[vtkusers] Another question on vtkLookupTable..!

[David Gobbi]

Hi Rakesh,

You can't change the fact that the binsize is uniform.  But I don't
understand why you don't just repeat the colors:

10     ==== (1.0, 0.0, 0.0)
20     ==== (1.0, 0.5, 0.0)
30     ==== (1.0, 1.0, 0.0)
40     ==== (0.5, 1.0, 0.0)
50     ==== (0.0, 1.0, 0.0)
60     ==== (0.0, 1.0, 0.5)
70     ==== (0.0, 1.0, 0.5)
80     ==== (0.0, 1.0, 1.0)
90     ==== (0.0, 1.0, 1.0)
100   ==== (0.0, 0.5, 1.0)
110   ==== (0.0, 0.0, 1.0)
... ditto for 120 to 190 ...
200   ==== (0.0, 0.0, 1.0)

 - David

On Tue, Feb 22, 2011 at 12:58 AM, rakesh patil
<prakeshofficial at gmail.com> wrote:
> Hey David,
>
> Thanks for that explanation. Now it's bit clear about how lookup table
> works. But in my case, I guess, binsize is not uniform. Let me put it in
> this form
>
> 10     ==== (1.0, 0.0, 0.0)
> 20     ==== (1.0, 0.5, 0.0)
> 30     ==== (1.0, 1.0, 0.0)
> 40     ==== (0.5, 1.0, 0.0)
> 50     ==== (0.0, 1.0, 0.0)
> 60     ==== (0.0, 1.0, 0.5)
> 80     ==== (0.0, 1.0, 1.0)
> 100   ==== (0.0, 0.5, 1.0)
> 200   ==== (0.0, 0.0, 1.0)
>
> in this case, bin size is not equal to (max-min)/n. I mean, lookup table
> might calculate it like that. But If dont want in that way, then what
> changes I have to do to implement? May be I am wrong in understanding the
> meaning of binsize. Please correct me if I'm wrong.
>
> Thanks
>
> Regards
> Rakesh Patil
>
> On Tue, Feb 22, 2011 at 11:58 AM, David Gobbi <david.gobbi at gmail.com> wrote:
>>
>> 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
>
>