+1 for `contrast_enhancement` (or enhance_contrast).

Since we're talking about some disruptive renaming (with deprecation, I assume), `meansubtraction` should probably be renamed `mean_subtraction` to match `percentile_mean_subtraction` (and to match the standard multi-word naming scheme).

And since we're talking about `percentile_*` functions (or at least I was ;) ), it might be nice to have a standard naming scheme for these types of functions/parameters. For example, `percentile_mean` -> `mean_pct` or `mean_frac`; `mean_percentile` is fine as well, though a bit verbose. See also https://github.com/scikit-image/scikit-image/pull/630#issuecomment-20547248. I think a suffix is nicer than a prefix for searching.