Glen,
I'm not sure this is the answer, but I noticed last year the low
precision of saved spmT maps, and how it influenced their accuracy,
and got the reply from Guillaume below about changing the precision of
the saved maps.
Best!
Jim
SPM Savants,
I often find a smaller minimum value in saved, thresholded spmT maps
than the height threshold displayed on the results page. Has anyone
else noticed this?
The attached text chronicles an experiment on two different runs, in
which half the saved spmT maps include T values less than the height
threshold. These statistics were calculated in SPM8 but I've noticed
the same thing in SPM5.
Many Thanks for your help!
Jim
Here is answer from Guillaume Jan 2011:
Hi Jim,
The thresholded SPM{.} maps are saved as UINT8, ie with a very low
precision, that could explain what you are observing. If it matters to
you, you can change spm_write_filtered.m to save those images using the
same precision as the original SPM{.} maps, ie FLOAT32. To do so, just
change l.44 so that:
'dt', [spm_type('float32') spm_platform('bigend')],...
Images will be 4 times bigger on disk though.
I'll make this as default in SPM from now on.
Best regards,
Guillaume.
On 5/30/12, Glen Lee <[log in to unmask]> wrote:
> Hello SPMers--
>
> I've created a mask image where all the significant voxels were assigned
> with '1' and others with '0'.
> However, after the mask image was created, I found those significant voxels
> were assigned with 0.9831, not 1.
> I don't know where the particular value came from and I'd like those voxels
> within the mask to be '1' to avoid any further confusion.
> Is there any way of doing it? Any help would be appreciated.
>
> Glen
>
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