I have a Bloom & Glare issue that I’ve been unable to solve.
I’m rendering a sequence in outer space that’s set around the Kuiper Belt.
I was testing what the sun would look like at the Intensity and Scale settings that would be accurate to the distance to the sun in that area in outer space.
Throughout the film we will be at different distances from the sun so it’s an important detail to get right.
However, the lens flare created by the sunlight is flicking very irregularly between frames. I’m trying to get the flare to be smooth and consistent throughout the shot.
I’ve turned ON “Animation (Flicker Free)” in the render settings.
I do have Motion Blur for both Objects and Camera turned on.
Here are the screenshots of my sun and bloom and glare settings, and the rendered clip with the flickering:
Animation Flicker Free only applies to the generation of the UHD or 4K Cache (I would expect any Cache to be off in this case and full PT + PT being used). The b&g is entirely post process, run on the finished render. It would be beneficial during a final render to enable “calculate at render end” though I doubt it would resolve the flickering (but it might).
Other question, do you have Auto turned on or off for the Exposure and White Balance? Probably best set to off in a case like this.
I think this may be caused by the fact that the sun ends up as a small patch of bright pixels in the image. With bloom and glare off, most likely there would not be a huge visual difference between the frames.* But when it is applied, this results in large differences depending if the bloom and glare effect is applied to a patch of 8 or 6 pixels. What would possibly help is:
Rendering more passes - btw, how many passes are you rendering per frame?
Rendering in a higher resolution
*actually it may be interesting to check how the frames look without bloom and glare
150-180 passes sounds like more than enough… If you could send us a sample scene - it can be the original, or a simplified version - then we could investigate. https://support.chaos.com/hc/en-us/requests/new
So I did spend some more time with this scene, and I think the issue comes from a mix of factors:
Using extreme values for bloom and glare (e.g. size set to 100, threshold 0.01) - using values closer to the defaults makes the b&g effect a bit more stable (especially on the sun).
“Compute after render” option working incorrectly when rendering from a Corona Camera. Computing b&g while rendering can make rendering slower resulting in less passes rendered. Unfortunately, the “compute after render” option doesn’t work when b&g override is enabled in the Corona Camera. This is now reported as (CC4D-1425) and hopefully will be fixed soon. The workaround is to transfer all b&g settings from the Camera to the VFB and then disable the b&g override in the Corona Camera. The “compute after render” option can be used then, which helps render more passes = more stable b&g.
Most importantly: the issue will be exaggerated when b&g is generated from a small, sharp, intensive light source, such as the sun or the reflection on the planet. As I mentioned in my previous message - a patch of 6 pixels will generate a very different b&g effect than a patch of 8 pixels, especially when using such a large b&g size. The number and intensity of pixels changes with the sun/camera movement resulting in flickering.
Sun - you can increase the sun disk size, or zoom in a bit, or increase the render resolution.
Planet - simplify the materials - the planet surface material is highly reflective. Making it rougher makes the b&g effect more subtle and stabilizes it.
Additionally, the volumetric material uses “inside volume” mode with a very small step size in relation to the object size. Hiding the object with this material makes rendering about 10x faster = more stable b&g. I would suggest generally simplifying this material so that it doesn’t impact render time that much (e.g. disable the “inside volume” mode completely or use a much higher step size).
