Stephen <mca### [at] aolcom> wrote:
> On 2/21/2017 10:59 PM, zhekai wrote:
> > Thanks for the reply. I did use sphere. But I am not sure if it is the same as
> > the "sky sphere". Here is my mini example, and I used "-W1920 -H1080 -A0.3 +UA"
>
> Your camera is looking at a white plane behind your spheres. That is one
> reason you are getting no transparency.
>
> Use a background colour with transparency set to 1

That should be it. Change from rgbt <1,1,1,0.2> to <1,1,1,1> and it's fully
transparent in the Alpha Channel.

Well, not completely true. Watch out for specular highlights from the lights,
and maybe reflections. Unless you need those as a backdrop. I forget what all
might cause unexpected results... shadows perhaps.

sky_sphere is like 'background', so I don't think those could be a problem
either way if those do get used, which you haven't there yet.

I checked your rendering in Internet Explorer after making the white plane
transparent and it shows the little color spheres against any background color
chosen for a web page.

Paintshop Pro also shows the Alpha Channel there. And is possible to use the
image again in POV-Ray if use_alpha keyword is added to its image_map.

Bob

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