Method, apparatus and system for encoding and decoding a coding tree unit

Abstract METHOD, APPARATUS AND SYSTEM FOR ENCODING AND DECODING A CODING TREE UNIT A system and method of decoding a coding unit of a coding tree from a coding tree unit of an image frame from a video bitstream, the coding unit having a luma colour channel and at least one chroma colour channel. The method comprises decoding (1610) a luma transform skip flag from the video bitstream for a luma transform block of the coding unit; decoding (1630) at least one chroma transform skip flag from the video bitstream, each decoded chroma transform skip flag corresponding to one of at least one chroma transform block of the coding unit; determining a secondary transform index, the determining comprising: decoding (1670) a secondary transform index from the video bitstream if at least one of the luma transform skip flag and the at least one chroma transform skip flags indicates that a transform of the respective transform block is not to be skipped, and determining (1660) the secondary transform index to indicate that a secondary transform is not to be applied if all of the luma transform skip flag and the at least one chroma transform skip flags indicate transforms of the respective transform blocks are to be skipped; and transforming the luma transform block and the at least one chroma transform blocks according to the decoded luma transform skip flag, the at least one chroma transform skip flags, and the determined secondary transform index to decode the coding unit. 23953864_1