Reversible color transform with compatiblity to irreversible transform

This report proposes a new transcoding between a lossless encoder and a lossy decoder for color image signals. It requires a reversible color transform (Rev.CT) with compatibility to an irreversible color transform (Irrv.CT). An existing Rev.CT guarantees lossless reconstruction of signals. However its compatibility to an Irrv.CT is not high enough for practical use. This is because a scaling is excluded from the Rev.CT for lossless coding. In this report, we embed the scaling into quantization in lossy decoding to realize both lossless coding and transcoding with high compatibility. It is experimentally confirmed that image quality is improved by more than 37.6 [dB]. We also evaluate its performance based on various criteria including, bit-extension, word-length of signals and coefficients.