Aliasing Reduction via Frequency Roll-Off for Scalable Image/Video Coding
The extracted low-resolution video from a motion compensated 3-D subband/wavelet scalable video coder is unnecessarily sharp and sometimes contains significant aliasing, compared to that obtained by the MPEG4 lowpass filter. In this paper, we propose a content adaptive method for aliasing reduction in subband/wavelet scalable image and video coding. We try to make the low-resolution frame (LL subband) visually and energy-wise similar to that of the MPEG4 decimation filter through frequency roll-off. Scaling of the subbands is introduced to make the variances of the subbands comparable in these two cases. Thanks to the embedded properties of the EZBC coder, we can achieve the needed scaling of energies in each subband by subbitplane shift in the extractor and value (coefficient) scaling in the decoder. Two methods are presented which offer substantial peak signal-to-noise ratio (PSNR) gain for lower spatial resolution, as well as substantial reduction in visible aliasing, with little or no reduction in full resolution PSNR.