Am image data encoding apparatus includes an entropy encoder to encode data items representing image data by an encoding system using a context adaptive binary arithmetic coding (CABAC) encoding system and a bypass encoding system. The data items include a first data item indicating whether a multi-direction linear model (MDLM) chroma mode applies to a current image region, and a second data item indicating a processing direction for operation of the MDLM chroma mode. The entropy encoder encodes instances of the first data item and instances of the second data item using different encoding systems.