2d blur and Defer atmosphere issue

Started by jdent02, June 06, 2014, 08:22:45 AM

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Typically when rendering animations I try to use 2d motion blur as it renders quicker and for the most part looks just fine.  On my most recent animation I have the camera flying over a thick cloud bank.  To speed up rendering I used defer atmosphere on the clouds.  When I went to check the progress it looked like the motion blur was missing.  I checked all my settings and the camera blur is set to .5 frames and the 2d motion blur box is checked in the render settings so I don't know what the problem is.  At the speed the camera is moving I should definitely be seeing some serious blur, but there is nothing.  I've included the file for reference.

Does the 2d blur not worked with raytracing?  I remember seeing something in the wiki about defer atmosphere allowing for 'volumetric motion blur' but it doesn't mention anything about the 2d not working with it.


There is blur.
You know the amount depends on the speed of the camera and how it moves related to the scene etc.
Here the movement is small so you can see it only at the lower part a little.


Something isn't adding up then, because in playing the animation back it had that jittery stop motion look that comes from not having motion blur.  I'm very familiar with that look as other animations I've done in the past didn't have the benefit of motion blur either (too expensive computationally).  The camera is moving fast enough that the jittering here was very noticeable.  I have a few frames re-rendering with 3d blur turned on so I'll see if those have any noticeable differences.


Quote from: jdent02 on June 06, 2014, 02:44:57 PM
...The camera is moving fast enough that the jittering here was very noticeable. ...

In which frames especially ?


The camera is on a linear path from point A to B with no speed ramping so all frames have approximately the same amount of camera motion.  I had edited together the first 70 or so frames for viewing since that's as far as my rendering had gone at that point.  I can post the Mp4 file this evening.



I see.
Have you tried with bigger numbers in the "Cloud top Camera" node in the "Motion blur length" setting?

Edit: I tried numbers bigger then 1 and they worked too. Not sure how they will look of course.


So I tried using the 3d blur, and that solved the problem, so there does appear to be an issue with the 2d blur and defer atmosphere.  I've attached a frame from each rendering and it clearly shows the motion blur does not affect on the clouds in 2d mode.  Haven't tried normal micropolygon based atmosphere with the 2d blur yet.

2d motion blur

3d motion blur

Edit: 2d motion blur did not affect the clouds even with defer atmosphere turned off.  Is this a bug or just the way it's supposed to work?  I still haven't found a good explanation of how the two blur methods actually go about their business.


Not sure where your problem is.
It renders with 2D motion blur in my tests without problem.
Don't assume the same kind of strength with those two different motion blur methods.
You might have to use a stronger-bigger setting for 2D maybe.
Look at my above post.
Render without motion blur and then with 2D motion blur and compare the two images.
You will see that there is motion blur .


As far as the blur length, that should be only determined by the camera blur setting.  All things being equal both the 2d and 3d blurs should be the same intensity, and in my renders they are clearly not.

I've used the 2d blur in the past and it has worked fine (and was very noticeable), but the focus of that animation was on a landscape, not a volumetric cloud bank.  I'm wondering if the volumetrics cause issues with the 2d blur system.  I'll try a couple of renders of just the landscape underneath the cloud bank to see if it works then.


Okay, some more experimenting.  I turned off the cloud layer and just rendered the terrain underneath.

2d blur:

3d blur:

As you can see, not only is the 2d blur producing a noticeable effect on the terrain (especially near the bottom), it is virtually identical in intensity to the 3d blur.  So once again there appears to be an issue with the 2d blur and clouds.  From my limited understanding the 2d blur is a post process effect on a flat image, wheras the 3d blur is done during the rendering itself in 3d space.  I wonder if the 2d blur gets confused by the varying depth information clouds cause and just kind of gives up........


I have no explanation for this. It's Planetsides turn.


I'd be curious to see what Oshyan or Matt have to say, but it seems pretty hit or miss whether they'll chime in.

Thinking more about the 2d vs 3d blur it makes sense why the 2d post process wouldn't work quite right when the image has semi transparent, volumetric shading.  I also use Blender, and its 2d motion blur doesn't work on volumetrics either.  That's probably why the default is 3d blur, as the 2d only works properly in certain situations.  I'm just glad I spent the change for the professional edition of T3, as the Creative+Animation only has the 2d blur. ;D


I haven't used it but just curious if using the "Render Elements"  "Cloud 2D Motion Vector" output in post would be more helpful or not.


Quote from: jdent02 on June 06, 2014, 08:22:45 AM
.... To speed up rendering I used defer atmosphere on the clouds. ....

defer atmosphere is usually much slower than leaving it unchecked for single renders that I've ever done. Have you run timing tests both ways ?


In the case of this particular render here's the time breakdown:

With defer atmosphere off it was about 2 hours and 15 minutes per frame.  To get the noise levels in the clouds and atmosphere down I really had to crank the sample levels up.  The clouds were set at a quality of 2 and I think the atmosphere was at 48.

With defer atmosphere on it was a little under an hour per frame.  I could drop the cloud and atmosphere samples down by quite a bit without really obvious noise.  Also, since the terrain is hidden I could also drop the overall detail slider an AA sampling too without negative effects.

Adding the 3d blur kicked it back up to about an hour and 15 minutes a frame.  Still way better than with defer atmosphere off.

I think this scene is probably a poster child for the advantages of using defer atmosphere.  It's a real lifesaver when it comes to rendering complex distant shapes at the horizon line.  With normal micropolygon clouds it would slow down so bad when the horizon line was being rendered.