[MINC-users] Register and Display: internal representation?

[Christopher Bailey]

Dear MINC-users,

I want to subtract one 3D (frame) from another:

newframe = frame1 - frame0

I use mincmath as follows (correct?):

mincmath -sub frame1 frame0 newframe

Both frames are signed floats with slightly different ranges (0->2e5 and 
0->2e6) and are coregistered. They both contain lots of zeros at the edges 
of the image. When I open "newframe" in either register or Display, those 
same voxels that should still be zero, now have a mysterious value of 
-185.253! Doing the subtraction the other way round yields +185.253.

I opened "newframe" in AFNI, which DID show zeros in the edge voxels! I 
also did a mnc2ana on the file and looked at it in mricro---again zeros 
on the edges as it should be.

So what is going on with register and Display? We have concluded it must 
be an internal representation issue, but I would still like comments on 
this. I'm of course concerned about doing further analysis on these 
files---I want zero to be zero!

All the best,
                                                                                
Chris Bailey
Center for Functionally Integrative Neuroscience
Aarhus General Hospital, Denmark