Encoder, a decoder and corresponding methods simplifying signaling slice header syntax elements

An apparatus for decoding a picture, comprising:

• one or more processors coupled to a memory that stores instructions, which when executed by the one or more processors, cause the apparatus to:
• receive a video bitstream including a slice header of a current slice and data representing the current slice, wherein the slice header comprises a picture_header_in_slice_header_flag, and a luma mapping with chroma scaling (LMCS) related flag is conditionally present in the slice header;
• when the LMCS related flag is not present in the slice header, infer a value of the LMCS related flag by determining whether a picture header structure is present in the slice header based on a value of the picture_header_in_slice_header_flag;
• in response to determining that the value of the picture_header_in_slice_header_flag indicates the picture header structure is present in the slice header, determine the value of the LMCS related flag is equal to ph_lmcs_enabled_flag, wherein the video bitstream includes the ph_lmcs_enabled_flag, and the ph_lmcs_enabled_flag indicates whether LMCS is enabled for the picture or not;
• and
• in response to determining that the value of the picture_header_in_slice_header_flag indicates the picture header structure is not present in the slice header, determine the value of the LMCS related flag is equal to 0 indicating that LMCS is disabled for the current slice.

A non-transitory computer-readable storage medium having a video bitstream including information for use in a decoding operation of a picture and instructions stored therein, the information comprising a slice header of a current slice and data representing the current slice, wherein the slice header comprises a picture header in slice header flag, and a luma mapping with chroma scaling (LMCS) related flag is conditionally present in the slice header, and the instructions, when executed by a processor, cause the processor to perform operations comprising:

• when the LMCS related flag is not present in the slice header, inferring a value of the LMCS related flag by determining whether a picture header structure is present in the slice header based on a value of the picture_header_in_slice_header_flag;
• in response to determining that the value of the picture_header_in_slice_header_flag indicates the picture header structure is present in the slice header, determining the value of the LMCS related flag is equal to ph_lmcs_enabled_flag, wherein the video bitstream includes the ph_lmcs_enabled_flag, and the ph_lmcs_enabled_flag indicates whether LMCS is enabled for the picture or not;
• and
• in response to determining that the value of the picture_header_in_slice_header_flag indicates the picture header structure is not present in the slice header, determining the value of the LMCS related flag is equal to 0 indicating that LMCS is disabled for the current slice.