identify
This program will use the voxel values in an image file
(.img file) to compute a (fairly) unique identifier value
for the file. This value can be compared to the computed identifiers in a
.air file to assure that the specified image file is the
one referred to in a given .air file.
identify
filename
- where the following definitions apply:
-
- filename
- the name of the image file to be identified (.hdr or .img suffix optional)
identify mri.hdr
identify mri.img
identify mri
- All of the above will return the same unique identifier for the file
- Computation of the identifier is basically a multi-bit parity check of the data in
the file. Although there are potentially as many different identifiers as there are
unsigned long int values on your machine (over 4 billion on a SPARCstation with the
standard C compiler), the probability of two unrelated files having the same identifier
may be less than this value if you don't use the full dynamic range of the possible
voxel values (e.g. in a particularly severe case, if you store data as 8 bits/pixel but
only store a 1 or a 0 for each voxel, you will reduce the number of unique identifiers
by a factor of 128).
- Many systematic remappings of the y- and z- coordinates will not alter the computed
value. Consequently, you cannot be certain that a file has not been reoriented using
reorient by using this program.
- Because identifiers are computed using AIR's internal representation of data,
8 and 16 bit versions of AIR will generate different identifiers. Also byte swapped data
may not generate the same identifiers. Since identifiers are merely a convenience and not
essential for any AIR functionality, such discrepancies have no consequence other than
raising concerns when identifiers are checked manually.
See also: Generic error messages
Modified: December 17, 2001
© 2001 Roger P. Woods, M.D.(rwoods@ucla.edu)