identify

• purpose
• usage
• examples
• comments
• error messages
• see also

Purpose:

Usage:

where the following definitions apply:

filename

the name of the image file to be identified (.hdr or .img suffix optional)

Examples:

• All of the above will return the same 10 digit value that identifies the file to the AIR package.

Comments:

• 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).
• The greatest shortcoming of the way the identifiers are computed is that any systematic remapping 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.
• A second shortcoming is that the identifier will depend upon the number of bits/pixel that the AIR package was compiled to use, as well as the values for global maximum and global minimum in the file header for 16 bit files.

Error messages: (alphabetical)

See also:

• scanair