Motion Blur is wrong by default ?!


I always felt something was a bit off about UE4 motion blur. The default amount of 0.5 should represent the average, commonly used 180°/half-frame shutter, but MB in Unreal Engine always felt a lot more smeary than 180° motion blur look I am used to see when rendering using offline renderers.

In one of the recent version, new setting was introduced in motion blur settings, called “Target FPS” with a tooltip saying:
“Defines the target FPS for motion blur. Makes motion blur independent of actual frame rate and relative to the specified target FPS instead. Higher target FPS results in shorter frames, which means shorter shutter times and less motion blur. Lower FPS means more motion blur. A value of zero makes the motion blur dependent on the actual frame rate.”

What caught me by a huge surprise was realization that the default value is 30 (Motion blur length adequate to half frame shutter at 30FPS), but when I toggle the Post Process volume override for this setting off, the motion blur remains exactly the same. Enabling it and raising the value to 120 radically shortened the motion blur length, making it exactly what I’d expect half frame shutter motion blur length to look like at any framerate. Setting the target FPS value to 0 as the tooltip says has identical effect.

The main point here is that pretty much everyone is getting wrong, much smearier motion blur than what the correct default of half frame shutter should be due to default target FPS for motion blur being 30, and it requires actively overriding the value to 0 so that your motion blur becomes correctly frame rate dependent. No wonder many people dislike Unreal’s out of the box motion blur, given all this.

By default, no matter what framerate you are running at, you are getting motion blur length for 30FPS, so if you are at 120FPS, you are getting 4x the motion blur size it should be in reality.

First of all, I am using UE4 for games, not just sequences. I can’t push my game through Adobe AE obviously.

Second of all, people dislike motion blur in games exactly because game developers pull off BS like this - having framerate independent MB that makes everything more smeary than mexican soap opera. You should really open up the engine, set the target FPS to 0 in postprocess volume, and see for yourself how natural can the motion blur look even at high (100+FPS) framerates. It’s just that the default is wrong, and has been wrong for years. It’s all the more unfortunate since it reinforces the nonsense myths such as that motion blur makes games look bad. Yes, a wrong one can, but so it can ruin also an AAA movie VFX shot. It’s not about media (game vs a movie) it’s about a common factor of using it wrong. And using it wrong should definitely not happen out of the box, since most newbies tend to trust the defaults.

Oh come on… are you even reading my posts? This thread is not about if there is a way to make motion blur framerate dependent. There is one, so no need to shoot random nonsense solutions out of the box. The point of this thread is just that the default value is wrong, giving users who are not experienced with/aware of how motion blur works wrong results out of the box.

You solved a problem I had in a long time and didn’t know what is causing it :smiley: Also doing a slomo / global time slow - was a disaster with motion blur as it was getting incrementally worse!