vtkImageInterpolator -> gradient

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vtkImageInterpolator -> gradient

Martin Genet-3
Dear all:

On the wiki page on image interpolators, I read the following:

> It would be possible to add methods to the interpolator classes so that they could return the gradient of the image at any (X,Y,Z) point.

I was wondering: has there been any progress on this side? It would quite useful. Any thought on the implementation? Thanks!

Martin


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Re: vtkImageInterpolator -> gradient

David Gobbi
On Mon, Jun 13, 2016 at 4:17 AM, Martin Genet <[hidden email]> 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:
Computing a gradient would be similar, but would need only three derivatives instead of nine.

 - David

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Re: vtkImageInterpolator -> gradient

Martin Genet-3

On 13/06/2016 14:00, David Gobbi wrote:
On Mon, Jun 13, 2016 at 4:17 AM, Martin Genet <[hidden email]> 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:
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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