How to get rid of this rings artifact in volumes?

[magneto]

Hi,

I noticed I am getting ring like effects if that's what it's called? But basically toggling Laser Scan didn't help and both standard Houdini volumes and VDB volumes have that. Increasing the volume resolution only makes the ring lines finer, but still visible.

It especially become apparent when I sample particle positions from the volume and the particles are accumulated in these ring areas, making it look very unnatural.

Thanks

Edited December 11, 2013 by magneto

[foam]

Do you have a hip file? Can't seem to recreate that issue. I know I've come across it before though.

I get smooth results with this -

https://drive.google.com/file/d/0B3wclDciEv7MNHZjdDVsZjlmaFk/edit?usp=sharing (uploading here seems to be broken)

[magneto]

Thanks, it happens when the noise/mountain is higher and the frequency is lower. Also the volume res should be fine enough to see it, for example 0.1 voxel size. Use this parameters for the mountain:

IsoOffset shows the problem afterwards. For VDB, I have to set Internal and External Band Voxels to 1 to see it. I should try to see if VDB that uses 3 for those parameters have the problem when I use it with the particles. Because the viewport representation of the volume might not be telling.

[ikarus]

Is that a render of the volume or a viewport screengrab?

[magneto]

Viewport screenshot.

[ikarus]

Possibly a result of sweeping a polygon surface (infinitely thin) to a finite resolution volume. The band is the finest representation of the surface the volume can hold.

 

If you want to make it 'thicker' I'd suggest scattering points and generate a volume from that, you can adjust the 'thickness' with offset/pscale that way.

[magneto]

Thanks ikarus. I just tried it, and when I use enough points, you get the same artifacts. I used VDB from Particles. I couldn't find a similar node for standard Houdini volumes.

 

I guess this normal to the nature of volumes like you said.

 

Although I noticed VDB from Particles result in less noticeable rings with relatively lower resolution. With 0.05 voxel size (1M voxels), I got better result from VDB than IsoOffset using 0.05 for the extruded mountain surface (15M voxels).

[merlino]

Just curious: but the problem is only in the viewport?

Sometime I have the same visualization in the viewport but then in the final render things changes drastically (better) as you can play with the volume filter type and width.

[magneto]

Just curious: but the problem is only in the viewport?

Sometime I have the same visualization in the viewport but then in the final render things changes drastically (better) as you can play with the volume filter type and width.

 

I never rendered it but it would be pretty cool if it was less visible in renders

[eetu]

Yeah, they changed the default volume filter from 1.5 voxel gaussian to 1.0 voxel box, to make highres volumes look sharper, I reckon. As merlino sugested, changing it to a 1.5 voxel gaussian filter makes lowres volumes render a lot smoother.