![]() However if you are using Light-Sampling things get a lot more efficient as you are now shifting the importance towards the lights: Note that all the renders are scaled up crops to better show the sampling problems. ![]() That way increasing the sampling on the Shader will result in a lot of wasted samples: Increasing the Bxdf samples in that case won’t benefit you much, because a diffuse surface naturally has a very wide lobe. Let’s say you have a plain diffuse material. The main indicator here is the lobe of the BXDF. It depends on what kind of surface you are shading. ![]() When to use LightSamples vs BxdfSamples isn’t quite as obvious at first. That way you can specify exact values for a given indirect ray type. You can gain finer control over the sampling counts on each of these by changing the SampleMode from “bxdf” to “manual”. This inhabits indirect diffuse, indirect specular (reflection/refraction) and subsurface. Increasing it will spawn more indirect rays after the first bounce (=rays that cannot be directly connected back to a light source). Which one of them to use in a particular scenario depends on a couple of factors. Therefore you also have Sampling controls for Lights, Bxdf’s and Indirect rays. So if your shadows are grainy for example, but speculars, GI, motion blur, etc look clean, increasing the MaxSamples or reducing the Pixel Variance might give you clean shadows but also waste samples for all other sampling methods in your scene. Therefore a lower Pixel Variance will increase the likelyhood of more rays being fired and therefore a better quality image (and also longer rendering time).Īs noted before the problem with just using Min/MaxSamples/Pixel Variance as your global is that it affects all the Sampling in your scene. If that contrast is higher than the value specified for Pixel Variance it will adaptively continue to shoot more Samples for that point until the contrast is equal or lower to the Pixel Variance (with Max Samples as a maximum). Starting with Min Samples RIS will check the contrast (=noise) between the current sampling-point and those around it. The parameter to control whether the Sampling biases towards Min or Max Samples is the Pixel Variance. The amount of Samples for each of those will never be higher than MaxSamples and never lower than Min Samples. The way it works is fairly straight forward: Min- and MaxSamples are a global setting for every kind of sampling in your scene (AA, Light, Shader, GI Sampling). The main settings in the render globals that control the quality of the final image are the following: Importance sampling is the standard sampling method in PRMan (both REYES and RIS) due to its obvious benefits. Here’s a good example comparison with 2 objects – just 1 high contrast environment light importance sampled vs uniformly sampled (same number of samples): RIS uses importance sampling, which in layman terms means instead of uniformly sampling an area above the hemisphere it concentrates samples around the areas that are more important (e.g. Now because there is not a lot of stuff you can tweak to squeeze rendering times it is important to understand how sampling in RIS works. However this comes at the price that compared to Reyes I have seen final rendering times increase by 3-6 times, because all the hacks are removed for a “physically plausible” workflow. The interface and controls are much simpler now and offer easier controls to tweak your renders. The good thing about RIS is that it offers a much more interactive way of working. And while I personally don’t like it completely yet it seems to get widely adopted in the film industry and we all have to adjust to it sooner or later :) That approach aims to make the render process more simple and interactive. Being a brute force path tracer (uni- and bidirectional modes) it works much more like other renderers that follow a similar approach (e.g. The new RIS mode introduced in RenderMan 19 is a completely new render-engine that is very different from REYES.
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