Phoenix Reflection is grainy

[joelly3d]

Below is an image that I am working on. I have a client that creates fireplace glass inserts, the fire is extra grainy in the reflection of the glass behind the fire. This is exactly the geometry we are showing off in these animations, so that surface has to be clean. It is tricky thing to troubleshoot because the fire itself does not draw until after GI prepass. I tried adjusting Min Shading Rate and Min Subdivs in VRay render settings. Adjusting those too high make the render unacceptably slow... I figure there has to be something more obvious i can try. I also tried the environment samples, which had no effect. I also tried turning off GI, no effect.

Below is a simple version of this file.... if anyone has any insight as to why ONLY the reflection is mad grainy, that would be so helpful for me!
https://drive.google.com/file/d/1nBY...ew?usp=sharing


Denoiser, helps, but what is the root cause of this?



Edit: I've found that lowering the Step% under rendering tab has helped it along with increasing the Fire Multiplier and Increasing Light Resolution inside the volumetric Render settings has helped.

[slavina.nikolova]

Hey,

Glad you solved it!
The Step % parameter is the main sampling control when rendering volumetric effects. The higher you can set the Step %, the faster the rendering will go. Eventually artifacts will start to appear for very high values, so that is where you must stop increasing the Step %. A lower percentage might be necessary so that fine details are not lost when custom changes are made. Keep in mind that decreasing the step will make the render slower. Here you could see an example - https://docs.chaos.com/display/PHX4M...ng-ExampleStep

The Light Resolution (%) specifies the resolution of the light grid as a percentage of the fire grid's resolution. Perfect illumination from fire could be achieved by placing a light in each fire cell, but this could take a tremendous amount of time to render and such accuracy is usually not necessary to approximate the fire's illumination convincingly. In order to speed up rendering, a separate light grid is created internally which can have a lower resolution than the fire grid, and this light grid is populated with one Omni light per each cell. The lower resolution (and thus fewer lights) speeds up rendering at the expense of some illumination detail, which might not always be visible anyway. At a value of 100, the light grid has the same resolution as the fire grid. The smaller the Light Resolution is, the smoother the illumination becomes and the faster the rendering is. However, at very low values the fire might not blend well with the light it casts on the smoke. Here you could see an example - https://docs.chaos.com/display/PHX4M...idReduction

On the Volumetric Rendering In-Depth page you can find very detailed explanations of the Rendering options along with examples that may be useful in your case - https://docs.chaos.com/display/PHX4M...ering+In-Depth



Cheers!