Blotching in Interior Renders

[ianmoran]

Hello everyone,

 

I am trying to render out a couple of quick interior shots. However, I am getting a lot of weird blotching on the ceiling and in other areas of the images. Does anybody know what i causing this? And how can it be resolved?

 

I am using Vray for Maya.

 

Thank you in advance.

 

Ian

 

 

[mattcooper]

I guess you're using Irradiance Mapping for your GI? In which case increasing the sampling should sort it out.

[Francisco Penaloza]

I guess you're using Irradiance Mapping for your GI? In which case increasing the sampling should sort it out.

 

In reality, this approach will require a lot of samples, and what is happening here is first there is a lack of samples, it is true that but also they are not interpolating correctly or they are not carrying enough energy (AKA Light information)

A very quick fix for this would be to just increase the interpolation values.

 

The drawback of this approach is you will loose details on small crevices. Then you need to increase samples.

So the final answer would be increasing the interpolation value and adjust the samples number until you get a better result.

 

Another lazy way to fix this would be to increase the interpolation values and activate the detail enhancement in Irr.

 

If you are using the latest VRay I would recommend using Brute force for the first bounce instead. it is simple to work with and get better results at not much time difference unless of course, you need a fast rendering.

 

But again when increasing Irr samples and interpolation you also increase render time so, you have to decide.

 

Fco.

[ianmoran]

Thank you so much for the responses guys. I found that some of the problem was caused by having a Vray Light Material turned up too high which seemed to cause some of the strange orange spill that I was getting.

 

I have decided to give Brute Force a go instead of the Irradiance Map. Something I have not tried before. However, I am getting quite a lot more grain with it. What would be some good settings to use with Brute Force to achieve a clean render?

 

Thanks again.

[mattcooper]

No worries!

 

Good idea, I almost always use Brute Force + Light Cache instead of Irradiance. In terms of noise, what are your current image sampler and DMC settings?

 

To almost guarantee clean renders I'd use an image sampler noise threshold of 0.005, and a DMC noise threshold of 0.002, and then adjust your min/max samples. Those settings will most likely be overkill and will lead to much longer render times, but those are generally good ways to fix noise issues (also add a denoiser render element as this will allow you to use lower/faster threshold settings, and play around with the denoise settings to ensure you don't lose too much detail).

 

Also check your materials and lights to check they don't have really high values, and aren't completely white (as you've already discovered with your Light Material!)

[ianmoran]

Hey Matt. I appreciate the quick response. I currently have the following:

Image sampler noise threshold: 0.004

DMC noise threshold: 0.040 (is this the one under DMC sampler - advanced -> Adaptive Threshold?)

Min subdivs = 1

Max subdivs = 10

 

I will also try to figure out how to use the denoiser render element, as I have not tried this one before.

[mattcooper]

Okay so the noise threshold is probably too low, I'd start with 0.008 and potentially go lower to 0.005 if needed.

 

The DMC is way too high for a final render (I usually test with 0.02, and do final renders with 0.002 - 0.008, depending on the detail of the scene and how well the denoiser deals with it) so by lowering that value you should see the most improvement.

 

The Max subdivs can be raised to 24 which is default (I think).

 

And with the denoiser it should be as simple as using the low/medium preset

[ianmoran]

Thank you so much, Matt. I will give these new settings a try now and let you know if I get a better result. I will also throw in a denoiser render element for good measure.

 

So is the DMC noise threshold the one under DMC sampler - advanced -> Adaptive Threshold? Just so I know I am modifying the right part as there is also one called Adaptive Amount = 0.6 and Adaptive Min Samples = 16.

[mattcooper]

No worries

 

Yes that sounds right (although on my version of VRay it's called Noise Threshold, not Adaptive Threshold), and I'd keep Adaptive Amount on 0.85 (default).

 

(and just to clarify, the LOWER your threshold settings (0.005 etc), the HIGHER the quality and render times)

[ianmoran]

Thanks Matt... This worked great and got rid of the blotches and grain. My only issue was that the render times increased a lot. I assume that playing with the noise threshold will affect this?

[mattcooper]

Great, glad to help!

 

Yeah that will happen as brute force is notoriously slower to render a clean image, and you're right, playing with the noise threshold will help this.

 

You can region render the noisier parts of the image and adjust the settings until those parts are clean, as i said, 0.005/0.002 is most likely going to be overkill so bare that in mind.

 

You could also play with the custom settings in the denoiser to see if that can help you use lower threshold settings but still get a clean image.