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How do I prevent ghost effect when rendering 59.94 to 27.97?

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Travis Taylor
How do I prevent ghost effect when rendering 59.94 to 27.97?
on Jan 31, 2011 at 1:03:42 am

Hi all... I'm having issues with a particular section of a video I'm working on. The video was shot in 720p at 59.94 and I'm rendering it out to 29.97. The video looks fine at the reduced frame rate except for a section of the video where there's a lot of motion going on. In this section, I have the camera in the center of the room spinning at a constant rate. Rendered out at 59.94 it's smooth as butter. Rendered out at 29.97 and this same section has a noticeable ghosting jitter effect (like if you were watching a modern 3D movie in the theater without your 3D glasses on). This effect is most noticeable where there are high contrast areas. I've tried setting the frame blend in AE to pixel motion and frame mix with the same results. Is there some effect (native or 3rd party), render setting or other technique that will solve this problem?

You can see exactly what I'm talking about here:



(the particular section I'm speaking of is at around 2:20)

Thanks in advance!


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Dave LaRonde
Re: How do I prevent ghost effect when rendering 59.94 to 27.97?
on Jan 31, 2011 at 2:33:06 am

[Travis Taylor] " The video was shot in 720p at 59.94 and I'm rendering it out to 29.97. The video looks fine at the reduced frame rate except for a section of the video where there's a lot of motion going on. In this section, I have the camera in the center of the room spinning at a constant rate. Rendered out at 59.94 it's smooth as butter. Rendered out at 29.97 and this same section has a noticeable ghosting jitter effect."

That's due to the lower frame rate to which you're rendering. You can't do anything about it. When you converted from 59.94, you tossed away half the motion information.

And what do you need for nice, smooth motion? As much motion information as you can get.



[Travis Taylor] "You can see exactly what I'm talking about here: "

Actually, that looks like a different problem than yours. It looks like the constant-pan was shot or composited at 23.976, then dumped into a 29.97 timeline. Dumb. Other than that brain fart, it's a nice effect.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Travis Taylor
Re: How do I prevent ghost effect when rendering 59.94 to 29.97?
on Jan 31, 2011 at 5:04:16 am

Thank you for your response. But, like I said, it was shot in 59.94. And to elaborate, I edited it in a Vegas timeline with a frame rate of 59.94. I rendered (lossless) from Vegas at 59.94 and dropped that into an After Effects comp at 59.94 for the final touches. So the frame rate was consistent up until the final render. My reason for shooting in 59.94 was to have a higher frame rate "resolution" to allow more wiggle room for shifts in velocity (to match up the composited footage).

I've tried straight renders, renders with pixel blend and renders with frame blend (which was super blurred) but with the same result. I understand that I'm loosing half the information when I drop down to 29.97 for the final render, but it seems like there should be a way to avoid the ghosting that results.


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Kevin Camp
Re: How do I prevent ghost effect when rendering 59.94 to 29.97?
on Jan 31, 2011 at 4:49:07 pm

pans and other camera movements can be hard to get smooth at lower frame rates, that's why the move industry has developed rates for those types of movements.

it is relatively easy to accidentally change a cameras settings, so you may want to double check the original shot to make sure that you do have unique frames every frame (it is possible to shoot 24p and record it as 59.94 fps, you just end up with duplicate frames).

once that's ruled out, there only a couple ways i can think of to try and smooth the pan out...

one, render interlaced. this will give you smoother motion, much like the original 59.94fps. if this is for dvd, or sd broadcast, that should be fine, if is is for web, then interlacing may not work as well.

another option would be to fake some motion blur by adding a little directional blur (or fast blur set to 'horizontal'). this would be to add the motion blur back in that you would have had if you had shot at a lower frame rate with a normal shutter angle. obviously there's only so far you can push that blur, but it may help.

you mentioned frame blending, frame mix would be the better of the two ae options, it would blend the one current frame with the 2 that you are losing on either side of it. that can often help to smooth motion by trying to replicate some motion blur that you lose when reducing the frame rate. effectiveness often comes down to how tight the shutter angle (or shutter speed) was when you shot the footage. shutter angles less than 180, or shutter speeds less than half the frame rate are tougher to smooth out.

you can also try to create motion blur with timewarp. add that effect to that shot and set the speed to 100, then go down to the motion blur settings, enable it and start tweaking the settings to see if you can get what you want.

i've found timewarp can help but you can't push it too far. revisionfx has an effect called reelsmart motion blur that does a better job of adding motion blur, you might see if they have a trial version to see if it will work for you.

you may also find that it will take a little of several of these tricks...

Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW


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Dave LaRonde
Re: How do I prevent ghost effect when rendering 59.94 to 29.97?
on Jan 31, 2011 at 5:10:44 pm

[Travis Taylor] " My reason for shooting in 59.94 was to have a higher frame rate "resolution" to allow more wiggle room for shifts in velocity (to match up the composited footage). "

But in the end, you dropped the frame rate to 29.97. That's when it happened. You now have half the motion information, but kevin's suggestions might help. Give 'em a shot.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Travis Taylor
Re: How do I prevent ghost effect when rendering 59.94 to 29.97?
on Jan 31, 2011 at 5:43:53 pm

Thanks so much for the feedback and suggestions. Kevin, I'll give the timewarp and revionsFX a shot. Ideally, I'd like to keep my subjects in focus while cheating the motion blur to get rid of the jutter. As far as the timewarp, there are two methods: pixel motion and frame mix. Do these methods have the same effect as the pixel motion and frame mix in the frame blend settings? I found that using the frame mix blend setting got rid of the jutter, but added way too much motion blur (given a choice between the two, I'd take the jutter).

Also, if you were to do the same shot (panning around a room at a relatively brisk pace), what frame rate and shutter speed would you use? (It's worth noting that this video will primarily be for the web.)

Thanks again!


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Kevin Camp
Re: How do I prevent ghost effect when rendering 59.94 to 29.97?
on Jan 31, 2011 at 7:15:50 pm

[Travis Taylor] "As far as the timewarp, there are two methods: pixel motion and frame mix. Do these methods have the same effect as the pixel motion and frame mix in the frame blend settings?"

those 2 settings are only used when changing the rate or speed of the clip using the effect, with speed at 100, they won't be used.. but yes they are similar to those in ae's frame blending, but the pixel motion option in timewarp can be 'tuned', or refined, in the tuning settings, but that is really only important for generating new frames and not much help when dropping frames.


[Travis Taylor] " if you were to do the same shot (panning around a room at a relatively brisk pace), what frame rate and shutter speed would you use? (It's worth noting that this video will primarily be for the web.)"

knowing that the final would be at 30fps (or 29.97), if i really wanted smoothness, i'd try for a shutter speed of 1/60 or 1/30 at 30fps, 1/60 if shot at 60 fps. of course this gives more motion blur to each frame, but that's where the sacrifice is... softer will be smoother, crisper will be jerkier (or at least less-smooth)...

which is better often comes down to what you want in the end. many action films are shot with a tight shutter angle (or higher shutter speed), which not only maintains detail in fast motion, but also creates a more aggressive, higher energy feel (think jason statham flims).

the problem you may get with a smooth pan, is that the camera movement itself may not lend itself to a tight shutter angle feel, so even though other parts of the video don't seem jerky at the same shutter speed, the pan does... so that's something else to consider, and out side of trial and error, i'm not sure how else to determine what would look best.

Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW


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