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 Post subject: 4K FOR 2K FINISH
PostPosted: Tue Jun 10, 2014 5:13 pm 
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Joined: Tue Jun 10, 2014 4:49 pm
Posts: 4
Greetings Camera Lab users:

How does one Downconvert GH4 4K to 2K or 1080? Best method for highest quality?

I'm using Premiere Pro. Is one software better than another in this regard?

Thanks


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 Post subject: Re: 4K FOR 2K FINISH
PostPosted: Tue Jun 10, 2014 7:02 pm 
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Joined: Tue Jun 10, 2014 4:49 pm
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Should I re-post this in another section?


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 Post subject: Re: 4K FOR 2K FINISH
PostPosted: Wed Jun 11, 2014 4:00 am 
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Joined: Wed Apr 08, 2009 2:29 am
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Currently, I don't see anything else giving you significantly better results than Premiere. (Although I personally switched to Final Cut Pro X, that was because of Adobe's Creative Cloud nonsense.) Further, I don't see this changing until someone writes conversion software that sums the luma values to give a 10-bit result. And that leads me to some unasked for advice which you may want to skip...

Really, at the moment, there isn't a lot of benefit to shooting 4k if your intended output is 1080, but there are a bunch of reasons not to. (e.g. higher hardware, software and storage requirements, more "jello", additional 30% crop, and you will lose the 1:1 benefit i.e. you will still have potential aliasing and moire issues, but they will be hidden until even later in the post process.) Yes, you can pan-and-scan, but IMO it would be better to get it right in-camera from the start. Yes, there are times (e.g. when shooting live events) that you may not be able to get it right in-camera, so the flexibility in post would be beneficial. But in most of those situations, the production would be better served by a dedicated video camera. So again, at this point, you'd likely be better off taking the money you would've spent on equipment to support 4k and spending it on an external HDMI recorder instead.

In any case, posting this question in this forum section seems fine to me - Mark


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 Post subject: Re: 4K FOR 2K FINISH
PostPosted: Sun Jun 15, 2014 5:14 pm 
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Joined: Tue Jun 10, 2014 4:49 pm
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I can't talk from experience regarding 4K to 2K video, but everything I read and see says there is indeed an image quality benefit to downsampling to 1080 Vs native 1080, at least with these large pixel count sensors.

See Gordon Laing's samples here:
http://www.cameralabs.com/reviews/Panasonic_Lumix_GH4/

Would anyone else care to chime in as far as best post practice is concerned?

Here is what Nick Driftwood briefly says about his sample vid :
"Here's a 14 second sampler from my previous Panasonic GH4 C4K (cinema 4K 4096x2160) video upload resampled by a little routine programmed by Thomas Worth at Rarevision. Employing 4K 4:2:0 to 2K 4:4:4 pixel summing Worth's code offers true 10 bit data in the luminance channel and spits them out in separate DPX files (each DPX=17.7MB) ready for grading/editing/rejoining/conversion to pro res, etc."

http://vimeo.com/91573346


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 Post subject: Re: 4K FOR 2K FINISH
PostPosted: Mon Jun 16, 2014 1:55 am 
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Joined: Wed Apr 08, 2009 2:29 am
Posts: 718
Sorry, I guess I shouldn't've said to skip the second paragraph. If I may restate:

"you'd likely be better off taking the money you would've spent on equipment to support 4k and spending it on an external HDMI recorder instead."

So yes, while there is "an image quality benefit to downsampling to 1080 Vs native [AVCHD in this case] 1080", I don't think the difference will be as pronounced when compared to 1080p 4:2:2 10-bit recorded from the HDMI out. Further, I don't think the difference will be worth all the downsides (which were also unfortunately listed in the second paragraph of my previous post).

Also, from the first paragraph of my previous post, "I don't see this changing until someone writes conversion software that sums the luma values to give a 10-bit result" which is what it seems Thomas Worth has done. ("Employing 4K 4:2:0 to 2K 4:4:4 pixel summing Worth's code offers true 10 bit data in the luminance channel".)

So yes, if you use Thomas' conversion routine and you are willing to accept the other downsides (more $$$, more jello, more crop, more moire, more noise), then shooting 4k and downconverting could be for you. But even then, I wouldn't call it "best practice" to do so. Nor would it necessarily result in the highest quality image.

Mark


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 Post subject: Re: 4K FOR 2K FINISH
PostPosted: Mon Jun 16, 2014 3:16 am 
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Joined: Tue Jun 10, 2014 4:49 pm
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Thanks Mark. I am setting up for 4K, of that I am sure, but I'm also aware of the current "popularity" of 1080/2K finish, and to that end I was curious about one route versus another, whilst retaining the 4k original. What you say makes a lot of sense though. Much appreciated.


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