Opera hat characteristic snapping sound heard upon opening a gibus suggested a third name, the "chapeau claque", "claque" being the French word for "slap". Opera hat An opera hat, also called a chapeau claque or gibus, is a top hat variant that is collapsible through a spring system, originally intended for less spacious venues, such as theatre and opera visits. Typically made of satin in black colour, its advantage is that it folds vertically through a push or a snap on the top of the hat, in order to be conveniently stored in a wardrobe or under the seat. Invertably, it opens
Top-hat filter average, with the exception of not introducing a shift in the output function. Top-hat filter The name Top-hat filter refers to several real-space or Fourier space filtering techniques (not to be confused with the top-hat transform). The name top-hat originates from the shape of the filter, which is a rectangle function, when viewed in the domain in which the filter is constructed. In real-space the filter performs nearest-neighbour filtering, incorporating components from neighbouring y-function values. However, despite their ease of implementation their practical use is limited as the real-space representation of a top-hat filter is the sinc function, which has