Optimal Patch Ranking for Coordinate Transform Estimation of Microscope Images from Sparse Patch Shift Estimates

A method of forming a composite image from a first image and a second image captured by a microscope, said first and second images having an area of overlap, said method comprising the steps of:

• determining a rate of change of pixel values for each of a plurality of locations on the first image to identify a set of candidate alignment patches in the first image;
• specifying a plurality of subsets of candidate alignment patches from the set of candidate alignment patches based on an error metric corresponding to each subset, said error metric depending upon said rate of change of pixel values for the patches in a corresponding subset;
• selecting a subset of candidate alignment patches from said plurality of subsets of candidate alignment patches based upon a predetermined criterion;
• estimating, for each patch in the selected subset, a shift between the patch and a corresponding patch in the second image, the location of the corresponding patch in the second image being determined from the location of the patch in the first image;
• determining a coordinate transform between the first image and second image based on the estimated shifts;
• and
• combining the first image and the second image using the coordinate transform to form the single composite image

A method of determining a coordinate transform between a first image and a second image from a selected subset of candidate alignment patches, said method comprising the steps of:

• determining a rate of change of pixel values for each of a plurality of locations on the first image to identify a set of candidate alignment patches in the first image;
• specifying a plurality of subsets of candidate alignment patches from the set of candidate alignment patches based on an error metric corresponding to each subset, said error metric depending upon said rate of change of pixel values for the patches in a corresponding subset;
• selecting, from said plurality of subsets of candidate alignment patches based upon a predetermined criterion, a subset of candidate alignment patches that minimises a maximum error in the coordinate transform;
• estimating, for each patch in the selected subset, a shift between the patch and a corresponding patch in the second image, the location of the corresponding patch in the second image being determined from the location of the patch in the first image;
• and
• determining the coordinate transform between the first image and second image based on the estimated shifts.

An apparatus for determining a coordinate transform between a first image and a second image from a selected subset of candidate alignment patches, said apparatus comprising:

• a processor;
• and
• a memory storing a computer executable software program for directing the processor to perform the steps of:
• determining a rate of change of pixel values for each of a plurality of locations on the first image to identify a set of candidate alignment patches in the first image;
• specifying a plurality of subsets of candidate alignment patches from the set of candidate alignment patches based on an error metric corresponding to each subset, said error metric depending upon said rate of change of pixel values for the patches in a corresponding subset;
• selecting a subset of candidate alignment patches from said plurality of subsets of candidate alignment patches based upon a predetermined criterion;
• estimating, for each patch in the selected subset, a shift between the patch and a corresponding patch in the second image, the location of the corresponding patch in the second image being determined from the location of the patch in the first image;
• and
• determining the coordinate transform between the first image and second image based on the estimated shifts.

A computer readable storage medium having a computer program recorded therein, the program being executable by a computer apparatus to make the computer perform a method for determining a coordinate transform between a first image and a second image from a selected subset of candidate alignment patches, said program comprising:

• computer executable code for determining a rate of change of pixel values for each of a plurality of locations on the first image to identify a set of candidate alignment patches in the first image;
• computer executable code for specifying a plurality of subsets of candidate alignment patches from the set of candidate alignment patches based on an error metric corresponding to each subset, said error metric depending upon said rate of change of pixel values for the patches in a corresponding subset;
• computer executable code for selecting a subset of candidate alignment patches from said plurality of subsets of candidate alignment patches based upon a predetermined criterion;
• computer executable code for estimating, for each patch in the selected subset, a shift between the patch and a corresponding patch in the second image, the location of the corresponding patch in the second image being determined from the location of the patch in the first image;
• and
• computer executable code for determining the coordinate transform between the first image and second image based on the estimated shifts.