[vtkusers] Volume Rendering Problem

[Kischell, Eric R.]

Timur,
Thank you for your posting.
I have also encountered similar VTK limitations--
http://public.kitware.com/pipermail/vtkusers/2011-November/120265.html

I'm currently prototyping an ITK alternative based on
itk::MaximumProjectionImageFilter.
I can share it with you after I make some refinements.
Regards,
e.-
===

-----Original Message-----
From: vtkusers-bounces at vtk.org [mailto:vtkusers-bounces at vtk.org] On
Behalf Of Timur Aksoy
Sent: Wednesday, December 14, 2011 8:36 AM
To: vtkusers at vtk.org
Subject: [vtkusers] Volume Rendering Problem

Dear VTK users,
I have been a user of VTK for one year and stuck in a problem about 
Volume Rendering.
Problem:
I have a Signed Short Distance Volume of an object where object's inside

has negative, outside has positive and boundaries have 0 level set 
scalar values.  I want to project this volume with Minimum Intensity 
Projection onto an image plane in off screen mode.  And then I want to 
convert the resulting render window into vtkimage data and finally to 
ITK image data for further processing.  That is the only way I can 
obtain MinIP in ITK, I believe.     However I want to preserve the 
negative values inside and 0-level set on the boundaries on 2D rendered 
image.  I have tried FixedPointRayCastVolume Mapper since it is the only

Ray caster that accepts signed data types.  However in the setColor 
method of Volume Property, I can map volume intensities only to positive

RGB values with color transfer function.  Therefore the negative values 
and 0-levelset are not preserved after rendering.   I have tried 
vtkPiecewise Function for gray level mapping to both negative and 
positive  intensities in SetColor method, but it did not produce an 
acceptable rendered image.   Is there a way I can project the negative 
intensities of the volume with MinIP and still get negative intensities 
in the render window.   I have also tried other VTK raycast functions 
but did not work.
The second related problem I have is that when I use vtkPiecewise 
Function to map gray intensity values to positive scalars in SetColor 
method, the rendered image is still unacceptable.  I was wondering why I

cannot map volume color with vtkPiecewise Function.
Last error I get is that I cannot export VTK image data to signed short 
ITK image type.  I could export to unsigned short image type in ITK  
though.
My related code is with vtkPiecewise Function is attached.
Thank you for your time.
Sincerely,
Timur Aksoy