Diverging Log Lookup Table

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#1

This question is prompted from the MakeLUT function in the DisplacementPlot example:

https://kitware.github.io/vtk-examples/site/Cxx/VisualizationAlgorithms/DisplacementPlot/

The MakeLUT function shows how to generate LUT’s with diverging color schemes as described by Kenneth Moreland on his website (given on the example’s webpage).

Is there a way to create these diverging LUT’s using a vtkLogLookupTable?

I know that for scalars I could always take the log of the scalar and use a linear vtkLogLookupTable.

#2

Hi,

What are you getting? An error? Wrong colors or no rendering at all?

regards,

Paulo

#3

Hi Paulo,

I didn’t try it – yet. In looking at the code in MakeLUT, it didn’t appear that a log table would work.

I’m curious if anyone has diverging log tables working.

BK

#4

Hello,

Well, give it a shot and see what happens. :slightly_smiling_face:

best,

Paulo

#5

Will do. I should have tried it, but have been juggling too much – still am.

BK

#6

Well, I tweaked the displacement example that I mentioned before and the log LUT worked. At first there was the error:

vtkLookupTable.cxx:160 ERR| vtkLogLookupTable (0x1ee46f0): Bad table range for log scale: [-1, 1]

When I changed the range in the example, it worked and there was no error message. I need to check this on something more complex in the future. But, at least there is something.

BK

#7

The log function is undefied for negative arguments, thus the error.

#8

Yes, I knew that. I just didn’t see that the example was setting a definite range.