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<P>James,</P>
<P> I noticed this behaviour also, just a week ago in fact. I dont know if it is new, or maybe always been that way. My interpretation was: if two points with low and high values were connected, the Red-Blue LUT resulted in shading from red to blue via purple, ie a mixture of red and blue. As though the interpolation takes a shortcut around the back making the LUT circular. I would much prefer it behaved as expected, ie non-circular. I suppose the same behaviour would be seen regardless of the colour range, I was actually using a Blue (low values) to Red (high values) LUT.</P>
<P>Anyone out there have any ideas on how to remedy this?</P>
<P> Dave<BR><BR></P></DIV>
<DIV></DIV>
<DIV></DIV>>From: James Perry <PERRYJ@SIMMETRIX.COM>
<DIV></DIV>>To: vtkusers@public.kitware.com
<DIV></DIV>>Subject: [vtkusers] Strange Color Interpolation
<DIV></DIV>>Date: Thu, 18 Oct 2001 18:22:16 -0400
<DIV></DIV>>
<DIV></DIV>>Hello fellow VTK users,
<DIV></DIV>>
<DIV></DIV>> Attached is a very small image (disp.jpg) of a simple finite element
<DIV></DIV>>analysis done on a single-hexagonal cell. The VTK script is attached
<DIV></DIV>>(really_simple.tcl, for the data in disp_hex.vtk). We can't understand why the
<DIV></DIV>>colors are being interpolated the way they are, the scalar bar in the figure
<DIV></DIV>>uses the same lookup table as the mapper used for the hex actor. In fact,
<DIV></DIV>>towards the middle of the color gradient is a purple-ish color that isn't even
<DIV></DIV>>represented in the color range on the scalar bar. For the solution, we'd expect
<DIV></DIV>>to see a linear interpolation from the value 0 to 1 in the y-direction (in the
<DIV></DIV>>direction of the color gradient), similar to that shown on the scalar bar.
<DIV></DIV>> We have tried this problem using tetrahedral elements, and output a vtk file
<DIV></DIV>>for cell type 10, and obtain the same colors shown in the attached figure. In
<DIV></DIV>>fact, we have even used cell type 9 (VTK_QUAD) on the 6 surfaces with the same
<DIV></DIV>>vector data in disp_hex.vtk, yet we obtain the same results as shown in the
<DIV></DIV>>attached figure. We are running vtk 3.2.
<DIV></DIV>> If someone could explain why the colors are interpolated this way, and
<DIV></DIV>>possibly how we can get the correct color-mapping (the linear interpolation as
<DIV></DIV>>shown in the scalar bar), we would certainly appreciate any suggestions.
<DIV></DIV>>
<DIV></DIV>>Thank you,
<DIV></DIV>>Jim Perry
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<DIV></DIV>><< disp.jpeg >>
<DIV></DIV>><< really_simple.tcl >>
<DIV></DIV>><< disp_hex.vtk >>
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