Rendertime penalties for using additive mode within VrayBlendmtl

[rjohnson33]

In order to mitigate any slow down in render times when using the additive mode in the VrayBlendmtl is it worth sticking it in an override material that has a 'non-additive' version in for GI/reflection?
Does this limit the penalty in render time to the rendering of the object itself or are there still associated reductions in speed throughout the entire scene when using an additive material?

I'm scared by that hazard sign that pops up when choosing to use additive mode! Can't seem to generate the effect I want without it right now though so have to break the rules.

[vlado]

In order to mitigate any slow down in render times when using the additive mode in the VrayBlendmtl is it worth sticking it in an override material that has a 'non-additive' version in for GI/reflection?

You could do that, certainly. But it would be best to actually test if there is any slowdown.

Does this limit the penalty in render time to the rendering of the object itself or are there still associated reductions in speed throughout the entire scene when using an additive material?

Any slowdown is related to that material only; other parts of the scene are not affected.

I'm scared by that hazard sign that pops up when choosing to use additive mode! Can't seem to generate the effect I want without it right now though so have to break the rules.

That's alright, that's why we added the option in the first place

Best regards,
Vlado

[Morbid Angel]

If you are adding multiple layers, you can be smart about how you are mixing them and minimize your render time. For example do not have two very strong reflections adding on each other, this would increase your render time considerably and also make the overall physical accuracy of your scene. You can however add specular from one shader and reflection from another to a diffuse base, this would not cause much of a slow down. Being aware of things like that will make additive option usable. The worst case would be to have many reflective layers adding over each other. Generally speaking you never need this in the first place. So I would search for a solution outside of the additive option.

[Dariusz Makowski (Dadal)]

If you are adding multiple layers, you can be smart about how you are mixing them and minimize your render time. For example do not have two very strong reflections adding on each other, this would increase your render time considerably and also make the overall physical accuracy of your scene. You can however add specular from one shader and reflection from another to a diffuse base, this would not cause much of a slow down. Being aware of things like that will make additive option usable. The worst case would be to have many reflective layers adding over each other. Generally speaking you never need this in the first place. So I would search for a solution outside of the additive option.

However its worth remembering that if u Have 1 shader diffuse+ screen reflection + screen specular. Then its not physically accurate. Its more than just that because basically : If you have shader diffuse+reflection then reflection substract light from diffuse pass making it darker depending on IOR etc etc. When using additive mode you will not get that darkening so keep in mind that ur shader will not behave properly... Unless u add fresnell in to ur diffuse slot to reproduce that effect as if you had reflection on...

[rjohnson33]

Thanks for the replies.

Morbid Angel - I feel like I should be able to create the same material by going 'non-additive' and adjusting the reflection amounts and mix amount but was trying to experiment with this for a while originally and just couldn't arrive at a similar end result. For the sake of the time it's going to take me to change it I might as well accept a slightly slower render and I don't think what I have now looks physically unrealistic.

By the way, when you suggest adding specular from one shader and reflection from another I don't entirely follow. Is it possible to split reflection from specular within the shader settings themselves?
Is it maybe something to do with the Highlight Glossiness setting? I don't tend to use it to be honest because I was led to believe it was kind of a 'fake' (says the person who is breaking energy preservation laws!)

I've attached an example of my material and the settings if anyone is interested in suggesting something similar but without resorting to an additive VrayBlendmtl. It's a silk velvet. I find I can't get the same vibrancy of sheen without additive.
Both chair examples are pretty much the same material with different colours in the diffuse and the pile (bump) on the slipper chair is shorter.

[Dariusz Makowski (Dadal)]

Hey

Can u attach scene model studio textures reference material ?

[rjohnson33]

Yep, I just archived the studio scene with that armchair in but not really sure how to attach it to this post. Do I have to upload it somewhere myself and then post a link to make it available?

[grantwarwick]

you can attach zip archives here I'm pretty sure?

Or, you can change the extension to .jpg and upload and users who download can swap it back to .zip

[tashko.zashev]

Do I have to upload it somewhere myself and then post a link to make it available?

You could add file attachments only in Advanced post mode. Just click on "Go Advanced" button when you write new post or reply on existing one. Then you will see new "Attachment" icon in the quick reply toolbar.

[rjohnson33]

Oh I see, cheers.

Right, it's attached here then. Just had to resize a few textures so I could get under the file limit here. I've also had to remove a few of the texture maps as I'm not licensed to pass them around so I've deleted the brass material from the studs and feet altogether (but they're not really the point of discussion).
I've removed one texture map that goes into making the bump in the velvet itself - it was a hand painted crease map that I've replaced with a grey VrayColor map.

The studio setup I was using is basically a scaled up version of the material test scene on Bertrand Benoit's blog which I trust is okay to post here being as the original is freely available. I haven't archived the HDRI that comes as part of that scene obviously so if you want to test with exactly the same lighting I think it's still available from his turbosquid site to download (just plug that HDRI into the dome light).

As a side note, does anyone know why 3ds max insists on archiving so many image files that are no longer part of the scene being archived?

VELVET ARMCHAIR 2.zip

[Neilg]

As a side note, does anyone know why 3ds max insists on archiving so many image files that are no longer part of the scene being archived?

reset your compact material editor before archiving - if it's in there even if not applied to an object, it's in the scene.

[jstrob]

For my part I always use additive mode in almost all my materials. I use it to add a second layer of specular. The coat material has a black diffuse and so only the reflection is used. the base material always has a lower glossiness. The trick is to get the right amount of reflection in each material so they don't get too high in the white values. And I also always use the clamp output in the color mapping to avoid getting too high in the white and keep render time low.

I don't really care if it's physically accurate or not, I just want my renders too look good! Movies should always look better than the physical world!