1. An explicit DST-based filter for filtering an information signal composed of input blocks of discrete cosine transform (DCT) coefficients to generate a filtered information signal composed of blocks of DCT coefficients, the filter having characteristics defined by a linear convolution kernel and comprising: a trigonometric transform module that applies a trigonometric transform to blocks of DCT coefficients related to the input blocks of DCT coefficients to generate corresponding input blocks of transform coefficients of a second type, the input blocks of transform coefficients of the second type being blocks of one of (a) mixed DST/DCT coefficients, (b) mixed DCT/DST coefficients and (c) DST coefficients; a first transform coefficient processor including matrix multipliers that generate at least one multiplied block of DCT coefficients and at least one multiplied block of transform coefficients of the second type by multiplying, by diagonal multiplying matrices, intermediate blocks of DCT coefficients derived from the input blocks of DCT coefficients; a second transform coefficient processor including matrix multipliers that generate at least one multiplied block of transform coefficients of the second type and at least one multiplied block of DCT coefficients by multiplying, by diagonal multiplying matrices, intermediate blocks of transform coefficients of the second type derived from the input blocks of transform coefficients of the second type; a first summing arrangement that sums the multiplied blocks of DCT coefficients generated by both the first and second transform coefficient processors to generate a first final block of DCT coefficients, and that sums the multiplied blocks of transform coefficients of the second type generated by both the first and second transform coefficient processors to generate a first final block of transform coefficients of the second type; an inverse trigonometric transform module that applies an inverse trigonometric transform to the first final block of transform coefficients of the second type to generate a second final block of DCT coefficients, the inverse trigonometric transform being the inverse of the trigonometric transform applied by the trigonometric transform module; and a second summing arrangement that sums the first and second final blocks of DCT coefficients to generate a block of DCT coefficients constituting a block of the filtered information signal.