How to get the alpha right when using glass ?

[kiwimage]

hello,

I have a little problem that I wanted to discuss.

This is my render, in png, and that's ok for a light background.


Alpha channel looks like this : pure white, pure black...



As you can see, the alpha channel isn't right, there should be semi-transparent areas in the glass.

Is there a way to achieve what i want or is it a limitation of Octane ?

[rosch]

Hey Guys,
I have exactly the same problem right now. Tried pretty much all the setting involving alpha/environment. Clueless right now. Please Help

[aoktar]

use some fake ways. With opacity and falloff

[kiwimage]

Thanks for your response, I guess I would know how to fake the effect and I don't really need this for this particular project, since I'll be integrating this on a light background, I was just being curious on how to do this.

I guess you can't do much about it Aoktar, as a plugin developper, but i have to say it's a very bad surprise that OctaneRender, wich can achieve amazing things really fast, won't be able to render a glass of water with acurate alpha.

[gabrielefx]

I requested this feature 3 years ago
Probably in Otoy think that we are hobbyists.

[slepy8]

One of few reasons Octane Render is still not Production Ready.

But we should stay positive. Lots of changes lately. Maybe this one is on schedule

[mbetke]

I use a lower opacity value on the glass.
Up to 0.25 if needed.

[abstrax]

Try using the material "glass fake falloff" from the LiveDB:

Of course, it doesn't have refraction, but refraction can't be captured with a simple alpha channel anyway.

[kiwimage]

OK I've been playing around and came up with the result above, which combines transparency and a mix of fake and real refractions.

Here are the steps I followed.

1/ render a RGBA picture with the material "glass fake falloff", as advised by Abstrax (on the glass and liquid)
2/ make another render with regular physically correct glass.
3/ In Photoshop, apply the alpha of the first render to the second render.
4/ Tweak the levels of this alpha channel (bump the contrast a bit, depending on what you want)
5 /Make a Background in photoshop
6/ The refraction of the letters behind the serynge are Photoshop cheating, with alpha masks and a contraction filter on the letters.

It's manageable to cheat the eye in still images, but this process would be very very tough to achieve in animation (the refraction part of it)

[abstrax]

OK I've been playing around and came up with the result above, which combines transparency and a mix of fake and real refractions.

Here are the steps I followed.

1/ render a RGBA picture with the material "glass fake falloff", as advised by Abstrax (on the glass and liquid)
2/ make another render with regular physically correct glass.
3/ In Photoshop, apply the alpha of the first render to the second render.
4/ Tweak the levels of this alpha channel (bump the contrast a bit, depending on what you want)
5 /Make a Background in photoshop
6/ The refraction of the letters behind the serynge are Photoshop cheating, with alpha masks and a contraction filter on the letters.

It's manageable to cheat the eye in still images, but this process would be very very tough to achieve in animation (the refraction part of it)

It's not possible to do this automatically in post, because of step 6). If you want correct refractions you need to do the compositing in the rendering.