[vtkusers] Adding a transparency mask to an image

[John Drescher]

> Is there a way to set a transparency mask for a vtkImageData displayed
> with a vtkImageActor? For example, I want to make a specific region
> (in the example below, the top half) of the image transparent. This
> would be used to overlay the result of a binary segmentation onto the
> original image.
>

For a Lung Segmentation application I created a vtkLookupTable for the
mask image and set different opacities for different values in the
mask. In my case I made 0 totally transparent. Then I added the mask
image to the scene using a second image actor.

Here are bits of the code:

void someFunction()
{
	vtkImageData* pMaskImage = InitializeMaskImage(pImage);

	vtkLookupTable* lut = vtkLookupTable::New();
	lut->SetNumberOfTableValues(7);
	lut->SetRange(0.0,6.0);
	lut->SetTableValue( 0, 0.0, 0.0, 0.0, 0.0 ); //label 0 is transparent
	lut->SetTableValue( 1, 0.0, 1.0, 0.0, 0.8 ); //label 1 is green
	lut->SetTableValue( 2, 1.0, 0.0, 0.0, 0.3 ); //label 2 is red
	lut->SetTableValue( 3, 0.0, 0.0, 1.0, 0.3 ); //label 3 is blue
	lut->SetTableValue( 4, 0.0, 1.0, 1.0, 0.3 ); //label 4 is cyan
	lut->SetTableValue( 5, 1.0, 1.0, 0.0, 0.3 ); //label 5
	lut->SetTableValue( 6, 1.0, 0.0, 1.0, 0.3 ); //label 6
	lut->Build();

	pImage->Update();
	

	for(int i=0; i < 3;++i) {

#ifndef LIB_SETS_OFFSET
		pViews[i]->SetFGImage(pMaskImage,lut);
#else
		pViews[i]->SetFGImage(pMaskImage,lut,MASK_COL_OFFS,MASK_ROW_OFFS,MASK_SLICE_OFFS);
#endif //ndef LIB_SETS_OFFSET

	}
}

void vtkViewImage2D::SetFGImage( vtkImageData* image, vtkLookupTable* lut,
								int xoffs/*=0*/,int yoffs/*=0*/,int zoffs/*=0*/ )
{

	if (FGImageActor != NULL) {
		this->GetRenderer()->RemoveViewProp(FGImageActor);
	}

	vtkImageMapToColors*	windowLevel = vtkImageMapToColors::New();
	windowLevel->SetLookupTable(lut);
	windowLevel->SetInput(image);
	windowLevel->PassAlphaToOutputOn();
	
	// set up the vtk pipeline
	
	vtkImageReslice*		relsice = vtkImageReslice::New();
	relsice->SetOutputDimensionality(2);
	relsice->InterpolateOff();
	relsice->SetInput(windowLevel->GetOutput());

	vtkImageActor*			actor = vtkImageActor::New();
	actor->SetInput(relsice->GetOutput());

	FGImageActor = actor;
	FGWindowLevel = windowLevel;
	FGImageReslice = relsice;

	this->FGImageActor->SetOpacity(0.95);

	Update();
	SetupAnnotations();

	FGImage = image;
	this->GetRenderer()->AddViewProp(this->FGImageActor);	
	this->GetRenderer()->Render();
}

John