[vtkusers] vtkLookupTable... cannot manually create table for red and blue values

[Luca Pamparana]

Hi Obada,

Thanks for replying!

I actually have those calls and the code for constructing the red color map
is the same as for the green and blue... I just have no idea why it would do
this!

Would someone happen to know how I can use the HSV values for setting the
color map?

I am currently doing...

vtkLookupTable * lut = vtkLookupTable::New();
lut->SetHueRange( 2.0/3.0, 2.0/3.0);
lut->SetSaturationRange(0.0, 1.0);
lut->SetValueRange(0.0, 1.0);
lut->SetAlphaRange( 1.0, 1.0);
lut->SetNumberOfColors(256);
lut->SetTableRange(range[0], range[1]);
lut->Build();

What I want is a pure blue mapping. The resulting image is a bit of a weird
blue color.

On 9/4/06, Obada Mahdi <omahdi at gmx.de> wrote:
>
> Hi Luca,
>
> here are some suggestions:
>
> On 04.09.2006, at 11:55, Luca Pamparana wrote:
> > Someone please help me with this vtkLookupTable problem. I was
> > trying all weekend but cannot figure out what I am doing wrong!
> >
> > I am constructing a vtkLookupTable manually as follows:
> >
> >
> > double * range = reader->GetOutput()->GetScalarRange();
>
> Just to be sure: Is the output of `reader' up-to-date?  Try a
> "reader->Update()", at least before using `range' below.
>
> > vtkLookupTable * greenMap = vtkLookupTable::New();
> > greenMap->SetNumberOfTableValues(256);
> > greenMap->Build();
> >
> [calls to greenMap->SetTableValue()]
> > greenMap->SetAlphaRange(1.0,1.0);
> >
> > greenMap->SetTableRange(range[0], range[1]);
>
> From the documentation and source code it seems that values provided by
> SetAlphaRange() etc. are used when constructing the lookup table in
> vtkLookupTable::Build() (based on linear ramps), so they should
> probably go
> before the call to Build().
>
>
> Try doing something like this:
>
> | double* range;
> | vtkLookupTable* greenMap;
> |
> | reader->Update();
> | range = reader->GetOutput()->GetScalarRange();
> | greenMap = vtkLookupTable::New();
> | greenMap->SetNumberOfTableValues(256);
> | greenMap->SetAlphaRange(1.0, 1.0);
> | greenMap->SetTableRange(range[0], range[1]);
> | greenMap->Build();
> |
> | [for loop with calls to SetTableValue()]
>
> > I see nothing but a black screen. However, when I generate the
> > table for
> > red... like:
> [...]
> > then my image is mapped correctly to red values...
> No idea about this one.
>
> I have no experience actually using vtkLookupTable; if the
> suggestions above
> do not help, I could try and have a closer look (maybe the output of
> greenMap->PrintSelf(cerr, vtkIndent(0))
> can help in understanding what goes wrong, and whether the lookup
> table is
> the problem after all).
>
>
> Regards
>
> Obada
>
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