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View Full Version : FPrime Refraction / Alpha Channel Bug


Matt
02-20-2006, 11:38 AM
Hi All!

I'm pretty sure this may have been posted before, but I couldn't find it. I was doing some renders for a client, that had some transparent areas with refraction on. The original background had a dark 'infinity wall' but after seeing the final render the client wanted a light background. No problem! I'd saved the alpha channel within the render and set the background object's surface to 'Unaffacted by Surface' while all foreground objects were on 'Surface Opacity'.

However, when I came to removing the background with the alpha channel it was incorrect. It was like the refraction just hadn't been calculated! See the attached test image to see what I mean.

I had to render out some patches of the affected areas using LightWave, even turned off reflections and shadows it still took a while (render size was a massive 9933 x 7016, basically A1 @ 300dpi).

Anyone else had this? Is Worley aware of this? Quite a fundamental cockup if you ask me!

Matt

Panikos
02-20-2006, 11:48 AM
Is this out of the FPrime renderer or Previewer ?
Renderer is the suggested way of producing final results.

Have you checked the Alpha Switch on FPrime renderer ?

Other that these, LW has a bug in the refraction, I reported it to Mr Worley long time ago.

Matt
02-20-2006, 02:09 PM
Everything raytraced is turned on, this was a render to disk (previewer doesn't let you see any other channels anyway!) and the alpha switch is definately on.

Thing is, on the normal render refraction is okay, just refraction in the alpha is wrong. The LightWave one is the correct one, so I'm more inclined to think this is a bug ini FPrime, unless anyone else can prove otherwise!

ColinCohen
02-20-2006, 03:17 PM
If you have DF, you may be able to transfer the alpha channel from LW image to the FPrime image.

Matt
03-04-2006, 01:39 PM
Well, I just used Photoshop! Much easier!!!

I had a reply from Worley ...

"Hi Matt,

It's not a bug really, but a design decision made after a *lot of heated* debate during FPrime beta testing. LW 7.5 and LW 8.0 rendered refracted alpha's as solid white, so matching LW behavior at the time wasn't the goal of FPrime. Both FPrime's and LW's method seem to have their own set of problems when compositing so we're not sure what the best solution is.
Either way is not technically difficult so perhaps we'll see some more options available in the next FPrime update.

-Worley Labs"