GH2 Upressing 1080 to 4k to key better... And other upressing advantages?

A

Andor

Active member
My brain hurts. This idea sounded so asinine that I wanted to laugh but couldn't. Please, can someone more intelligent than me tell me if this actually works at all:

Take in a 1080p image and "properly" upress it to 4k to have the pixels enlarged so your program that you're keying with can be more accurate.

Bonus: YouTube allocates more bitrate to files with larger resolution. By sending a "false" 4k file to YouTube, you gain a cleaner file for viewing (since it'll be compressed again anyway).

Other Bonus: How valid is the whole "2k MPEG" patches on GH2? I mean, sure, it's a 2k file in the end... But is it really as much detail as its hacked 1080 modes? What's the highest resolution that's been recorded from a GH2?

Regardless, I'm shooting a ton of green screen this Sunday, so I guess I will dick around with the footage in post and see what happens. I was going to use Quantum 9b, but does anyone else have a patch they think is best for green screen work?

Thanks.
 
Not that I'm more intelligent than you, but Uprezzing to 4 k won't give you better definition.

Greenscreen Keying improves with color depth, not definition. Not sure if converting 4:2:0 to 4:2:2 would help, but it's more logical to move in that direction.
 
Converting 420 to 422 would just add "empty spaces" in the file though, no?

I'm really curious to try this now. I have no clue what algorithms keying plugins use. In fact, I have only ever needed to key a green screen once before this. I guess the train of thought was to "make the pixels larger" for the program, and then hope it made it seem sharper if it was down-converted back to 1080.
 
M. Gilden said:
I'm running low on sleep, but I can't imagine how the 4k thing would be a good idea.
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That's what I thought immediately too. I think my ignorance on how keying plugins specifically pick their colors is what's causing my brain fart.
 
What's BEST for Green Screen is LIGHTING..... Instead of worrying about your footage resolution which makes no sense what you're trying to do, make sure you light it properly.
 
J.F.R. said:
What's BEST for Green Screen is LIGHTING..... Instead of worrying about your footage resolution which makes no sense what you're trying to do, make sure you light it properly.
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Woah, woah... That's using realistic logic here. I may as well worry about the validity of my message. God forbid I think about the story! Jokes aside, we're shooting in a pretty tricked out studio so I'm not worried about lighting at all. Let's return this thread to the retarded pixel-peeping I meant for it to be:

I'm betting that there's no discernible difference, but I'll post results regardless after the tests.
 
Andor said:
Woah, woah... That's using realistic logic here. I may as well worry about the validity of my message. God forbid I think about the story! Jokes aside, we're shooting in a pretty tricked out studio so I'm not worried about lighting at all. Let's return this thread to the retarded pixel-peeping I meant for it to be:

I'm betting that there's no discernible difference, but I'll post results regardless after the tests.
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So why shoot on a GH2? You can rent a 4:2:2 or even 4:4:4 camera for pretty cheap these days. If the best quality for keying is what I needed than that's where I would be looking.
 
J.F.R. said:
So why shoot on a GH2? You can rent a 4:2:2 or even 4:4:4 camera for pretty cheap these days. If the best quality for keying is what I needed than that's where I would be looking.
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Because this literally zero budget video for fun. I can use the studio for free and I have volunteers to work it.

I haven't been following closely with the patches, but do you think there's any difference there? I saw that Apocalypse Now attempts to emulate 444.
 
M. Gilden said:
I'm running low on sleep, but I can't imagine how the 4k thing would be a good idea.
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Maybe you should ask Roger Deakins, who blew up Skyfall to 4k because it looked better to him.

Which brings me to the question of, why do I need a 4k camera, when a 4k blow-up looks so great.
Andy yeah, folks coming out of a 4k projection of a 2k film keep telling me that it looks soooo much better.

It's beyond me, but what do I know.
 
Andor said:
Bonus: YouTube allocates more bitrate to files with larger resolution. By sending a "false" 4k file to YouTube, you gain a cleaner file for viewing (since it'll be compressed again anyway).
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I believe there's truth in this, in fact I've tried this myself and I do think the YouTube playback looks a tiny bit better, plus you can view in "original" mode which will allow higher res monitors (and presumably 4k TV when they arrive) to view the upscaled image (together with its better bitrate).

YouTube recommended you upload in the largest, best quality, noise reducted format you can, these days they keep the original file stored so they have the opportunity to re-encode it and to support future TV/Video standards.

A page worthy of bookmarking if you YouTube your video: http://www.streamingmedia.com/Articles/ReadArticle.aspx?ArticleID=83876

Colleen Henry said:
It's important to think of the files you upload to YouTube as golden masters, as they will be used as source material to generate video streams for years to come. Simply put, the better the quality of the file you upload to YouTube today, the better quality the viewer's experience will be throughout your video's life on YouTube.

As displays increase in size, compression techniques become more efficient, playback devices become more sophisticated, and internet connections improve, so will the quality YouTube will be able to provide to the viewers of your videos. This means, while you may reach a limit on perceived benefits from higher bitrates or more efficient encoding if you were to test it today, that does not mean you should stop there. You will see a huge benefit over the lifetime of your video being available on YouTube, as internet speeds, hardware, and software evolve. Upload the best quality video that you can create and squeeze through your internet connection!
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I agree that lighting and color depth will make way more difference than resolution. There's only one time to get your green screen shot right and this is at the time of shooting. Anything after that will produce very little improvement if any. Light separation, enough brightness difference, enough foreground and background separation will get you a better key than any post process. Some studios are still set up with tungsten lights to light the screen. This is not the best, although many still contest this notion. But I have always got better results lighting the screen with daylight bulbs. 4:2:0 will definitely be your pitfall here. An AF100 recorded to a Hyperdeck in 8bit 4:2:2 would give you a better key and would not cost much to rent. Maybe you even know somebody who has one. Any good camera that can output 4.2:2 would even if just 8 bit. But if you say it's all just for fun then none of the above may matter anyway.
 
Gary Huff said:
If Roger Deakins legitimately thought (source?) that uprezzing to 4k made the picture look "better", then I'd question his judgment.
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He didn't say he thought it looked better. He said he loved using the Alexa and was very happy at the way it uprezzed to 4k.
Which was worth staying with the Alexa rather than going RED.
 
Fresno Bob said:
He didn't say he thought it looked better. He said he loved using the Alexa and was very happy at the way it uprezzed to 4k.
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Source

Here's the thing, the article mentions The Dark Knight Rises due to its financial success as an iMax film. I saw that in iMax, terrific experience, and everytime it cut back down to 35mm, it was like cutting between the best Blu-ray I've ever seen to a first generation DVD clip. The resolution drop was incredibly apparent. The resolution of 35mm film is already primarily scanned at 4k (though it can resolve more actually), and Fotokem offers scanning services of 65mm up to 11k.

However, because I'm fair, this is also an interesting test. This one is similar as well.

Do I doubt the Alexa looks fine on 4k/iMax? Nope, looked fine to me in the Sony 4k projection I saw. Would one notice a difference between 2k/5k/70mm? I think so. But the film wasn't shot like that, it was all Alexa, and there are plenty of reasons to chose an Alexa over a Red besides resolution (and vice versa).
 
You might actually achieve better results with a GH1 which can shoot in 4:2:2 in high quality mjpeg with a hack
 
Let me just throw this in there. I use the Ultra Plugin for Adobe Premiere CS5. I haven't upgraded to 6 yet, but am planning to, or maybe 6.5 (as Adobe will inevitably make once they figure out the bugs of 6). Anyway, GH2 footage keys great. I shoot in the vibrant profile with -2 to all but saturation at 0.

Even when we do crazy things with different colors of green for props and what not, and even with some interesting lighting that sometimes makes our green screen unevenly lit, it still keys just fine.

I don't know of any program that would benefit from uprezzing, or changing the color space. At the end of the day, my experience has always been you have what you start with. You can't add more detail to your scene. If it has 4:2:0 sampling, upping it to 4:2:2 isn't doing any more than blowing up a jpeg image would.
 
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