Best motion blur solution?

#1

Whats the best free motion blur solution? I’m working on a short for my high school senior project, very cinematic, car chase, lots of speed, etc. Obviously I don’t have access to a render farm and time is important, but so are quality results. What are some of the best options for this?

#2

With something like a car chase with low cameras looking up post moblur will go belly up quite quickly on more shots than not, you’re definitely better off using “real” moblur.
Save on reflections as much as you can (in general avoid raytracing except for some specific passes only when necessary) and use the rasterizer, you’re more likely to have some luck with that than with other rendering modes.

#3

I guess I better start getting some shots ready to render out, got like 3 weeks left to get it done before competition due date. 30 seconds = 900 frames is going to take 450 hours to render out with the current (lower) settings, that’s 18 days, damn. AND I barely have any animation done.

#4

would it be worth to render a render it out separately and do a 2D motion blur to the blur reflective objects and trees and do the real motion blur with everything else?

#5

2D moblur being successful depends greatly from the camera movements and the foreground/background switching of the elements, overlaps etc.
For your average carchase cams (ample amounts of wide ground and radial movment) post moblur will usually fall apart.

Reflections in moblur become expensive when raytraced, but car reflections like what you’ll need you can probably do entirely, or almost entirely, with environment reflections, and only run a very minimalistic pass of raytraced reflections for some distinguishable elements.

Last but not least, rendertimes change a lot depending on camer blur.
In shots where you lock the camera to the car you don’t even need moblur on the car, only on the environment, and in shots where the camera is static and just doing something like tilting or slowly panning you can get away with only object moblur and no camera moblur.

It’s hard to give any more advice without seeing what the direction of the shots is like.

#6

So in shots where the camera is still, I want to render out the car/monster with an alpha map and blur the car in post? but what about if you see the car in the reflection of something, how do you work around that?

Also I’m trying to figure the best AA settings for a final animated render, I got the sampling contrast at .05 and AA 1, 2. I could probably lower that with motion blur right?

#7

I was suggesting if the camera doesn’t move you only moblur the car, which is best left to its own pass anyway. That’s also where you could use 2D moblur (with a proper plugin, directional blur on something masked always looks hideous and nothing like moblur).

If you need to see the car reflected in the environment then you need a pass for that too, or to have a cheap stand-in for the car.
Again, it’s hard to tell without knowing anything about this movie’s shots :slight_smile:
This discussion is normally one you should have shot by shot, or sequence by sequence. There’s only that far it can be taken in general terms.

What resolution are you rendering at btw? if it’s 1:85 fit into PAL you can get away with murder (with genocide in fact), if you output to 1080p things are different.

#8

I think final resolution is pretty open

#9

I know, it’s tempting to make it perfect but do you really need best quality motion blur? If you don’t have the hardware and time to do it the propper way perhaps it would be better to spend your time on the actual carchase. I bet most people won’t even notice a bad motion blur but they’ll shout out loud if they don’t like the colors of the cars involved.

#10

No moblur in a high speed car-chase would probably net you better bang for the buck than reflections or a lot of other things to be honest.
It’s hard for an audience to accept something is a real fast moving object without at least a modicum of blur on it.

Half way is still a valid compromise, your moblur doesn’t necessarily need to be on a real world type of shutter time. Reducing the length of it will also considerably reduce the amount of fragments where the object needs to be looked up for moblur, and consequently render times.

#11

I think the idea right now is to break up the shots and angles often enough that your eyes don’t have enough to realized the blur is flat/lacking/unrealistic. Kinda looking for a movie trailer feeling. I think most of these will just be done in post, but I think we’ll use some zdepth too to help push the depth of the blur.

#12

Not sure what you mean with post and zdepth…
Post moblur isn’t done by directional blurring, you do that and you end up with a worse result than not having it at all.
Post moblur is a blur derived from a motion vectors pass with plugins meant for that. Don’t even bother with just blurring things directionally in anything except a fully ortho shot (and even then multiframe blending would be advised).

#13

I meant just a depth pass.

#14

Depth has nothing to do with moblur though, that’s why I’m saying I’m not sure we’re on the same page or, no offense meant, you don’t completely understand post moblur operations.

Moblur is based on how something moves in screenspace relative to the camera, nothing else. Depth is irrelevant (except possibly for sorting/overlaps, but that’s not something any commercial solution around offers afaik).

Post moblur is run on top of two things: Your final footage you want blurred, and a motion vectors pass of that footage telling a plugin how much the content of each fragment (pixel at 0/0 aa) is moving by and in what direction.
Once you have those info a post moblur plugin can take care, based on shutter length and all, of motionblurring things correctly.

That only corresponds to linearly blurring something when you have an absolutely orthographic camera with objects moving so that their screen space displacement is exclusively some X and Y movement in the camera plane.

#15

well I was thinking depth could allow you to blur objects more or less depending on the distance from the camera, kinda how it appears to in real life.
I did 2 different approaches, one was with a post program (no need for motion vectors) the other was done with a depth pass and some composting. Basically the same results. Well back to work with the main project, got some more simulation and animation to do.

Sorry for the bad video quality

http://vimeo.com/4177830

#16

Objects don’t blur less in the distance.
Objects travelling at the same speed move less in screen space the further they are from camera due to perspective, but the length of the blur is always and solely dependent on shutter speed and screenspace movement.

Even if you had the depth of the scene it would be useless as a mask, unless you feed it to the linear blur filter to decide streak length before it runs, but at that point you’re still not taking into account speed or the direction of the motion.

You still want (and need) motion vectors for something like this, even if you’re using them to help some hacky filters instead of a proper post moblur one.

The video you linked only needs camera moblur on a fairly simple motion, so radial centric blur will get you 90% of the way there, but only because the set is static, as soon as you have cars moving in there (IE: different relative speeds to the camera) it won’t look anywhere as convincing.
You can still rely on it confusing things enough for people not to notice, but at that point you end up putting a lot of work into simulating moblur only to get a confused and bad looking shot out of it, which defies the point of working on introducing photographic elements for the sake of realism and aesthetics, and the final shot would probably look better if it wasn’t blurred at all :slight_smile:

#17

If you’re really skilled or leading a dull life you can always just use the smudge tool in PS on each frame…

I have 101 interns working on that right now…gotta start somewhere!

#18

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