[vtkusers] Possible bug in vtkImageResample or vtkImageReslic e when doing de mag

Leue, William M (Research) leue at crd.ge.com
Thu Dec 9 10:07:08 EST 2004

Thanks, you are correct: the cubic interpolation was overshooting badly at
high-contrast points in the image. Changing to trilinear interpolation fixed
the problem.

-Bill Leue

-----Original Message-----
From: Huntsinger, Reid [mailto:reid_huntsinger at merck.com]
Sent: Wednesday, December 08, 2004 5:24 PM
To: 'Leue, William M (Research)'; 'vtkusers at vtk.org'
Subject: RE: [vtkusers] Possible bug in vtkImageResample or
vtkImageReslic e when doing de mag

You seem to have asked for (tri-) cubic interpolation, which may indeed
introduce new maxima and minima, since your interpolation points are not
just data points (with a factor of 2 exactly they would be). 

Reid Huntsinger

-----Original Message-----
From: vtkusers-bounces at vtk.org [mailto:vtkusers-bounces at vtk.org] On Behalf
Of Leue, William M (Research)
Sent: Wednesday, December 08, 2004 4:52 PM
To: 'vtkusers at vtk.org'
Subject: [vtkusers] Possible bug in vtkImageResample or vtkImageReslice when
doing de mag

Hi, I appear to have found a bug when using vtkImageResample to do image
demagnification. I am guessing the bug is really in vtkImageReslice because
vtkImageResample is just a thin wrapper object. I am using VTK Release

The bug symptoms are that an image volume that has been demagnified by
approximately a factor of 2 (not exactly) has a small percentage of voxel
values that are outside the range of the input values. The image volume is
CT data with a range of 0..4095. The image data has been converted from the
original unsigned short format to float before demagnification. The output
volume after demagnification has a range of 0..4938. About 1.5% of the
original voxels now have values that are higher than 4095.

A snippet of the relevant code is:

  vtkImageResample* samp = vtkImageResample::New();
  samp->SetAxisMagnificationFactor(0, xratio);
  samp->SetAxisMagnificationFactor(1, yratio);
  samp->SetAxisMagnificationFactor(2, zratio);

xratio and yratio are about 2.0916, and zratio is exactly 2.

Any ideas?
-Bill Leue
William M. Leue
GE Global Research
M/S KWC-211
1 Research Circle
Schenectady, NY 12309
518-387-7210, 8*833-7210
leue at crd.ge.com

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