[MINC-users] mincreshape segfault and general behavior

[Alex Zijdenbos]

Hi Soren,

Andrew can throw in his $0.02, but to my knowledge, neither
mincreshape nor mincresample does the kind of volume averaging that
you describe. MINC considers voxel values as a lattice of
dimensionless point samples; the step sizes are distances between
those points, and are therefore attributes of the volume, not the
voxel.

mincresample will interpolate between the point samples when it needs
to, but it will not average. In other words, if you would use
mincresample to downsample by a factor of 3 in all dimensions
(collapse each 3x3x3 cube into a single voxel at the same point
location), you are simply tossing out 26 of the 27 voxel values in
each 3x3x3 cube - you are not averaging them. I have raised this a few
times (very recently even), but even though it may be
counter-intuitive to many, it is by Peter's design. In my scripts I
usually call mincblur before mincresample when I know I will be
downsampling.

mincreshape will only massage how the lattice is arranged, allowing
you to extract hyperslabs and etc; it does not change the point
samples (voxel values), will not interpolate, and would/should
certainly not do any averaging.

Well that is all my understanding at least :)

-- A

On Wed, Oct 2, 2013 at 5:21 PM, Soren Christensen <sorench at gmail.com> wrote:
> Hi Andrew,
> It's a MINC2 file.
>
> Sorry I meant mincresample where marked below:
>> > 3) Is it correctly understood that mincreshape does volume averaging for
>> > downsizing as opposed to *mincresample* that will just use the specified
>> > interpolation method?
>>
>
> Let me make sure I understand this right. Are you saying mincreshape does
> no volume averaging? If you reshape from a dimsize of 512 to 256 for
> example, then isn't each voxel a 4x4 average of the input?
>
>  I just verified that it is, but maybe we mean different things by volume
> averaging?
>
> Thanks
>
> Soren
>
>
>
>>
>> a
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