Method and apparatus for recognizing text in an image sequence of scene imagery

• US 7,031,553 B2
• Filed: 06/29/2001
• Issued: 04/18/2006
• Est. Priority Date: 09/22/2000
• Status: Active Grant

• Current Assignee: SRI International, Inc.
• Original Assignee: SRI International, Inc.
• Inventors: Myers, Gregory K., Bolles, Robert C., Luong, Quang-Tuan, Herson, James A.
• Primary Examiner(s): COUSO, YON JUNG
• Application Number:
  US09/895,868
• Publication Number:
  US 20020051575A1
• Time in Patent Office: 1,754 Days
• Field of Search: 382/181, 382/289, 382/290, 382/295, 382/296, 382/105, 382/173, 382/174, 382/176, 382/202, 382/177, 382/229, 382/143, 348/147, 348/144, 348/143
• US Class Current: 382/289
• CPC Class Codes: G06V 20/63 Scene text, e.g. street names
• CPC Class Codes: G06V 30/10 Character recognition
• CPC Class Codes: G06V 30/1478 of characters or characters lines

Abstract

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.

Claims

1. Method for recognizing text in a captured imagery, said method comprising the steps of:

(a) detecting a text region in the captured imagery;

(b) adjusting said detected text region to produce a rectified image;

(c) applying optical character recognition (OCR) processing to said rectified image to recognize the text in the captured imagery;

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;

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; and

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.

2. Method for recognizing text in a captured imagery, said method comprising the steps of:

(a) detecting a text region in the captured imagery;

(b) adjusting said detected text region to produce a rectified image;

(c) applying optical character recognition (OCR) processing to said rectified image to recognize the text in the captured imagery;

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;

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; and

wherein said top line is selected that corresponds to a rotation angle that yields a steepest slope on a top side of one of said plurality of horizontal projections.

3. Method for recognizing text in a captured imagery, said method comprising the steps of:

(a) detecting a text region in the captured imagery;

(b) adjusting said detected text region to produce a rectified image;

(c) applying optical character recognition (OCR) processing to said rectified image to recognize the text in the captured imagery;

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;

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; and

wherein said dominant vertical direction computing step (b2) comprises the step of computing a plurality of vertical projections over a plurality of vertical edge transitions after rotating said line of detected text in a plurality of degree increments.

4. The method of claim 3, wherein said dominant vertical direction is selected that corresponds to an angle where a sum of squares of said vertical projections is a maximum.

5. Apparatus for recognizing text in a captured imagery, said apparatus comprising:

means for detecting a text region in the captured imagery;

means for adjusting 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;

wherein said adjusting means computes a base line and a top line for a line of detected text within said detected text region;

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; and

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.

6. Apparatus for recognizing text in a captured imagery, said apparatus comprising:

means for detecting a text region in the captured imagery;

means for adjusting 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;

wherein said adjusting means computes a base line and a top line for a line of detected text within said detected text region;

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; and

wherein said top line is selected that corresponds to a rotation angle that yields a steepest slope on a top side of one of said plurality of horizontal projections.

7. Apparatus for recognizing text in a captured imagery, said apparatus comprising:

means for detecting a text region in the captured imagery;

means for adjusting 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;

wherein said adjusting means computes a base line and a top line for a line of detected text within said detected text region;

wherein said adjusting means further computes a dominant vertical direction of character strokes for a line of detected text within said detected text region; and

wherein said adjusting means computes said dominant vertical direction by computing a plurality of vertical projections over a plurality of vertical edge transitions after rotating said line of detected text in a plurality of degree increments.

8. 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, wherein said adjusting comprises the steps of;

(b1) computing a base line and a top line for a line of detected text within said detected text region; and

(b2) computing a dominant vertical direction of character strokes for a line of detected text within said detected text region, wherein said dominant vertical direction computing further comprises the step of computing a plurality of vertical projections over a plurality of vertical edge transitions after rotating said line of detected text in a plurality of degree increments; and

(c) applying optical character recognition (OCR) processing to said rectified image to recognize the text in the captured imagery.