velocity changes (slo-motion) are blurry-- why?

wheel wrote on 7/7/2009, 7:22 PM

Hi,
I have always never been satisfied with the slomo on Vegas, and I am just now thinking that it may be me and not Vegas. Whether with my CANON XL2s or my new Pansonic HMC150, when I try to do slow motion on Vegas there is a kind of blur that happens between frames that could be a cool effect, but it comes at the cost of clarity. I should say that I shoot in 24P (I know that 60P is better); and when I play back the 24P on the actual camera, frame by frame (slowmo, in otherwords) the motion looks great, clear, crisp. And even on Vegas when I scrub slowly over the clip I get the same kind of crispness, clarity and beautiful slomo. But as soon as a insert a velocity change and watch it in real time, the blurriness returns. I tell you this because I am quite certain that this isn't an issue of shutter speed (for example one shot is in 1/1000, plenty fast.
And I can't accept that Sony Vegas can't deliver on such a simple application.
Please, please inform me what I am doing wrong. I have ticked some boxes (like motion blur) etc with no results.
thanks
Wheel

Comments

farss wrote on 7/7/2009, 10:10 PM

Playing it back in the camera 1 frame at a time is not slow motion, there's no motion. You can force Vegas to do this by disabling resampling however shooting at 24fps and playing back at 24fps it's going to look like a juddery mess. If you slowed it down to 50% you then have an effective frame rate of 12fps, each frame is simply duplicated so you see it twice. 12fps is too slow for our brains to see smooth motion unless things are moving very slowly.

To get around this so you can sort of get smooth motion Vegas interpolates by default. In the above example to get 50% slomo your camera should have been running at 48fps. Vegas therefore needs to 'invent' every second frame and it does this by blending the adjacent frames hence every second frame will look blurry. Indeed starting from 24fps which is right at the bottom limit of what we can accept as smooth motion you'll quite likely notice this odd blurred - unblurred - blurred sequence of frames.

As you said, shooting at 60fps is better but for decent slomo for sports 150fps is about as slow as is generally considered adequate. For faster action / really impressive slomo anything from 500 to 50 million fps is used.

You can get better results than what Vegas does using pixel by pixel motion tracking. See a recent thread here for some clues on using free software. Commercial alternatives are also available AE CS3 and later will do this out of the box. The process is not entirely fool proof and render times are significant. If you want first class slomo the best way is to shoot at the correct frame rate. 50i/60i can give reasonable results down to around 30% simply using Vegas's native interpolation. At 24p you're already pushing the limit before you slow thing down.

Bob.

wheel wrote on 7/8/2009, 6:07 AM

Bob---
very helpful. So it looks like 24p is the problem. But I still have to wonder why scrubbing over the clip creates a _somewhat_ fluid sequence with no motion blurs. I am not looking for cinematic quality, but it seems to me that I have seen 24p in slomo even on Final Cut express and while not looking perfectly fluid (meaning there are obvious gaps from the 24fps) the motion at least is not interpolated.
Is there a way to turn this interpolation off? In other words, I now totally understand what you are saying about fluid motion and the ways in which anything like 12fps looks choppy--or even 20fps. But I'll take choppy over blurred motion. So can it be shut off somehow?

Lastly, if I shot in 60p (that's as high as the Panasonic goes) I simply slow it down in the Vegas timeline and it will automatically look better, more fluid, no interpolation blur, so long as I keep it above, say 24, or 30fps?

thanks again for the detailed and clearly written response!
mike (wheel)

farss wrote on 7/8/2009, 8:04 AM

Let me see if I can get this bit correct.
RClick the media and select Disable Resampling. That stop Vegas from resampling.

If you shoot 60fps and change the playaback rate then Vegas will not resample, it'll simply play the original 60fps at 24fps i.e. fixed speed slomo. If you use a velocity envelope to create a speed ramp Vegas will again resample and some frames will be blurred. However as your starting from a higher frame rate the outcome will not be anywhere near as bad as starting from 24fps.
Ideally if you know how much you want to slomo and your camera supports variable frame rates then shooting at the correct frame rate will give the very best result. For example if you wanted 50% slomo at 24p then shoot at 48fps.

I don't understand how FCE and even After Effects when doing the same kind of interpolation manages a better result than Vegas but I've certainly noticed the same thing. I can understand how in AE with pixel by pixel tracking and huge render times it leaves Vegas way behind but I've had quite good results without even that. Vegas was sure king of the mountain when we were all shooting interlaced.

Bob.

busterkeaton wrote on 7/8/2009, 9:08 AM

Lastly, if I shot in 60p (that's as high as the Panasonic goes) I simply slow it down in the Vegas timeline and it will automatically look better, more fluid, no interpolation blur, so long as I keep it above, say 24, or 30fps?

More frames per second equals better slo-mo period. So yes, putting 60p on the timeline and slowing it down will look better, will it be up to your standards. Well, that is up to you. Remember most slow-mo we are used to seeing are from specialized cameras.