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Does chroma subsampling ever cause problems, with vfx?


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#1 cole t parzenn

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Posted 10 August 2014 - 12:50 PM

I think the title says it all.


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#2 David Mullen ASC

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Posted 10 August 2014 - 05:40 PM

Sure, if you are talking blue screen work and recording 4:1:1...


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#3 cole t parzenn

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Posted 10 August 2014 - 05:47 PM

I figured but that doesn't seem to stop people, does it? Chroma key is used so widely. Other issues? I'd imagine that any kind of re-sampling could lead to noticeable softness.


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#4 Phil Rhodes

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Posted 10 August 2014 - 06:12 PM

Modern keyers are outrageously good, but sure, it doesn't help. Not the end of the world, usually. Quality of original photography is more important.


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#5 David Mullen ASC

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Posted 10 August 2014 - 06:15 PM

The compression / loss of resolution in some color channels will limit the aggressiveness of color-correction decisions unless you don't mind artifacts.  I also think that chroma subsampling, especially at the level of 4:1:1 DV, can reduce the visible complexity of colors, making them less subtle, which is one reason why caucasian skin tones can fall into a dull band-aid tan color... but that's just an unscientific observation of mine, not sure it holds up to testing.


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#6 cole t parzenn

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Posted 11 August 2014 - 09:51 AM

So why is HD commonly used for high speed shots? You can shoot 35mm at at least 2,500 fps and 65mm at at least 720 fps, fast enough, for most purposes. You might have to push the film a few stops but you'd still come out ahead, with image quality.


Edited by cole t parzenn, 11 August 2014 - 09:53 AM.

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#7 aapo lettinen

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Posted 11 August 2014 - 10:12 AM

So why is HD commonly used for high speed shots? You can shoot 35mm at at least 2,500 fps and 65mm at at least 720 fps, fast enough, for most purposes. You might have to push the film a few stops but you'd still come out ahead, with image quality.

with HD you are able to check the shot right afterwards and see if there is some problem which needs to be fixed before next take. with such high frame rates you simply cannot see by eye what's going on and whether the subject, for example liquid or explosion, is moving like you've planned. maybe if your video tap could shoot, say, 1000fps. but then you'd have high speed video camera onboard anyway so it's more practical to simply use video for capturing and skip the film step. 

Also lots of high speed is used in commercials and there it is very critical to be able to show the shot to the customers right after the take so they can see their products is presented just as planned.

 

Another reason is that with high speed you need LOTS of light, maybe hundreds of KW's in some setups. That means you need to have as sensitive camera as possible to save lighting gear, electricity and money...with digital high speed cameras you can use wider shutter angle if needed so you can get almost a stop more "sensitivity". But I think the biggest advantage with digital high speed cameras is that you can trigger whenever you want and change the triggering style shot by shot. No need to speed-upping a film camera and precise starting time for the action


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