Sampling Worklfows

[racoonart]

I've been testing a really heavy scene the last couple of days. 56.000.000 instanced polygons, about 7.000.000 unique. It's a cathedral with lots and lots of very small openings (windows) everywhere. I had big problems to get acceptable rendertimes with normal engines like vray etc. Now, after serveral renderings and different tests of various settings I'm getting better rendertimes with less noise.
Currently I'm using (besides the defaults):
Pathtracing as primary GI solver
HD Cache as secondary GI solver
Subpixel AA: 2
Display AA: 5
GI samples: 4
Lights group, samples:16

I've noticed that most of the noise is in the direct lighting pass, so i decreased GI samples and increased Lights samples. I think i'm getting a good balance now - more or less the comparable amount of noise in direct light and GI passes.
Now I'm wondering if there are some techniques to make it better. For example, I don't know what subpixel AA exactly does (since it's not explained somewhere).

Thanks for any suggestions ;)

[Ondra]

subpixel AA is only for antialiasing bright highlights. Display AA is just how well will zoomed-out image look in Corona VFB, it does not affect rendering itself.

Next corona version will come with manual, I hope I'll have some time for it next week.

You can post the render with stats and complete settings screenshot, I'll look into it.

[racoonart]

Ok, I will prepare some images this evening.
I noticed that much higher values for GI and Light samples work much better here. 20 for GI and 64 for Lights give a pretty clean result.
I've been testing several combinations of high sampling values which result in less and less passes (in the same time). The lower those sampling values are the more passes it will reach - but Rays/s will decrease (from about 2.600.000 to 1.600.00). As far as I understand the technique behind those passes and samples relationship it means that a pass is the "time it takes to go through every pixel in the image" and samples are of course the number of rays shot through every pixel.

1) My question is: Is it correct that it is faster to have high sampling values (and reaching less passes) than having a lower sampling setting and reaching more passes (which I think would result in a better antialiasing result but more noise in lighting and GI)

2) I've been using HD cache for secondaries now but I noticed slight lumincance differences between several renderings, which will result in flickering animations. I have set "Max records" to the highest possible value but I suppose I will need to increase "Pt samples" for a more stable solution. What do you think is needed to get a clean solution?

[Javadevil]

Hi Deadclown, you mention 64 light samples, the light sample multiplier only goes to 10.
Which one are you turning up ?

cheers

[racoonart]

Are you using the alpha v2 ? I'm using a later version so that may have changed or be a completely new setting :-/ . I have a "Lights" group here with a "samples multiplier" spinner.

[Javadevil]

I've got the latest build ( 27th Aug ), the samples multiplier spinner only goes to 10.

[racoonart]

I fear it's not the latest, I've got 30th August here.

[Ondra]

Hi,

this all should be improved in the next release:

1) GI should render with the same speed (maximal) regardless of the PT samples setting
2) Area light multiplier will go up to 999
3) It will be possible to crank up the quality setting of HD cache records, resulting in less flickering

[racoonart]

Awesome! That's great news, I'm looking forward to test that ;)

[michaltimko]

me 2 !

[Javadevil]

Great news !!!

Off to grab the latest build

[racoonart]

hmm.. it's kind of fitting into this topic so I'll ask that here: I've noticed that (big interior scene) distant objects will need way more time to get clean. Near objects are already clean in a short time, but walls which are relatively small in the rendering (far away) are still very noisy. Is there anything that can be done about that?

[Ondra]

Can you give and example (image or scene) of such situation? Is it when using PT+PT, or PT+HD?

[racoonart]

It happens mainly with pt+hd, pt+pt seems to be a bit more consistent here. I sent you an image via pm.

[racoonart]

mhh... Another thing I'm struggling with. Lets say I have a room with several little CoronaLight spheres. I'm using pt+pt. The lighting pass is clean in seconds, but in the GI pass I've a lot of little fireflies, which are of course samples hitting the light-spheres. So is there a way to exclude the lights from GI calculation (GI pass would be clean very fast then). I'm using the latest build.