[vtkusers] Using SetUpdateExtents of vtkImageData

[vidyadhar]

Hi
I wish to render a 2D image which has one component scalars of unsigned short type. I wish to update the scalars data at different time and display the change.
I am using vtkImageViewer2 class for my purpose. I creating a color lookup table and assigning it to the vtkImageMapToColors filter instance in the vtkImageViewer2 instance. Only the scalar data in the image changes over time and this also over some restricted (image) region. As of now, I have to call Modified() method of vtkImageMapToColors filter to see the updated image.
It SEEMS that the entire extent of input/output image are being processed by this filter when I invoke Modified() method. Is there some way to restrict this to some smaller region. I tried using SetUpdateExtent() method of both the input and output images of the filter but it does not seem to work. Since my code is modifying the scalars data, I can estimate the region which needs update. But I am not able to use it for some reason. Can somebody suggest how to achieve this.
I will like to use something similar using vtkVolume also where I will be updating the scalar data alone.
May be both can be made to work or one of them can work. Any help / suggestions will be appreciated.
Vidyadhar
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