Learned dictionary elements using SVD. Dictionary elements are constrained to be orthonormal. The patches consist of uniform patches and gradients in varied directions. The magnetogram patches are essentially zero when the continuum components are nonzero and vice versa. The dictionary size r is first chosen based on the intrinsic dimension estimates in Moon et al. (2015) and then refined by comparing dictionaries of various sizes in Section 3. Section 4.2 contains more details on choosing r.