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Anyone know what this is? Chromatic aberration maybe?

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Spencer TweedAnyone know what this is? Chromatic aberration maybe?
by on Jan 26, 2011 at 8:17:46 pm

Hello all,

I some sort of weird defect on some footage I am trying to key. It is an edge around contrasting colors that is being put in by the camera itself. It looks something like chromatic aberration, but I don't think that it actually is.

Here's a link to a still from the shoot:
http://f1.creativecow.net/1549/the-still?uploaded=file

- Spencer


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Walter SoykaRe: Anyone know what this is? Chromatic aberration maybe?
by on Jan 26, 2011 at 9:04:39 pm

[Spencer Tweed] "I some sort of weird defect on some footage I am trying to key. It is an edge around contrasting colors that is being put in by the camera itself. It looks something like chromatic aberration, but I don't think that it actually is."

What kind of camera? I'd guess it's a compression artifact on those high-contrast edges.

Walter Soyka
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
RenderBreak Blog - What I'm thinking when my workstation's thinking
Creative Cow Forum Host: Live & Stage Events


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Dave LaRondeRe: Anyone know what this is? Chromatic aberration maybe?
by on Jan 26, 2011 at 9:05:17 pm

[Spencer Tweed] "It is an edge around contrasting colors that is being put in by the camera itself. It looks something like chromatic aberration, but I don't think that it actually is."

Well, I don't think you have to answer my question about the kind of camera you used to shoot the chroma key and the reflection. I'll take a stab at it myself: you shot on XDCam, HDV or a similar camera. It certainly wasn't a Panasonic P2 camera or better -- I have one whole American Dollar that says so.

I believe you're seeing the combination of two things, a combination of a wide pixel aspect ratio and lousy color resolution (aka color sampling). Of the two, lousy color sampling is the more offensive.

In order to cram an HD picture into SD bandwidth, XDCam, HDV and their ilk cut a BIG corner on the color resolution, and it's most apparent at the edges. Clearly-defined edges. They use 4-1-1 or 4-2-0 color sampling, which is non-technically explained in this here podcast:
http://macbreak.libsyn.com/index.php?post_id=70596
Pay particular attention to the DV example; DV has the same stinky color resolution as HDV.

And on that chroma key shot with reflections, you owe your life to the good lighting; it's the only thing that saved you. Because of it, you were able to pull a good key.

Yet another reason to take that gaffer out for a beer.

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


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Olin PadillaRe: Anyone know what this is? Chromatic aberration maybe?
by on Jan 26, 2011 at 9:15:42 pm

I have gotten this exact same effect shooting with an HPX-500 on P2. In my case, I assumed it was a combination of bad lighting and contrast compensation in the compression.


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Spencer TweedRe: Anyone know what this is? Chromatic aberration maybe?
by on Jan 26, 2011 at 9:18:13 pm

Good call Dave it was an XDcam, though the DP told me she was shooting it 4-4-2.

I knew that the lighting would be key in this shot, so worked with both of the gaffers very closely. I'll forward your message to 'em!



- Spencer


PS

I'd love to take them out for beers but it'll have to be a few years - I'm 17.


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Dave LaRondeRe: Anyone know what this is? Chromatic aberration maybe?
by on Jan 26, 2011 at 9:30:32 pm

[Spencer Tweed] "...the DP told me she was shooting it 4-4-2."

That isn't a color resolution, that's the name of the only Muscle Car ever made by Oldsmobile.

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


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Spencer TweedRe: Anyone know what this is? Chromatic aberration maybe?
by on Jan 26, 2011 at 9:36:45 pm

Hah! Yeah, I thought that was a little funny... She's in Australia at the moment, I'll have to ask what she was talking about when she gets back.

But still, is there any way of fixing this in post? I know I can obviously do some edge detection and color correction (which I have already done, and it works out well) but I was wondering if there were some better way of handling it.

- Spencer


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Spencer TweedRe: Anyone know what this is? Chromatic aberration maybe?
by on Jan 26, 2011 at 9:38:13 pm

Never mind, I just saw your other post.

- Spencer


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Spencer TweedRe: Anyone know what this is? Chromatic aberration maybe?
by on Jan 26, 2011 at 9:23:30 pm

Allright, so we have established that it is a defect of the chroma sampling in the XDCam format - but what is the best way to correct this? What I am thinking is pre-comping my key and using it to create an edge mask from the alpha that I can then manually just bump up with some color correction. I know this will work, but perhaps there is a cleaner way?

- Spencer


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Dave LaRondeRe: Anyone know what this is? Chromatic aberration maybe?
by on Jan 26, 2011 at 9:28:56 pm

Watch the podcast I linked to. See how difficult it is to work with lousy color resolution. And while you're watching, remember that 1) HDV has the same color resolution as DV and 2) this guy makes software that's supposed to key DV video, okay? HE doesn't even like keying DV!

You're stuck with what you have, I'm afraid. The damage was done as it was being recorded. Unless you possess the capability of time travel, there isn't a thing you can do about it.

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


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Philippe LessardRe: Anyone know what this is? Chromatic aberration maybe?
by on Jan 27, 2011 at 8:51:49 pm

You could just use a matte choker, and/or chroma blur and/or a deartifactor.

Look at this:

http://pilalitos.blogspot.com/2006/10/magic-bullet-deartifacting-vs-chroma....


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Philippe LessardRe: Anyone know what this is? Chromatic aberration maybe?
by on Jan 27, 2011 at 8:56:14 pm

Sorry i forgot to paste this link, it's what you looking for.

http://www.redgiantsoftware.com/products/all/key-correct/


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Spencer TweedRe: Anyone know what this is? Chromatic aberration maybe?
by on Jan 27, 2011 at 9:49:32 pm

Thanks Philippe, I had forgotten about this plug-in suite. Sadly spending any money is out of the question, it simply takes too long to get through finance lines right now and I'm not willing to consider that option.

For the future though I would love to get this suite, I have seen a few videos on what it can do. It is great stuff!

- Spencer


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