Fog Bias parameter test in Vray Material

I did notice this new parameter¬† since the 1.5 Service Pack 1, and decided to make some test. Actually, this parameter does exactly what I need… but it’s quite hard to explain and an image will be clearer than thousands of word :

Let’s say that it quickens the darkening of the fog inside the material, like if it become exponential when the bias is set below 0. If you lower the bias too much, it’ll darken too fast and you’ll have to lower the multiplier accordingly.

The good point of the test is that it doesn’t involve any glossiness nor transluency, the rendering times were relatively low and the shadows of the object just perfect ;)

Here are the results of the test, I did start with THIS base material

Ok, it’s completely black now. Let’s see if we can have something going to pitch balck but more progressively while dividing the multiplier by 10

It seems to work ! Some further test with more extreme values

And the last one goes from almost clear to completely balck without excessive variations of thickness. Once again, chaosgroup gave us here a tool to fine tune some incredibly useful materials. Fitting perfectly in the VRay pipeline ! Congrats ;)


  1. Thnaks for your comments,

    That seems good Metatron, I think i’ve contrasted a bit the renders in photoshop after the render in LWF, always a bit washed out. Maybe the light setup add more color in my renders (sun & sky actually)

  2. Great little test you did here. Found it through the ChaosGroup forums. I’m actually doing a demo of VrayRT here in Chicago and, if you don’t mind, I was going to use this as one of the test scenes. It really is one of those settings in Vray that is highly intimidating, but once you understand what does what you can get some amazing results. Heck, with some of those shots you could make some pretty amazing artwork!

  3. fantastic renderings and an insight into this great vray setting which opens up all sort of possibilites.

    I love the fine noise in the renderings. i assume that you used brute force as, at least, you primary gi engine. Would you mind posting your rendering setting? thanks in advance,

  4. are these the universal settings. thats great news. never tried using them before! do they work well for external archviz scenes? thanks for the help. keep up the good work.

  5. I’m not sure but for my eyes and my time playing vray in rendering. That multiplier can’t go over 0.01 to smaller number anyway, you can put 0.001 but no matter what you put, Vray still render image with mimimum value 0.01 for final result. Use scroller beside that value field, whenever you go down 0.01 next step it go to pure zero ~0 in number value. Some input fields in Vray don’t allow extreme input value (different from each other, they’re not same about input range).

  6. Great Tutorial. I was wondering have you have any success doing this on a black background. I have been trying and while i get great results on white it dosen’t seem to workon black.

    • Not really played with the settings with a black background, but if you look at this post, you’ll see that some liquids are mad with this technique and it works well. It maybe has to do with the illumination which was a studio hdri in this case.

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