[Insight-users] Problem writing to Analyze file format

[Daniele Domenichelli]

Oleksandr Dzyubak wrote:
> The only problem is that the Analyze75 header does not have a tag with
> that info, right?

No, analyze has a tag "orient" (1 byte) but it has only 6 valid values

          0         transverse unflipped
          1         coronal unflipped
          2         sagittal unflipped
          3         transverse flipped
          4         coronal flipped
          5         sagittal flipped

Nifti uses quaternion for orientation. See nifti header if you are
interested:

     http://nifti.nimh.nih.gov/pub/dist/src/niftilib/nifti1.h



> The Analyze75 header size is 348 vs 352 for NifTI. Does it mean that
> those extra bites can hold all the directional info in case of the NIfTI
> format and well treated by the ITK filters?

No bytes from 349 to 352 are used for extensions.
Nifti header in not necessarily 352 bytes, it can contain extensions for
example to contain dicom tags (see nifti header for details)
Nifti stores informations about orientations of the image in bytes that
were not used in Analyze


> The question is since the Analyze image format has "poor performance" in
> a sense
> of the directional info, how does it affect the final results after ITK
> filters have been used
> on those images? Do any "info corruptions/changes" squeeze in
> automatically into
> the image info tags afterwards since it might be implemented in a filter
> by some defaults?

I think that the only thing you should take care of when using analyze
files is that you can't write them in any direction, so you may need to
reorient the image.

I'm not sure about this anyway, because I mostly use nifti, maybe
someone else on the mailing list who uses analyze can tell you something
more...


Regards,
Daniele