Method of extracting image data from an area generated with a halftone pattern

• US 6,023,534 A
• Filed: 08/04/1997
• Issued: 02/08/2000
• Est. Priority Date: 08/04/1997
• Status: Expired due to Term

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Handley, John C.
• Primary Examiner(s): Bella, Matthew C.
• Application Number:
  US08/905,610
• Time in Patent Office: 918 Days
• Field of Search: 382/199, 382/176, 382/200, 382/209, 382/217, 382/219, 382/257, 382/260, 382/266, 382/267, 382/268, 382/274, 382/275, 382/282, 382/283, 382/290, 382/291, 382/292, 382/301, 358/429, 358/453, 358/452, 358/456, 358/462, 358/538
• US Class Current: 382/275
• CPC Class Codes: G06V 30/10 Character recognition
• CPC Class Codes: G06V 30/1444 Selective acquisition, locating or processing of specific regions, e.g. highlighted text, fiducial marks or predetermined fields

Abstract

A method for generating forms using halftones along with a set of low-complexity image processing steps to extract the characters for recognition. The method exploits texture differences between character strokes and halftoned boxes or text fields. Form frames are rendered as black and white halftones and characters are extracted by exploiting differences in texture between the frames and the character strokes. A sequence of simple image processing operations, easily done in hardware, eliminates the frames while leaving the characters intact. Halftones, giving the appearance of a light color as in the dropout-color method, are easily produced by page description languages; thus, blank and filled-in forms can be scanned, printed, stored and photocopied at low cost.

Claims

1. A method for enhancing extraction of image data subsequently applied to distinct frame boxes of halftone patterns of alternating high (white) and low (dark) pixellated regions, comprising the steps of:

sharpening said image data using a convolution with at least one mask;

morphologically closing on said image data with at least one structured element;

thresholding said morphologically closed image into a binary image;

repeatedly lowering said threshold so that, as more of said pixellated regions become white, boxes of said frame are erased along with one or more spurious connected components of said image; and

electronically scanning said image to eliminate remaining halftone regions.