A method for processing image and video data, comprising providing high dynamic range image data (HDR) and a corresponding low dynamic range image data (LDR). The LDR image is encoded in a legacy code stream, while a residual code stream is generated and encoded containing data necessary for the reconstruction of the HDR image in a decoding phase. To generate the residual code stream, LDR image data are processed so as to obtain a processed LDR* image, then a component data of the HDR image and a corresponding component of the processed LDR* image are selected and residual data of the selected component data are calculated by dividing the component of the processed LDR* image data by the component of the HDR image data. The residual data of the selected component are scaled into the range of values comprised between 0 and 1 and are then encoded in a residual code stream. A decoding method is also disclosed which allows reconstruction of an HDR image from a legacy code stream and a residual data code stream.