[Neuroimaging] Nibabel API change - always read as float

[Satrajit Ghosh]

hi brendan,

here is the line:

Floating point types are presumed to be stored in IEEE-754 format.

this is about how data are stored on disk. nifti-1 does not say
anything about what a user does with data. i only intended to say that
data stored back should conform to ieee-754 when stored as dt_float.

cheers,

satra

On Tue, Jul 7, 2015 at 2:16 PM, Brendan Moloney <moloney at ohsu.edu> wrote:

>   > the nifti-1 standard (
> http://nifti.nimh.nih.gov/pub/dist/src/niftilib/nifti1.h)
> > has a datatype field. there are two scenarios with scaling:
> >
>  > 1. scl_slope == 0:
> >
>  > 2. scl_slope != 0:
> >    data should be converted to IEEE-754  floats as per the nifti
> standard.
> > given nifti was around 2001 this probably did not reflect the updated
> > IEE754-2008 standard, but > relied on the 1985 standard. i don't think
> the
> > nifti-1 standard makes it clear what this float should correspond to,
> i.e.,
> > 16/32/64/128 bit floats.
>
> I don't see that in the standard.  All I see is:
>
>    If the scl_slope field is nonzero, then each voxel value in the dataset
>    should be scaled as
>       y = scl_slope * x + scl_inter
>    where x = voxel value stored
>          y = "true" voxel value
>    Normally, we would expect this scaling to be used to store "true" floating
>    values in a smaller integer datatype, but that is not required.  That is,
>    it is legal to use scaling even if the datatype is a float type (crazy,
>    perhaps, but legal).
>
>
>
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