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'Marching Ants' on overexposed footage

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Ed Watkins
'Marching Ants' on overexposed footage
on Feb 4, 2013 at 9:23:08 pm

This may be a stupid question but:

On some of our footage wee keep seeing 'marching ant' / magic wand type borders around all the overexposed areas.

I'm not talking about zebras, just a dashed line around the highlights. We don't have any overlays turned on, and as far as I can tell its not a filter. Any ideas how to get rid of it?

Attached is a picture



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Mark Suszko
Re: 'Marching Ants' on overexposed footage
on Feb 4, 2013 at 9:39:17 pm

Try fixing it with the Broadcast Safe filter from effects>video filters> color correction, or the 3-way color corrector from that same path, see what happens and report back.


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Ed Watkins
Re: 'Marching Ants' on overexposed footage
on Feb 4, 2013 at 9:47:27 pm

Hi Mark,

Broadcast safe fixes the issue (as it should, as no areas are now over 100) but I still don't understand what is generating the 'marching ants' overlay on the image in FCP.

Is it a setting that can be turned off somewhere?
I've been editing for 6 years and I've never seen it before...

Thanks,
Ed


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Mark Suszko
Re: 'Marching Ants' on overexposed footage
on Feb 4, 2013 at 10:08:16 pm

I believe that what you're seeing is the result of the video signal being higher than the monitor can deal with, and the interface between edges is "vibrating" at the pixel level - especially if this is interlaced footage. BTW, hope you used the scopes and 3-way color corrector to fix it, because the broadcast safe filter is just a quick fix and not always actually within the strictest of broadcast tolerances. People too often use it quickly and unthinkingly as a crutch and only later does it bite them. The broadcast safe filter basically clamps the brights and darks but you might lose a lot of nuance in what's in-between so it's just better over-all practice to color correct with the 3-way.

Now I don't know why you're getting footage that is so very far out of spec to begin with, but you may want to go thru your overall signal chain/ intake practices and see if the footage was indeed that over-expsoed to start with (then dope slap the shooter) or do you have an analogue stage in your signal flow that perhaps has an unterminated signal? That can sometimes lead to overly-bright signals. When you get a chance, do an end-to-end check of your setup using color bars and scopes and see thateach stage is as close to spec as possible, so your monitors really show you what you're doing.


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Mark Suszko
Re: 'Marching Ants' on overexposed footage
on Feb 4, 2013 at 10:12:01 pm

That sky is blown out: all the detail was lost when you went over 100 IRE units. This is a good candidate for a sky replacement done in compositing. Add back a blue sky gradient using the blown out white as a luminance key, engage motion tracking, to lock the sky to the land, and it will look better.


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Ed Watkins
Re: 'Marching Ants' on overexposed footage
on Feb 4, 2013 at 10:24:03 pm

Hi,

The footage is 1080p, and it's not just this shot, it is any where the highlight values exceed 100.
The dashed lines do not show up on QT export they are definitely the result of an overlay or display issue within FCP.

As for sky replacement/color correction the online will deal with any actual color correction, I just used that shot as a simple easy to see example of the issue.

I just need to work out what is generating the overlay dashed lines and turn it off, before it drives all the offline editors crazy.

Thanks for all the help.


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Tony Brittan
Re: 'Marching Ants' on overexposed footage
on Feb 4, 2013 at 10:39:01 pm

Bottom line is that it isn't an overlay. It's just that FCP will show you the where the whites are blown out. It's so blown out in those areas that there's no info. So it displays it as black. Not an overlay. I doubt you can fix that with standard filters in FCP. Sky replacement is a good option. But not perfect. Know a really good After Effects artist? Rotobrush might be workable in AE for rotoscoping that.

Wish there was a better answer for ya.

Tony Brittan
Island Shore Productions
Posted from iPad, please excuse typos!

Tony Brittan
Island Shore Productions
Kill Devil Hills, NC


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Mark Suszko
Re: 'Marching Ants' on overexposed footage
on Feb 4, 2013 at 10:39:40 pm

I am saying I don't think it IS an overlay, unless you have the broadcast spec warnings turned on. I think it's an artifact of a heavily overdriven aliased display.

Run a calibration of your monitors and check your video card settings.


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Ed Watkins
Re: 'Marching Ants' on overexposed footage
on Feb 4, 2013 at 11:00:18 pm

I'm not sure it is the issue you are describing.
I just opened the footage on another of our FCP workstations and the issues disappears.
It seems specific to one machine.

Bizarrely putting "Range Check" on removes the dashed lines, on that machine.


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Ed Watkins
Re: 'Marching Ants' on overexposed footage
on Feb 4, 2013 at 11:07:08 pm

O.k solved it.

Incase any one has the issue themselves.
It was a Kona card issue, display needed to be 8bit rather than 10bit.
10 bit was causing a weird overlay issue at the highlight boundary.

Thank you for all your help on this issue guys.


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Tony Brittan
Re: 'Marching Ants' on overexposed footage
on Feb 5, 2013 at 12:01:26 am

Aha! Well, that is great news. I had that happen once and it was the overblown issue I'd described.

Posted from iPad, please excuse typos!

Tony Brittan
Island Shore Productions
Kill Devil Hills, NC


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