[vtkusers] Another question on vtkLookupTable..!

[David Gobbi]

Hi Rakesh,

The way that the lookup table maps values to colors is as follows:
If the Range of the table is set to [min,max] and the number of colors
in the table is n, then the equation that maps a value "v" to an
index "i" is:

 i = floor((v - min)*n/(max - min))

The bin size is uniform and equal to (max - min)/n.  Values in the
range [min, min + binsize] go into the first bin (and values less than
min also go into the first bin).

Since the bins are uniform in size, you will need a table with 20 values
and a binsize of 10, and some of the colors will have to be repeated.
Use lut->SetTableRange(0.5, 200.5), where the ".5" is for rounding.

 - David


On Mon, Feb 21, 2011 at 10:35 PM, rakesh patil
<prakeshofficial at gmail.com> wrote:
> Hello,
>
> I have to display contours, for a given range, by mapping values to colours.
> i.e. Consider I need to display contours between 1 and 200.
>
> I use the lookuptable as follows
>
> vtkSmartPointer<vtkLookupTable> lut =
> vtkSmartPointer<vtkLookupTable>::New();
> lut->SetNumberOfTableValues(9);
> lut->SetTableValue(0, 1.00, 0.00, 0.00);
> lut->SetTableValue(1, 1.00, 0.50, 0.00);
> lut->SetTableValue(2, 1.00, 1.00, 0.00);
> lut->SetTableValue(3, 0.50, 1.00, 0.00);
> lut->SetTableValue(4, 0.00, 1.00, 0.00);
> lut->SetTableValue(5, 0.00, 1.00, 0.50);
> lut->SetTableValue(6, 0.00, 1.00, 1.00);
> lut->SetTableValue(7, 0.00, 0.50, 1.00);
> lut->SetTableValue(8, 0.00, 0.00, 1.00);
> lut->Build();
> Now suppose I want the output like show below
>
> 01 - 10     ==== (1.0, 0.0, 0.0)
> 11 - 20     ==== (1.0, 0.5, 0.0)
> 21 - 30     ==== (1.0, 1.0, 0.0)
> 31 - 40     ==== (0.5, 1.0, 0.0)
> 41 - 50     ==== (0.0, 1.0, 0.0)
> 51 - 60     ==== (0.0, 1.0, 0.5)
> 61 - 80     ==== (0.0, 1.0, 1.0)
> 81 - 100    ==== (0.0, 0.5, 1.0)
> 101 - 200  ==== (0.0, 0.0, 1.0)
>
> How can this be done.?? So that the values supplied should be mapped to the
> corresponding colour and should be displayed.
>
> Thanks
>
> Regards
> Rakesh Patil