Denoising is becoming more and more popular to speed up rendering times, especially since denoisers feature Artificial Intelligence / Machine Learning algorithms. Among the most popular AI / ML denoisers are Intel's OIDN (Open Image DeNoise) and NVIDIA's OptiX denoiser. For final rendering, both OIDN and OptiX have already been implemented in Blender, but in the latest Blender 2.83 alpha builds you've now got access to OptiX viewport denoising as well. Let's take a look.
Intel's OIDN denoiser is only accessible in the Blender Compositor, and to get the best results, activating and rendering some extra passes is recommended. Alternatively, you can activate the OptiX denoiser or the native Blender denoiser or OptiX in View Layer Properties ➔ Denoising.
But all of this is for final rendering only, while the most recent denoising implementation in Blender affects the viewport as well. You can activate it in the Render Properties ➔ Sampling ➔ Viewport Denoising roll-out. Right now the only options are None and OptiX AI-Accelerated. If you're wondering why this isn't simply a checkbox, it's because in the future the native Blender denoiser and probably also OIDN will be added to the viewport denoisers.
An OptiX-compatible GPU is required for the Optix viewport denoiser. The first time you start viewport rendering with the OptiX denoiser activated, the render kernels have to be loaded, which may take a while. But once it works, the results are pretty impressive. You only need a low amount of samples such as 16 to already achieve an acceptable result, which brings Cycles viewport rendering closer to Eevee.
As with every denoiser there's some loss of detail, particularly in the textures, but it's still a lot better than looking at tons of noise.
Also very nice is the ability to denoise your final rendering with a different denoiser. For example, you can use OptiX denoising for the viewport, but use the native Blender denoiser for your final rendering.
If you want to try the new OptiX viewport denoiser, download and install the latest Blender 2.83 alpha build (link below).
Keep an eye on BlenderNation for more coverage of exciting new Blender features!