[Insight-users] SignedDanielssonDistanceMapImageFilter
Luis Ibanez
luis.ibanez at kitware.com
Wed Dec 10 15:49:39 EST 2008
Hi chensiqi
Here is the philosophical question that you must
answer before your proceed further.
You want to get the distance to "what" ?
Do you want the distance to the points ?
Do you want the distance to the boundary ?
From a set of points located in a boundary is
*very difficult* to find the inside of an object.
Do you have a topology connecting these points ?
e.g. a triangulated surface ?
How did you get these points ?
It may be easier to work with the data preceeding
your point extraction.
Regards,
Luis
==================
chensiqi wrote:
>
> Hi, Luis.
>
> Thanks for the clarification.
> My purpose is to build a signed distance function given a point clouds
> of a shape boundary. I know there are several options to do this. If the
> only input are those points, which is the best, fast and easiest way to
> do this? I know there are several options in ITK.
> 1. FastMarching.
> 2. Reinitiaze
> 3. DistanceMap (Danielsson).
>
> Another question would be regarding smart pointer and raw pointer. Is
> it OK to return a smart pointer from a function?
> E.g. I have this code:
> //////////////////////////////////////////////////////////////////////
> main.cpp
> typedef itk::Image< unsigned char, 2 > BinaryImageType;
> typedef itk::Image< float , 2> LSVImageType;
> LSVImageFilter::Pointer LSVImage = SDF(contour) // where the contour is
> binary image
> SDF.cpp
> LSVImageType::Pointer SDF(BinaryImageType::Pointer contour)
> {
> typedef itk::SignedDanielssonDistanceMapImageFilter <
> BinaryImageFilter, LSVImageFilter > FilterType;
> FilterType::Pointer filter = FilterType::New();
> filter ->SetInput ( contour ); // contour is the binary image
> return filter->GetOutput();
> }
>
>
> //////////////////////////////////////////////////////////////////////
>
>
> Thanks for any input
> Siqi
>
>
> > Date: Wed, 10 Dec 2008 15:16:08 -0500
> > From: luis.ibanez at kitware.com
> > To: pidanchen at hotmail.com
> > CC: insight-users at itk.org
> > Subject: Re: [Insight-users] SignedDanielssonDistanceMapImageFilter
> >
> >
> > Hi Chensiqi,
> >
> > You are misinterpreting the behavior of this filter.
> >
> > If you have a binary image, where
> >
> > * The foreground object is set to 1 and
> > * The background object is set to 0
> >
> >
> > Then the SignedDanielssonDistanceMapImageFilter will compute
> > the distances to the *transition* region between the 0s and
> > the 1s.
> >
> > All pixesl in the 0s region will have positive distances to
> > that boundary, while all pixels in the 1s region will have
> > negative distances to that boundary.
> >
> > In your case you are feeding an input image where the *boundary*
> > points are set to 1. Therefore, there is no "inside" to the
> > object.
> >
> > E.g. if you are feeding into this distance filter an image with
> > a thin ring, you are not going to find the "inside" of the ring.
> >
> > You should feed this filter with an image containing a filled
> > circle of radius R. Where all the points at locations r < R will
> > be set to 1s. Only in that case will the distance map be able to
> > find the "inside" of the object.
> >
> >
> > Regards,
> >
> >
> > Luis
> >
> >
> > ---------------
> > chensiqi wrote:
> > > Hi, Ghassan
> > >
> > > Thanks for the advice. I flip the input.
> > > The result now is both inside and outside are positive :(
> > >
> > > I use float type as the filteroutput instead of "unsigned short" in
> the
> > > example. I also tried unsigned short, the result is the same.
> > >
> > > Here is part of my code.
> > >
> ////////////////////////////////////////////////////////////////////////////////////////////////////
> > > typedef itk::Image< unsigned char, 2 > BinaryImageType;
> > > typedef itk::Image< float , 2> LSVImageType;
> > > typedef itk::SignedDanielssonDistanceMapImageFilter <
> BinaryImageFilter,
> > > LSVImageFilter > FilterType;
> > > FilterType::Pointer filter = FilterType::New();
> > >
> > > filter ->SetInput ( contour ); // contour is the binary image with
> > > BinaryImageType, 1 at boundary points, and 0 elsewhere.
> > >
> > > LSVImageFilter::Pointer LSVImage = filter->GetDistanceMap();
> > >
> > > Display (LSVImage) // this is a function that displays the image.
> > >
> //////////////////////////////////////////////////////////////////////////////////////////////////////
> > >
> > > I notice when I cout<<LSV_image->GetBufferedRegion().GetSize() , the
> > > output is [0,0]. I guess there is something wrong in my code that
> > > causes this weird output size. I can display LSVImage, although both
> > > inside and outside region are postive.
> > >
> > >
> > > Thanks for any input
> > > Siqi
> > >
> > > > CC: insight-users at itk.org
> > > > From: hamarneh at gmail.com
> > > > To: pidanchen at hotmail.com
> > > > Subject: Re: [Insight-users] SignedDanielssonDistanceMapImageFilter
> > > > Date: Tue, 9 Dec 2008 20:45:19 -0800
> > > >
> > > > Hello Siqi,
> > > >
> > > > You write: "The input is only a binary image with boundary points at
> > > > 0, and all other points at 1."
> > > > However, according to he documentation: "As a convention, the
> distance
> > > > is evaluated from the boundary of the ON pixels."
> > > > (from
> > >
> http://www.itk.org/Doxygen/html/classitk_1_1SignedDanielssonDistanceMapImageFilter.html
>
> > >
> > > > )
> > > > So, your input image should have boundary pixels set to 1 and all
> > > > other points to 0 (and not the other way around).
> > > > HTH,
> > > > /Ghassan
> > > >
> > > >
> > > >
> > > > On 9-Dec-08, at 7:24 PM, chensiqi wrote:
> > > >
> > > > >
> > > > > Hi, ITKers
> > > > >
> > > > > I got two ques tions regarding
> SignedDanielssonDistanceMapImageFilter.
> > > > >
> > > > > 1. The result I have is not "signed", both the inside and outside
> > > > > distance values are negative. The input is only a binary image with
> > > > > boundary points at 0, and all other points at 1. I was wondering
> > > > > how I was wondering how SignedDanielssonDistanceMapImageFilter
> > > > > determine the region of inside and outside.
> > > > >
> > > > > 2. In Examples of SignedDanielssonDistanceMapImageFilter. cxx, I
> > > > > notice that the OutputImageType of filter is unsigned short,
> which I
> > > > > don't quite understand. The output should contains both negative
> > > > > and positive distance, why use "unsigned" here?
> > > > >
> > > > > Thanks
> > > > > Siqi
> > > > >
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