This Recommendation addresses a method of colour conversion from Recommendation ITU-R BT.709 toRecommendation ITU-R BT.2020 for use when HDTV programme content is included within UHDTVprogrammes. Two sets of conversion equations are specified. One set is based on an opto-electronic transferfunction (OETF) and its inverse. The other set is based on an electro-optical transfer function (EOTF) and itsinverse.