Frosted glass very slow

[fraggle]

Hello,
what is the trick to create a fast render frosted glass?

Lowering the Refl.Glossiness increase the render time incredibly.

Thanks

[Morbid Angel]

Well, glossy refraction is one of the most expensive effects one can go for. There is a number of tricks to make it work, some times using just a matte pass and doing it in comp. You can first try just going refraction interpolation route. Though it wont work for animations.

[Morbid Angel]

Here is a quick test I did, the blur is done in nuke using a set of maps, including zdepth, since objects further from the glass will be blurred more.

[fraggle]

thanks,
I don't use nuke myself, but only basic photoshop tools. I will find a way to get it done. Thanks.

[Alain]

@fraggle
The z-depth pass does not give a correct result because it's depending from the cameraviewpoint. But the unsharpness of the objects behind frosted glass is pending from their distance to the glass and not to the distance of the cameraviewpoint.

@all
What other tricks are there to get correct, fast and clean (not grainy) renderings with frosted glass ?

Kind regards
Alain

[theedge]

I came across this plugin a few weeks ago : http://lastjedioutpost.ru/?l=en&p=ky_surfaceblur
It is supposed to blur objects as an effect. So extremely quickly. Unfortunately I haven't had time to install it and try it. Maybe it could work for you ?

[fraggle]

Thanks,
I'm trying to avoid plugin because I often carry the scene across several max version.
What is the best and fast practice to to it in post prod in the two case below:
- Frosted glass not visible in refraction
- Frosted glass visible in refraction

What about 2 render, one with full reflection and another one without reflection then mixed them in post prod before applying blur?

Thanks

[svetlozar.draganov]

Hello - your final question sounds a bit confusing - at first you are talking about frosted-glass behind another glass object but in the proposal bellow you mentioned about 2 passes with and without reflection ? Could you clarify what is the case (reflection/refraction)- a simple scene will illustrate it very clear.

Thank you very much in advance.