Alpha image (PNG) with bloom effect

[portnicki]

Hi,

I need to render a firefly bug. This is for a website and it has to be a transparent PNG.
I know I can render out a beauty pass and a post-process pass and composite them in photosop/After Effects. Problem is - I won't be compositing this onto any other background.

Is there a way to render out a beauty pass with bloom on transparent background. If not - what would be a way to composit this in Photoshop/AE in such a way that I can export a PNG with my object and the bloom effect with transparency

I found pretty 'meh' workaround. I can use the bloom pass as a mask for a color solid in photoshop. The problem is - I'm loosing all of the subtleties of the light. It no longer has different temperatures/color depending on the distance from it's source.
That's not the way this should be done but I can't think of any other way.

I'm on modo 13 and Octane 4.04

[bepeg4d]

Hi,
the workaround is to render the beauty with Alpha Channel active, but without Post-Effect.
Then set the Kernel to Max Samples = 32/64, and render again the scene, saving only the Post Effect pass, with Alpha Channel disabled.
In this way, you can compose the Post Effect pass in Linear/Add mode in post.

ciao Beppe

[portnicki]

Hi,
the workaround is to render the beauty with Alpha Channel active, but without Post-Effect.
Then set the Kernel to Max Samples = 32/64, and render again the scene, saving only the Post Effect pass, with Alpha Channel disabled.
In this way, you can compose the Post Effect pass in Linear/Add mode in post.

ciao Beppe

Hi Beppe, thank for your reply.
Unfortunately this doesn't work for me.
The resulting image still doesn't have an alpha channel.
I can not save a transparent PNG with this technique.

If I'd be using this image on top of some background in photoshop/After Effets, then yes, this would work. But I'm not compositing this on top of some other layers of footage. I need a transparent background upon exporting this to a PNG file.

Any other ideas?

[bepeg4d]

I see, but you can load the Post effect pass in an Alpha Channel:

And use it to mask the Post Effect pass itself:

ciao Beppe

[portnicki]

hey again beppe,

thanks for your reply.
I didn't think of using the post-process output as a mask for itself. That's clever.

... though that's still kind of a 'hack' right? because this technique doesn't produce the exact same effect as rendering the same object with background turned on.

Here's a comparison with this technique (on the left - the resulting PNG overlayed on a black background) and a regular render on black background (render out straight from octane, no compositing). The bloom is stronger I guess and overall better looking.
Surely there's a way to tweak the contrast of the mask for the post-process layer in photoshop but I don't think the exact same effect can be achieved.

I guess that's as far as we can go with that (?).

Thanks again beppe!