Glass / refraction effecting alpha channel, even when theres more geometry behind

[felixsebastian]

yeah not sure why but seemingly v-ray can't tell that theres more behind the glasses and that even though its not affecting the alpha theres plenty behind it that should

there is a railing behind the window as well and thats getting chopped up too because of the glass in front

this is really making me uneasy pls help

also the reflections in the windows don't stand out really, am i missing something ?

Edited July 29, 2015 by felixsebastian

[Chris MacDonald]

We're going to need more than a screenshot of the alpha channel if we're going to help with reflections?

[felixsebastian]

yes, sorry. actually i've fixed the alpha problem but i'm still having some trouble with compositing which i haven't done much of.. im working in after effects and the windows are only semi transparent above the horizon.. i'm using a dome light with a hdri and an environment map, which doesn't render obviously but for some reason i'm still getting some thing above the horizon.. also theres no reflections in the windows, do i need to do a separate reflection pass ? thanks for your help

[felixsebastian]

also what do people normally do about the white lines you get around the edges, its not as bad at high res but its still a problem for me sometimes

[Corey Beaulieu]

Are you rendering with anything other than a Black Background and then compositing a different image into the view in PS?

 

It just looks like alpha fringing.

[felixsebastian]

it renders with the hdri environment map, should that happen though ? i feel like you should be able to adjust the alpha blur/falloff around the edges

[Chris MacDonald]

yes, sorry. actually i've fixed the alpha problem but i'm still having some trouble with compositing which i haven't done much of.. im working in after effects and the windows are only semi transparent above the horizon.. i'm using a dome light with a hdri and an environment map, which doesn't render obviously but for some reason i'm still getting some thing above the horizon.. also theres no reflections in the windows, do i need to do a separate reflection pass ? thanks for your help

[ATTACH=CONFIG]53384[/ATTACH]

 

Right click the glass object(s) and go to VRay Properties and set their alpha contribution to -1, this should make them black on the alpha.

 

As for your reflections; you don't really see reflections from inside a building during daytime unless the lighting inside is as/i] bright as it is outside. Use some reference photography. Though if you do want to go down the non-photoreal route then increasing the IOR will make your glass more reflective.

[felixsebastian]

Yeah, one problem with that is that there is a railing behind which i will lose.. and with the reflections i want to do a night scene and i'm losing most of the reflections still but strangely not all of it its still just visible over a black background

[Chris MacDonald]

What is your glass material setup?

[felixsebastian]

thanks, here it is

[Chris MacDonald]

Try increasing the IOR, it'll increase the glass's reflectivity.

[D C]

Make sure the 'Affect channels' drop down is set to 'All channels' on your refraction setup.

[Corey Beaulieu]

Make sure the 'Affect channels' drop down is set to 'All channels' on your refraction setup.

 

I would actually not use "Affect All Channels" as a rule.... To be fare, this may wok in this instance, but generally speaking this can "double" the brightness of objects behind glass when compositing as the difference between Color+Alp[ha and All Channels is that Vray considers its elements as channels and will record the additional information is reflection and specular passes among others.

 

Just something to be aware of.

 

Edit:

 

You can see this effect if you rebuild the RGB pass using only elements in 32 bit. You will not get the proper result with "Affect All Channels" ticked, but will with "Color+Alpha."

[D C]

I would actually not use "Affect All Channels" as a rule.... To be fare, this may wok in this instance, but generally speaking this can "double" the brightness of objects behind glass when compositing as the difference between Color+Alp[ha and All Channels is that Vray considers its elements as channels and will record the additional information is reflection and specular passes among others.

 

Just something to be aware of.

 

Edit:

 

You can see this effect if you rebuild the RGB pass using only elements in 32 bit. You will not get the proper result with "Affect All Channels" ticked, but will with "Color+Alpha."

 

Just going back to this....

 

We've recently started using render elements and now have the exact problem you state above. This was never a issue before using a raw render.

 

I was under the impression that in order to see through glass onto a backplate (sky/clouds etc) the 'All channels' drop down needed to be selected on the refraction setup. Whilst using 'Colour+Alpha' does resolve the glass issue compositing the render elements, the alpha on the glass isn't the same as the beauty pass.

 

If there's a way around this I'd be extremely grateful to hear about it.

 

Many thanks!

Edited August 12, 2015 by Dan.Corris

[D C]

Test scene to illustrate. Note the difference in glass opacity between the sphere and right hand cube.

 

Edited August 12, 2015 by Dan.Corris
...

[D C]

We figured it out.

 

For future reference if anyone runs into a similar issue - Colour Mapping 'expert mode' - drop down box - 'Don't apply anything' in Vray 3.10.01