[Insight-users] Volume overlay

[Sara Rolfe]

Hello,

I'm attempting to overlay an image with color.  I've had trouble  
finding documentation on this, either in ITK or VTK.  The way I'm  
going about it is to scale the values of the image down and then use  
the add image filter to add the labels on top.  I could then use VTK  
to create a corresponding colormap.

However, I'm getting stuck on something that should be very simple.   
My operations to combine the two images are failing.  I think the  
problem is the SubtractConstantFromImageFilter.  I've checked the  
output and it looks like the constant is not being subtracted.  The  
input to this filter is an image with a value of 0 for the background  
and 255 for the object.  I'd like to change these to 0 and 1.  The  
pixel type is unsigned char.  I use the following:

	SubFilterType::Pointer subFilter = SubFilterType::New();
	InputPixelType subValue = 254;
	subFilter->SetConstant(subValue);
	subFilter->SetInput( imageInverter->GetOutput() );
	subFilter->Update();

But the output image is still 0 - 255.  Am I missing something simple?

Also, is there a better way to accomplish this task, or any examples  
showing something similar?

Thanks,
Sara
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