[Paraview] How to do volume rendering of image data?

[Steve Huntley]

The alpha values are in the lookup table.  Each line in the lookup table 
has four values: red, green, blue, opacity.  That's my understanding of 
a properly formatted lookup table in a vtk file.  I used: 
http://www.vtk.org/VTK/img/file-formats.pdf as a reference.

All opacity values are set to 1.0, except black which is set to 0.0.  
But when the file is opened in ParaView and volume representation 
chosen, it appears that not only the opacity values but the entire 
lookup table is ignored.

Assuming homogeneous opacity is the furthest thing from what I want.  I 
want to find a way to control opacity without destroying the colors in 
my image data file via mapping to the default color scale.  Getting away 
from homogeneous opacity is what I can't figure out how to do.  I want 
to see through the black background pixels to see the full color pixels 
of my 3D object.

--Steve H.

Moreland, Kenneth wrote:
> The data you sent has RGB values but no alpha values that I can see. 
>  Volume rendering is generally not very useful if you do not have some 
> representation of opacity.  If you were to assume a homogeneous 
> opacity, you would get a mostly black box with a blob of color in the 
> middle if you looked hard enough.  How exactly you expect the volume 
> renderer to behave?
>
> -Ken