Method and apparatus for recognizing text in an image sequence of scene imagery
An apparatus and a concomitant method for detecting and recognizing text information in a captured imagery. The present method transforms the image of the text to a normalized coordinate system before performing OCR, thereby yielding more robust recognition performance. The present invention also combines OCR results from multiple frames, in a manner that takes the best recognition results from each frame and forms a single result that can be more accurate than the results from any of the individual frames.
1. Method for recognizing text in a captured imagery, where said captured imagery is of a three-dimensional scene, said method comprising the steps of:
(a) detecting a text region in the captured imagery;
(b) adjusting along three axes said detected text region to produce a rectified image; and
(c) applying optical character recognition (OCR) processing to said rectified image to recognize the text in the captured imagery.
2. The method of claim 1 , wherein said adjusting step (b) comprises the step of (b1) computing a base line and a top line for a line of detected text within said detected text region.
3. The method of claim 2 , wherein said base line and said top line correlate substantially to horizontal parallel lines of a rectangular bounding box that is fitted to said line of detected text.
4. The method of claim 2 , wherein said base line and said top line are estimated by rotating said line of detected text at various angles and then computing a plurality of horizontal projections over a plurality of vertical edge projections.
5. The method of claim 2 , wherein said base line is selected comprising the steps of:
locating a plurality of bottom edge pixels, where each bottom edge pixel is located for each column in said rectangular bounding box;
rotating said plurality of bottom edge pixels through a series of angles around an initial estimated text angle for said line of detected text;
summing horizontally along each row; and
determining a baseline angle from a maximum sum of squared projections and determining a baseline position from a maximum projection.
6. The method of claim 2 , wherein said top line is selected comprising the steps of:
locating a plurality of top edge pixels, where each top edge pixel is located for each column in said rectangular bounding box;
rotating said plurality of top edge pixels through a series of angles around an initial estimated text angle for said line of detected text;
summing horizontally along each row; and
determining a top line angle from a maximum sum of squared projections and determining a top line position from a maximum projection.
7. The method of claim 2 , wherein said adjusting step (b) further comprises the step of (b2) computing a dominant vertical direction of character strokes for a line of detected text within said detected text region.
8. The method of claim 1 , further comprising the step of:
(b1) binarizing said detected text region prior to applying said OCR processing step (c).
9. The method of claim 8 , further comprising the step of:
(d) applying agglomeration processing subsequent to said OCR processing to produce the text in the captured imagery.
10. The method of claim 9 , further comprising the step of:
(e) applying lexicon processing subsequent to said agglomeration processing to produce the text in the captured imagery.
11. The method of claim 10 , further comprising the step of:
(f) applying false text elimination processing subsequent to said lexicon processing to produce the text in the captured imagery.
12. Apparatus for recognizing text in a captured imagery, where said captured imagery is of a three-dimensional scene, said apparatus comprising:
means for detecting a text region in the captured imagery;
means for adjusting along three axes said detected text region to produce a rectified image; and
means for applying optical character recognition (OCR) processing to said rectified image to recognize the text in the captured imagery.
13. The apparatus of claim 12 , wherein said adjusting means computes a base line and a top line for a line of detected text within said detected text region.
14. The apparatus of claim 13 , wherein said base line and said top line correlate substantially to horizontal parallel lines of a rectangular bounding box that is fitted to said line of detected text.
15. The apparatus of claim 13 , wherein said base line and said top line are estimated by rotating said line of detected text at various angles and then computing a plurality of horizontal projections over a plurality of vertical edge projections.
16. The apparatus of claim 15 , wherein said base line is selected that corresponds to a rotation angle that yields a steepest slope on a bottom side of one of said plurality of horizontal projections.
17. The apparatus of claim 13 , wherein said adjusting means further computes a dominant vertical direction of character strokes for a line of detected text within said detected text region.