Character recognition system

• US 4,850,025 A
• Filed: 09/23/1986
• Issued: 07/18/1989
• Est. Priority Date: 09/27/1985
• Status: Expired due to Fees

• Current Assignee: Sony Corporation (Sony Group Corp.)
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: Abe, Keiko
• Primary Examiner(s): Boudreau, Leo H.
• Application Number:
  US06/910,890
• Time in Patent Office: 1,029 Days
• Field of Search: 382/9, 382/51, 382/48, 382/18, 382/30, 382/37
• US Class Current: 382/220
• CPC Class Codes: G06V 30/10 Character recognition
• CPC Class Codes: G06V 30/158 using character size, text spacings or pitch estimation

Abstract

A character recognition system extracts character blocks to contain a minimum character unit therein. The character recognition system has the capability of re-combining and/or re-extracting character blocks during the character recognition process. Re-combination and re-extraction of the character blocks is controlled based on the history of the extraction process for each of the character blocks so that re-combination and re-extraction can be performed effectively.

Claims

1. A character recognition system for reading character image data from a document comprising:

optical scanning means for scanning the document to obtain a video signal containing image data from said document;

extracting means for extracting character blocks from the video signal, wherein each character block contains image data of individual characters from said document, said extracting means further producing predetermined history data of each character block indicative of the process of extraction of said character block;

combining means for comparing ratios of predefined dimensional attributes of each character block with predetermined standard ratios and selectively recombining two or more of the extracted character blocks based on such comparison in order to form a combined character block;

character recognition means for receiving the extracted character blocks and the recombined character blocks for performing character recognition according to predetermining algorithms and outputting a signal indicative of a recognized character; and

encoding means connected to said extracting means to obtain the extraction history data, for controlling the operation of said combining and character recognition means by means of the extraction history data in such a manner that when said character recognition means fails to recognize a character in said character block, said encoding means selectively causes said combining means to successively combine character blocks until said character recognition means recognizes the character in said character block formed by said combining means.

2. A character recognition system as set forth in claim 1, further comprising means for distinguishing between alphabetic characters and kanji, hiragana, and katakana characters.

3. A character recognition system as set forth in claim 1, wherein said extracting means extracts said character block in predetermined minimum character units.

4. A character recognition system as set forth in claim 3, wherein said extracting means defines a character area of each character block to have edges thereof striking upper, lower and side contours of said minimum character unit.

5. A character recognition system as set forth in claim 3, wherein said extracting means detects any overlap between adjacent individual characters for separately forming said character blocks for each individual character.

6. A character recognition system as set forth in claim 5, wherein said extracting means removes noise components in said character image data for each of said character blocks.

7. A character recognition system as set forth in claim 1, wherein said extracting means includes a plurality of stages for extracting said character blocks from said image data, and said history data includes data indicative of the extraction process at each of said plurality of character block extraction stages.

8. A character recognition system as set forth in claim 7, wherein said optical scanning means scans the document along horizontal and vertical lines and said extracting means includes a stage for segmenting the image data into separate character-string blocks, a stage for segmenting each character-string block into separate character blocks, and a stage for detecting overlapping character units in a single character block and separating said character block into two or more character blocks, each containing a different one of the overlapping character units.

9. A character recognition system as set forth in claim 8, wherein said segmentation stages output signals indicative of the height and width of each character block and the combining means is supplied with these character block height and width signals and uses them to determine whether or not a given character block contains only a character component which must be combined with another and subsequently segmented character block to yield a complete character.

10. A character recognition system as set forth in claim 9, wherein said combining means computes the ratio of the character block height to the character block width and, if the ratio is much greater than 1, it combines the next received character block from the segmentation means with the last received character block, recomputes the height to width ratio of the combined character block, compares this ratio with 1, repeats this process until the height to width ratio is approximately one, and then outputs the last combined character block.

11. A character recognition system as set forth in claim 9, wherein said character recognition means further comprises predetermined character detection means for detecting a predetermined character and controlling the character recognizing operation of said character recognition means for said predetermined character by selecting an auxiliary algorithm, which is simpler than the predetermined algorithms, for performing character recognition of the predetermined character.

12. A character recognition system as set forth in claim 11, wherein said encoding means is supplied with said character block height and width signals, compares the character block height and width to predetermined standard heights and widths and from this comparison, generates relative character block height and width signals, wherein said segmentation means detects whether the character is in the upper or the lower half of the character block and outputs a position data signal, and further wherein said predetermined character detection means is supplied with the character block height, width, relative height, relative width, and data position signals and uses said signals to determine if the character is said predetermined character and, if so, selects one of said auxiliary algorithms.

13. A character recognition system as set forth in claim 8, wherein said character-string segmentation stage checks the level of a y-projection profile of the document image data for selecting horizontal scanning lines from the optical scanning means to be included in each of said character-string blocks.

14. A character recognition system as set forth in claim 8, wherein said character block segmentation stage checks the level of an x-projection profile of the document image data with respect to a predetermined threshold level for selecting vertical scanning lines of said optical scanning means to be included in said character block.

15. A character recognition system as set forth in claim 14, wherein said character block segmentation stage, in checking the level of the x-projection profile, employs a plurality of mutually different threshold levels to obtain different levels of precision in segmenting the character blocks into minimum character units.

16. A character recognition system as set forth in claim 8, wherein said overlapping character unit detecting stage checks the continuity of the character units contained in said character block for detecting discontinuities in the character units.

17. A character recognition system as set forth in claim 16, wherein said overlapping character unit detecting stage checks the continuity between adjacent image data containing bits for detecting discontinuity of the character unit in said character block.

18. A character recognition system as set forth in claim 8, wherein said extracting means further comprises a stage for checking the level of a y-projection profile for the character image data in said character block for modifying the height of said character block so that the upper and lower edges of said character block strike the upper and lower contours of said character unit in said character block.

62. A character recognition method as set forth in claims 1, 19, 30 and 39 wherein the recognized character signal output by the character recognition means is a predetermined, computer recognizable code signal.

19. A character recognition system comprising:

scanning means for obtaining a video signal containing image data of said document;

extracting means, which is supplied with the video signal, for segmenting said image data into character blocks, each of which contains image data of an individual character unit, and outputting a corresponding character block signal, said extracting means including a plurality of segmentation stages including a first segmentation stage for segmenting character-string blocks and a second segmentation stage for segmenting each character-string block into separate character blocks each containing character image data of a character unit and wherein said first and second stages further output segmentation history data indicative of the manner in which each character-string block and character block have been segmented;

combining means, which is supplied with the character block signal, for selectively recombining two or more character blocks to form a combined character block and outputting a combined character block signal;

character recognition means, which is selectively supplied with either the character block signal or the combined character block signal, for performing character recognition according to predetermined algorithms and outputting a "recognized character" signal;

re-segmenting means, which is supplied with the character block signal and the combined character block signal, for re-segmenting a selected character block for forming a re-segmented character block; and

encoding means connected to said extracting means and supplied with the segmentation history data with respect to each of said character blocks segmented by said extracting means, for controlling the operation of said combining, re-segmentation and character recognition means based on said segmentation history data in such a manner that said encoding means selectively operates one of said combining and re-segmenting means when said character recognition means fails to recognize a character in said character block, so as to recombine or re-segment, respectively, one or more selected character blocks to assure recognition in said character recognition means of the character block formed by a selected one of said combining and re-segmenting means.

20. A character recognition system as set forth in claim 19, wherein said extracting means extracts said character block in minimum character units.

21. A character recognition system as set forth in claim 19, wherein said extracting means further comprises a third segmentation stage for detecting overlap between adjacent separable character units contained in a single character block for separately forming said character blocks for each of the respective character units.

22. A character recognition system as set forth in claim 19, wherein said extracting means further comprises a fourth segmentation stage for removing noise components in said character image data for each of said character blocks.

23. A character recognition system as set forth in claim 19, which further comprises predetermined character detection means for detecting a predetermined character and controlling the character recognizing operation of said character recognition means for said predetermined character by selecting an auxiliary algorithm which is simpler than the predetermined algorithms.

24. A character recognition system as set forth in claim 21, wherein said scanning means scans the document along horizontal and vertical lines and said first segmentation stage checks the level of a y-projection profile of the document image data for selecting horizontal scanning lines from the scanning means to be included in each of said character-string blocks.

25. A character recognition system as set forth in claim 21, wherein said second segmentation stage checks the level of an x-projection profile of the document image data with respect to a predetermined threshold level for selecting vertical scanning lines from the scanning means to be included in said character block.

26. A character recognition system as set forth in claim 25, wherein said second segmentation stage employs a plurality of mutually different threshold levels for segmenting said character block at different levels of precision in segmenting the character blocks into minimum character units.

27. A character recognition system as set forth in claim 26, wherein said third segmentation stage checks the continuity of the character unit contained in each character block for detecting discontinuity in the character unit in order to separate the character block into two or more character blocks.

28. A character recognition system as set forth in claim 26, wherein said third separating stage checks the continuity between adjacent image data containing bits for detecting discontinuity of the character unit in each said character block.

29. A character recognition system as set forth in claim 22, wherein said encoding means obtains the segmentation history data with respect to each character block in said respective second, third and fourth segmentation stages.

30. A character recognition system comprising:

scanning means for obtaining a video signal containing image data corresponding to said document and wherein said scanning means scans the document along horizontal and vertical lines;

extracting means for deriving from the video signal a plurality of character blocks, each of which contains image data of individual characters in said document, and outputting a corresponding character block signal, said extracting means including a plurality of segmentation stages including a first segmentation stage for segmenting character-string blocks, a second segmentation stage for segmenting each character-string block into separate character blocks each containing character image data of a character unit and a third segmentation stage for checking the continuity of image data containing bits within each character block for detecting discontinuities in order to separate the character blocks into two or more character blocks, each containing a minimum character unit;

combining means, which is selectively supplied with the character block signal, for recombining two or more character blocks to form a combined character block and outputting a combined character block signal;

re-segmenting means, which is supplied with the character block signal and the combined character block signal, for selectively re-segmenting one or more selected character blocks to form a re-segmented character block and outputting a corresponding re-segmented character block signal;

character recognition means, which is supplied with the character block signal, the combined character block signal and the re-segmented character block signal, for performing character recognition according to predetermined algorithms and outputting a "recognized character" indicative signal; and

encoding means for controlling the operation of said combining, re-segmentation and character recognition means in such a manner that said encoding means selectively operates one of said combining and re-segmenting means when said character recognition means fails to recognize a character in said character block, so as to assure recognition of character in said character recognition means with the character block formed by the selected one of said combining and re-segmenting means.

31. A character recognition system as set forth in claim 30, wherein said extracting means defines said character area to have edges thereof striking the upper, lower and side contours of said minimum character unit contained therein.

32. A character recognition system as set forth in claim 30, wherein said extracting means further comprises a fourth stage for removing noise components in the image data of said character units.

33. A character recognition system as set forth in claim 30, which further comprises predetermined character detection means for detecting a predetermined character and controlling the character recognizing operation of said character recognition means for said predetermined character by selecting an auxiliary algorithm which is simpler than the predetermined algorithms.

34. A character recognition system as set forth in claim 30, wherein said first segmentation stage checks the level of a y-projection profile of the document image data for selecting horizontal scanning lines to be included in each of said character-string blocks.

35. A character recognition system as set forth in claim 34, wherein said second segmentation stage checks the level of an x-projection profile of the document image data with respect to a predetermined threshold level for selecting the vertical scanning lines to be included in said character block.

36. A character recognition system as set forth in claim 35, wherein said second segmentation stage employs a plurality of mutually different threshold levels for segmenting said character block at different levels of precision into minimum character units.

37. A character recognition system as set forth in claim 36, wherein said extracting means generates segmentation history data indicative of the manner in which each character-string block and character block have been segmented and said encoding means is supplied with said segmentation history data with respect to said second, third and fourth segmentation stages to thereby control the operation of the character recognition means, the combining means and the re-segmenting means in accordance therewith.

38. A character recognition system as set forth in claim 37, wherein said encoding means obtains the segmentation history data with respect to each character block in the respective second, third and fourth segmentation stages.

39. A character recognition system comprising

first means for receiving a video signal containing character image data;

extracting means for deriving from the video signal a plurality of character blocks, each of which contains image data of individual characters, said extracting means including a plurality of segmentation stages inclucing a first segmentation stage for segmenting character-string blocks into character blocks, a second segmentation stage for segmenting each character block containing a character unit of image data and a third segmentation stage for checking the continuity of image data containing bits within each character block for detecting discontinuity in order to separate character blocks into more than one character block so as to obtain character blocks which each contain a minimum character unit and wherein the extracting means generates segmentation history data with respect to at least said second and third segmentation stages performed by said extracting means, which segmentation history data is indicative of the order of segmentation of each character block in each of said second and third stages;

combining means for recombining two or more character blocks for forming a combined character block;

re-segmenting means for re-segmenting character block for forming a re-segmented character block;

character recognition means for performing character recognition according to predetermined algorithms and outputting recognized character indicative signal; and

encoding means connected to said extracting means for obtaining the segmentation history data, and controlling the operation of said combining and character recognition means based on said segmentation history data in such a manner that said encoding means seletively operates one of said combining means and re-segmenting means when said character recognition means fails to recognize a character in said character block, so as to assure recognition by said character recognition means of the character in the character block formed by the selected one of said combining and re-segmenting means.

40. A character recognition system as set forth in claim 39, wherein said third stage further detects overlap between adjacent, but separable character units contained in a single character block and separates said character units into one or more separate character blocks.

41. A character recognition system as set forth in claim 40, wherein said extracting means further comprises a fourth segmentation stage for removing noise components in said character image data for each of said character blocks.

42. A character recognition system as set forth in claim 39, which further comprises predetermined character detection means for detecting a predetermined character and controlling the character recognizing operation of said character recognition means for said predetermined character by selecting an auxiliary algorithms which is simpler than the predetermined algorithms.

43. A character recognition system as set forth in claim 39, further comprising scanning means for repeatedly scanning, over a plurality of lines in the X and Y direction, a document on which are printed characters to produce the video signal containing the character image data and wherein said first segmentation stage checks the level of a y-projection profile of the image data for selecting the horizontal scanning lines of the scanning means to be included in each of said character-string blocks.

44. A character recognition system as set forth in claim 43, wherein said second segmentation stage checks the level of an x-projection profile of the image data with respect to a predetermined threshold level for selecting the vertical scanning lines of the scanning means to be included in said character block.

45. A character recognition system as set forth in claim 44, wherein said second segmentation stage employs a plurality of mutually different threshold levels for segmenting said character block at different levels of precision into minimum character units.

46. A character recognition system as set forth in claim 39, wherein said encoding means alternatively sets a flag to a logical HIGH level and a logical LOW level for character blocks segmented by each of said second and third segmentation stages in forming said segmentation history.

47. A method for recognizing characters contained in a document comprising the steps of:

generating a video signal containing image data of said document;

from the video data, extracting character blocks, each of which contains image data of individual characters in said document;

combining two or more character blocks for forming a combined character block;

re-segmenting a character block for forming a re-segmented character block;

from the character blocks, the combined character blocks and the re-segmented character blocks, performing character recognition according to predetermined algorithms and outputting a "recognized character" indicative signal; and

controlling the combining step, re-segmenting step and character recognition step in such a manner that the combining step, re-segmenting step and character recognition step are selectively performed to ensure recognition of characters by repeating said combining step, re-segmenting step and character recognition step with respect to a selected one or a selected succession of character blocks, combined character blocks or re-segmented character blocks until character recognition is achieved.

48. A character recognition method as set forth in claim 47, wherein said step of extracting said character blocks is performed to extract character blocks containing a minimum character unit.

49. A character recognition method as set forth in claim 47, wherein, in said character block extracting step, a character block area is defined to have edges thereof striking upper, lower and side contours of said minimum character unit.

50. A character recognition method as set forth in claim 47, wherein, in said character block extracting step, overlapping between adjacent individual characters is detected for separately forming character blocks for respetive individual characters.

51. A character recognition method as set forth in claim 50, wherein, in said character block extracting step, noise components contained in the character image data of each of said character blocks is removed.

52. A character recognition method as set forth in claim 51, which further comprises a step of detecting a predetermined character and controlling the character recognizing step for said predetermined character by selecting an auxiliary algorithm which is simpler than the predetermined algorithms.

53. A character recognition method as set forth in claim 47, wherein said step of controlling said combining step, said re-segmenting step and said character recognition step includes the step of obtaining segmentation history data of each character block indicative of the extraction process for said character block, for controlling the combining step based on said segmentation history data.

54. A character recognition method as set forth in claim 53, wherein said character block extracting step includes a plurality of steps for extracting said character blocks from said document image data, and said segmentation history data is obtained during the process of extraction performed in each of said plurality of character block extraction steps.

55. A character recognition method as set forth in claim 54, wherein said character block extracting step includes a step of segmenting each character-string block, a step of segmenting each character-string block into character blocks, a step of detecting more than one character unit in a single character block and separating said character block into more than one character block, each containing separated individual character units.

56. A character recognition method as set forth in claim 55, wherein said video signal generating step comprises optically scanning the document along a plurality of vertical and horizontal lines and the character-string segmentation step includes the step of checking the level of a y-projection profile of the document image data and using that information to select the horizontal scanning lines of the scanning step to be included in each of said character-string blocks.

59. A character recognition method as set forth in claim 56, wherein said character block separating step includes the steps of checking the continuity of the character unit contained in each character block, detecting the discontinuity in the character unit, and separating the character block at such detected discontinuities.

60. A character recognition method as set forth in claim 55, wherein said character block separating step includes the step of checking the continuity between adjacent image data containing bits for detecting discontinuity in the character unit in said character block.

61. A character recognition method as set forth in claim 56, wherein said character block extracting step further comprises a step of checking the level of a y-projection profile for the character image data in said character block for determining the height of said character block so that the upper and lower edges of said character block strike the upper and lower contours of said character unit in said character block.

63. A character recognition method as set forth in claim 47, wherein the recognized character signal output as a result of the character recognition step is a predetermined, computer recognizable code signal.

57. A character recognition method as set forth in cliam 56, wherein said character block segmentation step includes the steps of checking the level of an x-projection profile of the document image data with respect to a predetermined threshold level and using that information to select the vertical scanning lines of the scanning step to be included in said character block.

58. A character recognition method as set forth in claim 57, wherein said character block segmentation step employs a plurality of mutually different threshold levels for segmenting said character block at different levels of precision to have minimum character units.