[vtkusers] vtkusers Digest, Vol 75, Issue 22

[David Gobbi]

Yes, you can do that.  Just reverse the stencil, and apply it to the
image before you volume-render it.  You can also use a stencil with
vtkImageReslice (i.e. instead of vtkImageStencil) if you need to
resample the volume before rendering it.

The thing to watch out for is that this will only make the
outside-stencil parts black, it won't make them transparent.  So you
still need a color transfer function that will make black voxels
appear to be transparent when you render them.

   David


2010/7/15 6dgis at 163.com <6dgis at 163.com>:
> Hi david,
>
> I am not sure that the following problem is same as this subject
>
>        "I have a series of CT Images and render them in Volume by
>  vtkVolumeRayCastMapper. Now given a polygon by user clicking
>  on the screen, how to clip the volume with the inner objects removed?
>  I just want the "hole" effect for displaying."
>
> BTW, after rotating the scene, I want the hole also exist. Could I use
> vtkImageStencil to reach the  goal? Thanks in advance.
>
> Best Regards!
> ------------------
> 6dgis at 163.com
> 2010-07-16
>
> Date: Wed, 14 Jul 2010 16:31:13 -0600
> From: David Gobbi <david.gobbi at gmail.com>
> Subject: Re: [vtkusers] best way to clip vtkImageData using
>        vtkPloyData
> To: Prathamesh Kulkarni <prathameshmkulkarni at gmail.com>
> Cc: VTK Mailing List <vtkusers at vtk.org>
> Message-ID:
>        <AANLkTilNAcpAgK_gWTrZapFYogkvbmD6RgnoMRgjeQMn at mail.gmail.com>
> Content-Type: text/plain; charset=ISO-8859-1
>
> 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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> End of vtkusers Digest, Vol 75, Issue 22
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