Top hat top hat is a hard, black silk hat, with fur now often used. The acceptable colors of hats are much as they have traditionally been, with "white" hats (which are actually grey), a daytime racing color, worn at the less formal occasions demanding a top hat, such as Royal Ascot, or with a morning suit. In the U.S. top hats are worn widely in coaching, a driven horse discipline as well as for formal riding to hounds. The collapsible silk opera hat, or "crush hat", is still worn on occasions, and black in color if worn with evening wear as
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