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nifti1.h header documentation

NIFTI-1 FLAG (MAGIC STRINGS): ---------------------------- To flag such a struct as being conformant to the NIFTI-1 spec, the last 4 bytes of the header must be either the C String "ni1" or "n+1"; in hexadecimal, the 4 bytes 6E 69 31 00 or 6E 2B 31 00 (in any future version of this format, the 1 will be upgraded to 2, etc.). Normally, such a "magic number" or flag goes at the start of the file, but trying to avoid clobbering widely-used ANALYZE 7.5 fields led to putting this marker last. However, recall that "the last shall be first" (Matthew 20:16).

If a NIFTI-aware program reads a header file that is NOT marked with a NIFTI magic string, then it should treat the header as an ANALYZE 7.5 structure.

NIFTI-1 FILE STORAGE: -------------------- "ni1" means that the image data is stored in the ".img" file corresponding to the header file (starting at file offset 0).

"n+1" means that the image data is stored in the same file as the header information. We recommend that the combined header+data filename suffix be ".nii". When the dataset is stored in one file, the first byte of image data is stored at byte location (int)vox_offset in this combined file. The minimum allowed value of vox_offset is 352; for compatibility with some software, vox_offset should be an integral multiple of 16.

/* DATA STORAGE: ------------ If the magic field is "n+1", then the voxel data is stored in the same file as the header. In this case, the voxel data starts at offset (int)vox_offset into the header file. Thus, vox_offset=352.0 means that the data starts immediately after the NIFTI-1 header. If vox_offset is greater than 352, the NIFTI-1 format does not say much about the contents of the dataset file between the end of the header and the start of the data.

FILES: ----- If the magic field is "ni1", then the voxel data is stored in the associated ".img" file, starting at offset 0 (i.e., vox_offset is not used in this case, and should be set to 0.0).

When storing NIFTI-1 datasets in pairs of files, it is customary to name the files in the pattern "name.hdr" and "name.img", as in ANALYZE 7.5. When storing in a single file ("n+1"), the file name should be in the form "name.nii" (the ".nft" and ".nif" suffixes are already taken; cf. http://www.icdatamaster.com/n.html ).

MISCELLANEOUS C MACROS

/! Given a nifti_1_header struct, check if it has a good magic number.
    Returns NIFTI version number (1..9) if magic is good, 0 if it is not. /

#define NIFTI_VERSION(h) \ ( ( (h).magic[0]==n && (h).magic[3]==\0 && \ ( (h).magic[1]==i || (h).magic[1]==+ ) && \ ( (h).magic[2]>=1 && (h).magic[2]<=9 ) ) \ ? (h).magic[2]-0 : 0 )

/! Check if a nifti_1_header struct says if the data is stored in the same file or in a separate file. Returns 1 if the data is in the same file as the header, 0 if it is not. /

#define NIFTI_ONEFILE(h) ( (h).magic[1] == + )

Created by Alex Clark
Last modified 2005-04-14 18:42
 

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