[vtkusers] vtkImageInterpolator -> gradient

[Martin Genet]

On 13/06/2016 14:00, David Gobbi wrote:
> On Mon, Jun 13, 2016 at 4:17 AM, Martin Genet 
> <martin.genet at polytechnique.edu 
> <mailto:martin.genet at polytechnique.edu>> wrote:
>
>
>     I was wondering: has there been any progress on this side? It would
>     quite useful. Any thought on the implementation? Thanks!
>
>
> No progress, it's still just an idea.  When I wrote that wiki page, I 
> was thinking the gradient would be useful if these interpolators were 
> used for either isosurfacing or ray casting. What were you thinking of 
> using the gradient for?
>
> The computation of derivatives for b-spline interpolation is currently 
> implemented in the vtkBSplineTransform class, which uses the 
> derivatives to provide the Jacobian matrix for the transformation:
> https://gitlab.kitware.com/vtk/vtk/blob/master/Filters/Hybrid/vtkBSplineTransform.cxx#L202
> Computing a gradient would be similar, but would need only three 
> derivatives instead of nine.
>

Right now I'm working on some (finite element-based) image correlation 
tool, for which I need to compute some integral on the image (the 
residual), as well as some integral on the image gradient (the search 
direction).

For the moment I'm using an ImageInterpolator for the images, and an 
ImageGradient+ImageInterpolator for their gradients, but of course that 
way the interpolated gradients are not the actual gradients of the 
interpolated images.

Martin

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