Learned dictionary elements using NMF where the continuum dictionary elements are constrained to be nonnegative. All the dictionary patches consist of uniform patches or gradients in varied directions. The order of the elements is not significant. The dictionary size r is chosen to be approximately 1.5 times larger than the SVD dictionary size, which is chosen based on the intrinsic dimension estimates in Moon et al. (2015) and then refined using the results in Section 3.