Motion blur problem

[QuickHitRecord]

 

I just wrapped a talking head shoot against a white backdrop. The subject talked with his hands a lot and I noticed a ways into the interview that his hands would "disappear" when they were in motion (frame-by-frame above; click for closer view). 

 

I shot this on a Varicam with a Fujinon zoom lens in 23.98, 180 degrees / 1/48 shutter. I also had my GH2 running for an alternate angle (1/40 shutter), and it also exhibits this issue though to a lesser extent.

 

I speculate that it has to do with shutter angle. Perhaps the constant light being reflected off of the backdrop  was overwhelming the blurred frames. That would be my guess anyway, but I am posting it here to see if anyone else has come across this before.

[HurtinMinorKey]

It looks like ghosting to me, which can happen when you put things like 23.98fps into 24fps projects. I learned that the hard way with my ol' 5D2. 

 

Are you rendering both of those in the same project? What fps were you shooting the gh2 with?

[Bioskop.Inc]

Looks like a combination of all 3 - 23.98fps, white background & light.

Tough lesson to learn, but i'm sure you'll notice it more than anyone else - can you cut away at the worst bits or is it too much.

 

I once heard a Director tell a contributor that he'd tie his hands to the chair if he kept talking with them so much - its a very distracting habit when you finally watch a piece & you've just got to try to get them to stop or tone it down.

[QuickHitRecord]

It looks like ghosting to me, which can happen when you put things like 23.98fps into 24fps projects. I learned that the hard way with my ol' 5D2. 

 

Are you rendering both of those in the same project? What fps were you shooting the gh2 with?

 

Let's see. I conformed the sequence to the camera clip, so I don't think that the disconnect is there. I was shooting in the GH2's 24fps mode which I believe is actually 23.98fps. I haven't put any of those clips in a sequence yet. Also, files from both cameras exhibit this effect when I play them in QT7.

 

Looks like a combination of all 3 - 23.98fps, white background & light.

Tough lesson to learn, but i'm sure you'll notice it more than anyone else - can you cut away at the worst bits or is it too much.

 

I once heard a Director tell a contributor that he'd tie his hands to the chair if he kept talking with them so much - its a very distracting habit when you finally watch a piece & you've just got to try to get them to stop or tone it down.

 

Fortunately, the GH2 is punched in to a close up so his hands rarely get into the frame so I think that I'll be fine as far as the client is concerned. The footage out of the GH2 is much more pleasing anyway.

 

I wonder if this would have happened if I had shot at 1/60 shutter...

[Ernesto Mantaras]

It looks as if the background was overexposed, but in post, like what would turn out if I brought the whites to the left with a levels adjustment. Weird. Perhaps the camera was applying some sort of rare contrast? Which is difficult because the subject looks a bit washed out.

I know the background's supposed to be white, but perhaps the light shouldn't have been as bright and have the backdrop be a very light grey, just underexposed under 100 IRE? It looks to be overexposed, pure white, if you haven't touched the colors.

Perhaps this is a case of the gamma problem in Mac? Where blacks and whites get crushed into a 16-235 palette.

[QuickHitRecord]

It looks as if the background was overexposed, but in post, like what would turn out if I brought the whites to the left with a levels adjustment. Weird. Perhaps the camera was applying some sort of rare contrast? Which is difficult because the subject looks a bit washed out.

I know the background's supposed to be white, but perhaps the light shouldn't have been as bright and have the backdrop be a very light grey, just underexposed under 100 IRE? It looks to be overexposed, pure white, if you haven't touched the colors.

Perhaps this is a case of the gamma problem in Mac? Where blacks and whites get crushed into a 16-235 palette.

 

When I was lighting the shot, I initially had the white backdrop at about 95 IRE (using two Arri 1Ks). Space was limited, so I was having difficulty moving the lights to match exposure across the backdrop and ultimately decided that since the client wanted pure white, I could blow it way out above 105 IRE and that way it would look even. The subject was far enough forward that he should not have been affected by it.

 

I don't think that it is an issue with the camera, since both the Varicam and the GH2 struggled with this. I'll try it on a PC though, and see if it's the Mac gamma bug.

[Bioskop.Inc]

If it isn't a Mac bug, then yes don't need to follow the 180 rule for stuff like this or fps (there's a lot of misinformation about this cinematic rule, which is really a mechanical dimension of cinema cameras).

[Sean Cunningham]

Does the Mac gamma bug exist anymore?  I think I still had to watch out for it in 10.5 which still had the old oddball system gamma.

 

I don't see anything unexpected here.  Motion blur is transparent.  There's no way the thin, transparent pixels of the fingers can compete with that background.  If you were to have shot him against a greenscreen and composited him over white at that level you would have likely arrived at a similar end effect to avoid the motion blurred portions of his fingers looking like they had black halos.  

 

Shooting at a higher shutter speed to avoid motion blur would have likely been the compromise you'd need for virtually any camera in a non-raw situation (betting a few more stops of DR might get you some of your finger back).  You'd then just have to make the judgement call on strobing.

[QuickHitRecord]

Thanks, Sean. All good points. I think that I will stick with a green screen the next time I have to do this.

[Sean Cunningham]

You might also try lighting the white backdrop a stop or so under your target, evenly, but not at your desired final brightness level.  If you were to then pull a luma key you would be able to build up its exposure relative to your subject with a little finer control over the edging.  Granted, it will be harder to keep the razor sharp jump from talent to pure white but you could likely hit that and "power-window" a slightly modified mix around his hands when they pop up if necessary.  

 

I only suggest this alternative as a means of avoiding any possibility of clean keying issues, though contemporary keyers handle compressed, sub-sampled chroma in green screen plates a lot better than they used to.