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#1 David Bradley

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Posted 13 February 2007 - 06:54 PM

I'm a beginner so please be gentle.

Im trying to acheive a convincing slow motion effect with DV. I tried using the time warp function in Avid Xpress Pro but when I slowed it down it looked choppy and smeared. I use a DSR 570WSPL at Uni so I figured I could up the shutter speed to reduce the smear. It looked ok at about 1/250 but still noticeably smeared, anywhere past 1/500 and I got this nasty stroboscopic effect and vertical smearing on the highlights.

Anyone have any tips on the best settings for seamless slow motion?

kind Regards

David
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#2 Michael Nash

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Posted 13 February 2007 - 10:39 PM

I'm assuming the "time warp" function in Avid is just repeating frames to make a clip become a specified length (or percentage speed). That will never give you smooth slow motion -- it will always look stroby because it literally is strobing the image by repeating frames. Changing the shutter speed will change the amount of motion blur within each frame, but won't change the fact that you're still repeating frames.

Also, when changing speed the Avid has to choose how to render two-field motion; by using either the first or second field, or by interpolating the two fields together. If you're shooting 60i, there's always going to be a difference in motion capture between the two fields, which will look like a blur or smear when interpolated together (regardless of shutterspeed).

To get really smooth slow motion you need to capture at a higher frame rate, which of course means a camera that's capable of that. There is software such as Twixtor that can do a good job of interpolating the extra needed frames, once you learn how to use it!
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#3 David Bradley

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Posted 14 February 2007 - 05:02 AM

Ah so it is as I feared, I'm sick of DV....

Thanks for the the tips Micheal I'll look into Twixtor and try and figure out how to interpolate the fields.

Meantime im going to save up for the next 300 years until I can afford my very own arriflex 435 extreme.
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#4 Michael Nash

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Posted 14 February 2007 - 05:37 PM

Meantime im going to save up for the next 300 years until I can afford my very own arriflex 435 extreme.


The HVX-200 gives really nice slowmo at 60fps. Slow enough for some subjects, but not others. The JVC HD-200/250 also offer 60P recording, which when imported as 24P creates a nice slomo.

http://www.cinematog...showtopic=20499

http://web.mac.com/t...CA13U_Test.html

Thanks for the the tips Micheal I'll look into Twixtor and try and figure out how to interpolate the fields.


But when you interpolate fields you're combining information from both fileds, that were captured 1/60 second apart. So no matter what shutterspeed you use, you're creating an image that has an effective motion blur of 1/30 second. If you want less blur, you need to use only ONE field and find a shutterspeed that gives the blur you like.

Twixtor:
http://www.revisionf...oducts/twixtor/
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#5 David Bradley

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Posted 14 February 2007 - 06:23 PM

thank you so much for your time Michael, I will look into this but to be honest I cant wait to get onto film.
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#6 Michael Collier

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Posted 14 February 2007 - 09:42 PM

But when you interpolate fields you're combining information from both fileds, that were captured 1/60 second apart. So no matter what shutterspeed you use, you're creating an image that has an effective motion blur of 1/30 second. If you want less blur, you need to use only ONE field and find a shutterspeed that gives the blur you like.

Twixtor:
http://www.revisionf...oducts/twixtor/


This is not entirely correct. Most editing machines have the ability to recognize feilds, not frames. When you slowmo some automatically split the two and then begin the feild doubling. Some require you to manually tell it to do it. Thats what premiere calls it. When you click that (right click clip, click video settings, click 'always deinterlace'. at no point does a slowmo effect on any NLE I know of or have used actually combine the feilds into one (making an effective 1/30th sec exposure as you put it.)

Rather what is happening to his footage is the effect of playing an interlaced frame to TV and not keeping the pace up. Since each frame has two feilds, the TV will play one, then the next. If it sees the same frame twice, it will still play feild 1 then feild 2. The result is a stagger in motion (you call it strobe, but thats not an accurate discription, since actually you will see feild 1,2,1,2,3,4,3,4. essentially moving you forward 1/60th, forward 1/60, then back 1/30th then forward 1/60th then forward 1/60th then back 1/30th...if that makes sense to you) I suspect that is the 'strobe' you are seeing.

My favorite slow mo look (and I swear its not because of films 24fps, it was after lots of testing with snowboarding movies in my youth, before I knew much about 24p) is to take 30i and slow it by 40%, effectivley splitting each feild so you get 60fps played at 24fps. then add a 2:3:3:2 pulldown and not only do you get super-slow video, but the frame duplication isn't offensive, because instead of duplicating frames in an awquard fassion, its stretched using a pulldown cadence most audiences are used to seeing (and at this point there is no motion difference between film shot at 60fps and telecined at 24fps)

An interesting note: if you slow mo interlaced footage, you thereby cut the resolution in half, but turn the project into a progressive frame (since half the resolution goes to one frame, half to the other)

Edited by Michael Collier, 14 February 2007 - 09:44 PM.

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#7 Brian Wells

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Posted 14 February 2007 - 10:14 PM

thank you so much for your time Michael, I will look into this but to be honest I cant wait to get onto film.

Twixtor works well with film, too! Here's an example from 16mm... I was shooting handheld on a 70mm lens, so it's kind of shaky. Twixtor held up, tho. This is 50% slo mo from 24fps.[attachment=1746:attachment]
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#8 Michael Nash

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Posted 14 February 2007 - 11:18 PM

This is not entirely correct. Most editing machines have the ability to recognize feilds, not frames. When you slowmo some automatically split the two and then begin the feild doubling. Some require you to manually tell it to do it. Thats what premiere calls it. When you click that (right click clip, click video settings, click 'always deinterlace'. at no point does a slowmo effect on any NLE I know of or have used actually combine the feilds into one (making an effective 1/30th sec exposure as you put it.)


This was based on my experience with Avid Media Composer, which by now is several years out of date. It would always ask you to select your method of rendering two-field motion; duplicate first field, duplicate second field, or interpolate both fields. Through a lot of trial and error (prior to 24P video) I was able to use interpolation to create 30P footage that included both fields.

I don't how Avid Express does it now, and maybe you're right that it's not done that way anymore.
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#9 David Auner aac

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Posted 15 February 2007 - 09:47 AM

Hi David!

try to make the slomo in After Effects or Combustion. These will do frame blending and give a really nice slomo, much better that you average NLE program. As far as these go, I heard that Blue (formerly of Fast) does a nice slomo as well.

HTH, David
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#10 Thomas Worth

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Posted 15 February 2007 - 04:44 PM

Im trying to acheive a convincing slow motion effect with DV.

Check out my article on slow motion. It will give you a basic understanding of fields and the best way to use them to get a convincing slow-mo effect with DV footage:

http://rarevision.co...slow_motion.php
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#11 Michael Collier

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Posted 15 February 2007 - 05:31 PM

This was based on my experience with Avid Media Composer, which by now is several years out of date. It would always ask you to select your method of rendering two-field motion; duplicate first field, duplicate second field, or interpolate both fields. Through a lot of trial and error (prior to 24P video) I was able to use interpolation to create 30P footage that included both fields.

I don't how Avid Express does it now, and maybe you're right that it's not done that way anymore.



Sorry Nash, before I posted I read your whole post, but for some reason only the part about turning 1/60th into 1/30th effective shutter stuck out to me. I read it again and you said more or less what I said. Though I am not sure if most software can interpolate both feilds (ei, using both feilds but avereging them so it doesn't flicker, but still has the native 720x480 resolution at 30P) Composer might, as its much more advance than the stuff I usually use. I have less than 100 hours on composer, so I am not an expert at all of its features. DV Xpress 3.5 (which I have the most experience with after premiere) has de-interlace option and interpolate option, but the option only takes one feild and then fills the blanks by interpolating the space between each line of that feild. basicly if you shoot 1/250 shutter rate, the shutter is still 1/250, and the res is halved, though the interpolating makes it more like the resolution is halved and then that is up-ressed to the native resolution, if that makes sense. Most software I have used uses this method of interpolating. That algorythm applies weather you select interpolate or de-interlace. The only difference is if you slow-mo the footage, the software will split the feilds and treat them like 60p footage at 720x240 when de-interlace is clicked, and will treat the footage like 30p at 720x240 if interpolate is used (dropping the upper feild in DV).

I could see composer comparing the interpolated feild with the actual feild, and going with the actual feild as long as the difference wasn't too extreme (indicating fast motion that) that would make it sort of like a frankenstien image. part feild one, part feild two, part interpolated pixels all made to look like a progressive frame. I am sure it looks good (its avid afterall), just interesting that it may be able to do that....I need to pick up composer now they sell it software only. Too bad premiere is so cheap and getting much better...I end up spending all my money on production these days.
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#12 Michael Nash

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Posted 15 February 2007 - 08:47 PM

Found these:

http://www.eventdv.n...ArticleID=10629

http://www.eventdv.n...ArticleID=12331
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#13 Troy Warr

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Posted 15 February 2007 - 09:00 PM

Twixtor works well with film, too! Here's an example from 16mm... I was shooting handheld on a 70mm lens, so it's kind of shaky. Twixtor held up, tho. This is 50% slo mo from 24fps.

Hi Brian,

Do you happen to have a larger version of that film? It looks very smooth as-is - but I'm curious to see what it looks like at full size, or maybe half size. I used an earlier version of Twixtor years ago, and I think I remember it looking OK, but I'd love to see a larger sample if you have one handy.
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#14 Brian Wells

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Posted 15 February 2007 - 09:44 PM

Do you happen to have a larger version of that film? It looks very smooth as-is - but I'm curious to see what it looks like at full size, or maybe half size.

There's nothing like seeing it with your own footage. The full demo is available at www.revisionfx.com
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#15 Troy Warr

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Posted 17 February 2007 - 12:09 AM

There's nothing like seeing it with your own footage. The full demo is available at www.revisionfx.com

Cool, thank you. I'll download it and give it a whirl.
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#16 David Bradley

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Posted 19 February 2007 - 09:03 PM

Hi David!

try to make the slomo in After Effects or Combustion. These will do frame blending and give a really nice slomo, much better that you average NLE program. As far as these go, I heard that Blue (formerly of Fast) does a nice slomo as well.

HTH, David


Thanks David, just so happens that my Uni has after effects so I'll give that a shot. Thanks for your time.
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#17 David Auner aac

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Posted 04 March 2007 - 04:02 PM

Thanks David, just so happens that my Uni has after effects so I'll give that a shot. Thanks for your time.


You're welcome, David...

Cheers, Dave
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