This operation cannot be run from the public API right now because it
requires the "histogram" argument whose type is currently unknown to
libgimp/PDB.
Furthermore even if we were to add this type, there are some fundamental
issues with this op which makes it unsuitable (for now) as a
non-destructive filter:
1. Since the histogram is computed only once at op construction, it
wouldn't be rebuilt when the source buffer changes.
2. Using gimp_drawable_calculate_histogram() doesn't build from the
source buffer of the node anyway, but from the drawable buffer. This
would mean a broken histogram as soon as the filter is inserted in
the middle of other filters (anywhere but in the bottom).
We will need to fix these 2 points to consider using this as NDE (and
therefore also make it available in the API).
831cae29db