  In this paper, two 8-point multiplication-free DCT approximations based on
the Chen's factorization are proposed and their fast algorithms are also
derived. Both transformations are assessed in terms of computational cost,
error energy, and coding gain. Experiments with a JPEG-like image compression
scheme are performed and results are compared with competing methods. The
proposed low-complexity transforms are scaled according to Jridi-Alfalou-Meher
algorithm to effect 16- and 32-point approximations. The new sets of
transformations are embedded into an HEVC reference software to provide a fully
HEVC-compliant video coding scheme. We show that approximate transforms can
outperform traditional transforms and state-of-the-art methods at a very low
complexity cost.
