Patent ID: 7342962

Claim:
A method of downsampling a two-dimensional block of discrete cosine transform (DCT) coefficients, comprising: (a) providing a two-dimensional N×N block of DCT coefficients; (b) applying a one-dimensional N/2×N de-interlacing inverse discrete cosine transform (IDCT) with respect to a first dimension of said block; and (c) applying a one-dimensional de-interlacing inverse discrete cosine transform (IDCT) with respect to a second dimension of the results of step (b); (d) wherein said de-interlacing IDCT is x e =T t (N/2) z p +QT t (N/2)K t z r , where x e is a vector of four downsample values, z p is an N/2 component vector of the even-index components of a column of coefficients in said first dimension of said block, said even-index components in bit-reversed order, Z r is an N/2 component vector of the odd-index components of said column of coefficients in said first dimension of said block, said odd-index components in bit-reversed order, T t (N/2) is the N/2-point IDCT, K=RLR t , where R is a bit-reversal permutation matrix; and L is a N/2×N/2 lower-triangular matrix, and Q is a N/2×N/2 diagonal matrix: diag[ cos((4m+1)/2N)] for m=0, 1, . . . , N/2 1.