[vtkusers] A bug in Above/BelowRangeColor mapping?

[marcin.krotkiewski]

Hi,

I think the behavior of UseBelowRangeColor in both VTK 8.1.1, and 
Parview 5.5 is wrong. As an example, I load a surface into Paraview, 
rescale the color range to point data (elevation in this case, fig. 
paraview.png), and enable the 'Use Below Range Color' checkbox. What you 
see is that part of the surface are colored with black (fig. 
paraview_wrong.png), although they are in fact within the automatically 
computed value range. So they should get the usual color from the lookup 
table.

I also observe wrong behavior when I color the surface by a constant 
value. In VTK, I set lower/upper bound on data values in vtkLookupTable 
to be the same. Say, my point data has value 50. I set the lookup table 
range to [60,60] and turn on Above/Below range color. Figure 
constant_wrong.png shows that my surface is colored with the in-range 
color, although it is below range. To get a correct coloring I need to 
spread the range a little bit, e.g., [60,61] (constant_below.png), or 
[40, 41] (constant_above.png). But even in this case we go back to the 
first problem: for point values that are on the edge of the range VTK 
uses out-of-range color (range [50,51], constant_extreme.png).

So the question is - is this behavior intended, and if so - how should I 
organize my color mapping and data ranges to get the expected behavior?

Regards,

Marcin Krotkiewski


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