Random unwanted light flares in some frames

[cybernoid]

Using 3ds max v1.18 plugin in Max 2013 with post processing enabled and path tracing I have yet again encountered unwanted light flares turning up for no apparent reason.

In my 8 hour render animation of around 200 frames 2 of the frames had a bizarre over the top JJ Abrams streaky glares flash up for just one frame. If I render these specific frames manually through the Octane preview window via RenderSetup the flares disappear.

I do have post processing and a bit of glare and bloom enabled but set to subtle levels.

I have had it happen once before and got around it by just rendering the problem frames manually but unfortunately this time I have to redo the whole thing due to issues regarding a physics sim in the scene not playbacking the same and causing a jerk in the motion if I re-render just the affected frames

[roeland]

Those are fireflies which are picked up by the post processing. It is very hard to 100% avoid fireflies. If there are a few bright fireflies in the scene they can be filtered out by the hotpixel removal in the tone mapping. A value of 1.0 switches the filtering off. The lower the value the more likely that fireflies get filtered out but also the more blurring it causes in the rendered image.

For a batch render you have to pick some value before starting to render. I suggest a value of 0.75 if this doesn't result in visible blurring of the image.

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Roeland

[cybernoid]

Ah ok I understand it's the nature of the beast. Thanks for explaining this.

Could you efficiently add detection of such cases and disable postprocessing for those frames given a threshold value?

As that would be a useful 'save' for the situation otherwise we probably won't risk using octanes built in postprocessing for animations from now on for even our quick renders - but it is still a useful feature of course

[roeland]

This is exactly what the hotpixel filter is doing, it takes pixels that are significantly brighter than the surroundings and it sets it to some average of the surroundings. The lower the hotpixel removal setting, the lower the threshold. Lower values filter out less bright fireflies, but may also filter out small highlights and generally, fine detail in the rendered image.

I suggest selecting a frame from your animation with lots of fine detail, rendering it and experimenting with the hotpixel removal slider to see when visible blurring kicks in. Ideally you would be able to interactively look at what value you need to have the fireflies disappear, but since you only get fireflies very rarely this is not practical.

From your description it seems the fireflies are significantly brighter than the surrounding scene. If it is very bright then a value of 0.8 would very likely filter them out. Are you able to post (part of) a rendered image with the glares?

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Roeland

[dysfunctional]

I too experience this issue, not in animation but in static frames. It has happened in the last two images I've rendered. What I find odd about this giant starburst or flare that occurs is that it doesn't manifest itself until way into the render process. Both renders I've had issue with, I've rendered out to more than 24k Ms/px, and even checked them before going to bed (they both rendered overnight). At over 6k Ms/px, there was no sign of anything amiss. Then, next morning, a giant starburst or two has invaded my image, impossible to postwork out.

I also have only seen this happen when activating the postprocessing filters, but I also am only using a very subtle bloom effect; nothing pronounced or over the top.

Anyway, just wanted to point it out so that cybernoid doesn't think he's alone in this strange occurrence. I will try what you suggest Roeland and dial the hotpixel removal to 0.75 to start and see what effect it has on keeping this issue from occurring.

[gabrielefx]

hey guys,
don't use bloom or Max 2D post effects in animations.
add them in post production.

Octane 2D post effects are ok for static renders to have a realtime feedback.

A good idea could be an Octane After Effects plugin, Otoy engineers can develop it.

regards

[Dave_Yu]

I agree with Gabrielefx. The bloom and glare will flicker if your scene have noise or fireflies.
I usually just render a still frame in octane as a guide for comp