Sidebar to browse filters in filter UI
It would be convenient to have a collapsible sidebar on the left of the filter UI containing a tree view of the program's available filters.
A sidebar would make it quicker to discover and try out the filters available, making the program easier for the user to get acquainted with, and allowing the user to more easily compare several similar filters to find the effect that they're looking for.
The tree view could possibly take after the font/gradient/etc selection dialogs, with large tree items and potentially even example thumbnails. A text entry at the bottom to search filters by name could also be helpful.