METHODS FOR LOCATING AND DECODING DISTORTED TWO-DIMENSIONAL MATRIX SYMBOLS

• US 20090003722A1
• Filed: 07/03/2008
• Published: 01/01/2009
• Est. Priority Date: 06/25/2005
• Status: Active Grant

• Current Assignee: Cognex Technology & Investment Corporation (Cognex Corporation)
• Original Assignee: Cognex Corporation
• Inventors: Ye, Xiangyun, Nadabar, Sateesha
• Granted Patent: US 7,965,899 B2
• Time in Patent Office: Days
• US Class Current: 382/255
• CPC Class Codes: G06K 19/06037 multi-dimensional coding
• CPC Class Codes: G06V 10/34 Smoothing or thinning of the pattern; Morphological operations; Skeletonisation

Abstract

A method is presented for processing an image of a two-dimensional (2D) matrix symbol having a plurality of data modules and a discontinuous finder pattern, each distorted by “donut effects”. A resulting processed image contains an image of the 2D matrix symbol having a continuous finder pattern suitable for conventional 2D matrix symbol locating techniques, and having a plurality of data modules, each data module having a center more truly representative of intended data, and suitable for conventional 2D matrix symbol sampling and decoding. The method includes sharpening the distorted image of the 2D matrix symbol to increase a difference between low frequency and high frequency image feature magnitudes, thereby providing a sharpened image, and smoothing the sharpened image using a moving window over the sharpened image so as to provide a smoothed image, the moving window and a module of the 2D matrix code being of substantially similar size.

Claims

1-27. -27. (canceled)

28. A method for processing an image of a two-dimensional (2D) matrix code having a plurality of data modules and a discontinuous finder pattern, each distorted by “

donut effects”

such that a resulting processed image contains an image of the 2D matrix code having a continuous finder pattern suitable for conventional data matrix locating techniques, and having a plurality of data modules, each data module having a center more truly representative of intended data, and suitable for conventional 2D matrix symbol sampling and decoding, the method comprising;

removing noise from the distorted image so as to provide a noise-reduced image with improved signal-to-noise-ratio;

sharpening the noise-reduced image so as to remove low frequency image features while preserving high frequency image features, thereby providing a high-pass filtered image;

amplifying the sharpened image so as to increase contrast in the sharpened image, thereby providing an amplified sharpened image; and

smoothing the amplified high-pass filtered image using a moving window over the high-pass filtered image so as to provide a smoothed image, the moving window and a module of the 2D matrix code being of substantially similar size.

29. The method of claim 28, further comprising:

repeating the method at different resolutions so as to expand operating range over a variety of module sizes.

30. The method of claim 28, wherein sharpening includes:

computing gradient magnitude at each pixel using a Sobel edge detector.

31. The method of claim 28, wherein smoothing the amplified sharpened image includes:

convolving the amplified sharpened image with a smoothing kernel.

32-35. -35. (canceled)