Although it is not possible to save all the information of a multi-label image in the nifti format, it would be good to have a writer that at least guarantees no pixel information is lost. If a user really wants to use a different format than nrrd or dicom, they should be able to do so (in an informed way). So we want a writer that does as well as is possible, together with a warning about which information will be lost when saving this way.