Dark areas became really grainy

Development Rendering
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1

Hi people, for some reason after updating to 4.9 I’ve been getting lots of noise, which becomes really apparent in dark areas and makes edges look messed up.

1269×711 261 KB

I have not messed with the post process volume or added any grain by myself, and I’ve also noticed that this noise always has the same pattern to it, it’s doesn’t jitter randomly, but it moves in place a little bit.

Any ideas what could be causing this?

2

That looks like Distance Fields Ambient Occlusion. If you are using a Movable Skylight and don’t want to have this effect disable the cast shadows option on it. This may also be caused by Screen Space Ambient Oclussion if the contrast or the power values are too high.

3

Actually most of the noise went away after I turned off Temporal AA. http://i.imgur.com/fZI27Mf.png

I don’t understand why it’s causing so much noise.
And no I’m not using a skylight. just that one spotlight on the corner

4

I was having the same problem with Temporal AA.

Go to Engine/Shaders/PostProcessTemporalAA.usf and change both lines 319 and 348 from “#define AA_YCOCG 1” to “#define AA_YCOCG 0”.

That should fix the issue although performance will decrease a bit.