Animation flickering with HD cache

[fobus]

Hi guys.

I'm very interested in new to me Corona renderer. I'm doing a little clip of future interior with animated things like robots and furniture. Usually we're using V-Ray for our works but for this clip with lots of animation (usually we're have only people and cars moving in exterior scenes or just people in interiors). I found that Corona is great for animation and started to do animation with it.

During the previsualization I found a little strange thing with flickering the secondary GI named "HD cache" (it's not about the noise, but flickering of whole lighting of secondary GI). As you can see in attached file default settings (top video) of Corona flickering is quite pronounced. Of course I'm started to find the problem. And it was the parameter "Refl glossiness threshold". In default settings it has a value of 0.9. With this value it produces a cleaner image in blurry reflections, but in expense of flickering as I found. I don't know if it's right, but in my tests it is. Then I set "Refl glossiness threshold" to value 0.08 and render animation preview with it. As you can see at bottom video the flickering is much less pronounced in movie then with "Refl glossiness threshold" 0.9, but still there.

May be I'm doing something wrong and you know the way to turn this flickering down?

[Ondra]

reflection glossiness threshod disables HD cache for too specular objects. It seems you have probably disabled it for most of the scene in the second case. You can confirm by comparing the HD success rate % in the statistics in VFB between the two renders. The current best solution is to save and reuse the cache (save/load secondary GI option)

[fobus]

The current best solution is to save and reuse the cache (save/load secondary GI option)

Yea. This seem to work with  fly-through animation without moving elements, but with our animation full of moving subjects and turning lights on and off it is unusable as I see. I've tryed to save HD cache for first frame and reuse it in animation but it feels like all the lights bounces has gone for secondary GI.

In attachment you can see frame with saved HD cache (on left) and with computed during render (on right).

[Ludvik Koutny]

Keymaster probably forgot to mention saving HDcache only works in scenes with static lights and objects.

I would try reverting HDcache settings back to their defaults, and then increasing position sensitivity to 100, and see if that helps.

HDcache at the moment is unfortunately not flickerfree. So either you have to use Path Tracing as secondary GI, which will increase your rendertimes, or try increasing positional sensitivity of HDcache, or just wait until flickrefree cached secondary solution is implemented. It is very high on priority list.

[fobus]

Thank You for possible solution. I'll try to check it and reply soon.

[racoonart]

or just wait until flickrefree cached secondary solution is implemented. It is very high on priority list.

What's the "technical idea" behind the flickerfree hdcache - how is it supposed to be working?

[fobus]

I would try reverting HDcache settings back to their defaults, and then increasing position sensitivity to 100, and see if that helps.

Wow! It seems that it works for this scenario. It doubles rendertimes, but 40 sec of 57 sec of render was the preparation of Secondary GI (HD cache ia mean), so I hope with final render it will be almost no cost (if it will not scales with final quality).

Update:
For the final quality (720p) HD cache was computed in 2:30 min. Super. I'll post final quality report a bit later and full clip in gallery as it will be done.

[rafpug]

Hello fobus

compliments , a great test!

[michaltimko]

Keymaster probably forgot to mention saving HDcache only works in scenes with static lights and objects.

Worked for my with loading saved GI even in scene with moving light. (sun moving)
Had no any flickering so far.

[racoonart]

Worked for my with loading saved GI even in scene with moving light. (sun moving)
Had no any flickering so far.

Yes, it works, but with outdated lighting information in the secondaries. As soon as your light moved, your primary (pt) bounces are still calculating with the secondaries information of where the sun was before. So if you really push the limits (e.g. a full day circle) you will easily see things getting weird.

[michaltimko]

I had movement from midday to evening in two 5second animations. I saved HD cache (computed 8192) without any issue.
I had few issues with reflections on glossy objects, mostly on edges.

[racoonart]

I'm not talking about technical issues. I'm talking about realism. It's like shooting brightly lit people on greenscreen and composing them into a dark night scene. It's just not fitting lighting information. Technically it's still valid but it does not make any sense in respect to realism. It's the same thing in Corona - you can do a lot of nonsense with moving objects, lights and what-not, but you're starting to use simply wrong information as soon as you change something after caching your secondaries.

[michaltimko]

Gotcha...but i dont care abour realism in commercial projects anyway. I just wanted to say that i had no flickering with moving sun.
Moving smaller light sources should be problem of course.

[rafpug]

Hello fobus

You can show the setting of all the values ​​of this material in your scene? .. screenshot 
HDRI in environment - Portal - number light (values) .. etc etc !!?

In this curved surface was applied Normal modifiers?

[fobus]

Hello fobus

You can show the setting of all the values ​​of this material in your scene? .. screenshot 
HDRI in environment - Portal - number light (values) .. etc etc !!?

In this curved surface was applied Normal modifiers?

Of course I can. More of that: I'll share this test scene.
All scene surfasec is real geometry without any normal modifiers. Simple CoronaSky in background. No portals. Just look in attach.

BTW
As I tested this flickering was only presented with blurry reflections materials on surfaces. With standart materials without reflections I hasn't catched it. So my first try to reduce this flickering was to get "Refl glossiness threshold" as low as possible to archive acceptable render times. But this way  was wrong. It reduces the flickering but increases rendertimes for clean image.