical signals from the scanner may be in the form of a digital signal which corresponds to the light and dark elements of the symbol as it is being scanned. Scanner 26 interface 130 converts the electrical signals into a sequence of integer values representing the varying widths of the bars and spaces and stores them in a buffer area of a memory 134. In order to accomplish this, scanner interface 130 is connected to a bus 132 to which the other hardware elements of the lowlevel decoder are also connected. Scanner interface 130 has direct memory access (DMA) capability which allows it to store the converted scanner data directly in the memory for decoding.

Low-level decoder also includes a central processing unit IO (CPU) 136 and a second interface 138 for communicating with the host computer. The interface to the host computer may be one or more standard interfaces such as an RS-232 interface.

Figure 12 is a flow chart showing the sequence of operation of the low-level decoder for decoding a two-dimensional bar code symbol such as PDF417 into a matrix of codeword values; The various steps in the sequence are embodied in a software computer program which is stored in memory 134 and executed by CPU 136 shown? in Figure 11.

In the first step 150 in Figure 12, the low-level decoder 2o initializes the scanner interface and initiates scanning of the symbol. The actual functions performed in this step will depend 0e on the type of scanner and will involve various scanner dependent routines to initialize the scanner interface and to start scanning.

In step 152, the low-level decoder attempts to determine the dimensions and the security level of the symbol being scanned.

Specifically, this step determines the number of rows, the number 27 of data columns, and the security level of the symbol from the left and right row indicator codewords. These dimensions are then used to initialize a two-dimensional codeword matrix and other related parameters for decoding the symbol. Each location in the matrix contains both a codeword value and an associated confidence weight, which are initially set to a null or empty value. If the dimensions and security level of the symbol cannot be determined, then the scan is aborted. This step will be discussed in further detail below in connection with Figure 13.

\o Continuing in Figure 12, step 154 is the first step in a control loop in which the rows of the two-dimensional bar code symbol are repeatedly scanned and the codeword values are filled into the codeword matrix. The steps of the control loop are each repeated until the number of codewords remaining in the matrix which have not been successfully decoded is small enough that rest of the matrix can be determined using the built-in error correction capability of the symbol. Thus, in step 154, if the number of codewords which have not been successfully decoded is less than the error correction capability of the symbol based on the security level (see Figure an attempt is made to correct the matrix using the error-correction codewords. If the attempted 0* error correction is successful, then in step 256, the control loop is exited and scanning is terminated in step 158. Otherwise, if the attempted error correction is not successful, then the ii following steps 160-164 are performed to try to decode additional codewords to fill in the matrix.

°009• 28 First, step 160 searches a scan line of data obtained from the buffer area of the memory for a start or a stop pattern. If either a start or a stop pattern is found, then in step 162, the low-level decoder attempts to decode as many codewords as possible from the scan line. Specifically, the scan line of data is parse, into individual codewords whose values and cluster numbers are placed in a codeword vector ready for incorporation into the codeword matrix. Both steps 160 and 162 are discussed in further detail below in connectionwith Figures 14 and 16, respectively.

1o The codeword vector produced in step 162 is analyzed and then used to update the codeword matrix in step 164. In particular, step 164 assigns a confidence weight to each codeword value depending on whether its nearest neighbors were also decoded. Row numbers are also assigned to each codeword value based on the left *l or right row indicator codewords and the corresponding cluster i. number for the codeword. If the scan line crosses a row boundary,

**O

the cluster numbers of the codewords can be used to determine the o* *6 S* correct row number for each individual codeword. For example, if a decoded scan line has a left row indicator with row number 2, W: and the cluster numbers of the following codewords are 6, 0, 0, 3,f the codewords are accordingly placed in the following locations: (row 2, column (row 3, column (row 3, column and (row *0 4, column In this way, a single scan line of data can contain codewords from more than one row, which can then be stitched into 2 the appropriate location in the codeword matrix. This step is discussed in further detail in connection with Figures 19A and 19B below.

29 if Figure 13 is a flow chart showing in greater detail the sequence of steps for determining the dimensions and security level of a symbol as referred to in step 152 of Figure 12 above.

In the first step 170 of Figure 13, the low-level decoder searches a scan line of data obtained from the buffer area of the memory for a start or a stop pattern. This step is the same as step 160 in Figure 12 and is discussed in further detail in connection with Figure 14 below.

Step 172 then decodes the first codeword immediately adjacent( o1 to either the start or stop pattern found in the previous step.

As shown in Figure 3, this codeword will be either a left or right row indicator codeword containing the row number and either the number of rows, the number of data columns, or the security level of the symbol. If both a start and a stop pattern are found, then 1'both the left and the right row indicators are decoded. The sequence of steps for decoding an individual codeword are discussed further below in connection with Figure 18.

Continuing in Figure 13, in step 174 the particular dimension S or security level encoded in the row indicator is extracted from the codeword value and the cluster number determined in the S. previous step 172. For example, for a left row indicator codeword with a cluster number of 0, the number of rows is extracted from S* the codeword value.

A confidence weight assigned to each of the dimensions and 2.1the security level is initially set to 0. Steps 176-184 update both the current value and the confidence weight of the dimension or security level extracted in the previous step in the following 30 way. First, the particular parameter, say the number of rows, is compared to the current value of the number of rows obtained from previous decodes. If the current value of the number of rows and the newly decoded value are the same, as determined in step 176, then the confidence weight assigned to the number of rows is increased in step 178. If the current value and the newly decoded value are different, however, then the confidence weight is decreased in step 180. If the confidence weight assigned to the particular parameter is decreased below zero as determined in step 1o 182, then the newly decoded value is substituted for the current value and a new minimum weight is assigned to the parameter in step 184.

Step 186 determines whether the confidence weight for all three parameters, number of rows, number of data columns, and security level, exceeds a predetermined thres, If so, then the two-dimensional codeword matrix is initia' in step 188 based on the current values of the number of rows and the S number of columns. The number of correctable errors may also be determined from the current value of the security level according o0 to the table in Figure 4. If all three confidence weights do not eb exceed the threshold in step 186, however, then program control returns to step 170 to begin searching for the start and stop a. patterns in a new scan line. Steps 170-184 are repeated until all three parameters have been successfully decoded with a high degree 2! of confidence.

Figure 14 is a flow chart showing in greater detail the sequence of steps for searching a scan line of data for a start or 31 I stop pattern as referred to above in step 160 of Figure 12 and step 170 of Figure 13. Briefly, the search begins at the first location of an individual scan line of data obtained from the buffer area of the memory and is repeated at sequential locations either a match is found or the length of the scan line is exceeded. When a match is found, an index is set to a location immediately following or preceding the pattern for decoding the adjacent code word.

As shown in Figure 14, the first step 200 sets an index to \o the location of the data elements in the scan line to indicating the first data element or integer value of the scan linLe. This index is used to identify the first element of each sequence of eight elements in the scan line for comparison to the start and stop patterns.

Step 202 is the first step of an iterative loop for searching the scan line from left to right for either a start or a stop pattern. In this step, if the current index is less than the length of the scan line, then the remaining steps are executed and the search continues. Once the index exceeds the length of the to scan line, however, thnhe loop is exited and an indication is 00 returned signifying that the\search failed and a start or stop 00 pattern was not found.

Rather than using the X-sequence of codeword, the low-level o decoder decodes a symbol by using "edge to similar edge"

S~

4 measurements to compensate for ink spreading which occurs when printing'the symbe-s. Thus, in step 204, a raw "t-sequence" is obtained from the scan line by adding pairs of consecutive integer 32 values beginning at the location specified by the index.

Specifically, the raw t-sequence, which corresponds to the seven width measurements t, 11 t 2 7 shown in Figure 15, is calculated by adding pairs of the consecutive integer values xoxl,...x 7 f representing the widths of the bars and spaces, as follows: t I x 0 x 1 t x x 2 t 3 x 2 x 3 etc.

o A width W for the entire codeword is also calculated in step 204 by summing the eight integer values x 0 x 1 x 7 For the codeword in Figure 15, for example, the sequence of Ce..

oo.. integer values from the scan line, representing the widths of the e*g.

bars and spaces might be something like: 43, 19, 21, 19, 22, 18, o'ITl03, 96. The raw t-sequence t, 1 t 2 t 7 would then be 62, 40, @6030 41, 40, 121, 199, and the width W would be 341.

In step 206 in Figure 14, the raw t-sequence obtained in step 2.04 is normalized and rounded to integer values. Specifically, a -e.e value for the codeword's "module" or "unit" is first established by dividing the width W of the codeword by the total number of units for each codeword. In a PDF417 symbol, each codeword is seventeen units, so that the width W is divided by seventeen to S: obtain the unit of the codeword. Thus, for the example in Figure .55• 15, the unit would be (341/17) 20.0. Each value of the raw tsequence is then divided by the unit and rounded to an integer to normalize the t-sequence. The normalized t-sequence for the codeword in Figure 15 is 3, 2, 2, 2, 2, 6, 33 The normalized t-sequence is then compared to the t-sequences of the start and stop patterns of the code is step 208. If the scanner scans from both left to right and right to left, then the t-sequence must be compared to the start and stop patterns in both 6 their normal and reverse orientatidhs.

If there is a match in step 210, then the index is set in step 2i4 to a location in the scan line immediately following the pattern if it is a start pattern or immediately preceding it if it is a stop pattern. If the current t-sequence does not match 1aeither the start or the stop pattern, however, then in step 212, the index is incremented by one and steps 202 through 210 are repeated until either a match is found or the length of the scan 4 line is exceeded.

Figure 16 is a flow chart showing in greater detail the sequence of steps for decoding a scan line of data into a vector of codewords and their clusters as referred to in step 162 of Figure 12 above. In decoding the individual codeword values and S cluster numbers from the scan line, the low-level decoder begins decoding at the start or stop pattern and decodes as many Ao codewords possible. For those codewords that are not successfully decoded, the codeword values in the codeword vector are set to

"BAD".

S* At the completion of the sequence of steps shown in Figure 16, the cod-word vector will contain certain codeword values and 2' cluster numbers in locations corresponding to the appropriate columns of the codewords that were successfully decoded. Figure 17A shows an example of a codeword vector in which the codewords 34 .in eight of the ten columns were successfully decoded. The codeword values in columns 1 and 10 correspond to the left row indicator codeword in row 2 (L 2 and the right row indicator codeword in row 1 respectively. The codewords in columns 7 were not successfully decoded as indicated by the notation "BAD" in those locations of the codeword vector.

Returning to the first step 220 of Figure 16, an upper limit on the number of codewords that may be decoded ("cwlimit") is set equal to the number of columns in the codeword matrix. If this io number of codewords is successfully decoded, then the decoding process for the current scan line is obviously complete.

"o Step 222 determiles the direction of the scan if the scanner scans from both left to right and right to left. If the particular scan was -rom left to right as determined in step 222, then the column number of the first codeword is set to in step *eoS@* S 224 and the amount that it will incremented by ("incr") each time a subsequent codeword is decoded is set to If the scan was from right to left, however, then in step 226, the column number S" of the first codeword in the scan line will be the last column of S26 the codeword matrix, and the incremental value is set to Step 228 is the first step of a control loop in which individual codeword values and their cluster numbers are decoded from the scan line of data. In step 228, the codeword limit is tested to see if it is still greater than zero. If not, then all ~2of the codewords in the scan line have been decoded and the loop is exited.

35 -7--t.T1-rri~---TI I".

Otherwise, step 230 obtains the next codeword value and its cluster number from the scan line. This step will be discussed in further detailbelow in connection with Figure 18.

If the codeword decoded in the previous step is a valid Scodeword as dete ined in step 232, then in step 234 the codeword value and its'cluster number are saved in the codeword vector at a location corresponding to the column of the codeword. The codeword values thus placed in the codeword vector are ready for incorporation into the codeword matrix.

S\ If the codeword decoded in step 230 is not a valid codeword, however, then the codeword value in the codeword vector corresponding to the current column is set to "BAD" in step 236 to indicate that this codeword was not successfully decoded, A "BAD" codeword is most likely to occur when the scan line crosses the 0 15 boundary between two rows in the middle of the codeword.

Finally, in step 238, the current column number is either incremented or decremented depending on the direction of the scan, and the codeword limit is decremented by one. Steps 228-236 are 00 @6 then repeated until there has been an attempt to decode all of the S2 codewords in the scan line.

Figure 18 is a flow chart diagram showing the sequence of steps corresponding to step 230 in Figure 16 and step 172 in Figure 13 in which an attempt is made to decode an individual codeword value and cluster number from the scan line. In the 2afirst step 240, a raw t-sequence and the width W are obtained from the scan line. This same step was discussed previously in connection with step 204 in Figure 14.

36 In step 242, the width W of the eight elements presumed to be -the next codeword are compared to the width of the previously decoded codeword. If the current width W is not within a range of plus or minus a predetermined difference (delta), then there is probhbly a split (undercount by a multiple of two elements) or a merge (overcount by a multiple of two elements) error in the current-codeword. This codeword is not decoded further, but rather in step 244 its value and cluster number are both set to BAD to indicate that it could not be decoded.

1o Then in step 246, an attempt is made to resynchronize to the boundary of the next codeword by finding a t-sequence with a corresponding width W that falls within a given tolerance of the expected width of a codeword, based on the width of the previous codeword. If the current width W is significantly greater than 'ithe expected width, indicating a possible merge error, then the last two integer values are dropped from the t-sequence until it falls within the proper limits. Likewise, if the current width W is significantly less than the expected width, indicating a possible split error, the next two integer values in the scan line I 2,Oare added to the t-sequence until it falls within the proper limits.

If the current width W is within a certain tolerance of the expected width, as determined in step 242, then an attempt is made to decode the codeword. In step 248, the raw t-sequence is n*normalized as described above in connection with step 206 in Figure 14. Then in step 250, the cluster number is determined from the normalized t-sequence. The cluster number may be 37 determined from the t-sequence (as opposed to the X-sequence described above) as follows: cluster nubber= (T T T T6) mod 9 For codewords in PDF417, valid cluster numbers are 0, 3, and S6. If in step 252 it is determined that the cluster number is not 0, 3, or 6, then the codeword is not valid. Accordingly, in step 254 the cluster number and value are set to "BAD" to indicate that the codeword was not successfully decoded.

Otherwise, in step 256, the normalized t-sequence and its o cluster number are used to find the corresponding codeword value in a look-up table. If no corresponding codeword value is found for the t-sequence, then the codeword value is set to "BAD" to indicate that it was not successfully decoded.

Finally, in step 258 the "last width" value is updated to the Scurrent width W of the codeword for use in decoding the next codeword value from the scan line.

Figures 19A and 19B together comprise a flow chart of the sequence of steps executed by the low-level decoder in order to update the codeword matrix using the cod& word vector. These ao figures explain in greater detail step 164 in Figure 12 discussed previously.

The first step 260 of Figure 19A checks the first and last values in the codeword vector to see if either is a valid row indicator. If neither the first nor the last values in the 14 codeword vector are valid row indicators, then in step 262, the 38 program exits the routine and no attempt is made to update the codeword matrix using the codeword vector.

If a valid row indicator is present, however, then in step 264 confidence weights are assigned to each codevword value in the codeword vector. Specifically, a confidence weight is assigned to each codeword depending on whether its nearest neighbors and their cluster were also decoded. For example, as shown in Figure 17B, the codeword values in columns 1, 2, 3, 9, and 10 are assigned high confidence weights because their immediate neighbors \0 were also successfully decoded and have the same cluster number.

The codeword values for columns 4 and 8 are assigned medium confidence weights because one of their neighbors was i Successfully decoded and has the same cluster number but the other neighboring codeword value is "BAD". The codeword value in column 3 is assigned a very low confidence weight because neither of its neighbors was successfully decoded. Thus, the confidence weight for a codeword value at column i in the codeword vector is essentially a function of the cluster numbers of the codewords at columns i i, i, and i 1. This function may be implemented by I a look-up table whose index is calculated from the cluster numbers of the three codewords.

In step 266, a row number is assigned to each codeword value in the codeword vector based on the row indicator codewords and s* the cluster numbers. As shown in the example in Figure 17C, the 2 left row indicator codeword L 2 indicates that the row number is 2 and the cluster number is 6. The cluster numbers for the codeword values in columns 2-4 are also 6. Therefore, row number 2 is 39 assigned to the codeword values in the first four columns of the codeword vector.

Also in the example in Figure 17C, columns six and 8-10 all have a cluster number of 3 and the right row indicator codeword R 1 indicates that the row number is 1. Therefore, it can be assumed that the scan line crossed the row boundary between row 2 and row 1 and the codeword values in columns 6 and 8-10 should be assigned to row 1.

Ouce the confidence weights and row numbers have been o assigned to each of the codeword values in the codeword vector, the codeword matrix is updated one codeword at a time. In step S 268, the column number C of both the codeword vector and the codeword matrix is set is initially set to Step 270 is the first step of an iterative loop which steps through the codewords t* e in the codeword vector and uses them to update the corresponding codewords and their associated confidence weights in the codeword matrix. When the column number C exceeds the number of columns in step 270, then all of the codewords in the codeword vector have been processed and the routine ends.

:o For each codeword in the codeword vector, step 272 sets the row number R of the codeword matrix to the row number assigned in step 266 to the codeword in the codeword vector at the location C.

Thus, for each codeword value in the codeword vector, there is a corresponding value in the codeword matrix at location Continuing in Figure 19B, step 274 determines whether the current codeword value in location in the codeword matrix is the same as the corresponding codeword value in the codeword 40 vector at column C. If the values are the same, then in step 276, Sthe confidence weight assigned to the codeword value in matrix location is increased by the confidence weight of the corresponding codeword value in the codeword vector. If not, the weight of the codeword value in the matrix is decreased by the confidence weight of the codeword value in the vector in step 278.

If the confidence weight was decreased in step 278, then in step 280 that confidence weight is tested to see if it was iodecreased. below zero. If the confidence weight is less than zero, then in step 282 "'ie new codeword value in the codeword vector is substituted for the current codeword value in the corresponding location in the codeword matrix. The confidence weight assigned 9000 to the codeword value in the matrix is also changed to a positive value in step 284.

Finally, in step 286 the column number C is incremented by 1 S for processing the next codeword value in the codeword vector and program control is returned to step 270 for repeating steps 272 through 286 for all of the columns in the vector.

Returning briefly to step 154 in Figure 12, each time after the codeword matrix has been filled in with the new vector of codeword values and the confidence weights have been updated, an attempt is made to fill in the rest of the matrix using the builtin error correction capability of the symbol. The number and location of codewords which have not yet been successfully decoded may be determined by comparing the confidence weights assigned to each of the codeword values in the matrix with a predetermined 41 threshold. Those values having confidence weights below the threshold are considered to not yet be decoded. If the number of codewords not yet decoded is less than the error correction capability of the symbol as determined by the security level, then an attempt is made to correct the matrix.

It will be apparent to those skilled in the art that various modifications and variations can be made in the decoding method and apparatus without departing from the scope or spirit of the invention. Other embodiments of the invention will be apparent to S o those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be ,'.:nsidered as exemplary 0 only, with a true scope and spirit of the invention being indicated by the following claims.

o* *s 0 a ar 42

Claims (34)

1. A system for representing and recognising data in the form of a machine readable two-dimensional bar code structure comprising: encoding means including:- entering means for entering data in said encoding means; processing means for encoding said data into a two-dimensional bar code structure, said bar code structure including a plurality of ordered, ,ent rows of codewords of bar-coded information, each of said codewords representing at least one information-bearing character; and recognition means including: scanning means for scanning an image of the two-dimensional bar code structure and for converting the codewords into electrical signals representative of the information-bearing characters; and decoding means for decoding the electrical signals into output signals representative of said data.

2. A system as claimed in claim 1, wherein the processing means generates first transfer device signals, and which further comprises transferring means for transferring an image of the two-dimensional bar code structure onto a portable record carrier in response to said first transfer drive signals. o* 20 3. A system as claimed in claim 1 or 2, wherein said recognition means includes an output device for displaying said data in human readable form.

4. A system as claimed in claim 3, wherein said output device is a liquid crystal display. A system as claimed in claim 3, wherein said output device is a CRT 25 display. A system as claimed in claim 3, wherein said output device is a printer.

7. A system as claimed in any preceding claim, wherein said recognition means includes means for transmitting the output signals of the decoding means to a computer.

8. A system as claimed claim 7, wherein said transmitting means includes a modem.

9. A system as claimed in any preceding claim, wherein said recognition means includes means for transmitting the output signals of the decoding means to a microprocessor.

10. A system as claimed in claim 9, wherein the microprocessor controls the operation of one of a facsimile machine, a VCR, a microwave oven, a robot and a weight/price label scale, in response to said decoder output signals.

11. A system as claimed in any preceding claim, wherein said entering means includes a keyboard for entering said data. [N:\lIibe]00108:rhk r 44,- S I

12. A system as claimed in any preceding claim, wherein said entering means includes means for scanning data from a sheet.

13. A system as claimed in any preceding claim, wherein said processing means includes means for generating second transter drive signals in response to a second set of data, and wherein said transferring means includes reading means for transferring onto said carrier means both the image of the two-dimensional bar code structure in response to the first transfer drive signals and said second set of data in human readable form in response to said second transfer drive signals.

14. A system as claimed in claim 13, wherein said portable record carrier is a single carrier, and wherein said reading means includes signal means for transferring the two-dimensional bar code structure and the second set of data in human readable form onto the portabe carrier. A system as claimed in any preceding claim, when dependent directly or indirectly on claim 2, wherein the transferring means is a printer.

16. A system as claimed in any preceding claim, which is adapted for secure transmission of data from a first station to a second station, wherein said encoding means forms part of said first station, and said recognition means forms part of said second station, and wherein: processing means encrypts at least some of said data using an encryption algorithm based upon an encryption key, and S6 represents said encrypted data in the form of a two-dimensional bar code structure, said bar code structure including a plurality of ordered, adjacent rows of codewords of bar-coded information, each of said codewords representing at least one information-bearing charcter, and said decoding means includes decrypting means for 25 decrypting at least some of said information-bearing characters using a decryption algorithm based upon said encryption key.

17. A method for representing and recognising data on a record carrier in the form of a machine readable two-dimensional bar code structure using a system as .0060: S claimed in any preceding claim, the method comprising the steps of: entering data into said encoding means using said entering means; encoding said data, by means of said processing means, into a two-dimensional bar code structure, said bar code structure including a plurality of ordered, adjacent rows of codewords of bar-coded information, each of said codewords representing at lease one information-bearing character; transferring an image of the two-dimensional bar code structure onto a portable record carrier using said transferring means; scanning the image of the two-dimensional bar code structure, using said scanning means, and converting the codewords into electrical signals representative of the information-bearing characters; and S"" F NAfibc00108:rhk decoding the electrical signal into output signals representing said data using said decoding means.

18. A method of encoding and decoding data for secure transmission using a system as claimed in claim 16, the method comprising the steps of: entering data into said encoding means using said entering means; encrypting at least some of said data, by means of said processing means, using the encryption algorithm based upon an encryption key, and representing said encrypted data in the form of a two-dimensional bar code structure, said bar code structure including a plurality of ordered, adjacent rows of codewords of bar-coded information, each of said codewords representing at least one information-bearing character; scanning the two-dimensional bar code structure in said second decoding station using said scanning means and converting the codewords into output signals representative of said information-bearing characters; and decrypting at least some of said information-bearing characters using said decryption algorithm based upon said encryption key by means of said decrypting means.

19. An encoding apparatus for use in a system for secure transmission of data, the apparatus comprising: means for entering data; 20 means for encrypting at least some of said data using an encryption algorithm based upon an encryption key; and means for representing said encrypted data in the form of a two-dimensional bar S ode structure, said bar code structure including a plurality of ordered, adjacent rows of codewords of bar-coded information, each of said codewords representing at least one 25 information-bearing character. *20. A decoding apparatus for use in a system for secure transmission of data s by a two-dimensional bar code structure, said bar code structure including a plurality of ordered, adjacent rows of codewords of bar-coded information, each of said codewords representing at least one information-bearing character, the apparatus comprising: means for scanning the two-dimensional bar code structure and converting the codewords into output signals representative of said information-bearing characters, and means for decrypting at least some of said information bearing characters using a decryption algorithm based upon an encryption key.

21. A facsimile communications system for transmitting a document to a destination comprising: means for entering transmission information including a destination telephone number; means for converting said transmission information into a two-dimensional bar code representation; T 'v N:\libe]00108:rlk 46 means for affixing said two-dimensional bar code representation of said transmission information, including the destination telephone number, to said document; means for scanning said document, including said two-dimensional bar code representation fixed thereto, and for producing signals representing spid transmission information; and means for transmitting said document to said destination in accordance with said signals representing said transmission information, including the destination telephone number, wherein said two-dimensional bar code representation includes a plurality of ordered, adjacent rows of codewords of bar coded information, each of said codewords representing at least one information-bearing character.

22. A system as claimed in claim 21, wherein said means for affixing said two-dimensional bar code representation to said document includes a printer for printing said two-dimensional bar code representation on said document.

23. A method of operating a facsimile communications system for transmitting a document to a destination, comprising the steps of: 1:1oo k entering transmission information including a destination telephone number on a keyboard; converting said transmission information into a two-dimensional bar code o 20 representation; affixing said two-dimensional bar code representation of said transmission information, including the destination telephone number, to said document; scanning said document, including said two-dimensional bar code representation affixed thereto, and producing signals representing said transmission information; and transmitting said document to said destination in accordance with said signals 25 representing said transmission information, including the destination telephone number, oowherein said two-dimensional bar code representation includes a plurality of ordered, adjacent rows of codewords of bar-coded information, each of said codewords representing at least one information-bearing character.

24. The method of claim 23, wherein said step of affixing said two- dimensional bar code representation to said document includes the substep of printing said two-dimensional bar code representation on said document. An apparatus for decoding a two-dimensional bar code symbol, the bar code symbol including a plurality of ordered, adjacent rows of codewords of bar-coded information from a set of codewords, the set of codewords being partitioned into at least three mutually exclusive clusters, each row in the symbol having at least one row indicator codewords and containing only codewords from a cluster different from the codewords in an adjacent row, comprising: means for scanning t e two-dimensional bar code symbol to produce scan lines of data representing the bar-coded information in the codewords of the symbol; hr fL [NAIibe]00108:rhk I I -47 S.. S *1 a S a. S. a a~ 0* a. *Sa** means for decoding a scan line of data into a vector of codeword values corresponding to the codewords that were scanned, at least one of the codeword values being for a row indicator codeword; means for assigning a row number to each of the codeword values in the vector based on the value of the row indicator codeword and the cluster of the codeword; and means for filling in a codeword matrix with the codeword values in the vector according to their assigned row numbers.

26. The apparatus of claim 25, wherein the row indicator codewords contain information regarding the number of rows in the symbol and the number of codewords in each row, and wherein the apparatus further comprises: means for decoding a scan line of data to obtain a codeword value for a row indicator codeword, and means for determining one of the number of rows and the number of codewords in each row from the codeword value for the row indicator codeword.

27. The apparatus of claim 26, wherein each row of the symbol contains a start and a stop pattern of bar-coded information, and wherein the means for decoding a scan line of data to obtain a codeword value for a row indicator codeword includes means for locating a sequence of data in the scan line corresponding to one of the start and the stop pattern. 20 28. The apparatus of claim 25, wherein the symbol contains at least one error correction codeword and the row indicator codewords contain information regarding the number of rows in the symbol, the number of codewords nr each row, and the number of error correction codewords, and wherein the apparatus further comprises: means for decoding a scan line of data to obtain a codeword value for a row 25 indicator codeword, means for determining a value for one of the number of rows, the number of codewords in each row, and the number or error correction codewords from the codeword value for the row indicator codeword, means for adjusting a confidence weight for a corresponding one of the number of rows, the number of codewords in each row, and the number or error correction codewords based on the value determined in the preceding step and a previous value obtained by decoding a row indicator codeword, and means for initialising the codeword matrix when the confidence weights for the number of rows, the number of codewords in each row, and the number of error correction codewords all exceed a predetermined threshold.

29. The apparatus of claim 28, wherein each row of the symbol contains a start and a stop pattern of bar-coded information, and wherein the means for decoding a scan line of data to obtain a codeword value for a row indicator codeword includes means for locating a sequence of data in the scan line corresponding to one of the start and the L;.,40 stop pattern. I L iI& VW [N:\libe]00108:rhk I t -48 The apparatus of claim 25, wherein each row of the symbol contains a start and a stop pattern of bar-coded information, and wherein the means for decoding a scan line of data to obtain a codeword value for a row indicator codeword includes means for locating a sequence of data in the scan line corresponding to one of the start and the stop pattern.

31. The apparatus of claim 25, further comprising means for assigning a confidence weight to each of the codeword values in the vector, and means for adjusting a confidence weight of each of the corresponding codeword values in the matrix based on the codeword value in the vector and a current value of each of the corresponding codeword values in the matrix.

32. The apparatus of claim 25, wherein the symbol contains at least one error correction codeword, and wherein the apparatus further comprises means for locating in the matrix the codeword values for any codewords that have not been successfully decoded, and S* means for correcting any erroneous codeword values in the codeword matrix using the error correction codeword.

33. A method for decoding a two-dimensional bar code symbol using an 20"apparatus as claimed in any one of claims 25 to 32, wherein the bar code symbol includes a plurality of ordered, adjacent rows of codewords of bar-coded information from a set of codewords, the set of codewords being partitioned into at least three mutually exclusive clusters, each row in the symbol having at least one row indicator codeword and containing only codewords from a cluster different from the codewords in an adjacent row, the method comprising the steps of: 25 scanning the two-dimensional bar code symbol to produce scan lines of data representing the bar-coded information in the codewords of the symbol; decoding a scan line of data into a vector of codeword values corresponding to the codewords that were scanned, at least one of the codeword values being for a row Sindicator codeword; assigning a row number to each of the codeword values in the vector based on the value of the row indicator codeword and the cluster of the codeword; and filling in a codeword matrix with the codeword values in the vector according to their assigned row numbers.

34. A system as claimLed in any one of claims 1 to 16, wherein said bar code structure includes a plurality of ordered, adjacent rows of codewords of bar-coded information from a set of codewords, the set of codewords being partitioned into at least three mutually exclusive clusters, each row in the two-dimensional bar code structure having at least one row indicator codeword and containing only codewords from a cluster different from the codewords in an adjacent row, wherein the scanning means scans the o. [N:\libe]00108:rhk *rA'T 3j: t -49- image of the two-dimensional bar code structure to produce scan lines of data representing the barcoded information in the codewords of the two-dimensional bar code structure, and said decoding means decodes a scan line of data into a vector of codeword values corresponding to the codewords that were scanned, at least one of the codeword values being for a row indicator codeword, and wherein said recognition means further comprises assigning means for assigning a row number to each of the codeword values in the vector based on the value of the row indicator codeword and the cluster of the codeword, and filling means for filling in a codeword matrix with the codeword values in the vector according to their assigned row numbers. The system of claim 34, wherein the row indicator codewords contain information regarding the number of rows in the two-dimensional bar code structure and the number of codewords in each row, and wherein the recognition means further includes means for decoding a scan line of data to obtain a codeword value for a row indicator codeword, and means for determining one of the number of rows and the number of codewords in each row from the codeword value for the row indicator codeword.

36. The system of claim 35, wherein each row of the two-dimensional bar Scode structure contains a start and a stop pattern of bar-coded information, and wherein S 20 the means for decoding a scan line of data to obtain a codeword value for a row indicator S° codeword includes means for locating a sequence of data in the scan line corresponding to one of the start and the stop pattern.

37. The system of claim 34, wherein the two-dimensional bar code structure contains at least one error correction codeword and the row indicator codewords contain 25 information regarding the number of rows in the two-dimensional bar code structure, the number of codewords in each row, and the number of error correction codewords, and S wherein the recognition means further includes means for decoding a scan line of data to obtain a codeword value for a row indicator codeword, means for determining a value for one of the number of rows, the number of codewords in each row, and the number of error correction codewords from the codeword value for the row indicator codeword, means for adjusting a confidence weight for a corresponding one of the number of rows, the number of codewords in each row, and the number of error correction codewords based on the value determined in the preceding step and a previous value obtained by decoding a row indicator codeword, and means for initialising the codeword matrix when the confidence weights for the number of rows, the number of codewords in each row, and the number of error correction codewords all exceed a predetermined threshold. [N:libe]00108:rhk

38. The system of rlaim 37, wherein each row of the two-dimensional bar code structure contains a start and a stop pattern of bar-coded information, and wherein the means for decoding a scan line of data to obtain a codeword value for a row indicator codeword includes means for locating a sequence of data in the scan line corresponding to one of the start and the stop pattern.

39. The system of claim 34, wherein each row of the two-dimensional bar code structure contains a start and a stop pattern of bar-coded information, and wherein the means for decoding a scan line of data to obtain a codeword value for a row indicator codeword includes means for locating a sequence of data in the scan line corresponding to one of the start and the stop pattern. The system of claim 34, wherein the recognition means further includes means for assigning a confidence weight to each of the codeword values in the vector, and means for adjusting a confidence weight of each of the corresponding codeword values in the matrix based on the codeword value in the vector and a current value of each of the corresponding codeword values in the matrix.

41. The system of claim 34, wherein the two-dimensional bar code structure contains at least one error correction codeword, and wherein the recognition means S further includes 20 means for locating in the matrix the codeword values for any codewords that have not been successfully decoded, and means for correcting any erroneous codeword values in the codeword matrix ge: using the error correction codeword.

42. A method for representing and recognising data on a record carrier in 25 the form of a machine readable two-dimensional bar code structure using a system as S claimed in any one of claims 34 to 41, the method comprising the steps of: entering data into said encoding means using said entering means; encoding said data into a two-dimensional bar code structure, the two- dimensional bar code structure including a plurality of ordered, adjacent rows of codewords of bar-coded information from a set of codewords, the set of codewords being partitioned into at least three mutually exclusive clusters, each row in the two-dimensional bar code structure having at least one row indicator codeword and containing any codewords from a cluster different from the codewords in an adjacent row, transferring an image of the two-dimensional bar code structure onto a portable record carrier; scanning the image of the two-dimensional bar code structure to produce scan lines of data representing the bar-coded information in the codewords; decoding a scan line of data into a vector of codeword values corresponding to the codewords that were scanned, at least one of the codeword values being for a row -40 indicator codeword; PT' [N:libe]00108:rhk 51 assigning a row number to each of the codeword values in the vector based on the value of the row indicator codeword and the cluster of the codeword; and filling in a codeword matrix with the codeword values in the vector according to their assigned row numbers.

43. A system for representing and recognising data, substantially as hereinbefore described with reference to the accompanying drawings.

44. A method of representing and recognising data, substantially as hereinbefore described with reference to the accompanying drawings. DATED this Seventeenth Day of August 1994 Symbol Technologies, Inc. S: Patent Attorneys for the Applicant SPRUSON FERGUSON o• *ooo "e' [N:Mibe]00108:rhk S'Systems for Encoding and Decoding Data in Machine Readable Graphic Form ABSTRACT A system (10) for representing and recognizing data in machine readable graphic image form in which data to be encoded is entered into the system and a processor (24) encodes k12) the data into a two-dimensional bar code symbol and generates transfer drive signals representative of the symbol. A transferring device (26) such as a printer transfers an image of the two-dimensional bar code symbol onto a carrier (16) such as a card or paper document in response to the transfer drive signals. A recognition device (28) converts the image on the carrier into electrical signals representative of the symbol by scanning the image. A low-level decoder (30) decodes the signals by decoding each scan line into a vector of codeword values corresponding to the codewords in the two-dimensional bar code symbol, assigning a row number to each of 15 the codeword values, and then filling in a two-dimensional matrix with the codeword values. A high-level decoder further decodes the codeword 0. values into data which can then be output for processing or use. *u Figure