Compensating for geometric distortion of images in constrained processing environments

An image processing device comprising:

• a memory in which is stored a suspect image in an image feature space;
• a first buffer;
• a second buffer;
• a processor system comprising a first processing unit and a vector processing unit;
• the first processing unit configured to load reference signal coordinates of reference signal components into the first buffer, to obtain transformed reference signal coordinates for a geometric transform candidate, and for each of the transformed reference signal coordinates, locate updated coordinates of a potential reference signal component in the suspect image in neighborhoods around the transformed reference signal coordinates, and configured to load the updated coordinates into the second buffer;
• the vector processing unit configured to obtain a vector of the reference signal coordinates from the first buffer and obtain a corresponding vector of updated coordinates from the second buffer and execute dot product operations on the vectors to determine a new geometric transform that provides a least squares mapping between the reference signal coordinates and updated coordinates, the vector processing unit further configured to compute additional dot products used as input to compute a least squares error metric, the least squares error metric comprising a sum of squared differences between the coordinates of the reference signal components and the updated coordinates, after applying the new geometric transform to fit the reference signal components and updated coordinates;
• the processor system configured to compute the least squares error metric from output of the additional dot products for plural geometric transform candidates processed by the vector processing unit to determine corresponding new geometric transform candidates, and configured to select new geometric transform candidates to refine by selecting candidates for which the least squares error metric is below a threshold.

A non-transitory computer readable medium on which is stored instructions, which when executed by one or more processors, performs a method of determining a geometric transform of an image for digital payload extraction, the method comprising:

• transforming a suspect image into an image feature space;
• for plural geometric transform candidates, determining new geometric transform candidates by acts of:
• a) obtaining transformed coordinates of reference signal components, the transformed coordinates having been geometrically transformed by a geometric transform candidate;
• b) for the reference signal components, determining updated coordinates by locating an image feature in a neighborhood in the suspect image around the transformed coordinates of a reference signal component, the image feature corresponding to a potential reference signal component in the suspect image;
• c) determining a new geometric transform candidate that provides a least squares mapping between coordinates of the reference signal components and the updated coordinates;
• parameters of the new geometric transform candidate being computed by dot product operations on the coordinates of the reference signal components and the updated coordinates;
• and
• d) from the dot product operations, obtaining a least squares error metric for the new geometric transform candidate, the least squares error metric comprising a sum of squared differences between the coordinates of the reference signal components and the updated coordinates, after applying the new geometric transform to fit the reference signal components and updated coordinates;
• discarding new geometric transform candidates having a least squares error metric exceeding a threshold;
• refining new geometric transform candidates having a least squares error metric that does not exceed the threshold;
• applying a geometric transform candidate from the refining to compensate for geometric distortion and extract a digital payload encoded in the suspect image;
• wherein the medium comprises instructions configured to perform act b) and act c) on different types of processors.