Optically readable two-dimensional code and method and apparatus using the same

• US 5,726,435 A
• Filed: 03/14/1995
• Issued: 03/10/1998
• Est. Priority Date: 03/14/1994
• Status: Expired due to Term

• Current Assignee: Denso Wave Inc (DENSO Corporation), Kabushiki Kaisha Toyota Chuo Kenkyusho (Toyota Motor Corporation)
• Original Assignee: Nippondenso Co., Ltd. (DENSO Corporation), Kabushiki Kaisha Toyota Chuo Kenkyusho (Toyota Motor Corporation)
• Inventors: Uchiyama, Yuji, Watabe, Motoaki, Nagaya, Takayuki, Hara, Masahiro, Nojiri, Tadao
• Primary Examiner(s): Hajec, Donald T.
• Assistant Examiner(s): Le, Thien Minh
• Application Number:
  US08/403,548
• Time in Patent Office: 1,092 Days
• Field of Search: 235/456, 235/454, 235/494, 235/460, 235/470, 235/465, 250/566, 382/56
• US Class Current: 235/494
• CPC Class Codes: G06K 7/14 using light without selection of wavelength, e.g. sensing reflected white light G06K7/10831 - G06K7/1097 take precedence
• CPC Class Codes: G06K 7/1417 2D bar codes
• CPC Class Codes: G06K 7/1443 locating of the code in an image
• CPC Class Codes: G06K 7/1456 determining the orientation of the optical code with respect to the reader and correcting therefore

Abstract

A two-dimensional code 1 consists of three positioning symbols 2, a data region 3, timing cells 4 and an apex detecting cell 5. The shape of the whole code 1 is a square having the same number of vertical and lateral cells. A scanning line passing through the center of each positioning symbols 2 always gives a constant frequency component ratio--dark:light:dark:light:dark=1:1:3:1:1, irrespective of the scanning direction. For this reason, even if a rotational angle of the two-dimensional code is not certain, the specific frequency component ratio of each positioning symbol 2 can be easily detected by executing only one scanning operation in a predetermined direction. Hence, the coordinates of the center of each positioning symbols 2 can be easily found. Thus, the position of the two-dimensional code 1 is quickly identified.

Claims

1. A two-dimensional code comprising:

a plurality of cells, each of said plurality of cells representing a binary-coded datum;

said plurality of cells forming a two-dimensional matrix pattern readable by a scanning operation along any arbitrary scanning lines; and

at least three positioning symbols disposed at predetermined positions in said two-dimensional matrix pattern, at least two of said at least three positioning symbols having a pattern capable of gaining an identical frequency component ratio irrespective of an orientation of said any arbitrary scanning lines whenever said arbitrary scanning lines pass through a center of each of said at least three positioning symbols.

2. The two-dimensional code in accordance with claim 1, wherein:

at least two of said at least three positioning symbols comprise respective apex cells of said two-dimensional matrix.

3. The two-dimensional code in accordance with claim 1, wherein:

said two-dimensional matrix pattern comprises said at least three positioning symbols including concentric similar figures overlapped successively.

4. The two-dimensional code in accordance with claim 1, further comprising:

a series of timing cells including light and dark cells alternately arrayed with an inclination of 1/1 in said two-dimensional matrix.

5. The two-dimensional code in accordance with claim 1, wherein:

said binary-coded datum includes a plurality of characters, each of said plurality of characters being represented by a character cell group representing only one character disposed in a two-dimensional square region of said two-dimensional matrix, and said two-dimensional square region being defined by vertically stacked and horizontally arrayed ones of said plurality of cells.

6. The two-dimensional code in accordance with claim 1, further comprising:

an apex detecting cell disposed on an apex of said two-dimensional matrix where said at least three positioning symbols are not disposed.

22. The two-dimensional code in accordance with claim 5, wherein said square region is a regular square consisting of n×

n cells, where n is a positive integer.

34. The two-dimensional code in accordance with claim 5, wherein said two-dimensional code has a code-reading-prohibition cell to prohibit an operation of reading said two-dimensional code when said code-reading-prohibition cell is a predetermined color.

7. A two-dimensional code reading apparatus for optically reading a two-dimensional code including a plurality of binary-coded cells in a two-dimensional matrix pattern, said two-dimensional code including a symbol disposed in a vicinity of an apex of said two-dimensional matrix, said symbol having a specific pattern including concentric similar figures overlapped successively, said reading apparatus comprising:

an image pickup device to take an image of said two-dimensional code to convert said image pixel by pixel into a resultant image signal in response to a light intensity of said image, and to successively output said resultant image signal; and

a decoder unit to decode said resultant image signal into a binary-coded signal, said decoder unit comprising;

binary-encoding means for binary encoding said resultant image signal in accordance with a level of said resultant image signal, and outputting said binary-coded signal successively;

memory means for storing said binary-coded signal as image data in accordance with a position of a pixel where said image was taken;

symbol detecting means for detecting said specific pattern corresponding to said symbol based on said binary-coded signal;

apex detecting means for detecting coordinates of said symbol from said image data stored in said memory means based on said specific pattern detected by said symbol detecting means;

matrix position determining means for finalizing a contour and an orientation of said two-dimensional matrix based on coordinates of said symbol detected by said apex detecting means, thereby identifying all coordinates of said plurality of binary-coded cells; and

reading means for reading out said image data stored in said memory means in accordance with said finalized contour and said orientation of said two-dimensional matrix.

8. The two-dimensional code reading apparatus in accordance with claim 7, wherein:

said plurality of binary-coded cells comprise a series of timing cells including light and dark cells alternately arrayed in said two-dimensional matrix, and optically readable by said image pickup device; and

said decoder unit further comprises timing cell detecting means for detecting coordinates of each timing cell of said series of timing cells from said image data stored in said memory means in accordance with coordinates of said symbol obtained by said apex detecting means, said series of timing cells determining a cell position of said image data in accordance with intervals of said series of timing cells.

9. The two-dimensional code reading apparatus in accordance with claim 7, wherein:

said two-dimensional code is created by performing an exclusive-OR operation between a predetermined provisional two-dimensional code and a two-dimensional cell-feature-conversion code which includes a specific conversion pattern represented by light cells and dark cells corresponding to a data region of said provisional two-dimensional code; and

said reading means restores information of said provisional two-dimensional code by performing said exclusive-OR operation between said image data obtained from said image taken by said image pickup device and two-dimensional image data of said two-dimensional cell-feature-conversion code stored in said memory means.

32. The two-dimensional code reading apparatus in accordance with claim 9, wherein an orientation symbol comprises three of said symbols, one of said symbols has a predetermined frequency component ratio, and said operation of exclusive-ORing being executed to prevent said plurality of binary-coded cells other than said orientation symbol from having a frequency component ratio being one of identical to said frequency component ratio of said one of said symbols and similar to said frequency component ratio of said one of said symbols.

10. A two-dimensional code reading method for optically reading a two-dimensional code including binary-coded cells placed in a two-dimensional matrix pattern, comprising steps of:

disposing a symbol in a vicinity of an apex of said two-dimensional matrix, said symbol having a specific pattern including concentric similar figures overlapped successively;

taking an image of said two-dimensional code by an image pickup device, converting said image pixel by pixel into an image signal in response to a light intensity of said image, binary encoding said image signal in accordance with a level of said image signal, and storing a resultant binary-coded signal as image data in memory means in accordance with a position of a pixel where said image was taken;

detecting said specific pattern corresponding to said symbol based on said resultant binary-coded signal in parallel with storage of said binary-coded signal in said memory means;

detecting coordinates of said symbol from said image data stored in said memory means based on said detected specific pattern;

finalizing a contour and an orientation of said two-dimensional matrix based on coordinates of said symbol, thereby identifying all coordinates of said binary-coded cells; and

reading out said image data stored in said memory means in accordance with said finalized contour and said orientation of said two-dimensional matrix.

11. A two-dimensional code comprising:

a plurality of cells, each of said plurality of cells representing a binary-coded datum;

said plurality of cells forming a two-dimensional matrix pattern readable by a scanning operation along scanning lines; and

timing cells arrayed in said two-dimensional matrix, said timing cells including light and dark cells arrayed alternately with an inclination of 1/1.

12. The two-dimensional code in accordance with claim 11, further comprising:

at least two positioning symbols disposed at predetermined positions in said two-dimensional matrix, each of said at least two positioning symbols having a pattern capable of gaining an identical frequency component ratio irrespective of an orientation of said scanning lines when said scanning lines pass through a center of each of said at least two positioning symbols.

13. A two-dimensional code comprising:

a plurality of cells, each of said plurality of cells representing a binary-coded datum;

said plurality of cells forming a two-dimensional matrix pattern and being readable by a scanning operation along scanning lines;

a two-dimensional code being created by operation of an exclusive-ORing between a predetermined provisional two-dimensional code and a two-dimensional cell-feature-conversion code which includes a specific conversion pattern.

14. The two-dimensional code in accordance with claim 13, wherein said specific conversion pattern comprises:

light and dark cells; and

said exclusive-Oring is operated in a cell by cell manner between said predetermined provisional two-dimensional code and said two-dimensional cell-feature-conversion code.

15. A two-dimensional code formed from a two-dimensional matrix having a plurality of binary-coded cells, said two-dimensional code comprising:

total symbol cells representing an orientation of said two-dimensional matrix;

said total symbol cells forming a two-dimensional matrix pattern and being readable by a scanning operation along scanning lines; and

at least one data cell group, each of said at least one data cell group comprising a group of said plurality of binary-coded cells, each of said at least one data cell group representing only one character and being disposed in a two-dimensional n×

m square region in said two-dimensional matrix, said two-dimensional n×

m square region being defined by vertically stacked binary-coded cells and horizontally arrayed binary-coded cells, in which said n is a number of said vertically stacked binary-coded cells and said m is a number of said horizontally arrayed binary-coded cells.

16. The two-dimensional code in accordance with claim 15, wherein:

said two-dimensional matrix is a square matrix; and

said total symbol cells are comprised of a plurality of symbol cells disposed at apex positions in said square matrix, said symbol cells having a same pattern capable of gaining a same identical frequency component ratio irrespective of an orientation of said arbitrary scanning lines whenever said scanning lines pass through a center of said two-dimensional pattern.

29. The two-dimensional code in accordance with claim 15, wherein said plurality of binary-coded cells in said two-dimensional n×

m square region comprise a plurality of bits dedicated to data of said one character and one of said plurality of bits dedicated to a parity.

35. The two-dimensional code in accordance with claim 15, wherein said two-dimensional code has a code-reading-prohibition cell to prohibit an operation of reading said two-dimensional code when said code-reading-prohibition cell is a predetermined color.

17. A two-dimensional code comprising:

a plurality of cells, each of said plurality of cells representing a binary-coded datum;

said plurality of cells being placed on a two-dimensional matrix, said two-dimensional matrix having a square shape and being enclosed by straight peripheral lines so as to form a pattern readable by a scanning operation along any arbitrary scanning lines;

at least two positioning symbols disposed at apex positions in said two-dimensional matrix, each of said at least two positioning symbols having a pattern capable of gaining an identical frequency component ratio irrespective of an orientation of said arbitrary scanning lines whenever said arbitrary scanning lines pass through a center of each of said at least two positioning symbols, said at least two positioning symbols being square in shape and having straight peripheral lines parallel to said straight peripheral lines of said two-dimensional matrix; and

said plurality of cells being processed through a predetermined conversion processing into a characteristic pattern different from said pattern of said positioning symbols.

18. The two-dimensional code in accordance with claim 17, wherein said positioning symbols are disposed at three of four corners of said two-dimensional code and characterized by a pattern consisting of a large square of black cells, a middle square of white cells concentric with but smaller in size than said large square, and a small square of black cells concentric with but smaller in size than said middle square.

19. The two-dimensional code in accordance with claim 18, wherein an apex detecting cell is located at a remaining corner of said two-dimensional code, said remaining corner not having said positioning symbol disposed therein.

20. The two-dimensional code in accordance with claim 19, wherein said apex detecting cell comprises a single square cell.

21. A two-dimensional code formed on a two-dimensional matrix comprising:

at least two positioning symbols disposed at predetermined positions in said two-dimensional matrix, each of said at least two positioning symbols having a pattern capable of gaining an identical frequency component ratio obtainable from any arbitrary scanning line passing through a center of said positioning symbol, said frequency component ratio being defined as dark;

light;

dark;

light;

dark=1;

1;

3;

1;

1, irrespective of an orientation of said arbitrary scanning line whenever said arbitrary scanning line passes through said center of said positioning symbol; and

a plurality of data cells, each of said plurality of data cells representing a binary-coded datum, said plurality of data cells being placed on said two-dimensional matrix pattern being readable by any scanning operation along said arbitrary scanning line, said plurality of data cells being processed by predetermined conversion processing into a characteristic pattern different from said pattern of said at least two positioning symbols.

23. A two-dimensional code reading apparatus for optically reading a two-dimensional code including a plurality of binary-coded cells placed on a two-dimensional square matrix pattern, said two-dimensional code including an orientation symbol and timing cells, said orientation symbol being disposed in a peripheral region of said two-dimensional square matrix pattern and comprising three apexes of said two-dimensional square matrix pattern, said reading apparatus comprising:

an image pickup device to take an image of said two-dimensional code, to convert said image pixel by pixel into an image signal in response to a light intensity of said image, and successively outputting said image signal; and

a decoder unit for decoding said image signal into a plurality of binary-coded signals;

wherein said decoder unit comprises;

binary-encoding means for binary encoding said image signal in accordance with a level of said image signal, and outputting said plurality of binary-coded signals successively;

memory means for storing said plurality of binary-coded signals as image data in accordance with a position of a pixel where the image was taken;

symbol detecting means for detecting a specific pattern corresponding to said orientation symbol based on said plurality of binary-coded signals;

apex and timing cell detecting means for detecting coordinates of said three apexes of said orientation symbol and coordinates of said timing cells from said image data stored in said memory means based on said specific pattern detected by said symbol detecting means;

matrix position determining means for finalizing a contour and an orientation of said two-dimensional square matrix based on the coordinates of said orientation symbol detected by said apex and timing cell detecting means, and identifying all coordinates of said plurality of binary-coded cells placed on said two-dimensional square matrix pattern with reference to said coordinates of said timing cells; and

reading means for reading out said image data stored in said memory means in accordance with the finalized contour and said orientation of said two-dimensional square matrix pattern.

36. The two-dimensional code reading apparatus in accordance with claim 23, wherein said two-dimensional code includes a code-reading-prohibition cell, and said reading apparatus further comprises a reading operation prohibition means for prohibiting an operation of optically reading said two-dimensional code when said code-reading-prohibition cell is a predetermined color.

37. The two-dimensional code reading apparatus in accordance with claim 36, wherein:

said plurality of binary-coded cells cooperatively represent a plurality of characters, a group of said plurality of binary-coded cells being disposed in a two-dimensional square region of said two-dimensional square matrix being allocated to only one character of said plurality of characters, and

said square region being defined by vertically stacked and horizontally arrayed ones of said plurality of binary-coded cells.

38. The two-dimensional code reading apparatus in accordance with claim 37, wherein said two-dimensional square region is a regular square consisting of n×

n cells, where n is a positive integer.

39. The two-dimensional code reading apparatus in accordance with claim 23, wherein said plurality of binary-coded cells include an error-correcting code to restore a predetermined data region when said predetermined data region is one of contaminated by a stain and otherwise damaged.

40. The two-dimensional code reading apparatus in accordance with claim 39, wherein:

said two-dimensional code has a code-reading-prohibition cell, and

said reading apparatus further comprises a reading operation prohibition means for prohibiting an optical reading operation of said two-dimensional code when said code-reading-prohibition cell is a predetermined color.

24. A two-dimensional code reading apparatus for optically reading a two-dimensional code including a plurality of binary-coded cells placed on a two-dimensional square matrix pattern, said two-dimensional code including timing cells and total symbol cells, said total symbol cells representing an orientation symbol and being disposed in a peripheral region of said two-dimensional matrix pattern and comprising a plurality of separate apex cells, said reading apparatus comprising:

an image pickup device to take an image of said two-dimensional code, to convert said image pixel by pixel into an image signal in response to a light intensity of said image, and successively outputting said image signal; and

a decoder unit for decoding said resultant image signals into a plurality of binary-coded signals;

wherein said decoder unit comprises;

binary-encoding means for binary encoding said image signal in accordance with a level of said image signal, and outputting said plurality of binary-coded signals successively;

memory means for storing said plurality of binary-coded signals as image data in accordance with a position of a pixel where the image was taken;

symbol detecting means for detecting a specific pattern corresponding to said total symbol cells based on said plurality of binary-coded signals;

apex and timing cell detecting means for detecting coordinates of said timing cells and coordinates of each of said plurality of separate apex cells comprised by said total symbol cells;

matrix position determining means for finalizing a contour and an orientation of said two-dimensional square matrix pattern based on the coordinates of said plurality of said separate apex cells detected by said apex and timing cell detecting means, and identifying all coordinates of said plurality of binary-coded cells placed on said two-dimensional square matrix pattern with reference to said coordinates of said timing cells; and

reading means for reading out said image data stored in said memory means in accordance with said finalized contour and said orientation of said two-dimensional square matrix pattern.

25. The two-dimensional code reading apparatus in accordance with claim 24, wherein said two-dimensional code further includes an apex detecting cell having a predetermined binary-coded value at a portion of said two-dimensional code having none of said total symbol cells disposed, and said apex and timing cell detecting means further detects said apex detecting cell according to said detected coordinates of said plurality of separate apex cells.

26. The two-dimensional code reading apparatus in accordance with claim 24, wherein:

said apex and timing cell detecting means detects said coordinates of said separate plurality of apex cells and coordinates of a remaining apex cell of said two-dimensional square matrix, and said total symbol cells are a plurality of separate symbol cells.

27. The two-dimensional code reading apparatus in accordance with claim 26, wherein said coordinates of said remaining apex cell X₀, Y₀) is defined by the following equation:

space="preserve" listing-type="equation">X.sub.0 =x.sub.0 +(x.sub.2 -x.sub.1)

space="preserve" listing-type="equation">Y.sub.0 =y.sub.0 +(y.sub.2 -y.sub.1)

where (x₀, y₀), (x₁, y₁), and (x₂, y₂) represent said coordinates of each of said plurality of separate apex cells.

28. The two-dimensional code reading apparatus in accordance with claim 25, wherein said apex and timing cell detecting means detects said apex detecting cell by searching a vicinity of a candidate coordinate position calculated using said detected coordinates of said plurality of separate apex cells.

30. A two-dimensional code reading apparatus for optically reading a two-dimensional code including a plurality of white binary-coded cells and a plurality of black binary-coded cells in a two-dimensional matrix pattern, said plurality of white binary-coded cells and said plurality of black binary-coded cells comprising dummy cells in a data region so as to prevent one of said plurality of white binary-coded cells and said plurality of black binary-coded cells from being consecutively and extensively arrayed, said two-dimensional code comprising an orientation symbol disposed in a peripheral region of said two-dimensional matrix, said reading apparatus comprising:

an image pickup device to take an image of said two-dimensional code, to convert said image pixel by pixel into an image signal in response to a light intensity of said image, and successively outputting said image signal; and

an encoder unit for encoding said image signal into a plurality of binary-coded signals;

wherein said encoder unit comprises;

binary-encoding means for binary encoding said image signal in accordance with a level of said image signal, and outputting said plurality of binary-coded signals successively, said binary-encoding means comprising;

a comparator means for comparing a white level and a black level of an input waveform representing said image signal with a follow-up waveform which approaches one of said white level and said black level of said input waveform when one of said plurality of white binary-coded cells and said plurality of black binary-coded cells are so consecutively and extensively arrayed;

memory means for storing said binary-coded signals as image data in accordance with a position of a pixel where the image was taken;

symbol detecting means for detecting a specific pattern corresponding to said orientation symbol based on said binary-coded signals;

apex detecting means for detecting coordinates of said orientation symbol from said image data stored in said memory means based on said specific pattern detected by said symbol detecting means;

matrix position determining means for finalizing a contour and an orientation of said two-dimensional matrix based on the coordinates of said symbol detected by said apex detecting means, thereby identifying all the coordinates of said plurality of binary-coded cells placed on said two-dimensional matrix; and

reading means for reading out said image data stored in said memory means in accordance with said finalized contour and said orientation of said two-dimensional square matrix.

31. A two-dimensional code reading apparatus for optically reading a two-dimensional code including a plurality of white binary-coded cells and a plurality of black binary-coded cells placed on a two-dimensional matrix pattern, said two-dimensional code created by an operation of exclusive-ORing between a predetermined provisional two-dimensional code and a two-dimensional cell-feature-conversion code including a specific conversion pattern represented by light cells and dark cells so as to prevent said one of said plurality of white binary-encoded cells and said plurality of black binary-coded cells from being consecutively and extensively arrayed, said two-dimensional code comprising an orientation symbol disposed in a peripheral region of said two-dimensional matrix, said reading apparatus comprising:

an image pickup device taking an image of said two-dimensional code, to convert said image pixel by pixel into an image signal in response to a light intensity of said image, and successively outputting said image signal; and

an encoder unit encoding said image signal into a plurality of binary-coded signals;

wherein said encoder unit comprises;

binary-encoding means for binary encoding said image signal in accordance with a level of said image signal, and outputting said plurality of binary-coded signals successively, said binary-encoding means comprising a comparator means for comparing a white level and a black level of an input waveform representing said image signal with a follow-up waveform which approaches one of said white level and said black level of said input waveform when one of said plurality of white binary-coded cells and said plurality of black binary-coded cells is so consecutively and extensively arrayed;

memory means for storing said plurality of binary-coded signals as image data in accordance with a position of a pixel where the image was taken;

symbol detecting means for detecting a specific pattern corresponding to said orientation symbol based on said plurality of binary-coded signals;

apex detecting means for detecting coordinates of said orientation symbol from said image data stored in said memory means based on said specific pattern detected by said symbol detecting means;

matrix position determining means for finalizing a contour and an orientation of said two-dimensional matrix based on the coordinates of said orientation symbol detected by said apex detecting means, thereby identifying all coordinates of said plurality of binary-coded cells in said two-dimensional matrix; and

reading means for reading out said image data stored in said memory means in accordance with the finalized contour and said orientation of said two-dimensional matrix, said reading means restoring information of said two-dimensional code by said operation of exclusive-ORing between said image data obtained from said image taken by said image pickup device and image data of said two-dimensional cell-feature-conversion code stored in said memory means.

33. The two-dimensional code reading apparatus in accordance with claim 31, wherein said two-dimensional code stores information data indicating a type of said two-dimensional cell-feature-conversion code used for said operation of exclusive-ORing.

41. A two-dimensional code formed as a two-dimensional matrix including a plurality of binary-coded cells, comprising:

total symbol cells representing an orientation of said two-dimensional matrix, said total symbol cells on said two-dimensional matrix pattern to be readable by a scanning operation along scanning lines;

a plurality of data cells, each of said plurality of data cells comprising a group of said plurality of binary-coded cells, each of said plurality of data cells representing only one character and disposed in a two-dimensional square region in said two-dimensional matrix;

an error-correcting code to restore a predetermined data region when said predetermined data region is one of contaminated by a stain and otherwise damaged; and

a code-reading-prohibition cell to prohibit a reading operation of said two-dimensional code when a code-reading-prohibition cell disposed within said two-dimensional code is a predetermined color.

42. A two-dimensional code formed as a two-dimensional matrix having a plurality of binary-coded cells, comprising:

total symbol cells representing an orientation of said two-dimensional matrix, said total symbol cells being placed on said two-dimensional matrix pattern and readable by a scanning operation along scanning lines; and

a plurality of data cells, each of said plurality of data cells comprising a group of said plurality of binary-coded cells being disposed in a two-dimensional region of said two-dimensional matrix, each of said plurality of data cells representing only one character; and

dummy black lines having an optimal placement pattern to distinguish said total symbol cells from said plurality of data cells.

43. A two-dimensional code formed as a two-dimensional matrix having a plurality of binary-coded cells, comprising:

total symbol cells representing an orientation of said two-dimensional matrix, said total symbol cells on said two-dimensional matrix forming a pattern readable by a scanning operation along scanning lines; and

a plurality of data cells, each of said plurality of data cells comprising a group of said plurality of binary-coded cells, each of said plurality of data cells representing only one character and disposed in a two-dimensional region in said two-dimensional matrix, said plurality of data cells having an optimum placement pattern of said plurality of binary-coded cells, said optimum placement pattern being created by an operation of exclusive-ORing between a predetermined provisional two-dimensional code and a two-dimensional cell-feature-conversion code including a specific conversion pattern, whereby said plurality of data cells are distinguished from said pattern of said total symbol cells.

44. The two-dimensional code in accordance with claim 43, wherein a subset of said total symbol cells form a positioning symbol which is capable of gaining an identical frequency component ratio whenever one of said scanning lines passes through a center of said positioning symbol formed by said subset of said total symbol cells and said optimum placement pattern does not have a frequency component ratio being one of identical to a frequency component ratio of said pattern of said positioning symbol and similar to said frequency component ratio of said pattern of said positioning symbol.

45. A two-dimensional code reading method for optically reading a two-dimensional code including a plurality of binary-coded cells placed on a two-dimensional square matrix pattern, said two-dimensional square matrix pattern comprising an orientation symbol and timing cells, said orientation symbol being disposed in a peripheral region of said two-dimensional square matrix pattern as a specific pattern and including three apexes of said two-dimensional square matrix pattern, comprising steps of:

taking an image of said two-dimensional code by an image pickup device, then converting said image pixel by pixel into an image signal in response to a light intensity of said image, and binary encoding said image signal in accordance with a level of said image signal, then storing a plurality of binary-coded signals as image data in a memory in accordance with a position of a pixel where the image was taken;

detecting said specific pattern corresponding to said orientation symbol based on said plurality of binary-coded signals;

detecting coordinates of said three apexes of said orientation symbol and coordinates of said timing cells from said image data stored in said memory based on the detected specific pattern;

finalizing a contour and an orientation of said two-dimensional matrix based on the coordinates of said orientation symbol, thereby identifying coordinates of said plurality of binary-coded cells placed on said two-dimensional matrix pattern; and

reading out said image data stored in said memory in accordance with the finalized contour and said orientation of said two-dimensional square matrix pattern.

49. The two-dimensional code reading method in accordance with claim 45, further comprising steps of:

reading out one cell-feature-conversion matrix pattern prepared beforehand;

performing an operation of exclusive-ORing between said readout one cell-feature-conversion matrix pattern and said image data stored in said memory, and storing an obtained exclusive-OR result; and

dividing a data region of said obtained exclusive-OR result into a plurality of individual character cell groups, and converting each of said plurality of individual character cell groups into a corresponding character.

50. The two-dimensional code reading method in accordance with claim 49, wherein said two-dimensional code includes an error-correcting code, and said two-dimensional code reading method further comprises a step of making a judgment based on said error-correcting code as to whether an error exists after converting each of said plurality of individual character cell groups to said corresponding character, and executing an error correction of said corresponding character when said error is found.

53. The two-dimensional code reading method in accordance with claim 45, wherein:

each of said three apexes is disposed at a separate corner of said two-dimensional square matrix pattern, each of said three apexes comprising an apex cell,

said two-dimensional square matrix comprises an apex detecting cell at a remaining corner of said two-dimensional square matrix pattern, and

said step of detecting coordinates includes detecting coordinates of each of said apex cells and further detects said apex detecting cell by searching a vicinity of coordinates of said remaining corner obtainable from said coordinates of each of said apex cells.

46. A two-dimensional code printing method for optically printing a two-dimensional code including a plurality of binary-coded cells placed on a two-dimensional matrix pattern, said two-dimensional matrix pattern comprising an orientation symbol disposed in a peripheral region of said two-dimensional matrix pattern as a specific pattern, comprising steps of:

setting objective data in a work memory;

binary encoding each of said objective data into one of "0" and "1";

arranging said encoded objective data in a two-dimensional data pattern according to a predetermined rule;

performing an operation of exclusive-ORing between said two-dimensional data pattern and each of a plurality of cell-feature-conversion matrix patterns prepared beforehand, to obtain placement patterns;

selecting an optimum placement pattern from said placement patterns;

placing said selected optimum placement pattern in said two-dimensional code; and

printing said two-dimensional code by a printing device.

48. The two-dimensional code in accordance with claim 46, further comprising a step of adding an error-correcting code to said encoded objective data.

47. A two-dimensional code reading method for optically reading a two-dimensional code including a plurality of binary-coded cells placed on a two-dimensional matrix, said two-dimensional matrix comprising an orientation symbol disposed in a peripheral region of said two-dimensional matrix as a specific pattern, comprising steps of:

taking an image of said two-dimensional code by an image pickup device;

converting said image pixel by pixel into an image signal in response to a light intensity of said image;

binary encoding said image signal in accordance with a level of said image signal, thereby successively producing a plurality of binary-coded signals;

executing storing processing while performing detecting processing in parallel, wherein said storing processing successively stores said plurality of binary-coded signals into a memory as image data while said detecting processing detects said specific pattern corresponding to said orientation symbol based on said plurality of binary-coded signals;

finalizing a contour and an orientation of said two-dimensional matrix based on coordinates of said plurality of binary-coded cells on said two-dimensional matrix; and

reading out said image data stored in said memory in accordance with said finalized contour and said orientation of said two-dimensional matrix.

51. A two-dimensional code reading method for optically reading a two-dimensional code including a plurality of binary-coded cells on a two-dimensional square matrix pattern, said two-dimensional square matrix pattern comprising an orientation symbol and timing cells, said orientation symbol comprising a plurality of apex cells of said two-dimensional square matrix pattern, said two-dimensional code reading method comprising steps of:

taking an image of said two-dimensional code by an image pickup device, then converting said image pixel by pixel into an image signal in response to a light intensity of said image, and binary encoding said image signal in accordance with a level of said image signal, then storing a plurality of binary-coded signals as image data in a memory in accordance with a position of a pixel where the image was taken;

detecting a specific pattern corresponding to said orientation symbol based on said plurality of binary-coded signals;

detecting coordinates of each one of said plurality of apex cells comprised by said orientation symbol, and coordinates of said timing cells from said image data stored in said memory based on said detection of said specific pattern;

finalizing a contour and an orientation of said two-dimensional matrix based on said detected specific pattern and said coordinates of said plurality of apex cells, and identifying coordinates of said plurality of binary-coded cells placed on said two-dimensional square matrix pattern with reference to said coordinates of said timing cells; and

reading out said image data stored in said memory in accordance with said finalized contour and said orientation of said two-dimensional square matrix pattern.

52. The two-dimensional code reading method in accordance with claim 51, wherein said step of detecting coordinates further comprises calculating coordinates of an intended apex cell (X₀, Y₀) using equations:

space="preserve" listing-type="equation">X.sub.0 =x.sub.0 +(x.sub.2 -x.sub.1)

space="preserve" listing-type="equation">Y.sub.0 =y.sub.0 +(y.sub.2 -y.sub.1)

where (x₀, y₀), (x₁, y₁), and (x₂, y₂) represent said coordinates of three of said plurality of apex cells of said two-dimensional square matrix pattern other than said intended apex cell.

54. A two-dimensional code comprising:

a plurality of cells, each of said plurality of cells representing a binary-coded datum, said plurality of cells on a two-dimensional matrix pattern readable by a scanning operation along scanning lines;

at least two positioning symbols disposed at predetermined positions in said two-dimensional matrix pattern, each of said at least two positioning symbols having a pattern capable of gaining an identical frequency component ratio irrespective of an orientation of said scanning lines when said scanning lines pass through a center of each of said at least two positioning symbols; and

a series of timing cells including light and dark cells alternately arrayed with an inclination of 1/1 in said two-dimensional matrix pattern.

55. A two-dimensional code comprising:

a plurality of cells, each of said plurality of cells representing a binary-coded datum, said plurality of cells on a two-dimensional matrix pattern readable by a scanning operation along scanning lines;

at least two positioning symbols disposed at predetermined positions in said two-dimensional matrix pattern, each of said at least two positioning symbols having a pattern capable of gaining an identical frequency component ratio irrespective of an orientation of said scanning lines when said scanning lines pass through a center of each of said at least two positioning symbols; and

an apex detecting cell disposed on an apex of said two-dimensional matrix pattern where said at least two positioning symbols are not disposed.

56. A two-dimensional code comprising:

a plurality of cells, each of said plurality of cells representing a binary-coded datum, said plurality of cells being placed on a two-dimensional matrix pattern readable by any scanning operation along arbitrary scanning lines; and

at least two positioning symbols disposed at predetermined positions in said two-dimensional matrix pattern, each of said at least two positioning symbols having a pattern capable of gaining an identical frequency component ratio irrespective of an orientation of said arbitrary scanning lines whenever said arbitrary scanning lines pass through a center of each of said at least two positioning symbols.

57. The two-dimensional code in accordance with claim 56, wherein:

each of said at least two positioning symbols includes a pattern including concentric similar figures overlapped successively.

58. A two-dimensional code comprising:

a plurality of cells, each of said plurality of cells representing a binary-coded datum;

said plurality of cells being placed on a two-dimensional matrix, said two-dimensional matrix having a square shape and being enclosed by straight peripheral lines so as to form a pattern readable by a scanning operation along any arbitrary scanning lines;

at least two positioning symbols disposed at apex positions in said two-dimensional matrix, each of said at least two positioning symbols having a pattern capable of gaining an identical frequency component ratio irrespective of an orientation of said arbitrary scanning line whenever said arbitrary scanning lines pass through a center of each of said at least two positioning symbols, said at least two positioning symbols being square in shape and having straight peripheral lines parallel to said straight peripheral lines of said two-dimensional matrix.

59. A two-dimensional code formed from a two-dimensional matrix having a plurality of binary-coded cells, said two-dimensional code comprising:

a plurality of symbol cells representing an orientation of said two-dimensional matrix;

said plurality of symbol cells forming a two-dimensional matrix pattern and being readable by a scanning operation along any arbitrary scanning lines, said pattern being capable of gaining an identical frequency component ratio irrespective of an orientation of said arbitrary scanning lines whenever said arbitrary scanning lines pass through a center of said pattern; and

at least one data cell group comprising a group of said plurality of binary-coded cells, each of said at least one data cell group representing only one character and being disposed in a two-dimensional square region in said two-dimensional matrix, said two-dimensional square region being defined by vertically stacked binary-coded cells and horizontally arrayed binary-coded cells.

60. The two-dimensional code in accordance with claim 59, wherein said plurality of binary-coded cells in said two-dimensional square region comprise a plurality of bits dedicated to data of said one character and one of said plurality of bits dedicated to a parity.

61. The two-dimensional code in accordance with claim 59, wherein said two-dimensional code has a code-reading-prohibition cell to prohibit an operation of reading said two-dimensional code when said code-reading-prohibition cell is a predetermined color.