How to turn off interpolation for discrete label segmentation image?

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1

I’m rendering a segmentation overlay with discrete labels 1, 2, 4 and background 0 in the image. And looks like I have to pick interpolation type between Linear and Nearest. Either interpolation type renders the data incorrectly, with a thin layer of interpolated “labels” surrounding the structure.

image

Is there a way to turn off interpolation for label image rendering? Or should I use some other ways rather than ImageSlice + ImageMapper?

Thanks!

2

What does your lookup table look like? Does it have defined colors for each of your label values?

3

Thanks for the reply!

Just want to confirm that the Nearest Neighbor Interpolation is not taking average of the neighboring voxels, right? I’m asking because now I suspect the issue might be caused by the incorrect interpolation in the downsampling from the upstream data pipeline (not vtk-js related).

Here’s my lut configuration. The original segmentation should only have label 4. But now 1, 2, 3, are also showing up at the border.

image

const seg_lut = vtkColorTransferFunction.newInstance();
seg_lut.setIndexedLookup(true);
seg_lut.setMappingRange(0, 4);
seg_lut.addRGBPoint(0, 0, 0, 0);
seg_lut.addRGBPoint(1, 1, 0, 0);
seg_lut.addRGBPoint(2, 0, 1, 0);
seg_lut.addRGBPoint(3, 0, 0, 1);
seg_lut.addRGBPoint(4, 1, 0.87, 0.74);

seg_actor.getProperty().setRGBTransferFunction(0, seg_lut);
seg_actor.getProperty().setColorLevel(2);
seg_actor.getProperty().setColorWindow(4);

const ofun = vtkPiecewiseFunction.newInstance();
ofun.addPoint(0, 0);
ofun.addPoint(1, 0.8);

seg_actor.getProperty().setScalarOpacity(ofun);
seg_actor.getProperty().setInterpolationTypeToNearest();
4

Nearest should not be taking averages of neighbors, so I would also double check that you only have a label value of 4 in the final labelmap.

5

It was my data issue. Thanks for confirming about the interpolation type!