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

[Christopher Bailey]

Hi Bert,

I tried minccalc out with -expression (A[1]-A[0]) and got the same result 
as with mincmath. I'm inclined to believe this is not a big problem---as 
Jason pointed out it is a representation-issue. 

Thanks! -Chris

On Fri, 25 Jun 2004, Robert VINCENT wrote:

> Christopher,
> 
> I'm not certain what's going on here, but it could be that the valid_range
> attribute is not set properly.  Could you send me the output of
> mincinfo or mincheader on the input & output files?  It might also be
> interesting to compare the results when performing the equivalent
> subtraction with minccalc.
> 
> 	-bert
> 
> On Fri, 25 Jun 2004, Christopher Bailey wrote:
> 
> >
> > 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
> >
> >
> >
> > _______________________________________________
> > MINC-users@bic.mni.mcgill.ca
> > http://www.bic.mni.mcgill.ca/mailman/listinfo/minc-users
> >
> 
>