Block DCT to wavelet transcoding in transform domain

The Discrete Cosine Transform (DCT) to wavelet transcoding provides input for several wavelet-based post-processing techniques of the DCT-coded image/video signals. Transcoding in domain transform avoids inverse transform and retransform operations and saves computation. In this paper, we propose a new technique for transcoding the DCT blocks to wavelet coefficients directly in the transform domain. We perform filtering, IDCT and downsampling operations in a single combined step. The proposed technique achieves the same computational result as that of a spatial domain technique. The transcoding matrices used in the proposed technique are found to satisfy certain symmetric and sparse properties, which are exploited to reduce the computational cost. As the number of zeros in the DCT coefficients is significantly higher compared to the spatial domain, computational cost reduces significantly. Also, with the proposed technique, it is possible to speedup the operation by ignoring some elements in the filtering matrices whose magnitudes are smaller than a threshold value. We demonstrate the application of the proposed transcoding for deblocking of the DCT-coded images in wavelet domain.