[Insight-users] Creating a 2D binary image from a polygon

[Xabier Artaechevarria Artieda]

Hi Aurelie,

there was a discussion last year on the same topic, I think.
Have a look at:

http://www.itk.org/pipermail/insight-users/2008-May/025963.html

Regards,
Xabier

-- 
Xabier Artaechevarria
Cancer Imaging Laboratory
Centre for Applied Medical Research
www.cima.es



AurelieC <aurelie.canale at sophia.inria.fr> ha escrito:

>
> Hello,
>
> I have a 2D polygonal region of interest defined by a list of points (x and
> y coordinates). I am trying to create a new image of a given size which will
> be white inside the polygon and black outside.
>
> What I tried to do :
> I create a mesh, I add in the mesh the points, then LineCell between the
> points and vertexCell at each points.
> Then I create a MeshSpatialObject which take the created mesh.
> Then I try to create a binary image using the MeshSpatialObject : first I
> was using the MeshToImageFilter but it did not work so I tried to scan all
> the image and for each pixel I just check if it is inside or outside the
> polygon, if it is inside it gets the value 1.
> The code compiles, but nothing happens, no point is considered as inside the
> mesh, the outside image is black, so I think I made a mistake while creating
> the mesh. Maybe I should use PolygonCell, or PolygonGroupSpatialObject?
>
> Please help me.
>
> This is my code:
>
>
> // creating the mesh
>
> typedef   float   PixelType;
> const unsigned int Dimension = 2;
> typedef itk::Mesh< PixelType, Dimension>   MeshType;
> MeshType::Pointer  mesh = MeshType::New();
>
> // adding points and creating the cells
>
> MeshType::PointType p;
>
> typedef MeshType::CellType CellType;
> typedef itk::LineCell< CellType > LineType;
> typedef itk::VertexCell< CellType > VertexType;
>
> // tab contained the coordinates of each points
> for (int i = 0; i < nbPoint; i++)
> {
>     p[0] = tab[i*2];
>     p[1] = tab[i*2+1];
>     mesh->SetPoint(i,p);
> }
>
> //creating lines between points
> CellType::CellAutoPointer cellpointer;
>
> for(int cellId=0; cellId < nbPoint-1; cellId++)
> {
>     cellpointer.TakeOwnership( new LineType );
>     cellpointer->SetPointId( 0, cellId ); // first point
>     cellpointer->SetPointId( 1, cellId+1 ); // second point
>     mesh->SetCell( cellId, cellpointer ); // insert the cell
> }
>
> cellpointer.TakeOwnership( new LineType );
> cellpointer->SetPointId( 0, (nbPoint-1) ); // first point
> cellpointer->SetPointId( 1, 0 ); // second point
> mesh->SetCell( nbPoint-1, cellpointer); // insert the cell
>
> for(int cellId=0; cellId < nbPoint; cellId++)
> {
>     cellpointer.TakeOwnership( new VertexType );
>     cellpointer->SetPointId( 0, cellId );
>     mesh->SetCell( cellId + nbPoint, cellpointer );
> }
>
>
> std::cout << "# Points= " << mesh->GetNumberOfPoints() << std::endl;
> std::cout << "# Cell  = " << mesh->GetNumberOfCells() << std::endl;
>
>
> // creating the MeshSpatialObject
> typedef itk::MeshSpatialObject<MeshType>     MeshSpatialObjectType;
> MeshSpatialObjectType::Pointer myMeshSpatialObject =
> MeshSpatialObjectType::New();
>
> myMeshSpatialObject->SetMesh(mesh);
>
>
> // creating the output image
>
> typedef itk::Image<float, 2>      ImageType;
> ImageType::Pointer image = ImageType::New();
>
> // dimX and dimY given dimensions
> size[0] = d->dimX;
> size[1] = d->dimY;
> ImageType::IndexType start;
> start[0] = 0; // first index on X
> start[1] = 0; // first index on Y
> ImageType::RegionType region;
> region.SetSize( size );
> region.SetIndex( start );
>
> image->SetRegions( region );
> image->Allocate();
>
> myMeshSpatialObject->Update();
>
>
> // region to scan. I reduce the region to scan using the
> mesh->GetBoundingBox()
>
> typedef itk::FixedArray< float, 4> FixedArraySize;
> FixedArraySize test;
> myMeshSpatialObject->GetBoundingBox()->ComputeBoundingBox();
> test =  myMeshSpatialObject->GetBoundingBox()->GetBounds();
>
> ImageType::RegionType roi;
>
> size[0] = int(test[1])+2 -  int(test[0]);
> size[1] =  int(test[3]) +2 - int(test[2]);
> roi.SetSize( size );
> // roi.SetIndex( start );
>
>
> // test each pixel of the boundingbox, check if it is inside or outside the
> polygon
> itk::Point<float,2> point;
> typedef itk::ImageRegionIterator<ImageType> Iterator;
> Iterator it( image, roi );
> it.GoToBegin();
>
>   while( !it.IsAtEnd() )
>     {
>
>     image->TransformIndexToPhysicalPoint(it.GetIndex(), point );
>
>     if (myMeshSpatialObject->IsInside(point))
>     {
> 	qDebug() << "isinside "<< endl; // no point is in this case...
> 	image->SetPixel(it.GetIndex(), 1);
>     }
>     else
> 	image->SetPixel(it.GetIndex(), 0);
>
>     ++it;
>     }
>
>
>
> // write the result
>
> typedef itk::ImageFileWriter< ImageType > ImageWriterType;
> ImageWriterType::Pointer imgWriter = ImageWriterType::New();
> imgWriter->SetInput(image);
> imgWriter->SetFileName(filename);
> imgWriter->Update();
>
>
>
>
> Thank you!
> --
> View this message in context:   
> http://www.nabble.com/Creating-a-2D-binary-image-from-a-polygon-tp22804986p22804986.html
> Sent from the ITK - Users mailing list archive at Nabble.com.
>
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