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Direct homography computation by local linearization

  • US 7,403,658 B2
  • Filed: 04/15/2005
  • Issued: 07/22/2008
  • Est. Priority Date: 04/15/2005
  • Status: Expired due to Fees
First Claim
Patent Images

1. A process for determining a homography matrix by processing an image containing codes, the process comprising the steps of:

  • extracting features from the image;

    determining four candidates for main directions of parallel lines within the image;

    identifying two pairs of near perpendicular directions from the four candidates;

    determining two main directions from the two pairs of near perpendicular directions;

    creating a homography matrix from the extracted features and from the two main directions, wherein the homography matrix is based on the parallel lines in the image, and the homography matrix attempts to minimize a distance between the features and the parallel lines;

    wherein the codes are EIC codes arranged in EIC symbols, and the creating step attempts to minimize distance between lines and the EIC codes such that g

    ( H )
    = 1 2

    N




    m h
    i = 1




    m i h
    j = 1


    γ

    ij h


    ( x ij h

    c i h
    + y ij h

    s i h
    + R i h
    )
    2
    + 1 2

    N




    m v
    i = 1




    m i v
    j = 1


    γ

    ij v


    ( x ij v

    c i v
    + y ij v

    s i v
    + R i v
    )
    2
    is minimized where N =

    i = 1 m h


    m i h
    +

    i = 1 m v


    m i v
    ,


    N is the total number of effective EIC pattern pixels associated with all the lines, and γ

    ijh and γ

    ijv are weights; and

    wherein EICs are embedded interaction codes, H is a homography matrix, and each ci, si, and Ri are coefficients defining straight lines defining the two main directions determined from the near perpendicular directions.

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