[vtkusers] Piecewise Function for Volume Rendering

[anast.jm at pg.com]

Yuan,

This is always a tough one. Every volume is different it seems so defining the
values can take some work. Most programs use interactive adjustment of the point
position and value to get it right, however there is not a standard "interactor"
implemented in vtk. I've always wished for a vtkTransferFunctionWidget! In tcl
you can hook up some simple sliders to change the values but its a bit of a pain
and not as flexible as sliding points and values around on a graph. I've had in
the back of my mind to build an interface in tcl by picking/moving points in a
2D render window but haven't got to it yet. To see a nice implementation of
interactivity in the setup of the opacity, color and gradient transfer functions
download the trial version of VolView from the Kitware web site.

Certainly examining the histogram range and shape could lead to to some good
estimates of the transfer functions but its typically non-linear and would take
some extra work to get it just right. (I think transfer functions are like art,
a matter of taste to some)...certainly possible though. It all really depends on
what you want to emphasize, which is why this is often done
interactively......john




                                                                
 Internet Mail Message                                          
 Received from host:      public.kitware.com                    
 [24.97.130.19]                                                 
                                                                


From: "Yuan Jin" <yjin76 at hotmail.com>@public.kitware.com on 08/22/2002 01:47 AM
GMT
                                                                                              
         "Yuan Jin" <yjin76 at hotmail.com>           To:   vtkusers at public.kitware.com          
                     @public.kitware.com           Cc:    (bcc: John Anast-JM/PGI)            
                                           Subject:      [vtkusers] Piecewise Function for    
                                                Volume Rendering                              
                                Sent by:                                                      
       vtkusers-admin at public.kitware.com                                                      
                     08/21/2002 09:47 PM                                                      
                                                                                              
                                                                                              




Hi all,

Does anyone have experience in setting up the piecewise function for the
volume rendering? ie. which points should be added to the piecewise
function? Is the histogram for the 3D image helpful?

For instance, in the example: VolCutKnee.py

white_tfun = vtkPiecewiseFunction()
white_tfun.AddPoint(0,1.0)
white_tfun.AddPoint(255,1.0)
tfun = vtkPiecewiseFunction()
tfun.AddPoint(70,0.0)
tfun.AddPoint(80,1.0)
vol_prop = vtkVolumeProperty()
vol_prop.SetColor(white_tfun)
vol_prop.SetScalarOpacity(tfun)

How to find out tfun.AddPoint(70,0.0) and tfun.AddPoint(80,1.0) ?

Thanks a lot,

Yuan



_________________________________________________________________
MSN Photos is the easiest way to share and print your photos:
http://photos.msn.com/support/worldwide.aspx

_______________________________________________
This is the private VTK discussion list.
Please keep messages on-topic. Check the FAQ at: <
http://public.kitware.com/cgi-bin/vtkfaq>
Follow this link to subscribe/unsubscribe:
http://public.kitware.com/mailman/listinfo/vtkusers