Methods and Systems for Identifying Text Orientation in a Digital Image

• US 20080317343A1
• Filed: 06/21/2007
• Published: 12/25/2008
• Est. Priority Date: 06/21/2007
• Status: Active Grant

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Speigle, Jon M., Ferman, Ahmet Mufit
• Granted Patent: US 8,208,725 B2
• Time in Patent Office: Days
• US Class Current: 382/176
• CPC Class Codes: G06V 30/10 Character recognition
• CPC Class Codes: G06V 30/1463 Orientation detection or correction, e.g. rotation of multiples of 90 degrees

Abstract

Aspects of the present invention relate to systems and methods for determining text orientation in a digital image.

Claims

1. A method for determining a text orientation in a digital image, said method comprising:

a) in a first text line comprising a first plurality of text characters in a digital image, determining a first text-line orientation of said first text line;

b) computing a first first-alignment feature value relative to said first text-line orientation for said first text line in said digital image;

c) computing a first second-alignment feature value relative to said first text-line orientation for said first text line in said digital image; and

d) determining a first text orientation of said first plurality of text characters in said digital image based on said first first-alignment feature value and said first second-alignment feature value.

2. A method according to claim 1, wherein said determining a first text orientation comprises:

a) determining a baseline-side of said first text line, wherein said determining said baseline-side of said first text line is based on the relative values of said first first-alignment feature value and said first second-alignment feature value and a relative frequency of occurrence of text characters with ascenders and text characters with descenders in a written language.

3. A method according to claim 1 further comprising:

a) in a second text line comprising a second plurality of text characters in said digital image, determining a second text-line orientation of said second text line;

b) computing a second first-alignment feature value relative to said second text-line orientation for said second text line in said digital image;

c) computing a second second-alignment feature value relative to said second text-line orientation for said second text line in said digital image;

d) determining a second text orientation of said second plurality of text characters in said digital image based on said second first-alignment feature value and said second second-alignment feature value; and

e) determining a page text orientation based on said first text orientation and said second text orientation.

4. A method according to claim 1, wherein said determining a first text-line orientation comprises:

a) determining a text-line bounding box for said first text line;

b) calculating an aspect ratio for said text-line bounding box; and

c) determining said first text-line orientation based on said aspect ratio.

5. A method according to claim 1 further comprising:

a) determining, for each of said first plurality of text characters, a first-edge position measurement corresponding to a bounding edge associated with a first side of said first text line, thereby producing a plurality of first-edge position measurements;

b) determining, for each of said second plurality of text characters, a second-edge position measurement corresponding to a bounding edge associated with a second side of said first text line, thereby producing a plurality of second-edge position measurements;

c) wherein said computing a first first-alignment feature comprises;

i) calculating a sample mean for said plurality of first-edge position measurements, thereby producing a ceiling measurement; and

ii) calculating an error measure between said ceiling measurement and said plurality of first-edge position measurements, thereby producing said first first-alignment feature value; and

d) wherein said computing a first second-alignment feature comprises;

i) calculating a sample mean for said plurality of second-edge position measurements, thereby producing a floor measurement; and

ii) calculating an error measure between said floor measurement and said plurality of second-edge position measurements, thereby producing said first second-alignment feature value.

6. A method according to claim 5 further comprising projecting said first plurality of text characters according to a skew angle prior to said determining, for each of said first plurality of text characters, said first-edge position measurement and prior to said determining, for each of said first plurality of text characters, said second-edge position measurement.

7. A method according to claim 5, wherein said determining a first text orientation comprises:

a) determining a baseline-side of said first text line, wherein said determining said baseline-side of said first text line is based on the relative values of said first first-alignment feature value and said first second-alignment feature value and a relative frequency of occurrence of text characters with ascenders and text characters with descenders in a written language.

8. A method according to claim 7, wherein said determining a baseline-side of said first text line comprises:

a) associating said baseline-side of said first text line with said first side of said first text line when said first first-alignment feature value is less than said first second-alignment feature value; and

b) associating said baseline-side of said first text line with said second side of said first text line when said first second-alignment feature value is less than said first first-alignment feature value.

9. A method according to claim 7, wherein said determining a baseline-side of said first text line comprises:

a) receiving a language indicator for said digital image, wherein said language indicator indicates the language in which said first text line is written;

b) determining a relative likelihood of text characters with descenders to text characters with ascenders in said language;

c) associating said baseline-side of said first text line with said first side of said first text line when said first first-alignment feature value is less than said first second-alignment feature value and said relative likelihood indicates that text characters with descenders are less likely than text characters with ascenders;

d) associating said baseline-side of said first text line with said second side of said first text line when said first second-alignment feature value is less than said first first-alignment feature value and said relative likelihood indicates that text characters with descenders are less likely than text characters with ascenders;

e) associating said baseline-side of said first text line with said first side of said first text line when said second first-alignment feature value is greater than said first second-alignment feature value and said relative likelihood indicates that text characters with ascenders are less likely than text characters with descenders; and

f) associating said baseline-side of said first text line with said second side of said first text line when said second first-alignment feature value is less than said first and said relative likelihood indicates that text characters with ascenders are less likely than text characters with descenders.

10. A method according to claim 5, wherein said error measure between said floor measurement and said plurality of second-edge position measurements is an error measure selected from the group consisting of mean absolute error, mean-square error and root mean-square error.

11. A method according to claim 5, wherein said error measure between said ceiling measurement and said plurality of first-edge position measurements is an error measure selected from the group consisting of mean absolute error, mean-square error and root mean-square error.

12. A method according to claim 1 further comprising:

a) determining a first-side reference line for a first side of said first text line, said first-side reference line characterized by a first-side-reference-line position measurement;

b) determining a second-side reference line for a second side of said first text line, said second-side reference line characterized by a second-side-reference-line position measurement;

c) determining, for each of said first plurality of text characters, a first-edge position measurement corresponding to a bounding edge associated with a first side of said first text line, thereby producing a plurality of first-edge position measurements;

d) determining, for each of said second plurality of text characters, a second-edge position measurement corresponding to a bounding edge associated with a second side of said first text line, thereby producing a plurality of second-edge position measurements;

e) wherein said computing a first first-alignment feature comprises;

i) calculating a difference between each of said plurality of first-edge position measurements and said first-side-reference-line position measurement, thereby producing a first plurality of difference measurements;

ii) calculating a first maximum, said first maximum corresponding to the maximum value of said first plurality of difference measurements;

iii) calculating the absolute value of the difference between each of said first plurality of difference measurements and said first maximum, thereby producing a first plurality of difference-from-maximum values; and

iv) summing said first plurality of difference-from-maximum values, thereby producing said first first-alignment feature value; and

f) wherein said computing a first second-alignment feature comprises;

i) calculating a difference between each of said plurality of second-edge position measurements and said second-side-reference-line position measurement, thereby producing a second plurality of difference measurements;

ii) calculating a second maximum, said second maximum corresponding to the maximum value of said second plurality of difference measurements;

iii) calculating the absolute value of the difference between each of said second plurality of difference measurements and said second maximum, thereby producing a second plurality of difference-from-maximum values; and

iv) summing said second plurality of difference-from-maximum values, thereby producing said first second-alignment feature value.

13. A method according to claim 12, wherein said first-side reference line corresponds to a first side of a bounding box for said first text line and said second-side reference line corresponds to a second side of said bounding box for said first text line.

14. A method according to claim 12, wherein said determining a first text orientation comprises:

a) determining a baseline-side of said first text line, wherein said determining said baseline-side of said first text line is based on the relative values of said first first-alignment feature value and said first second-alignment feature value and a relative frequency of occurrence of text characters with ascenders and text characters with descenders in a written language.

15. A method according to claim 14, wherein said determining a baseline-side of said first text line comprises:

a) associating said baseline-side of said first text line with said first side of said first text line when said first first-alignment feature value is less than said first second-alignment feature value; and

b) associating said baseline-side of said first text line with said second side of said first text line when said first second-alignment feature value is less than said first first-alignment feature value.

16. A method according to claim 14, wherein said determining a baseline-side of said first text line comprises:

a) receiving a language indicator for said digital image, wherein said language indicator indicates the language in which said first text line is written;

b) determining a relative likelihood of text characters with descenders to text characters with ascenders in said language;

c) associating said baseline-side of said first text line with said first side of said first text line when said first first-alignment feature value is less than said first second-alignment feature value and said relative likelihood indicates that text characters with descenders are less likely than text characters with ascenders;

d) associating said baseline-side of said first text line with said second side of said first text line when said first second-alignment feature value is less than said first first-alignment feature value and said relative likelihood indicates that text characters with descenders are less likely than text characters with ascenders;

e) associating said baseline-side of said first text line with said first side of said first text line when said second first-alignment feature value is greater than said first second-alignment feature value and said relative likelihood indicates that text characters with ascenders are less likely than text characters with descenders; and

f) associating said baseline-side of said first text line with said second side of said first text line when said second first-alignment feature value is less than said first and said relative likelihood indicates that text characters with ascenders are less likely than text characters with descenders.

17. A method according to claim 12 further comprising projecting said first plurality of text characters according to a skew angle prior to said determining, for each of said first plurality of text characters, said first-edge position measurement and prior to said determining, for each of said first plurality of text characters, said second-edge position measurement.

18. A system for determining a text orientation in a digital image, said system comprising:

a) a text-line orientation determiner for determining a first text-line orientation of a first text line in a digital image, wherein said first text line comprises a first plurality of text characters;

b) a first alignment feature calculator for computing a first-alignment feature value relative to said first text-line orientation for said first text line in said digital image;

c) a second alignment feature calculator for computing a second-alignment feature value relative to said first text-line orientation for said first text line in said digital image; and

d) a text orientation determiner for determining a text orientation of said first plurality of text characters in said digital image based on said first first-alignment feature value and said first second-alignment feature value.

19. A system according to claim 18, wherein said text orientation determiner comprises:

a) a baseline-side determiner for determining a baseline-side of said first text line, wherein said determining said baseline-side of said first text line is based on the relative values of said first first-alignment feature value and said first second-alignment feature value and a relative frequency of occurrence of text characters with ascenders and text characters with descenders in a written language.

20. A system according to claim 18 further comprising:

a) a bounding-box determiner for determining a bounding box for each of said first plurality of text characters, thereby producing a plurality of bounding boxes, wherein each of said bounding boxes comprises;

i) a first edge, said first edge characterized by a first-edge position measurement, thereby producing a plurality of first-edge position measurements, and said first edge associated with a first side of said first text line; and

ii) a second edge, said second edge characterized by a second-edge position measurement, thereby producing a plurality of second-edge position measurements, and said second edge associated with a second side of said first text line;

b) wherein first-alignment feature calculator comprises;

i) a first sample-mean calculator for calculating a sample mean for said plurality of first-edge position measurements, thereby producing a ceiling measurement; and

ii) a first error-measure calculator for calculating an error measure between said ceiling measurement and said plurality of first-edge position measurements, thereby producing said first first-alignment feature value; and

c) wherein said second-alignment feature calculator comprises;

i) a second sample-mean calculator for calculating a sample mean for said plurality of second-edge position measurements, thereby producing a floor measurement; and

ii) a second error-measure calculator for calculating an error measure between said floor measurement and said plurality of second-edge position measurements, thereby producing said first second-alignment feature value.

21. A system according to claim 18 further comprising:

a) a text-line bounding box determiner for determining a first-text-line bounding box for said first text line, wherein said first-text-line bound box comprises;

i) a first-text-line first edge, said first-text-line first edge characterized by a first-text-line-first-edge position measurement and said first-text-line first edge associated with a first text-line-side of said first text line; and

ii) a first-text-line second edge, said first-text-line second edge characterized by a first-text-line-second-edge position measurement and associated with a second text-line-side of said first text line;

b) a character-bounding-box determiner for determining a bounding box for each of said first plurality of text characters, thereby producing a plurality of bounding boxes, wherein each of said bounding boxes comprises;

i) a first edge, said first edge characterized by a first-edge position measurement, thereby producing a plurality of first-edge position measurements, and said first edge associated with a first side of said first text line; and

ii) a second edge, said second edge characterized by a second-edge position measurement, thereby producing a plurality of second-edge position measurements, and said second edge associated with a second side of said first text line;

c) wherein said first-alignment feature calculator comprises;

i) a first difference calculator for calculating a difference between each of said plurality of first-edge position measurements and said first-text-line first-edge position measurement, thereby producing a first plurality of difference measurements;

ii) a first maximum calculator for calculating a first maximum, said first maximum corresponding to the maximum value of said first plurality of difference measurements;

iii) a first absolute-value calculator for calculating the absolute value of the difference between each of said first plurality of difference measurements and said first maximum, thereby producing a first plurality of difference-from-maximum values; and

iv) a first accumulator for summing said first plurality of difference-from-maximum values, thereby producing said first first-alignment feature value; and

d) wherein said second-alignment feature calculator comprises;

i) a second difference calculator for calculating a difference between each of said plurality of second-edge position measurements and said first-text-line second-edge position measurement, thereby producing a second plurality of difference measurements;

ii) a second maximum calculator for calculating a second maximum, said second maximum corresponding to the maximum value of said second plurality of difference measurements;

iii) a second absolute-value calculator for calculating the absolute value of the difference between each of said second plurality of difference measurements and said second maximum, thereby producing a second plurality of difference-from-maximum values; and

iv) a second accumulator for summing said second plurality of difference-from-maximum values, thereby producing said first second-alignment feature value.