> I've realized spm_write_vol do not write data exactly as they are. Besides
> I saw the corresponding help where says "Write an image volume to disk,
> setting scales and offsets as appropriate". I've been using spm_slice_vol
> to write my data the to the disk. However I'd like to know what the message
> means.
If data are written as integer types, then they are scaled so that the maximum
in the image is the maximum value for that datatype (or the minimum is the
minimum value for signed types). The scalefactor is then set appropriately.
In NIFTI, there is also the ability to have an offset (i.e. y = a*x + b), but
I decided to disable this feature because it did not guarantee that zero
values would be exactly zero - which would mess up various "implicit masking"
procedures.
Best regards,
-John
|