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Old April 12th, 2007, 01:55 AM   #1
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The DV Codec

Greetings,

I have been working on a documentary piece and as well just did a test shoot for a new piece with a Z1U set-up in DV mode, and I am disappointed in how poorly the DV codec stands up to saturated colors, especially the reds. I am fully aware of the fact that it is in my best interest to avoid saturated reds wherever possible, but it is not always possible to not have reds in the shot. The attached frame grab is a green screen test shot I did with with an assistant to check lighting, levels, etc. I have never seen as much pixelation/shearing as this in an image before. This is happening on both my edit-only machine and my laptop. I have also encountered this type and level of pixelation from other footage shot on a Canon GL1 as well in an outdoor environment. According to my vectorscope, I'm a long ways from saturation at 64% in the reds. the only thing that helps to clean this up in post is to drop a chroma blur filter on the clip and blur the horizontal pixels like crazy.

Is this normal with DV footage?

Shot on Z1U in DV mode
Raw interlaced screen grab - identity of stand-in blurred to protect the innocent. :)
Vegas 6.0D

your comments and advice are more than appreciated!

Thanks!
Attached Thumbnails
The DV Codec-dv_pixelation_shearing.png  
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Old April 12th, 2007, 02:10 AM   #2
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Sorry to answer your question with another question, but why did you capture the footage as DV? Couldn't you have captured with HDV with markers on the side to show your 4:3 aspect ratio? DV doesn't have much chroma information and you are trying to do chromakey. There are specialized applications that can sometimes pull a decent key from DV, but they are expensive. It would probably be cheaper and easier to edit in HDV.
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Old April 12th, 2007, 09:06 AM   #3
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Marcus,

Yes, for keying, I usually capture in HDV, and convert to a cinefrom codec upon capture and then key in keylight (after effects) or Ultra from there, with tremendous results. Actually, most of my shooting is now in HDV these days

I had captured this frame in DV purely to show the effects that I am getting in the DV codec. that being said, I have had a similar issue in some HDV clips as well to a lesser extent.


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Old April 12th, 2007, 09:30 AM   #4
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"then key in keylight (after effects) or Ultra from there, with tremendous results."

I think that is exactly the advice some expert around here would give you. If you already have a good workflow and tremendous results, don't change anything. DV is not the pinnacle of digital video and HDV is also highly compressed. HDV obviously has an advangate due to more resolution, but it still has limitations. The software you are using takes into account those limitations and works with the format probably in the best way possible. If you want anything greater, you would need to start working in a less compressed format like HDCAM or take video from an uncompressed output like SDI or HDMI.

I think you already had the answers you needed. Use HDV and Ultra instead of DV. I've been impressed with samples from Ultra and your comments seem to back up it's quality. The only thing you might be able to improve without jumping into a different method/workflow would be the render time with a faster computer.
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Old April 12th, 2007, 09:42 AM   #5
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Marcus,

when I am in control of shooting, yes, I have the answers I need. However, I often get footage from other shooters for documentaries and such that exhibit this same issue.

really my question is - is this artifacting/pixelation normal for DV, and if so, how do I best deal with it in post when it comes across my desk?

I have been using a chroma blur filter, but what are my other options if any?


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Old April 13th, 2007, 05:02 AM   #6
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Hopefully, someone else will answer about how to deal with DV in post. I can only answer that it is fairly normal for DV to have that chroma "pixelation" as there is only one color sample for every four pixels. Put it this way; DV is really only 320x240 in it's color information. If you can get a decent key with DV, you are very good at your job.
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Old April 14th, 2007, 12:25 PM   #7
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Don't Blame the DV codec:

From Chris Watts, the Visual Effect Supervisor of 300, quoted from "Inside 300" by Gerri Miller published in "How Stuff Works": (http://entertainment.howstuffworks.com/inside-3002.htm)

"Blue screen, rather than green, was chosen for several reasons. “We have a lot of red in the movie, and sometimes when you have saturated red on a green screen you often have edge problems, where you get a yellow edge. It has to do with the way light travels through film and interacts with the emulsion layers,” explains Watts. “Also, the amount of light that bounces back off a blue screen vs. a green screen is different. The green bounces back a little more light, and we would have ended up with screens that were a little brighter than I like to shoot them. Some say that the color of the spills that come off a blue screen are less objectionable than those that come off a green screen.”"

No format, not even film is perfect. The solutions are how we distinguish ourselves.

Green screen is simply one solution. Blue screen is another.

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Old April 15th, 2007, 09:39 PM   #8
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Please note that I have experienced this not only with shooting green/blue screen, but also with a regular shot with a broad rage of colors in the frame. Mt intention is not to point this out only in a green screen shot, but in any shot.

Brian, I fully understand and agree with your quote. And by no means am I 'blaming' the DV codec. The DV codec and its associated equipment and workflow has allowed me to make a living that I previously was not able to as I couldn't afford to get 'into the business'. Really, my intention with this thread is to point out some experiences that I have had with this type of issue, and find out how others have dealt with it when it happens. I don't want this to become a codec bashing session........ rather, I want to see how others deal with it aside from not shooting any subject that has red in it...

Keep it coming!
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Old April 15th, 2007, 10:04 PM   #9
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....intention is not to point this out only in a green screen shot, but in any shot.

I'd like to hear novel solutions as well.

I stumbled upon the 300 quote addressing the very same concern, and had to share it simply because it demonstrates that the problems we solve at this level are no different from those faced by professionals working on films which pass $200 Million at the box office.

Brian
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