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 theoretically possible. Top-hat filters can be constructed by chaining theoretical low-band and high-band filters. In practice, an approximate top-hat filter can be constructed in analogue hardware using approximate low-band and high-band filters. In Fourier space, a top hat filter selects a band of signal of desired frequency by the specification of a lower and upper bounding frequencies. Top-hat filters are particularly easy to implement digitally. The top hat function can be generated by differentiating a linear ramp function of width formula_1. The limit of formula_1 then becomes the Dirac delta function. Its real-space form is the same as the moving