Lighting in this project is really challenging, because I have so many lights that are coming from different directions, and especially it’s a night scene.
I did a test render and it took me more than one hour to render one image, and it’s very grainy. So I looked up on google to find a solution to reduce my render time. I found this video and I tried almost every tip to see if my render time gets faster.
Firstly, I tried to find where my noise come from. I cropped region to render just one small area and tested all the sample values in the render setting, such as diffuse, specular, SSS. If I changed one of the samles and there is no difference, then I would keep a very low sample value. So what I found is that the camera AA and lighting samples are the main reason why I have the noise. But the problem is that if I increase those samples, my render time is still too slow.
In the video, he mentioned that mesh lights produce lots of noise. Almost every lights I used in the scene was mesh lights, so I swithed all my mesh lights to area lights. And it didn’t really reduce my render time.
And then I saw someone on Reddit mentioned Low Light Threshold in Arnold. I go to my render settings and increased the value of low light threshold to the maximum, then my render time incredibly reduced to 9 minutes.
I also found this page about low light threshold.
There is definitely some loss of quality or color in the image with high samples of low light threshold. But there is no big difference between these two images, at the same time my render is much more faster now.
Now it’s still grainy but much better than before. In the youtube video, he talked about arnold denoiser is really helpful for removing the noise. So I tried it for the first time and it worked really great.
A comparison of the undenoised and denoised image with arnold denoiser.