Image-Based (FFT) Convolution for Bloom - May 25 - Live from Epic HQ


Image Based (FFT) Convolution for Bloom is a brand new rendering feature in 4.16. With this new post-process upgrade, you can create physically-realistic star-burst effects for your bloom. David Hill joins the stream to show off how to activate the feature and when you will want to use it for the best performance to quality tradeoff.

Download the Powerpoint

Thursday, May 25th @ 2:00PM ET Countdown]


David Hill - Principal Mathematician
Alexander Paschall - Community Manager - @UnrealAlexander](

Feel free to ask any questions on the topic in the thread below, and remember, while we try to give attention to all inquiries, it’s not always possible to answer everyone’s questions as they come up. This is especially true for off-topic requests, as it’s rather likely that we don’t have the appropriate person around to answer. Thanks for understanding!


wowsers! that looks amazeballs!

DOn’t you love it when people reply to their own comments?

Just a point but the launcher say “Tues 5/25 @ 2PM ET” when tomorrow the 25th is clearly Thursday considering today is Wednesday, and we don’t have access to a planet sized DeLorean.

Amazing!! can’t wait to join this event.

Hey guys I have created a Skype group in this group we shall try to help each other
and everyone can join the group. If there is any group please tell me so I can join that group too.
MY skype name : atayzuljalal217
Skype group : UE4_DEVS


Has the way the editor builds the Post Process Details panel been changed in 4.16? I can no longer get custom Post-Process variables to show up. For example, I’ve added Anamorphic Bloom to my engine version with a couple of sliders - but they don’t show up in the editor anymore after updating to 4.16 (using source build)

It will be interesting to see what you can do with this :smiley:

will watch this just to find out what it is! lol :stuck_out_tongue:

altho it looks like some of my old airbrush work :slight_smile:

Thoughts on feeding this into a neural net to get some kind of faster FFT algorithm?

is this possible to share your exr image for star glow ?

Just watched this. Thanks David Hill for this presentation. The Maths went over my head quite a bit, but i’ve played around with FFTs in the past (black magic i say).

What other uses do you think could be found for this sort of filtering? I think it’d be great to soften hard specular lights with something like this.

I’d love to see some more examples of your experimental kernels - what happens if you have more than one strong point of light (double vision I guess). What happens if you put a lens flare type outer ring around the center hot spot?

Is there an FFT library associated with this available to use for other applications?

I didn’t check on the engine source, but you should anyway. As this is one of my research areas lately (FFT for ocean simulation) I have been in touch with this library:
Have fun!

Yeah I’m been looking at the same. FFTW is great but doesn’t integrate with GPU. The one these guys are using utilizes the GPU. Thought it would be useful to have their version which is already integrated with the engine + gpu.

I noticed that beyond 1440p Resolution the convolution bloom gets a bit out of hand: screen getting blurry and way darker, suggesting that if working with higher resolution, 4K and such, you need to adjust your convolution kernel adequately ?

Unless i’m missing something :stuck_out_tongue:




Are you using the default kernel bloon texture? Maybe at higher resolutions will need a better one.

In those screenshot i was trying a custom , but the default one has the same outcome. I’ll try something silly like expanding the resolution of the Kernel texture.

I didn’t see the pictures 1st time, but now I can see. For the darkening Im not sure if thats the clouds moving in front of the sunlight. The bloom kernel should only affect small light reflections to shiny like a star would (the texture just is a gradient to tell the directions of the small shafts from the center), it should not affect the whole screen like that anyway.

Im not sure if David Hill check the forums, but if thats the case @Amanda.Bott can follow up with him to check your screenshots and doubts.

I was just talking about this on Twitter with TheJamsh and was trying to figure out if there were any asset samples/packages or docs on how to best author these things. I’ve tried before, but the results have not been… Spectacular.