nii (NIFTI1 data format)


The NIfTI-1 (Neuroimaging Informatics Technology Initiative) format has been adapted from the Analyze (7.5) format. It is managed by a Data Format Working Group (DFWG) with a focus on neuroimaging and fMRI in particular. Some effort has been made to keep it compatible with software that can already read Analyze files, these were typically stored as a separate header file (.hdr) and volume data (.img).

The file is generally made up of a header followed by volumetric data. The format supports up to 5 dimensions, each value in the volume can range from unsigned characters up to long double precision numbers, and includes support for r,g,b volumes. It is assumed that the data is regularly sampled. One of the key capabilities of the format (stored in the header) is an affine mapping between voxel indices (i,j,k) and real world spatial location (x,y,z).