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Correcting color stripes in AE

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Chase Carnahan
Correcting color stripes in AE
on May 15, 2012 at 8:20:21 am

Hey all,

I'm having some serious trouble with some footage I shot a week ago. (This seems to happen on most of my footage in bright settings, too).

Canon 7D
Canon 10-22mm 3.5
1920x1080p 29.97fps square pixels.

I am experiencing (for lack of a better term) color striping on some of the surfaces. Admittedly, my exposure might not have been that great, due to the fact that I did not have a mattebox or any filters available, but I was hoping to get 3 answers from this post.

1. Is there a name for this?
2. What exactly causes this striping?
3. How do I correct this in post?

Here is an example of a frame that is experiencing the issue. And yes, those purple and orange waves move frame to frame.



Any help at all much appreciated.

Chase


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Roland R. Kahlenberg
Re: Correcting color stripes in AE
on May 15, 2012 at 11:28:50 am

[Chase Carnahan] "1. Is there a name for this?
It's called Chromatic Abberation.

[Chase Carnahan] 2. What exactly causes this striping?
http://en.wikipedia.org/wiki/Chromatic_aberration


[Chase Carnahan] 3. How do I correct this in post?"
Take a look at this COW Tutorial by Carl Larsen -
http://library.creativecow.net/articles/larsen_carl/removing_chromatic_aber...

HTH
RoRK

Intensive AE & Mocha Training in Singapore and Malaysia
Adobe ACE/ACI (version 7) & Imagineer Systems Inc Approved Mocha Trainer


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Chase Carnahan
Re: Correcting color stripes in AE
on May 15, 2012 at 7:37:19 pm

Thanks for the help Roland, it's hard to find this info when you don't know the terms.

Much appreciated. Now, off to find some lenses that have less Chromatic aberration!

Chase


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Jeff Brown
Re: Correcting color stripes in AE
on May 16, 2012 at 3:28:32 pm

I believe chromatic aberration would not be exhibited in that way. What you have looks more like moire artifacts from compression, i.e., I don't think a new lens would help.

-Jeff


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Nevin Styre
Re: Correcting color stripes in AE
on May 16, 2012 at 5:53:03 pm

It is moire that you are experiencing. Basically it is a limitation of DSLR's because when they record video they are skipping lines on the sensor to record your 1080p image rather than taking the whole 18mp image and scaling it down(which would require way too much processing in the camera to do at 24-30fps). Fine details on things like shutters, bricks, power lines, and even some clothing will exhibit this rainbow pattern that you see because of the limitation

Bad news, it's hard to fix the issue in post. Good news, there is a company making a product for exactly this limitation, it's an optical anti-aliasing filter that you put behind your lens & in front of the sensor (you would want to take it off when shooting photos).

http://www.mosaicengineering.com/products/vaf/7d.html


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Chase Carnahan
Re: Correcting color stripes in AE
on May 17, 2012 at 11:13:12 pm

Hey Nevin,

That looks more like the problem I am experiencing.

Thanks again for the response. Doesn't the 7D have an anti-aliasing filter already installed on the sensor? If not, why not?

But thank you, I will do a bit more research and then post again on this thread.

Chase


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Nevin Styre
Re: Correcting color stripes in AE
on May 17, 2012 at 11:31:27 pm

While it likely has an anti aliasing filter like many/most DSLRs, the filter is designed for edges/detail on the full 18 megapixel resolution of stills on the camera. It isn't designed for the sub-2 megapixel resolution of HD video. This is why you are supposed to take this after-market video anti aliasing filter off when taking stills, as it would likely make your 18mp stills pretty blurry as it is designed to "soften" the edges on a 1080p image.


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Barend Onneweer
Re: Correcting color stripes in AE
on May 18, 2012 at 7:22:38 pm

My solution usually is to select the offending area and re-colour it. So you want to either mask or find a way to key the window blinds and make them monochrome blue. One way to do this is fill the matted layer with the right colour (by adding the Fill effect and sampling the colour) and then setting layer blend mode to 'color'.

Barend

Raamw3rk - independent colourist and visual effects artist


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