The flickerfree animation challenge

[mischterlampe]

So is it light tracing ?

Yes, only if I disable light tracing, I get a flickerfree result.
If I use Bidir, it is also flickerfree, too.
What can I do now?

What if all the meshes are shaded as flat, will the pure 100% light tracing with envc flicker?
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EDIT
The blend file looks broken.
When i append objects to new blend file, the light tracing looks better.

Shaded all as flat with pure 100% light tracing and envc persistent flickers, too.

I appended the whole collection to a new blender. Used the same hdri and added a sun, but same result.

[epilectrolytics]

I've not looked into your file yet but this problem appears in all my animation attempts too.
example
Light tracing is not consistent in animation, the caustic brightness is always varying to different degrees depending on the scene.
It may be caused by the metropolis algorithm finding paths with different efficiency in every other frame or a floating point precision problem when the caustics cover a small area compared to the scene bounding box (issue#312).
Sun and sky is always more problematic than lamp lights and HDRIs are worst in this respect.

BiDir doesn't show this problem but without BiDirVM SDS-caustics are missing and it's slow on CPU.
You might try caustic cache instead of light tracing.
It's slower but sometimes it works, at least without flicker from frame to frame though I have noticed that cached caustics tend to get darker with more samples.

[Dade]

I'm able to reproduce the problem here, the frame 54 (and 58) is fine (caustics only rendering):

while there is a jump in brightness in frame 56:

I'm checking what is going on.

[epilectrolytics]

You might try caustic cache instead of light tracing.

Just tried, doesn't work
I guess the many glossy materials in the scene make the problem somewhat worse.

[mischterlampe]

Your example looks very similar.
Thank you for the explanation. But what is the solution to this? No light tracing for animation in this case?

When I use caustic cache instead and make it persistent, I get flickering, too.
But when I don't use the persistent mode, I get a flickerfree version.
https://streamable.com/ygoi9r
But you can see the cache in the image, mainly on the black bowl. So I decreased the lookup radius of the caustic cache and made it 10 times smaller and the result I get with a value of 0.0005 m is good.

It takes forever, almost 10times. And this is just a 1/3 of the resultion. So at the end 1 frame will take 10min*3*3=180min. Uhh.

Do you have any caustic setting tips?

Nonetheless, the caustics of the glass bottle are very weak

[epilectrolytics]

But what is the solution to this? No light tracing for animation in this case?

Do you have any caustic setting tips?

Sadly I don't have any solution for this except waiting until the developer finds a fix.
It's a problem I struggle with since light tracing was introduced.
Since fixing issue #312 things have gotten more stable but not entirely.
In some scenes (see my example above) there are only a couple of frames overblown, then I render those again manually.

Settings depend on each scene, in my experience glossy materials worsen the problem but again in this scene they cannot be disabled without destroying the danish mood.

I'd go for rendering the thing with light tracing and indirect PGI only (fastest method) and rerender the failed frames.

[Dade]

I may have fixed the problem (Metropolis initial bias is a very delicate matter). The animation is rendering fine here. Can you try (when is ready in ~3 hours) a new automatic build ?

[epilectrolytics]

Somehow light tracing with sun & sky is now broken.
Refractive caustics are way slower than before and in hybrid mode illumination from the sky is missing

See test file with or without light tracing activated.

test.blend.zip

(496.2 KiB) Downloaded 258 times

[mischterlampe]

The flickering is way better, but there is still an increase of brightness. It feels more linear.
https://streamable.com/411d7q

But what I miss are the refractive caustics. Light tracing and PhotonGI ind. cache is on and persistent.
Here is the old flickering version:

and here the new version:

[Dade]

But what I miss are the refractive caustics. Light tracing and PhotonGI ind. cache is on and persistent.

I should I have fixed this problem too:

About the flickering, there are 2 problems:

1) the halt condition is currently based on the sum of eye (GPU) and light (CPU) samples. Clearly if your GPU(s) is fast enough (and/or the CPU is slow enough), you can end rendering only (or nearly only) eye samples in a short rendering.

2) Metropolis has a warm up period and is unbiased on the long run. This mean that an early stage of the rendering can look quite different from a long run. This is an early stage:

and this is the long run of exactly the same rendering:

The perceived brightness of the 2 images is clearly different but there is nothing wrong, it is just a large initial error (aka noise) that is reduced on the long run.
Clearly, problem #1 can exacerbate the #2.

So, my theory is that flickering, with the very latest version should disappear more samples you render (i.e. if try to render the animation with a lot more time per frame, it should disappear).

I have some idea to alleviate the problem but the end result is still you need to render more time per frame (they takes about 20secs on my PC).