underfilter

English edit

Etymology edit

under- +‎ filter

Noun edit

underfilter (plural underfilters)

(signal processing) A morphological filter (idempotent operator) whose image is a subset of the domain.
- 1999, Edward R. Dougherty, Jaakko Astola, Nonlinear Filters for Image Processing, page 180:
  It is clear that overfilters and underfilters are dual in the sense of the duality principle.
A filter that is positioned beneath something.
- 1967, Journal of the Institution of Engineers Pakistan:
  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]
- 1988, Árpád Kézdi, László Rétháti, Handbook of Soil Mechanics, page 61:
  Since there is no underfilter, the top flow line emerges on the downstream slope.
- 1992, Margaret M. Manson, Immunochemical Protocols, page 445:
  A single sheet of filter paper is used as an underfilter.
- 2004, R.F. Craig, Craig's Soil Mechanics, →ISBN, page 430:
  In addition, the flow from the underfilter, which had previously been clear, became cloudy, indicating that the filter had failed to block particles from the core.

Coordinate terms edit

overfilter

Verb edit

underfilter (third-person singular simple present underfilters, present participle underfiltering, simple past and past participle underfiltered)

To filter insufficiently.
- 1966, William P. Braker, Know how to Keep Saltwater Fishes, page 19:
  It is not possible to overfilter your tank but marine aquaria are frequently underfiltered.
- 1978, Hydraulics and Pneumatics:
  You don't want to underfilter. Nor do you want to filter beyond what is economically justifiable.
- 1994, Douglas Van Nostrand, Selected Atlases of Cardiovascular Nuclear Medicine, →ISBN, page 35:
  Underfiltering by using too high a cut-off frequency leaves too much noise in the reconstructed images (bottom row).