Controlling rendering noise

The rendering quality, that is the amount of noise, is controlled by the Render Settings > Samples, Render Settings > Adaptive Threshold and Render Settings > Adaptive Min Samples.

Using Fixed Sampling

Set Adaptive Threshold to 0. The renderer will shoot Samples per pixel uniformly.

Decrease the rendering noise by increasing Samples. This will naturally increase the rendering time.

The same scene rendered with 4 samples, 16 samples and 256 samples.

Use the Confidence AOV to inspect the rendering noise level estimated by the renderer. The darker the image, the lower the noise is.

The Confidence levels rendered for the previous images. Note that even at 256 samples, the bright bokehs are still undersampled, while the rest of the image is very smooth.

Fixed sampling produces images which are evenly sampled, but not evenly noisy, since some parts of the image can be much more difficult to render and require much more samples than the rest. Use Adaptive Sampling to control the overall image quality instead.

Using Adaptive Sampling

The renderer will keep on sampling pixels until their noise level is below Adaptive Threshold, in the limit of Adaptive Min Samples and Samples.

Adaptive sampling produces images which are evenly noisy, and is very helpful to render effects notably difficult, like bokehs, motion blurred specular highlights or fireflies, and last but least, prevents oversampling areas of the image that already achieved an acceptable level of noise.

While fixed sampling produces images in a fairly predictable time, adaptive sampling produces images in a fairly predictable quality, although Guerilla provides means of estimating the final rendering time. This statement should help you choose between fixed and adaptive sampling.

Samples

Samples is the maximum number of samples per pixel the renderer can shoot. This value is safety guard against ultimately difficult situations, where it would shoot to millions samples per pixel. It is recommended to set this as high as possible (yet reasonably) to prevent undersampling artefacts.

Adaptive Threshold

Set Adaptive Threshold to any positive value, the lower it is, the lower the noise level is.

Comparing the image, the Confidence and the Heat for Adaptive Threshold = 0.2, 0.06 and 0.02.

Adaptive Min Samples

Adaptive Min Samples is the minimum number of samples per pixel the renderer will shoot before going adaptive. This parameter is useful in (rare) situations where the renderer requires a minimum number of samples per pixel to discover a feature of the image, such as a caustic or a glossy motion blurred specular for instance. 16 is considered a rather safe value, while 2 is fairly aggressive, and may produces noticeable artefacts.

More controls on sampling

Time Jitter

This option enables the sampling pattern to be dependent on the frame number. When rendering large depth of field blurs, you can turn this option off so the noise in the blur doesn't change from a frame to the next (but this can cause disturbing aliasing patterns if the camera moves.)

Motion Blur

This option enables the motion blur sampling. If you want to recreate motion blur from motion vectors in compositing, turn this option off.

Motion Blur Density

This option changes the way the shutter range is sampled. By default, the shutter range is uniformly sampled, resulting in a uniform trail of blur.

Change this option to Trailing if you want the motion blur to appear behind, or to Leading if you want the motion blur to appear in front.