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Erik Hammen

Dead space in otherwise moving video images

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Hi folks -- I'm relatively new still with DSLR video shooting (coming from film). I've noticed that movies shot digitally can sometimes have areas in the image that seem "dead" in spots, usually colorfields, like a blue skylook, in which that area of the image looks more like a computer that's seized up and stopped playing than simply part of an otherwise "moving image".

 

I've seen this in films shot on low-end DSLRs, but also on big budget films, where I assume they are using state of the art cameras.

 

Anecdotally, I've seen it more on black and white films than color, and I've seen it both in the theater and on small screens.

 

I'm assuming that this is an element of how the microprocessors save space: if something isn't moving in a way it detects (like a sky) the processor will not refresh the image for as long as it can to save processing speed/space. Or something to that effect.

Also it's usually in well lit shots, so I'm guessing the absence of video "grain" contributes to the problem.

 

But... does this ring any bells, and is there something one can DO about this phenomenon? I've seen it in some of my work, (Panasonic G7) and I hate it. It seems to me that adding some kind of grain plugin is crummy solution, but maybe I need to get used to that idea.

 

Thanks for your time!

EH

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digitally displayed images do not have the flicker that film projection had. And also can be very clean and grain free. I think this is what you are reacting to. Mostly the absence of flicker (and shake) from the projector. Even movies shot on film and scanned and digitally projected will probably show this too, as well exposed scanned negative film looks quite clean as well.

 

All you can really do is add noise or "grain" to your images, or... create a film negative from your digital files and project your projects on film!

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Its only the low end and DSLR type camera that are using Long GOP.. to save recording all the data in a frame..they will only record what changes in a "Group of Pictures" .. can be up to 30 frames I think.. but higher end cameras on movies will be recording Intra frame for sure.. all the data in each frame is being recorded .. no frame is dependent on a previous one.. as Bruce says it might be film "weave".. that of course doesn't happen in video as nothing is moving through a gate..

 

But end of the day.. if the audience is noticing stuff like this .. with the exception of banding thats really off putting and you should never see in a decent budget film.... then the film itself is probably not very good in the fist place, if your attention is wandering that much.. it could also be crap projection in the actual theatre .. seems to be becoming more common even as they fight for bums on seats..

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I have done some compression-experiments with the "VP9 .webm" codec, and one of the features is that you can lower the frame-rate in sections of the intra-frame that has little difference between adjacent temporal inter-frames.

Basically this means you can have a main frame-rate of 60fps (or whatever is the main frame-rate of your video) and then smaller sections of the image can have an individual lower frame-rate.

I believe the purpose is to decrease band-width and/or increase compression-ratio relative to your quality-target and I see it frequently on LIVE-broadcasts (somebody doing an interview on some outdoor location, for example) on TV (mostly when they seem to use internet-connections for their ENG-links, which appear to happen more and more often now)

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