Hat box collapsible version for evenings, known as a gibus. They might also include storage space for items such as a hat brush. Designs became quite large during the Victorian era. A letter to "The Times" in 1844 warned travellers that Blackwall Railway's porters had charged a 1d to carry a hat box onto the train and a further 6d for transporting it to the London terminus, with the traveller himself paying only 4d for the journey. He recommended that travellers with luggage should go by steamboat. While traditionally hat boxes are circular or square in shape, some versions may follow the
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