[vtkusers] Displaying a 2D image as a volume

[Francois Bertel]

Dimension[i] is the number of points along axis i, not the number of cells. Number of cells along axis i is Dimension[i]-1. If Dimension[i]=1, number of cells[i]=0, so no thickness.

J.S.Wijnhout at lumc.nl wrote:
> Hi,
> 
> Thanks for the suggestion, that actually worked! I'm not sure what is
> wrong with my original approach (a bug perhaps?), but padding the image
> with transparent voxels work. For those of you who have the same
> problem:
> 
>     double minValue = _image->GetScalarTypeMax ();
>     double maxValue = _image->GetScalarTypeMin ();
>     // This is a custom function to determine the min/max gray values:
>     DetermineMinMax ( _image, minValue, maxValue );    
>     vtkImageShiftScale *scaler = vtkImageShiftScale::New ();
>     scaler->SetInput ( _image );
>     scaler->SetOutputScalarTypeToUnsignedChar ();
> 
>     // Map to [1,255], the value 0 is reserved for a transparency hack:
>     int delta = maxValue - minValue;
>     scaler->SetShift ( ( delta / 254.0 ) - minValue );
>     scaler->SetScale ( 254.0 / delta );
> 
> 
>     vtkImageConstantPad *padder = vtkImageConstantPad::New ();
>     int extent [ 6 ];
>     _image->GetExtent ( extent );
>     extent [ 2 ] = 3;
>     extent [ 5 ] = 3;
>     padder->SetOutputWholeExtent ( extent );
>     padder->SetInput ( scaler->GetOutput () );
>     padder->SetConstant ( 0.0 );
> 
>     // Modify the transfer functions such that pixel value 0 (the 
>     // value the image is padded with in the z-dimension) corresponds to
> a
>     // completely transparent voxel and value 1 to pure black:
>     vtkPiecewiseFunction *opacityTransferFunction =
> vtkPiecewiseFunction::New ();
>     opacityTransferFunction->AddPoint ( 0, 0.0 );
>     opacityTransferFunction->AddPoint ( 0.5, 1.0 );
>     opacityTransferFunction->AddPoint ( 1, 1.0 );
>     opacityTransferFunction->AddPoint ( 255, 1.0 );
>     vtkColorTransferFunction *colorTransferFunction =
> vtkColorTransferFunction::New ();
>     colorTransferFunction->AddRGBPoint ( 0, 0.0, 0.0, 0.0 );
>     colorTransferFunction->AddRGBPoint ( 1, 0.0, 0.0, 0.0 );
>     colorTransferFunction->AddRGBPoint ( 255, 1.0, 1.0, 1.0 );
> 
>     vtkVolumeProperty *volumeProperty = vtkVolumeProperty::New ();
>     volumeProperty->SetColor ( colorTransferFunction );
>     volumeProperty->SetScalarOpacity ( opacityTransferFunction );
> 
>     vtkVolumeRayCastCompositeFunction *rayCastFunction =
> vtkVolumeRayCastCompositeFunction::New ();
>  
>     vtkVolumeRayCastMapper *hiResVolumeMapper =
> vtkVolumeRayCastMapper::New ();
>     hiResVolumeMapper->SetInput ( padder->GetOutput () );
>     hiResVolumeMapper->SetVolumeRayCastFunction ( rayCastFunction );
> 
>     vtkVolume *volume = vtkVolume::New ();
>     volume->SetProperty ( volumeProperty );
>     volume->SetMapper ( hiResVolumeMapper );
> 
> 
> best,
> Jeroen
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-- 
François Bertel, PhD  | Kitware Inc. Suite 204
1 (518) 371 3971 x113 | 28 Corporate Drive
                       | Clifton Park NY 12065, USA