[vtkusers] best way to clip vtkImageData using vtkPloyData

[Prathamesh Kulkarni]

I managed use vtkImageStencil and vtkImageAccumulate, but could not get a
proper blended image output with vtkImageBlend. Following is my code snippet
for vtkImageBlend:

        blended_image->SetInput(image_data);
        blended_image->SetStencil(image_stencil_data);

        blended_image->SetOpacity(1, opacity)
        blended_image->Update();

When I try to render blended_image->GetOutput(), I simply get the input
image, as if setting the stencil had no effect. I expected to see a
different opacity in the stencil region. Please tell me if I am missing
anything here.


Also, I was wondering how to add multiple stencils to vtkImageStencil so
that at the output I can have a vtkImageData showing multiple stencils with
different colors.

In any case, I did not understand how to set the foreground color of a
single stencil.



Sorry for putting in 3 questions together.. Thanks for your answers in
advance.


Prathamesh


On Wed, Jul 14, 2010 at 5:31 PM, David Gobbi <david.gobbi at gmail.com> wrote:

> Hi Prathamesh,
>
> You should use either vtkClipVolume or vtkImageStencil, based on what
> you want as an output. The vtkClipVolume filter will output an
> unstructured grid, i.e. it will produce a geometric data set
> consisting of voxel cells (each voxel cell will be a little cube with
> eight points at its corners).  If you want the output to be an actual
> image, with the background set to black or to transparent, then you
> should use vtkImageStencil.
>
> In either case, the best place to start is vtkImplicitLoop, which
> takes a contour and produces an "implicit function", which in
> VTK-speak, is a function used to define the inside vs. the outside of
> a selection area.  Then the vtkImplicitLoop can be used as an input to
> vtkImplicitFunctionToImageStencil.  The output of
> vtkImplicitFunctionToImageStencil can then be used as an input to e.g.
> vtkImageBlend (for pasting a cut-out image onto another image),
> vtkImageStencil (for blacking out the non-selected region of the
> image), or vtkImageAccumulate (for computing the average value,
> standard deviation, or the histogram of the image area inside the
> stencil).
>
>   David
>
>
>
>
> On Wed, Jul 14, 2010 at 4:13 PM, Prathamesh Kulkarni
> <prathameshmkulkarni at gmail.com> wrote:
> >
> > Hello all,
> >
> > I want to extract a sub-image from vtkImageData given a closed set of
> points
> > forming any arbitrary shape (may be a vtkPolyData).
> >
> > I have been looking at vtk classes like vtkClipVolume, vtkExtractVOI,
> > vtkImageStencil. I am no able to understand which way should be preferred
> > over which to do my task. Also, I am not able to figure out the exact
> > pipeline structure for these clipping methods.
> >
> > Could someone please throw some light on this?
> >
> > Thanks,
> > Prathamesh
> >
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