underfilters

Noun

underfilter (plural underfilters)

1. A morphological filter (idempotent operator) whose image is a subset of the domain.
   • It is clear that overfilters and underfilters are dual in the sense of the duality principle.1999, Edward R. Dougherty, Jaakko Astola, Nonlinear Filters for Image Processing, page 180
2. A filter that is positioned beneath something.
   • The paving downstream consisted of 18x18x8-inch blocks laid on edge over a brick base which in turn was underlain with a gravel or brick chip filter. Since there was some controversy as to whether an underfilter was necessary, the first test was made with the filter omited.^([sic])1967, Journal of the Institution of Engineers Pakistan

See all 3 meanings of underfilter