DrDre said:

Although the function seems to work very well for the dark halos, the light halos are much less affected (I've tried multiple settings). Also, the edges are generally softened, ...

DeHalo_alpha() settings are very non-intuitive and there is little clear idea what those numbers actually do. (It's been an "alpha" for a decade, and probably will remain so 'til the end-of-the-age. :D So we're stuck with puzzling it out ourselves.)

Settings I tried in that link were applied to a letterboxed standard definition source. For your high definition source, I can guess the radius would be generally increased for that addition coverage -- keeping in mind the independent x,y settings to reduce influence in a direction less needed. Same with dark,light halos being independently adjustable, as needed.

The sensitivity settings probably are key. My original tests early in the THX 1138 preservations thread were way too strong (caused noticeable smear-softening). Later, I discovered what was happening and significantly back them off for better effect.

At best, it's a band-aid that might be better than a gaping wound. :)

P.S. - Would you also post your non-compressed (.PNG) base-picture used for your above HD GOUT creation steps demonstration? Thanks.

P.P.S. - Also, I suggest having DeHalo_alpha() as step 2b. This will ensure it applies brightness manipulation only to legitimate targets and not tricked by the original "grain" into processing other areas. Further, when grain is restored picture-wide, that will help mask any weakness in the DeHalo_alpha() result.