Vray Displacement Modifier issues / light leak / blotches / spots

[johnharrison]

The images show the vray displacement modifier used on a brick wall and im wondering what it is that introduces those bright blotches on the wall. As you can see the windowframe has also got some, so I'm thinking too low render settings (hsphere subdivs) (?)

 

Anyway, the first imaged attached took over 3 hours to render, and thats just a tiny region render. You can see my settings to the right. Does any have any tips on how to correctly set up the displacement modifier's settings? I've seen some good renderings with the use of displacement but this is abit discouraging.

 

Thanks.

[Chris MacDonald]

Firstly I think you're right in suggesting your render settings are what is causing the splotchiness, and I'm also fairly sure that you'd be able to track it down to the Irradiance Map.

 

Secondly, for displacement I always felt the same as you too - other peoples looks great, but mine doesn't and it takes forever. I began to notice quite a difference in render times and the quality of displacement when I pre-subdivided the mesh a little bit.

 

What I've found is that when I have a large area that needs displacement is that VRay spends a lot of time subdividing the geometry, then hits the "max subdivs" limit which hinders the quality of the displacement. I've found that by simply sticking something like a quadify mesh on top of whatever it is I'm displacing I can achieve a much better quality and I think this is because over the same area as before VRay now has a lot more quads in which it can subdivide, thus enabling it to create far more detail before it hits the "max subdivs" limit. I have found it to be a double edged sword however, because if you subdivide your geometry too much it will slow the render down. I'll see if I can provide some pics to back up what I'm saying, fingers crossed it doesn't prove me wrong.

[maxryhan]

What I've found is that when I have a large area that needs displacement is that VRay spends a lot of time subdividing the geometry, then hits the "max subdivs" limit which hinders the quality of the displacement.

+1

[johnharrison]

 

I don't feel much wiser on this subject. I've been doing testrenders, the latest of which had extremely high GI settings in order to remove the white spots and high modifier settings to get good displacment that's efficiently rendered.

Edited May 1, 2013 by johnharrison

[Francisco Penaloza]

Chris is right, displacement is very tight connected to the resolution of the mesh, if you want great results you need to subdivide your mesh enough so the modifier does not do all the work, usually 3d displacement is slower than 2D displacement, the problem with 2D displ is it will open the edges of your mesh, you can sort of fix this adding a smooth modifier in your mesh but making it zero (0) but still make your mesh looks strange. Your GI looks very low, and BTW Lightcache is not displacement friendly

What you can do is, add extra polys to your wall try different amounts and see how it goes, also create extra edges in your corners, keep them sharp but this edges will help the displacement mod to keep continuity of your mesh and prevent light leak from outside.

Other approach is use 3dsMax displacement mesh, then freeze or mesh your new displaced mesh, it will be high in polygons but it will not eat your ram, BTW what are your values of Dynamic memory on VRay? if still default to 400 increase this to 3/4 of your total RAM or half if not VRAy will start writing to disk before using all the memory and this really increase render time.

 

And last but not least simple black and white image won't produce good displacement, your map is as important as everything else you need a smooth transition between black and whites and avoid small black spots.

[Chris MacDonald]

Agreed with the above, especially the dynamic memory limit; shit if vray hits that whilst on a big render then the amount of time it spends "unloading geometry" is astonishing - make sure you have it set plenty high enough, or in the latest versions of VRay you can set it to minus figures I think, to tell VRay to "reserve" x amount of memory.

 

To track down what the white dots are you should try using some render elements, doing so will split the render into its constituent parts and narrow down where you need to be looking. A few that I always use when tracking down oddities are;

 

- Raw GI

- Raw Lighting

- Raw Reflection filter

- Raw Refraction filter

 

As these are what VRay calculates to create your render you wont see any increase in render time, but they could prove useful in finding the source of the problem. I'd still bet the problem is the GI/lighting, specifically the irradiance map.

 

Just out of curiosity what are your GI settings?

[johnharrison]

Thanks alot for the tips, I'll definitely get busy testing out some of these tips.

 

The Irradiance settings were set very high; 175 hpshere subdivs, with preset set to High. Light cache settings weren't that high, with a 1000 subdivs. I have 32 GB of ram so I set the dynamic memory limit to 10 GB. Maybe I could have gone higher, and yes I did experience quite a bit of "unloading geometry" but I didn't think I would with such a high memory limit.