Algorithm 2.

Algorithm for generating rotation-invariant patch-based description of image.

Input: patch neighborhood operator (xn), input image I, rotation-invariant dictionary W from Algorithm 1.
N ← number of voxels in I.
p ← number of voxels in (xn).
Initialize P ← [ ]	▷ N × p patch matrix for every pixel in image.
for i = 0,...,N −1 do
t ← vector representation of {xj : xj ∈ (xi)}.
t ← t − mean(t).
Reorient t to W1.
P ← [P t].	▷ Concatenate patches.
end for
F → PW	▷ Project patches of input image onto eigenvectors.
Output: F.	▷ Matrix with response of each image voxel to each eigenpatch.