  It is desirable to support efficient lossless coding within video coding
standards, which are primarily designed for lossy coding, with as little
modification as possible. A simple approach is to skip transform and
quantization, and directly entropy code the prediction residual, but this is
inefficient for compression. A more efficient and popular approach is to
process the residual block with DPCM prior to entropy coding. This paper
explores an alternative approach based on processing the residual block with
integer-to-integer (i2i) transforms. I2i transforms map integers to integers,
however, unlike the integer transforms used in HEVC for lossy coding, they do
not increase the dynamic range at the output and can be used in lossless
coding. We use both an i2i DCT from the literature and a novel i2i
approximation of the DST. Experiments with the HEVC reference software show
competitive results.
