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<DIV>Hi David,</DIV>
<DIV>Thanks for your help. I have been able to fix the colour-spot problem by clamping the scalar values as you suggested. However, I am still getting black scalars on the boundaries at high levels of decimation (2**7 or more) so I will look further into it.</DIV>
<DIV>Nigel</DIV>
<DIV> </DIV>
<DIV><BR>>>> David Gobbi <david.gobbi@gmail.com> 18/03/2013 22:09 >>><BR>Hi Nigel,<BR><BR>I'm certain that you are correct, it is an overflow bug. I looked at<BR>vtkQuadricDecimation::SetPointAttributeArray() and it calls the<BR>following vtkDataArray method for each component (in your case,<BR>for R, G, B):<BR><BR>scalars->SetComponent(pointId, i, v);<BR><BR>SetComponent() just calls static_cast, it does no clamping. So<BR>overflows are likely to occur.<BR><BR>Ideally vtkQuadricDecimation::SetPointAttributeArray() should call<BR>GetDataTypeMin() and GetDataTypeMax() on the scalar array and<BR>clamp the value to this range before inserting it into the array. If you<BR>are able to fix the code, we can get your fix into VTK 5.10.2/VTK 6.0.<BR><BR>- David<BR><BR><BR>On Mon, Mar 18, 2013 at 11:53 AM, Nigel Mcfarlane<BR><Nigel.Mcfarlane@beds.ac.uk> wrote:<BR>> I am using vtkQuadricDecimation to reduce a triangular mesh with<BR>> color_scalar attributes. After decimation, I get single-point errors in the<BR>> colors which look as if they might be an overflow error in the color<BR>> interpolation. If the decimation is repeated recursively, the errors<BR>> accumulate and start to form on the boundary points, turning the mesh edges<BR>> black. The errors appear when there is high-frequency noise in the color<BR>> pattern; if the color is smooth there is no problem. It does not seem to<BR>> depend on the topography of the mesh. The color scalars are unsigned char<BR>> with 3 components. AttributeErrorMetric is On, NormalsAttribute is Off, and<BR>> the TargetReduction is 0.5. I am using VTK5.10, but it also happens in<BR>> VTK4. Is this a known problem, and if so is there anything I can do about<BR>> it?<BR>> Thank you<BR>> Nigel McFarlane<BR>> University of Bedfordshire, UK<BR></DIV></BODY></HTML>