Particle alpha woes 2005-05-15 - By Alan Jones
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Hi Andy,
Perhaps you could use a lens shader to adjust the alpha? Hopefully
with it still being in floating point at that stage it won't have lost
the detail you're after.
Just get a fast lens effects or whatever it's called (something that
does next to nothing) and run it through a color math node.
Cheers,
Alan.
On 5/15/05, Andy Jones <andy@(protected)> wrote:
> Hey,
>
> Has anyone had problems getting proper alpha channels on particles? I
> just inherited a bunch of scenes from some artists we contracted some
> particle work to, and the renders don't give proper alpha channels.
> Instead of giving nice gradients as the particle effect fades off at the
> edges, I get mostly white balls, with a short little gradient on the
> outside edges. The straight color channels also don't behave correctly,
> as there are traces of black left in them from the background, as you
> would expect from unmultiplying an incorrect alpha. I've actually
> encountered this problem before myself, and haven't been able to find a
> good workaround. I did just find a really crazy work-around, by
> sticking a color math basic node between the particle renderer node and
> the cloud material volume input. The color math node is set to multiply
> the alpha channel by .1. The result is that everything works
> correctly. Also strange is that if I multiply by a value less than .1,
> nothing changes, but a value like .2 produces an intermediate result.
> And the result isn't a grey alpha like you might think -- instead it's
> just a normal black to white alpha, but with a much better gradient. I
> rendered this out and compared the result composited onto a black
> background an got the exact same result as if I had rendered the
> particles premultiplied on black. It's as though the particle renderer
> accidentally multiplies its alphas by a factor of 10.
>
> The only drawback to my workaround is that using the color math node
> seems to disallow having particles from multiple clouds in the same
> particle volume. So, I have two basic smoke trails being emitted from
> rocket engines, and without the color math node, they both render (but
> with a screwy alpha channel). Then, when I add the color math node,
> particles don't render in a box-shaped area between the two particles
> clouds.
>
> Does anyone have an explanation for this and/or a better workaround?
>
> -Andy
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