Longer render time with Basic materials than with complex ones

[NicollasRk]

Hello everyone, im having some problems lately with Corona.

Basically when i render a scene with all materials as they should (translucency, reflect, refract, etc i got x render time, but if i take all those materials and remove reflect, translucency and refract (usually vegetation) the render time gets longer. This logic is wrong,  right?

Look at the attachments, the time 1 has all materials unchanged (4 min elapsed - 22:24 left), and time 2 are without all the things i said above, in theory it should be faster but isnt (4 min passed - 23:59 left). Can you help me?

**Both are with 7,5 noise limit without pass limitation...

[TomG]

Not necessarily true, depends on the scene - the more complex materials may take longer to calculate, but sometimes that could mean light at certain areas is in fact easier to calculate, or that noise generated is in fact less. Also, renders will in general take a little bit of different time every time you run them (even with everything being identical). Also, looks like the Cache has a different success rate in one and the other, and that too could influence render time.

[NicollasRk]

Right, just my biggest problem is that this issue happens with every single file, every time i try to lower the render time it gets longer, in this case this is an animation with 480 frames, i was trying to achieve up to 15 minutes per frame, but if i just cant make the shaders simplier i will try another alternative (just dont know what).

[romullus]

From render engine point of view, your scene didn't get much simpler - 40,0 vs. 39,3 rays/sample. Also don't forget that such things are view dependant, e.g. if you'd move the camera to the point where trees occupies significant portion of view, you may get much bigger difference in render time.

[NicollasRk]

Is there something i can do to decrease render time? I never fully understand GivsAA even reading the docs, the same with uhd cache or path tracing, looks like is very random when it decides to increase or decrease the times.

[romullus]

There's always something you can do to optimize a scene even if a tiny bit, but not always saved render-time is worth the effort. Of course when we talk about animation, then every shaved second counts. 40 rays/sample metric is about normal for such scene, that means most likely there's no fundamental issues with your scene. Judging from the rays per second metric, i guess you're rendering on a single i7 or equivalent amd machine - not sure how much more you can squeze here, as estimated render time already looks pretty good for such setup.

[NicollasRk]

Ah ok i see, im using a Ryzen 7 3700x with 32gb ram, i was trying to get 15 minutes max, but maybe i will have to start deleting some objects from the scene and reduce forest pack distribution.

[sprayer]

Very strange romullus did't said what you need to turn off refraction and clip transparency on greenery for optimization as he made nice tutorial for leaves =3
You should turn off UHD as it's exterior scene.
And lower GI\AA for cleaning up AA faster on small objects like vegetation, so you may see better result on lower passes and stop to render faster.
If you use B&G or sharpening, better turn it off and add in post, it will render a bit faster as updating VFB also take time for effects

[romullus]

Actually sprayer is right. I've looked at the screens again and i think that it should render faster on 3700x. 20% noise after 4 minutes seems too much. Maybe you should ask for support team if they could take a look at your scene and see if things could be improved. Bear in mind that at this time they're pretty busy with upcoming Corona 6 and may not have time to provide swift support.

[NicollasRk]

Thank you all fot the tips! I was making those tests with path tracing and lowered GivsAA and i it went from 25 minutes to 18, thats a great win for me already. But i will submit the scene to the team so maybe they can find something im missing. Theres no hurry now since i lowered the times ill be able to render it in time, but for future renders will be nice to have a clear vision of what i need to do!