William Tracy wrote:

> So it just disappears into the background. (If you render with a
> different background color, just use the same color as the background,
> and use ambient 1.) Then, in your image editing program, grab the "magic
> wand" tool, select the background area, and delete it. (The exact steps
> vary depending on what software you use.)
>
> Basically, instead of rendering to an image with an alpha channel, just
> cut out the background manually in Photoshop or whatever.

Yes, thank you. Your suggestion seems to be the best working technique for
now - turn off any reflection for the object which need to be cleared and
delete it later in some image editing software. This way will be not
completely automatic (as I initially wanted), still possible.

Tim Attwood wrote:
> >> You can then compose your object layers seperately.
> >
> > Sorry, I didn't get your idea.
>
> If the objects are separate you could render them separately,
> but I now see from your example that they aren't really
> separate.  With the overlapping rings which image would
> be on top?  The way that you envision it either of the rings
> might be.  In order to cut up your object you will need to
> resort to further CSG or use clipped_by.

Thank you very much for explanation and example, although I'm not sure that
it will work in general case. It would be very complex to split objects and
calculate clipping planes. I need to process the scene of about dozen
objects of complex shape to make a set of images with picture of each
single object only. All objects are not intersected in terms of CSG. It is
2D image where their projections are overlapped.

Actually, the only thing which I needed, is to instruct POV-Ray to replace
every visible pixel of selected object(s) with alpha-transparent one. And I
still can not find the way how to do it.

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