direct and indirect samples information

[Em_Fn]

This is my first time rendering in Houdini (Mantra), I have been trying to learn how to optimise my renders. I have looked at the documentation and it recommends adding direct and indirect samples image planes. I am not sure what to do with the information provided by them. What do these numbers refer to and how can I use this information to reduce noise?

[davpe]

well I usualy dont look at mentioned image planes, but i suppose it simply indicates how many samples was used for each particular pixel in the image. in the same way thou, you can output each ray channel (by that i mean direct diffuse, indirect diffuse, direct reflect, indirect reflect, etc...) into an image plane and see where noise is present. then you just bump up sampling rate for that kind of rays. in general, min and max ray samples and Noise level helps to reduce general noise in shader evaluation, set of "Qaulity" sliders helps to reduce noise for indirect rays and Pixel samples are improving overal picture quality and reducing noise in motion blur samples.

also, note that optimizing renders and reducing noise is not only a matter of typing "good" numbers in mantra node. you can run into renders that are impossible to sample properly if you choose inapropriate lighting strategy or rendering engine. it is quite comprehensive topic so I suggest you making a lot of experiments, ask specific questions and post scene files if possible.

cheers, d.

[JarJarShaq]

Those 2 aov's are my go to, in combination with direct_component and indirect_component. With these aov's you can identify where your noise is (ie, direct reflect, or indirect_refract, etc) and see how many samples are currently being used. If you're not reaching the upper limit of your max direct samples in noisy areas, decrease your noise threshold value to force mantra to sample that area more. If you are reaching the upper limit of your max samples but noise persists, then increase the number of max samples. It's definitely a balancing act and something you'll gain a better feel for over time.