Geometric registration of images by similarity transformation using two reference points

A method for registering a first image to a second image using a similarity transformation, the first image including a first plurality of pixels mapped to a set of first image coordinates and the second image including a second plurality of pixels mapped to a set of second image coordinates, the method comprising the steps of:

• a) determining a first plurality of reference points in the first image;
• b) determining a second plurality of reference points in the second image;
• c) identifying a set of reference points common to the first plurality of reference points and the second plurality of reference points;
• d) determining the first image coordinates and the second image coordinates of each reference point in the set of reference points identified in step (c);
• e) performing a Cartesian translation of the set of second image coordinates such that the second image coordinates of a first reference point of the set of reference points match the first image coordinates of the first reference point;
• f) if the set of reference points includes exactly two reference points, performing a similarity transformation of the translated set of second image coordinates to scale the second image coordinates and rotate the second image coordinates about the first reference point such that the second image coordinates of a second reference point of the set of reference points match the first image coordinates of the second reference point;
• and
• g) if the set of reference points includes more than two reference points and no less than two reference points, performing an affine transformation of the translated set of second image coordinates to register the second image coordinates of the set of reference points to the first image coordinates of the set of reference points.

A non-transitory computer readable medium adapted to instruct a general purpose computer to register a first image to a second image using a similarity transformation, the first image including a first plurality of pixels mapped to a set of first image coordinates and the second image including a second plurality of pixels mapped to a set of second image coordinates, the method comprising the steps of:

• a) determining the first image coordinates of a plurality of reference points in the first image;
• b) determining the second image coordinates of the plurality of reference points in the second image;
• c) performing a Cartesian translation of the set of second image coordinates such that the second image coordinates of a first reference point of the plurality of reference points match the first image coordinates of a first reference point;
• and
• d) if the plurality of reference points includes exactly two reference points, performing a similarity transformation of the translated set of second image coordinates to scale the second image coordinates and rotate the second image coordinates about the first reference point such that the second image coordinates of a second reference point of the plurality of reference points match the first image coordinates of the second reference point;
• and
• e) if the plurality of reference points includes more than two reference points and no less than two reference points, performing an affine transformation of the translated set of second image coordinates to register the second image coordinates of the plurality of reference points to the first image coordinates of the plurality of reference points.