The present disclosure generally relates to a method and device for encoding an image block, characterized in that it comprises: obtaining (101) a low-spatial-frequency version (Llƒ) of a luminance component of the image block, said the obtained luminance component of the image block; obtaining a quantized luminance component (Llƒ,Q) of the image block by quantizing (102) the obtained luminance component (Llƒ) of the image block; obtaining (103) a differential luminance component (Lr) by calculating the difference between the luminance component (L) of the image block and either the quantized luminance component (Llƒ,Q) of the image block or a decoded version (Llƒ,Q) of the encoded quantized luminance component of the image block; encoding (104) the quantized luminance component (Llƒ,Q of the image block using at least one frequency coefficient of a set of frequency coefficients which is usually obtained from a block-based spatial-to-frequency transform for encoding the luminance component of the image block; and encoding (105) the differential luminance component (Lr) using the remaining frequency coefficients of said set of frequency coefficients.