(fixed) [HOU-4041] Interactive/production-mode discrepancy w. vdb

[Dan Andersen]

Hello,

I noticed that vdb temperature renders differently between interactive and production-mode.

Houdini 19.5.605
VRay 6.1 22555

If it helps, I have a hip/vdb that shows the issue, but the file's too big for forum upload (36MB).

Production Mode


Interactive Mode

[Dan Andersen]

Could anyone confirm this, or tell me if I'm wrong? bdancer

[viktor_angelov]

Hello Dan Andersen Please share the file by Submitting a Request to us and we will investigate further: https://support.chaos.com/hc/en-us/requests/new

[Dan Andersen]

Thanks Viktor, I've submitted a request as instructed.

[tsvetomira.girginova]

Dear Dan, hello.

Feel free to test the same setup with our latest stable builds: https://nightlies.chaos.com/main#/vray6houdini/stable/6.1/20231125
No discrepancy is shown anymore.

Since kept now is the Production result which should be the proper one, please increase the Scale parameter (V-Ray > PhxShaderSim > Fire > Intensity) or decrease the Source Range (V-Ray > PhxShaderSim > Fire > Intensity & Color) to receive a brighter result.

Best regards,
TS

[Dan Andersen]

Hi TS, thanks for investigating this, I can confirm that both modes now render identically.

However, I'm a bit surprised it was the Production-mode interpretation that was the correct one. No matter how I adjust the Scale and Source Range parameters I don't seem to be able to get a similar look as before - the distribution of the fire is now very different and the range feels very flat.

I did a quick render of the same cache in RenderMan just to have something to compare it to.

Is there any way I could get the rendered look of the explosion closer to what I had before? Or are the values in the vdb simply not geared for that?


VRay 6.1 - 22595 (scale=1.0, sourceRange=(0.0, 25.0), I think)


RenderMan 25.2

[tsvetomira.girginova]

Hi again, Dan.

We will double check this and contact back.

[tsvetomira.girginova]

Hi,

Via the opened ticket I have sent you the scene.
Huge thanks to georgi.zhekov who looked to it with his pyro expert eye.

Sharing a screenshot also here:

Changes were applied not only to Fire parameter section.
I've tested it also with sRGB and OCIO Display Corrections.

Please check out the file.

[Dan Andersen]

Hi Tsvetomira, thanks for the adjusted scene!

While Georgi's adjustments definitely make it look better, the underlying difference is unchanged I think. If I open the scene you sent me and bring down the viewport exposure by a few stops it looks flat again, with little range/contrast in the fire.

Unfortunately I no longer have access to RenderMan, but I tried rendering the same cache in Karma and was able to have it matching the look from the "pre-fix" interactive VRay - a thing I simply can't achieve anymore in the latest VRay nightlies.

See attached screenshots. To make the difference even more clear I disabled density and only rendered the temperature grid.





I also want to mention again that I don't know which of the 2 looks is actually "correct". Perhaps VRay's interpretation of the VDB is the more accurate one. Either way, it would be nice to be able to match the old look somehow.

[tsvetomira.girginova]

Hi again,

We discussed internally how possible changes are applied.
Thank you for answering to the ticket.

The topic is very interesting indeed, thank you for it.
I will keep you posted by any news.

[tsvetomira.girginova]

As just written in the ticket - you are welcome to test the last changes available in nightlies: https://nightlies.chaos.com/#/vray6houdini/nightly/20240116

Happy New Year.

[Dan Andersen]

Thank you, I can confirm that the latest nightly build matches the "interactive" look from the pre-22595 builds in both interactive & production mode. Just what I need

[tsvetomira.girginova]

Great!

We are all happy. Thank you for sharing.