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Old February 9th, 2010, 03:56 AM   #1
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Black Backdrop a Codec Killer?

I've read that subtle shadow details can be murderous on codecs. I'll be shooting some sitdown interviews infront of a black duvetyne backdrop. There won't be a lot of movement--only the subject talking, but I'm concerned about the backdrop.

I'll be filming using an HV-20 at 23.976. I've considered bypassing HDV by using Cineform to a capture pc or even a nanoFlash.

Any thoughts on if this setup is especially challenging for compression? I also realize that Cineform uses a wavelet based compression instead of DTC that nanoFlash, Prores and others use. IIRC, wavelet is better for naturally ocurring shapes, but I have no idea if fabric detail qualifies as "natural" or not.

I'd give the trial a shot, but to test the capture I'd also need a BMI card and a PCI-Express computer. So I'd like to get a little info. before ploping down the $.

Thanks very much!
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Old February 9th, 2010, 08:33 AM   #2
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Peter.... I'm not sure how to define that a codec is killed other than breakup of the image or lost frames.

I've done many interviews as you describe, and if the shading and darkness that you describe is problematic for a codec (I think fine, high contrast lines and movement are a bigger challenge... or something like a sparkling body of water), then having your camera locked down will more than offset that issue in my opinion.

With a high percentage of your frame not changing, the codec is working much less, at least on those areas.

This is a layperson's interpretation, but with a lot of practical experience.

It shouldn't be difficult to set up a test and roll some footage to verify, but I really doubt you'll have problems.
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Old February 9th, 2010, 08:40 AM   #3
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I have done that exact shot on a JVC HD110 and as long as you have the color right going into the camera you will be OK. The second you start to push the color in post you will get noise. Or at least I did.
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Old February 9th, 2010, 09:10 AM   #4
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Inter-frame differences are what really kill codecs, so solid colors are actually better for reducing compression artifacts. However, all cameras produce noise, so this can create compression artifacts on its own.

In my experience (HDV, MiniDV, HD-DSLR), shooting against all black or white is just fine, provided that you set your exposure properly and light the background properly. Against black, this means that you should be driving the background to pure black, lighting your talent significantly, and flagging those lights (and having good FG/BG separation distance) so that light doesn't spill on your background.

In the final result, you can always crush the blacks just a smidge to ensure that your final delivery codec, which is usually less forgiving than your capture codec, reads that background as solid digital-zero black.
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Old February 9th, 2010, 09:20 AM   #5
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Extreme detail wherever it is, in shadows, in the background or forground, is only a codec killer for CBR codecs. CineForm is constant quality codec, our bitrate climbs to meet the information need --- blue sky or rain forrest, the quality is the same, the bitrate will change a lot.
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Old February 9th, 2010, 10:48 AM   #6
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My recommendation would be to angle the black back drop so the bottom is further from the camera than the top...effectively 'tilting' the plane of the fabric forward...and keeping it from becoming incident with the angle of any of your should be as black as possible this way and keep any texture on the fabric from appearing.

I'd also (obviously) create as much distance between your interview subject and the fabric. If the fabric is far enough out of the field of focus, any unwanted detail should be reduced in the optics...before the camera even deals with it.

Otherwise, i'd have to agree with Dave N...the CineForm codec will handle whatever is there faithfully...the question is whether you want it or not.

The HV20 is...HDV? I'd say that the camera's MPEG2 compression probably won't handle it as gracefully...and of course, transcoding (even to CineForm) can't bring back what is already gone.

I'd recommend a test shoot so you at least know what you'll have to work with.
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Old February 10th, 2010, 06:21 AM   #7
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Thanks for the info and tips guys :). Very much appreciated.
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