  We propose a new gradient-domain technique for processing registered EM image
stacks to remove inter-image discontinuities while preserving intra-image
detail. To this end, we process the image stack by first performing anisotropic
smoothing along the slice axis and then solving a Poisson equation within each
slice to re-introduce the detail. The final image stack is continuous across
the slice axis and maintains sharp details within each slice. Adapting existing
out-of-core techniques for solving the linear system, we describe a parallel
algorithm with time complexity that is linear in the size of the data and space
complexity that is sub-linear, allowing us to process datasets as large as five
teravoxels with a 600 MB memory footprint.
