Volumetric render artifacts related to grid resolution or render settings?

[hmercado]

Hi,
I am getting some grid like artifacts when doing volumetric rendering and was wondering if this a grid resolution problem or a render setting thing.
I tried lowering Step % in render settings but it makes no difference. Please see attached image.


My grid has 41,098,104 cells
Do I need a higher grid resolution to remove those artifacts?

[joconnell]

Either that or lower your opacity for the smaller values so you get more transparent cells at the edges to disguise it a bit more!

[Svetlin.Nikolov]

Please switch the Sampler from Linear to Spherical.

Cheers!

[hmercado]

Thanks joconnell,
I set lower opacity but still get the artifacts.

Thanks Svetlin,
I set the sampler to spherical but I get a more "noisy" render.
This is a new sim at 157,107,200 cells and the artifacts are still visible.
Linear Sampler

Spherical Sampler

[Svetlin.Nikolov]

Yep, now these are light cache artifacts - try reducing the phoenix light cache speedup option or turn the phoenix light cache off completely.

[hmercado]

Thanks,
Lowering light cache speedup and light cache off makes the render slower but does not make it better.

[Svetlin.Nikolov]

Ah, wait, I just also figured out that these could be RGB channel artifacts - if you switch the smoke's Based On to Constant Color, is it better?

[hmercado]

With constant colors I can still see some verticals and horizontal lines in a lot of places. That means I need higher grid resolution?
So how do I get mixing colors if I don't use the RGB channel? Any way to remove RGB channel artifacts?

Thank you.

[Svetlin.Nikolov]

Hey,

The horizontal and vertical lines are related to the Sampler option - if they still do appear with Spherical, I guess that is all that can be done at the moment.

If the black artifacts disappear with constant color, then it's the default black color bleeding into the renderable RGB channel - in this case you could try to bring in the RGB color using the Phoenix grid texture - set the smoke color to be based on a texture, plug a Phoenix grid tex there, load the grid rgb channel in it and try linear or box samplers for the grid texture.

Cheers!

[hmercado]

Thanks,

This is with the grid texture but still there are lots of artifacts in the render

(render sampler: spherical | grid texture sampler: box)


(render sampler: spherical | grid texture sampler: linear)


(render sampler: spherical | grid texture sampler: spherical)

[Svetlin.Nikolov]

Hmm, I'm out of ideas - if you can send the scene over, will check what's going on and see how to fix it.

Cheers!

[hmercado]

Thanks,
I have attached the scene file.

[George Barzinski]

Hi there,

I made some changes which improve the render quality. You may tweak this options too:

- In Volumetric Options, External Scatter multiplier was 2.0, now it's 1.0. Notice that as high this option is the more visible are the artifacts because on some places the smoke color "burns".
- Smoke Opacity --> Simple Smoke, now it's set to Smoke and an opacity curve is used. Actually, this curve has a great effect on the final result, so you can play with it until you're happy with the result.

paint-02.zip

[Svetlin.Nikolov]

The idea is to provide you with a workaround until we get to the issue. The smoke opacity curve should make the parts of the volume with low density completely transparent, while keeping dense areas opaque, so the semi transparent borders of the fluid where the black bleeding occurs are made invisible

[hmercado]

Thanks,
I kept the External Scatter at 2 and used a tighter Smoke curve and the artifacts are not visible anymore using the Grid texture map. The RGB color still creates artifacts.
Some "stepping" are still visible though in some areas where the colors are mixing together.