The present principles relates to a method for encoding an image unit comprising image data represented by a luminance channel and at least one chrominance channel, the method comprising obtaining a luma coding-tree by splitting a luminance unit representative of the luminance channel of said image unit and obtaining a chroma coding-tree by splitting a chrominance unit representative of at least one chrominance channel of said image unit. The method is characterized in that obtaining said chroma coding-tree comprises: —determining whether said chroma coding-tree and said luma coding-tree are identical; and —signaling an information data indicating whether said chroma coding-tree and said luma coding-tree are identical.