A method and device for encoding or decoding a picture block having a luminance component. The method includes obtaining a luminance residual block (Lr) by subtracting a first representation (Ll, LlD) of an average value of the luminance component calculated from the luminance component, obtaining a second representation (ƒ(Ll), ƒ(Ll)D) of the average value by applying a transfer function to the average value (Ll) of the luminance component in order to reduce the dynamic range of the average value and encoding a luminance block (Le) obtained by adding (105, 302) together the luminance residual block (Lr) and the second representation (ƒ(Ll), ƒ(Ll)D) of the average value.