[vtk-developers] The ImageStencil Issue
Karthik.Krishnan at kitware.com
Mon Aug 28 11:41:49 EDT 2006
Karthik Krishnan wrote:
> Hi David,
> I find stencils very useful. I've been using them as a data structure
> for representing segmentations.
> One of the things I would like to contribute to stencils is minkowski
> operators or "set" operations on stencils. For instance union of two
> stencils, stencilA-stencilB, intersection of stencils etc.. The need
> for these arises when a 3D volume has a few disconnected hand-drawn
> segmentations and as a user, I would like to discard a segment etc..
> I've been using these separately in a derived class, but I could move
> them to the vtkImageStencilData class itself.
They've have been added to the vtkImageStencilData class.
> Another addition, I would hope to see would be grayscale stencils for
> fuzzy segmentations. Imagine a brush widget dabbing a fuzzy / dithered
> stroke and you would like to use the stencildata to represent opacity.
> It would be great if the stencils could store a DataArray in addition
> to maintaining the ExtentLists. This could possibly be done in a
> David Gobbi wrote:
>> Hi All,
>> I'd like to redress some ugliness that I introduced to VTK a few
>> years back.
>> The vtkImageStencilSource class requires the Spacing and Origin of
>> whichever image eventually uses the stencil to be propagated the
>> wrong way along the pipeline. Ouch!
>> Obviously the vtkImageStencilSource should actually take an Image as
>> an input and should then use that image to get the Spacing and Origin
>> to use for the stencil. This is a fairly minor change. For VTK 5.2,
>> I can then make VTK produce a deprecation warning if people don't set
>> an input.
>> I would call the method SetInformationInput() to make it clear that
>> only the information (the Spacing, Origin, and WholeExtent) of the
>> data would be used. Also, vtkPolyDataToImageStencil() needs it
>> SetInput() method for the polydata input.
>> For example:
>> stencilSource = vtkImplicitFunctionToImageStencil()
>> histogram = vtkImageAccumulate()
>> Do people think this is a good change? Are there many people out
>> there who even use stencils in VTK? How many people know what a
>> stencil is? (Hint: it is an image mask stored in an efficient
>> run-length format instead of vtkImageData format).
>> Also, I'm not sure what the methods should be named in light of the
>> VTK 5 pipeline changes. Maybe I should name them as follows:
>> SetInformationInputConnection(vtkAlgorithmInput *) instead of
>> SetInformationInput(vtkImageData *)
>> SetStencilInputConnection(vtkAlgorithmInput *) instead of
>> SetStencil(vtkImageStencilData *)
>> I'd like to get this right, and I think that only small changes are
>> necessary to do so.
>> Also, of course, I'd like to see more of the filters in Imaging
>> utilizing stencils. Right now only a handful do (Blend, Reslice,
>> Stencil, Accumulate). The potential here is very high... a stencil
>> allows you to perform an operation only within a specified region of
>> interest, where the shape of the region can be whatever you desire.
>> The ROI can even be described by a vtkPolyData mesh or by a
>> vtkImplicitFunction, since these types can be converted efficiently
>> into vtkImageStencilData.
>> - David
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