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Progressive to Interlaced and back again?

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Andy Galloway
Progressive to Interlaced and back again?
on Jun 3, 2013 at 8:59:07 pm

Hi guys,

Right this a bit complicated but here it goes.

We shot a TV spot on Red epic at 1080 50fps that consisted of a track shot through a room. Unfortunately it was not taken into account that the camera move would have to be double speed to compensate for the speed change when conformed to 25fps.

So the simple solution was to then speed ramp the footage in FCP to 200% which gave us the shot at the correct speed. However, the dropped frames caused an undesired judder/stepping and ghosting effect. To fix this I took the footage into AE and conformed it to it's native 50fps, dropped it in a 25fps comp and rendered it with fields. This has given me an almost perfect 1080i video at the correct speed that will be fine for broadcast.

However, I will have to do web versions of the advert so will want a fairly decent progressive version. If I deinterlace my new 1080i footage it has some pretty severe strobing in high contrast areas. I've also used Twixtor, timewarp and time stretch on the original progressive footage to try and get a decent double speed 25fps export however, the strobing is severe using this method and so is the stepping between frames.

Obviously this issue should have been avoided by shooting at 25 but they thought they were doing me a favour. So if anyone has a good workaround for deinterlacing or reducing flicker and stepping whilst speed ramping I'd appreciate the help.

I'm currently working with graded Pro Res 4444 files but my thoughts at the minute are to try again with the Red Raw to see if it gives me better results. I'm also considering going into Photoshop and using the deinterlacing tools in there.

Thanks in advance for any help,

Andy


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Dave LaRonde
Re: Progressive to Interlaced and back again?
on Jun 4, 2013 at 12:34:54 am

After Effects can do this frame rate change just as easy as pie.

Make a 25FPS comp. Add the 50 FPS footage. Render in the appropriate media container and codec. Don't render fields.

Done. Really. No fooling.

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


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Andy Galloway
Re: Progressive to Interlaced and back again?
on Jun 4, 2013 at 2:16:23 pm

Cheers Dave,

Unfortunately there is camera horizontal movement in the shot which is creating a vibrating/flicker effect as high contrast objects move through it. I am assuming this is a shutter speed issue as everything in shot is super sharp. At 50 fps it looks acceptable however using your method and every other one I have tried this flicker is way more pronounced at 25.

However, because the shot was shot at the the wrong speed I was able to export the advert at 50fps and it looks great. Don't suppose you know if a 50fps video can be used for internet use? I'm unsure whether websites that host content convert footage to a different frame rate or keep the frame rate from the source. I guess I will have to experiment with that.

Thanks for your help though it's much appreciated.

Andy


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Dave LaRonde
Re: Progressive to Interlaced and back again?
on Jun 4, 2013 at 2:50:07 pm

[Andy Galloway] "...there is camera horizontal movement in the shot which is creating a vibrating/flicker effect as high contrast objects move through it... At 50 fps it looks acceptable... is way more pronounced at 25..."

You are seeing the dreaded judder -- a real term describing just what you see in the horizontal motion -- and it manifests itself more often at lower frame rates. If you have no other choice than to shoot at a lower frame rate, you can alter the speed of the horizontal motion to make it go away.

As you mentioned earlier, you may have to re-shoot to eliminate it.


Here's a good discussion about judder:
http://kb2.adobe.com/community/publishing/908/cpsid_90843.html

Yes, it addresses motion graphics, but the principles still apply to photography.

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


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Andy Galloway
Re: Progressive to Interlaced and back again?
on Jun 4, 2013 at 7:36:19 pm

Cheers Dave,

It's a problem I have encountered before in motion graphics, obviously that's way more controllable though.

Oh well it looks great 50i and 50p which I think has narrowly avoided a re-shoot... thank god.

Cheers for your help mate.

Andy


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Keith Slavin
Re: Progressive to Interlaced and back again?
on Jun 26, 2013 at 9:32:17 pm

Hi Andy,

If you want to redo your footage for 25P distribution, you need to add some motion blur. We (isovideo) have advanced processing tools to do just that. If the clip is not too long (say 5 minutes max), we could convert it for free if you would like to try us out. What would work best for us would be the original 50P, which we would then downsample to 25P, while also adding blur. We can handle prores4444 input, but can only generate prores444 (no alpha) on the output. If you are interested, send me email at keith@isovideo.com with a link to download the clip.

Keith


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