NII

File Format
Name	NII
Ontology	Electronic File Formats Health and Medicine NII
Extension(s)	.nii, .nii.gz
PRONOM	fmt/1094

For the animated image format, see Naïve Image Formats.

General description

NII (or NIfTI) files are probably the most commonly-used format for multi-dimensional neuroimaging data as of this writing (late 2012). NIfTI is a raster format, with files generally containing at least 3-dimensional data: voxels, or pixels with a width, height, and depth. NIfTI files can be up to 7-dimensional: the first four dimensions are defined as 3 spatial dimensions and time, with the other dimensions used for "other stuff" -- though the time dimension is often to encode something other than time.

Most packages also support reading gzip-compressed NIfTI files, which should have the extension .NII.gz.

The format is extensively supported and documented by the NIH.

Software

• NIH Documentation and reference C header
• NiftiLib, a full C implementation
• NiBabel, a Python neuroimaging file format library