Extract text from NIfTI neuroimaging files (NII)
To convert NII NIfTI files to another format, you need FSL or other Data software.
To convert other file formats to the "Medical Imaging File" file type, you need software like FSL or a similar tool.
The .NII file extension is a NIfTI (Neuroimaging Informatics Technology Initiative) data file used primarily for storing 3D and 4D magnetic resonance imaging (MRI) and functional MRI (fMRI) data. You can open these files using specialized scientific software like FSL, AFNI, SPM, or ITK-SNAP.
The main disadvantage of the .NII format is its exclusivity and massive file size. Standard operating systems and web browsers cannot read voxel data natively. The format combines an image matrix with a complex 348-byte header containing affine coordinate systems and scanner metadata. Because it holds raw uncompressed 3D or 4D arrays, a single file can easily exceed several gigabytes.
Users typically convert .NII files to .NII.GZ to compress the data and save disk space, or to DICOM for standard clinical workflows. For research publications and presentations, users often extract single slices to standard raster formats like PNG or JPG. Converting to 2D formats will inevitably result in the loss of 3D depth, temporal data (in fMRI), and essential spatial orientation metadata.
This file format is highly specialized and difficult to open or convert with standard tools. Generic online converters fail to process it because they lack the medical imaging libraries required to parse the header structure correctly.
Convert.Guru analyzes your NII file, detects the exact format, and lets you read the text inside.
Users also converted GZ, ZIP, NIF, NBIB, EXE, AAE, SPV, ACSM, TGA, ART, JPG, DICOM and STL files.
If you want to convert NII file to JPG, DICOM, STL, PNG, DCM or TIFF, you can use FSL or similar software from the "Medical Neuroimaging Data" category. In the File menu, look for Save As… or Export….
To convert files to NII, try FSL or another comparable tool in the "Medical Neuroimaging Data" category.
The history of Convert.Guru began over 25 years ago in California with Tom Simondi’s file-format database. A former contributor to Space Shuttle development and a software pioneer of the 1980s, Simondi established a trusted resource for file type analysis that was even referenced by Microsoft Windows XP. Today, we use modern technology to process and convert thousands of file formats while continually improving our NII converter.