Abstract
A highly efficient video downscaling algorithm for any arbitrary
integer scaling factor performed in a hybrid pixel transform
domain is proposed. This algorithm receives
the encoded DCT coefficient blocks of the input video sequence
and efficiently computes the DCT coefficients of
the scaled video stream. The involved steps are properly
tailored so that all operations are performed using
the encoding standard block structure, independently of
the adopted scaling factor. As a result, the proposed algorithm
offers a significant optimization of the computational
cost without compromising the output video quality,
by taking into account the scaling mechanism and by
restricting the involved operations in order to avoid useless
computations. In order to meet any system needs,
an optional and possible combination of the presented algorithm
with high-order AC frequency DCT coefficients
discarding techniques is also proposed, providing a flexible
and often required complexity scalability feature and
giving rise to an adaptable tradeoff between the involved
scalable computational cost and the resulting video quality
and bit rate. Experimental results have shown that the
proposed algorithm provides significant advantages over
the usual DCT decimation approaches, both in terms of
the involved computational cost, the output video quality,
and the resulting bit rate. Such advantages are even more
significant for scaling factors other than integer powers of
2 and may lead to quite high PSNR gains.