Adding hybrid log-gamma (https://en.wikipedia.org/wiki/Hybrid_Log-Gamma) based on the standardization in ARIB STD-B67: http://www.arib.or.jp/english/html/overview/doc/2-STD-B67v1_0.pdf The choice of enum value of 18 is consistent with HEVC: http://phenix.it-sudparis.eu/jct/doc_end_user/current_document.php?id=10481 And also with latest proposal for color format in mkv: https://mailarchive.ietf.org/arch/search/?email_list=cellar&gbt=1&q=Colour+Format+proposal The implementation assumes a nominal input range of [0, 1], which is consistent with HEVC. Signed-off-by: Neil Birkbeck <neil.birkbeck@gmail.com> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
