[vtkusers] inverse of an image, how to?

[yala kaluma]

Hi,

I have a black and white image and i would like inverse it.
i.e. Switch the black zone into white zone and the whiye zone into black.
In theory it seems pretty easy. I only need to change the value of every 
pixel to 255-its former value.
But i don t know how to manipulate pixel' s value one by  one in VTK.

I tried to use vtkImageDifference too but it only accept rgb images. And I 
don t know how to transform on into the other.


Any kind of help is welcome!
Thank u...
Long lives VTK..

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