Ondra, is there any reason we should *not* enable static noise when rendering animation with denoising also enabled? We're currently rendering a full animation like this but using standard temporal noise. Results look great and the render-time saving is simply massive... in some cases it seems to be cutting our render times by about 60%..... well, this is combined with adaptive, which has also helped hugely. But if we swap over to static noise might we expect better results?
If you denoise quite noisy output, let's say more than 10% noise threshold, then you may see some sort of flickering or shimmering on your surface, because after all, denoiser just blurs the noise. If you make the noise pattern static, then you will likely be able to denoise even quite undercooked renders without any flickering, where as if you denoise undercooked renders with moving noise pattern, then you may get that flicker.
Basically, there are two reasons to use temporal noise:
1, Postprocessing denoisers can then identify what is noise and separate it from detail that's supposed to be in the scene. If the noise is static, they can not, they will think it's some lens or surface feature.
2, If you intend to render output that's not too clean and do not intend to denoise, then having static pattern enabled could result in dirty lens syndrome, seeing noise pattern sliding across the image. That is often undesired.
There are also quite a few reasons to use static noise pattern:
1, If you use Corona's denoiser, you it is less likely you will see flickering
2, If you intend to render very clean animation. Under certain noise level value, static noise is indistinguishable by naked eye, where as temporal noise is still visible. So if you know your output will be quite clean, making noise static will make it appear even cleaner.
3, If you are rendering animation from static camera, where there are some features that are hard to sample for antialiasing. For example thin, highly reflective features with strong highlights. In case of moving noise patterns, these will flicker and shimmer even when camera doesn't move. When you lock the noise pattern, they will look exactly same each frame, so you will require a LOT less passes to reach noise and flicker free result. This in some cases can save up to 75% of rendertime.