[Paraview] Problems positioning image slices in 3D

[Richard Beare]

Hi,
I have a set of slices extracted from a 3D volume. These slices have
been processed with image magick to produce a transparent background
and a colour overlay. I can load several into paraview, feed them
through the image to pointset filter and then transform them so that
they are in a 3D stack with space between each slice. The problem is
that the transparent background isn't properly transparent. Depending
on the angle I view at, the background definitely obscures slices
behind it. It seems arbitrary whether this occurs when viewing from
above or below (note that I don't mean it changes as I'm viewing a
given data set, but if I load in an equivalent dataset at the same
time, it is likely to behave differently to the first. It almost
appears as though the front face can be either side of the image. I'm
finding it tough to describe without a screenshot.

Does this ring any bells with anyone? Is it possible to flip the
direction of front? Is there some other way I should read this data
(currently starting as png with an alpha channel). One option I've
considered is deleting the transparent points after conversion to a
point set, but I can't see how to do that.

All advice welcome.

Thanks