[vtkusers] question abotu output spacing for the reslicer

[Luca Pamparana]

Hello David,

Thank you for answering my query. That was very kind of you.

I have one further question on a related note about the zooming itself. So,
the interpolation. Does it take the 4 pixels around a pixel to do the
interpolation. So, if I am to zoom by a factor of 2 (or 0.5 as you mentioned
in the VTK context), if the pixel does not lie on the border, does it take
the  pixels on the left, right, top and bottom to calculate the resulting
interpolated pixel intensities.

Also, what happens to the pixels that lie on the corner ot the image
borders?

Thank you again for your help. I appreciate it sincerely.

Luc

On 12/21/06, David Gobbi <dgobbi at atamai.com> wrote:
>
> Hi Luca,
>
> You are correct about the interpolation part, but the spacing works
> opposite to the way you guessed.
>
> If you want to zoom the image by a factor of 2.0, you should set the
> OutputSpacing to half of the original image spacing.
>
> A good way to explain it is like this.  The OutputSpacing is the size of
> the output pixels.  So, if you have an MRI image that covers a square
> area of 256mm by 256mm, if the OutputSpacing is 1mm then the number of
> pixels in the output image will be 256x256.  If the OutputSpacing is
> 0.5mm, the number of pixels will be 512x512.
>
> - David
>
>
>
> Luca Pamparana wrote:
> > Hi everyone,
> >
> > I was wondering what exactly the OutputSpacing parameters are doing to
> > the input image.
> >
> > So, if I double the OutputSpacing in the x and y direction, I can
> > achieve a zoom of factor 2.0.
> >
> > However, what does it mean for the pixels in the output image? So, one
> > data pixel now takes 2 pixels in the x and y directions. How is the
> > data for these pixels calculated? Does the slicer take the adjacent
> > pixel and interpolates based on the interpolation scheme selected?
> >
> > I know this is a very basic question but I will be grateful if someone
> > can answer this.
> >
> > Thanks,
> >
> > Luc
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