Material override gives different GI

[sany]

I am rendering a scene with a flat white material applied throughout, but there seems to be a GI difference when I use that same material within the material override option in my render settings, even though the render settings are absolutely identical other than that check box being ticked. does anyone have any ideas why this would happen?

Mat Applied throughout






Same Mat as Override

[TishoChaos]

I quick-tested this here and there is absolutely no difference in the images if you have a global white material or you have the same applied from the mat editor. Your problem is maybe in the Secondary Ray Bias - increase that in the Global Subdivs to 0.001 /0.0 default/. Also, if you have a non-vray light with Vrayshadows - play with the bias value to remove any artifacts.

[sany]

Thanks for the reply.

as my scene consists of mainly snow covered landscape I was refining my GI with the override ticked and then rendering with textures once I was happy. as the material I'm using for the override is currently the snow material of my scene I was expecting slight changes to the renders but wasn't expecting the scene to be much darker and flatter as its turning out at the moment. my only concern was that if there is a change in the output by merely ticking the material override button whilst using identical materials throughout in both examples, that would make the use of checking gi with the override option redundant.

If I understand your instructions correctly, I accept that the GI needs work done to rid it of artefacts however even by making those changes there will still be a discrepancy between override and not. I was curious to know if enabling this option tinkered with anything else?

Must obviously just be my scene as its not happening in your test

[TishoChaos]

A quick explanation - SRB takes a ray and shifts it slightly so that artifacts can disappear. If you want, send me the scene to my email and i will have a look at it.

[sany]

Tisho thanks for the offer!

I've done what you suggested and it seems to work fine. Still a bit confused as to why that would solve it?

another small point you might be able to help with I seem to have misplace the VRay frame buffer and was wondering if there is a way of reseting it to 0,0 as can be done through changing the max ini file for the max one?

Once again thanks!

[TishoChaos]

When you have global illumination in the scene, there are rays bouncing off things. Sometimes, a ray can't get information from the surface it is bouncing off so it leaves a black area there. Shifting the ray a bit, can solve this - i hope it is a bit more clear now.

As for the other problem - as far as I understood, the size of your window containing VFB is resized. Restart max and it will be back to default dimensions.

[sany]

thanks for your time