Methods and apparatus for one-dimensional signal extraction

• US 9,122,952 B2
• Filed: 12/23/2011
• Issued: 09/01/2015
• Est. Priority Date: 12/23/2011
• Status: Active Grant

• Current Assignee: Cognex Corporation
• Original Assignee: Cognex Corporation
• Inventors: Silver, William M., Bachelder, Ivan
• Primary Examiner(s): Mehta, Bhavesh
• Assistant Examiner(s): Dunphy, David F
• Application Number:
  US13/336,275
• Publication Number:
  US 20130163876A1
• Time in Patent Office: 1,348 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: G06F 18/00 Pattern recognition
• CPC Class Codes: G06F 2218/02 Preprocessing
• CPC Class Codes: G06K 7/00 Methods or arrangements for sensing record carriers, e.g. for reading patterns methods or arrangements for marking the record carrier in digital fashion G06K1/00; pattern recognition G06F18/00; arrangements for image or video recognition or understanding G06V10/00; character recognition, recognising digital ink or document-oriented image-based pattern recognition G06V30/00
• CPC Class Codes: G06K 7/10 by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
• CPC Class Codes: G06K 7/10722 Photodetector array or CCD scanning
• CPC Class Codes: G06K 7/1413 1D bar codes
• CPC Class Codes: G06K 7/1456 determining the orientation of the optical code with respect to the reader and correcting therefore
• CPC Class Codes: G06K 7/146 the method including quality enhancement steps
• CPC Class Codes: G06K 7/1478 adapting the threshold for pixels in a CMOS or CCD pixel sensor for black and white recognition
• CPC Class Codes: G06V 10/242 by image rotation, e.g. by 90 degrees
• CPC Class Codes: G06V 10/44 Local feature extraction by analysis of parts of the pattern, e.g. by detecting edges, contours, loops, corners, strokes or intersections; Connectivity analysis, e.g. of connected components
• CPC Class Codes: G06V 10/94 Hardware or software architectures specially adapted for image or video understanding
• CPC Class Codes: G06V 30/224 of printed characters having additional code marks or containing code marks

Abstract

Methods and apparatus are disclosed for extracting a one-dimensional digital signal from a two-dimensional digital image along a projection line. In some embodiments a repeating sequence of pixel weight templates, and a sequence of relative positions, are selected in response to the orientation of a projection line and used to compute a sequence of weighted sums. The sequence can be selected to achieve desirable properties, for example photometric accuracy, geometric accuracy, resolution, and/or noise reduction. In some embodiments registers and multiply-accumulators are arranged and controlled so as to compute the 1D signal.

Claims

1. A computerized method for extracting from a two-dimensional digital image a one-dimensional digital signal along a projection line, comprising:

receiving the two-dimensional digital image, which comprises a plurality of pixels arranged on a pixel grid;

receiving information describing the projection line, from which can be obtained an orientation of the projection line, wherein the orientation is one of a set of allowable orientations, the set of allowable orientations including a plurality of orientations that are not parallel to the pixel grid and are not diagonal to the pixel grid;

selecting, responsive to the orientation, a repeating sequence of pixel weight templates and a sequence of relative positions, wherein the sequence of pixel weight templates comprises at least two distinct pixel weight templates; and

computing a sequence of weighted sums of pixels of the digital image using the sequence of pixel weight templates placed at the sequence of relative positions.

2. The method of claim 1, wherein selecting the repeating sequence of pixel weight templates and the sequence of relative positions comprises making the centers of mass of the sequence of pixel weight templates, when placed according to the sequence of relative positions, substantially equally spaced along a straight line.

3. The method of claim 2, wherein the straight line is substantially parallel to the projection line.

4. The method of claim 1, wherein for a majority of the set of allowable orientations, pixels of the digital image contribute to at most two weighted sums.

5. The method of claim 1, wherein for a majority of the set of allowable orientations, pixels of the digital image that contribute to the weighted sums contribute to two weighted sums.

6. The method of claim 1, wherein the repeating sequence of pixel weight templates is pre-computed and stored in a digital memory.

7. The method of claim 1, wherein selecting the repeating sequence of pixel weight templates and the sequence of relative positions comprises making the centers of mass of the sequence of pixel weight templates, when placed according to the sequence of relative positions, have a spacing along the projection line that is less than one pixel.

8. The method of claim 1, wherein selecting the repeating sequence of pixel weight templates and the corresponding sequence of relative positions comprises making the centers of mass of the sequence of pixel weight templates, when placed according to the sequence of relative positions, have a spacing along the projection line that is responsive to the orientation of the projection line.

9. The method of claim 1, wherein the repeating sequence of pixel weight templates repeats with a period that is responsive to the orientation of the projection line.

10. The method of claim 9, wherein the orientation of the projection line has a slope that is the ratio of an integer N to an integer D, and wherein the period is equal to the sum of N and D.

11. The method of claim 1, wherein selecting the repeating sequence of pixel weight templates comprises making standard deviations along the projection line of the pixel weight templates be proportional to the spacing of the centers of mass of the pixel weight templates.

12. The method of claim 1, wherein the set of allowable orientations comprises a normal zone and a degenerate zone, and wherein for the normal zone pixels of the digital image that contribute to the weighted sums contribute to two weighted sums, and wherein for the degenerate zone, pixels of the digital image that contribute to the weighted sums contribute to one weighted sum.

13. The method of claim 1, wherein the set of allowable orientations comprises a normal zone and a degenerate zone, and wherein selecting the repeating sequence of pixel weight templates and the sequence of relative positions comprises making the centers of mass of the sequence of pixel weight templates, when placed according to the sequence of relative positions, have a spacing along the projection line that is obtained from a first formula for the normal zone and from a second formula for the degenerate zone.

14. The method of claim 1, wherein set of allowable orientations comprises a normal zone, a parallel zone, and a diagonal zone, and wherein selecting the repeating sequence of pixel weight templates comprises a different procedure for the normal zone, the parallel zone, and the diagonal zone.