Dear Shan & Maulin,
the scale factors and offsets are used for volumes of any integer datatype
to make best use of the dynamic range of the datatype when storing
floating point data. As an example, tissue probability maps which contain
values between 0 and 1 would become binarised when stored as uint8 data if
there was no scaling factor to map 0 to 0 and 1 to 255.
DICOM conversion does not scale the data, therefore raw images will have
scale factor 1. In other places in SPM, scaling is also used to do global
scaling etc.
If you need to export data with fixed scaling factors, use the Volumes
toolbox available from the SPM extensions page.
Volkmar
On Mon, 11 Sep 2006, Maulin Shah wrote:
> SPMers,
>
>
> I have run into the same problem and I am trying to figure out a way
> around it as the intensity of the image is very important in our study.
>
> Maulin
>
> On 9/11/06, Shan Shen <[log in to unmask]> wrote:
> >
> > Dear SPMers,
> >
> >
> >
> > I've noticed that the intensities of each processed image in SPM have a
> > scale factor and an offset (Y=scale*X+offset), which were 1 and 0 in an
> > un-processed image. I would like know why the scale factor and offset are
> > required, and how they are calculated. Many thanks
> >
> >
> >
> >
> >
> > shan
> >
> >
> >
> >
> >
> > Dr Shan Shen
> >
> > Cognitive Neuroscience Research Team
> >
> > Department of Psychology
> >
> > University of Surrey
> >
> > Guildford GU2 7XH
> >
> > UK
> >
> >
> >
>
--
Volkmar Glauche
-
Department of Neurology [log in to unmask]
Universitaetsklinikum Freiburg Phone 49(0)761-270-5331
Breisacher Str. 64 Fax 49(0)761-270-5416
79106 Freiburg
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