[vtkusers] problems with LookupTable

[Chr. Rossmanith]

Hi,

I think I have a relatively simple problem defining a lookup table for
an image but I'm not able to solve it  :-(


My testimage consists of 5 vertical stripes with grey levels 0, 63, 127,
191, 255. I'd like to create a lookup table converting the grey levels
to shades of red.

First I create a LUT and set some table values. I'd expect, that it is
enough to set those entries of the LUT, which are used later...

vtkLookupTable    lut
   lut   SetNumberOfTableValues 255
   lut   SetTableRange 0 255

   lut   SetTableValue 0 0.2 0 0 1
   lut   SetTableValue 63 0.4 0 0 1
   lut   SetTableValue 127 0.6 0 0 1
   lut   SetTableValue 191 0.8 0 0 1
   lut   SetTableValue 255 1.0 0 0 1


Next I read the image data and set up the rendering stuff...

vtkTIFFReader reader
  reader SetFileName ./test.tif

vtkRenderer ren1
vtkRenderWindow renWin
  renWin AddRenderer ren1
vtkRenderWindowInteractor iren
  iren SetRenderWindow renWin

vtkDataSetMapper dataMapper
    dataMapper SetInput [reader GetOutput]
    dataMapper SetLookupTable lut                                 <-
now the image could become coloured....

vtkActor dataActor
    dataActor SetMapper dataMapper

ren1 AddActor dataActor
    renWin SetSize 500 500

renWin Render


The image gets rendered but in shades of grey. Obviously I'm missing
something, but what?


The documentation of SetTableValue looks like

void vtkLookupTable::SetTableValue (
                             int indx,
                             float r,
                             float g,
                             float b,
                             float a = 1.0 )
<-  does this mean that a always has to be 1 or is it 1 if I don't
specify it



Thank you in advance,

Christina Rossmanith