TG4 cloud GI quality

[masc]

hello everybody,
Sorry if it sounds messy but it's really fuzzy in my head and this is not my mother tongue.

I 'm trying to deal with GI cloud flicker and I have several questions. Especially about how the GI prepass and GI in cloud are related.


I tried to write a sparse GI cache sequence, then read it at render stage but still had some flicker. So I went for a "one frame" cache, just to experiment, and surprise It still flickers.
The cache settings were pretty low (2,2,8 + Cloud GI quality still/low) but my assumption was, as Terragen read a cache, the lighting may be not subtile but it should be, at least, stable.

I've noticed (no surprise) that when i crank up the "Cloud GI quality" the cache size is getting bigger. When I use the written cache, why does changing the "Cloud GI quality" later on, has a direct impact on the render. Shouldn't the GI info be stored in the cached frame?
In short even if I use a cached GI, with Cloud GI Quality @ Still/low, it won't flicker if I render with the Cloud GI Quality @ Sequence x1.

I'm missing something...


Thx for your help.

Chris

[Oshyan]

Cloud GI for new "v3" clouds (new in Terragen 4) is separate from overall GI. If you have flicker *in clouds* you need to increase the Cloud GI only.

Also, per-frame GI solutions (i.e. 1 cache per frame) are generally going to be *more* flickery than e.g. every fifth frame and using interpolation. So you sort of went the opposite direction to solve the problem than what could actually work. Although as I said above if the flicker is in the clouds and they are "v3" clouds, then using the GI cache won't help there.

- Oshyan

[masc]

Hi Oshyan,

Sorry if I was unclear, I tried to read one GI cache only for the entire sequence , not one cache per frame. So the cache.0001.gic was used for the 1-10 render output.

If I understand correctly, you mean we can't cache the GI solution in the V3 clouds.
Do the V3 clouds still use the result of the prepass as part of GI calculation?

thanks
Chris

[Matt]

If I understand correctly, you mean we can't cache the GI solution in the V3 clouds.

That's correct, in the current version. We'd like to make it possible to cache them in future.

Do the V3 clouds still use the result of the prepass as part of GI calculation?

The clouds are lit by their environment, and their environment is also lit by GI which is calculated during the prepass (or cached in the GI cache). For example the colours of the surrounding atmosphere and the ground below are partially affected by GI which is calculated during the prepass (or read from GI cache files). Therefore the prepass has some influence on the clouds, so GI prepass quality (and caching) can somewhat affect the results, but usually it's less significant than the Cloud GI Quality setting.

Matt

[masc]

thx for the clarifications, I start having a better view on the whole mechanic

[birdalert]

Hi, this is my first post... woot!

I'd like to bump this thread as it has solved my problems with cloud GI in my animations. Currently I'm working on two different cloud renders, both from an aerial perspective of approx. 30,000 feet. I was struggling with flickering GI in the clouds and then came across this thread which solved everything!

In case anyone else is struggling with this same problem I thought I'd share what worked for me.

I've broken the scene into three render passes: one for terrain, one for clouds and atmos, and one for the GI cache process. This setup was mostly to help in the iteration process, so I could iterate on the clouds by themselves to get client buy-off. Anyways, in the GI cache pass I've set the GI prepass to write out every 10th frame, GI cache detail to 2, GI sample quality to 2, GI blur radius to 24, and I've checked on supersample prepass. I've unchecked GI surface details in the Image Pass tab, because as I understand it (PLEASE correct me if I've misunderstood) this isn't handled during the GI prepass phase but during the actual image pixel rendering. I've also turned Cloud GI quality to Still / Low because my Clouds pass will have that set to Sequence Quality x1 which is also handled after the prepass (Again, correct me if I'm wrong). These settings have given me good results, very fast render times (approx 3 mins to generate the GIC file, on very good machines), and a file size of about 150 mb each.

So once I got a decent GI cache, I've setup my Clouds pass to read and interpolate 3 files of the cache, GI surface details turned off, and Cloud GI quality set to Sequence Quality x1. I was ecstatic to find my renders were flickerless!!

Also note that I have my cloud quality set to 1, set the voxels to 60 million, and Atmosphere quality at 32.

I'm rendering quite a lot of clouds at the moment (the radius is set to 170,000 because I can see very far into the distance). Test renders are rendering at between 10 - 15 minutes per frame with the render quality settings at AA 2, 1/16 fist samples, and pixel noise threshold of 0.05 using machines with 12 cores. Granted they are still pretty noisy renders, and only at half res of 1440x540, I'm happy with how things are looking! I'll be honest. After a few weeks of learning Terragen and getting frustrated numerous times, I wasn't convinced it would be able to do what I was hoping. But I think I understand it better now and its all thanks to these forums! Especially this thread.

Cheers, everyone. Terragen 4 is great so far and I'm hoping to use it in more projects.

Bradey

[Oshyan]

Hi Bradey, welcome! Glad to hear you seem to have solved your issues (or at least most of them). Just a few corrections and clarifications.

GI Surface Details (GISD) is partly handled after the render, but is also partly implemented in the GI prepass phase. So to get accurate GISD (which only affects *surfaces*, not clouds), you should have GISD enabled when you create your GI Caches. I am honestly not sure if the cloud GI setting affects the GI cache, I would guess not, but I'll check with Matt.

AA2 is quite low considering Defer Atmo (ray-trace atmosphere) is enabled by default in Terragen 4, which means that atmosphere rendering quality (including clouds) is in large part determined by antialiasing level. The number of samples for your clouds is heavily influenced by the AA. So 2 is going to give you few samples and noisy results, as you found. I would suggest that, as you increase AA to reduce noise in clouds, you can reduce atmosphere samples to improve render times while maintaining the same level of quality.

- Oshyan

[birdalert]

Awesome! Thanks Oshyan.

I'll definitely be upping the AA to about 6 for final renders, but its good to know I can reduce the Atmosphere samples once I do that. I guess its similar to most other render engines (Arnold, Mantra, etc.) where AA samples is a multiplier of all other samples in the scene.

Thanks for the explanation of the GISD. That makes sense now that I think about it.

Any idea when caching for V3 clouds might be added?

[SILENCER]

Here I am, resurrecting an old thread.

But I have some sky over the ocean shots to do next week, so I thought I'd toss this out there before I get moving in TG again.

The new easy clouds take a lot of previz pain away, but I can't recall if they are based on V2 or V3 clouds.
If easy clouds are V3 based, then GI caching them is pointless, as that quality value is controlled in the GI in Clouds tab, correct?

No landscape here, just water and clouds.

[D.A. Bentley (SuddenPlanet)]

That was a great thread to resurrect!  I learned something new! 

Thanks all,

-Derek

[Matt]

Easy Clouds are based on V3 clouds, yes. But sometimes you may need to generate a GI cache file anyway. See Reply #3 above.