A method and a device are described for modifying a video frame for encoding or decoding wherein values of pixels of the video frame are represented an increased bit depth.The described method comprises using processing means for executing the step of offsetting the pixel values of increased bit depth with offsets, the offsets depending on a spatial neighbourhood of the pixel to-be-offset.Such local adaptive offsetting of pixel values de-emphasizes high frequencies in the transform domain artificially emphasized by the bit depth increase.