[vtkusers] Opacity of vtkImageConstantPad

[Margaretha Sulistyoningsih]

Hallo,
 
I blend two images using vtkImageBlend, namely image A and B. 
Before I blend those images, each of them is padded using vtkImageConstantPad.
I have a slider to set the opacity value (range: 0-1). 
As the slider move, I get the position and use it to set the opacity.
Opacity of image A = slider position.
Opacity of image B = 1 - slider position.
 
Everything looks perfect if both images are overlapped. Images could be fadded out
as I move the slider.
 
And then, I move or rotate image B until some part of image A are not covered
by image B anymore, but covered only by the constantpad of image B.
My question is: How to set opacity of vtkImageConstantPad? 
My problem is: Only the parts of image A which are covered by image B can be faded out. It looks like the opacity value of parts of image A which are covered by constantPad of image B is always 1, until the slider hit value 0, image A is missing.
I want to have a result that all parts of image A could be faded out even it is covered only
by the constantPad of image B.
 
Please help me to solve this problem. Thanks in advance.
 
br,
.Margaretha.
 
 

		
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