Low-bitrate encoding of high dynamic range content

Abstract

Low bitrate encoding of HDR-coded content with codecs that achieve compression by lowering the precision of encoding can result in significant loss of color fidelity. The problem stems from the logarithmic nature of the HDR encoding and consequent excessive quantization of color components of HDR-coded material. The loss is ameliorated by applying a saturation emphasis function that boosts color values of the HDR-coded material prior to compression. In various implementations the saturation emphasis function is a monotonically increasing function that preferentially boosts lower color values. Following compression and subsequent decompression, the color boost is reversed. In video post-production workflows proxies may be compressed to very low bitrates. For such workflows, the described methods significantly reduce codec-induced color artifacts in the decompressed proxy, thus restoring the ability of editors to make valid technical decisions based on the proxy during post-production.