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Calling all colourists - Grade Panasonic GH4 4K ProRes next to Arri Alexa 2K ProRes

Andrew Reid

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I haven't posted here, but I have to say this post bothered me a little bit so I had chime in. I'm a colorist for a living in between directing and editing, I grade Alexa footage constantly and I have to work with everything from that to RED, to DSLR stuff all the time. As much as I love my GH2 and GH3, I had a pretty good suspicion there was no way this comparison would remotely hold up. I let it go, but the latest post seems to be pushing the argument farther. 


I've included an example here from the downloaded gh4 footage and the publicly available Alexa footage to illustrate my point, which is, theres a million factors that go into a comparison like this. Glass, codecs, bit rates, resolution, color space, dynamic range and more, but for the purpose of this illustration, I'm just talking about dynamic range, codec, and color space.


There is no comparing what an Alexa is putting out in S-log, vs the modes this GH4 footage was shot in. As shown in the example, the first cut of the guy on the bongos is S-log. There isn't a single pixel in that image that is clipping one way or the other. This means in a perfect world I have full control over what i want to make black and what I want white. The Panasonic isn't giving me nearly as much. Whether thats simply the color profile thats on, the codec squeezing it, the quality of the glass, or simply the cameras dynamic range ability, there is simply no way to take a GH4's image to the places you can take an Alexas.


The example videos point that out. For the Alexa, it starts as S-log, than kinda normalized start no detail lost yet, then a nice little crushed punchy look, then an extreme s-curve look, than a completely ludicrous version. Of course no one is grading at ludicrous speed that often, but the illustration is that even at that level, the image is tight as can be and nearly noise free. pretty incredible


A real test of how strong an image holds up is fixing a broken one, rather than slightly grading a nicely exposed one. Luckily there were a few good examples to use in the supplied link and in those you can see where the GH4 cannot hold a candle to the Alexa. In the spire shots where I tried to neutralized all the haze, the image gets noisy as heck. Even the sky has pretty noticeable banding if you look close or put up on a waveform monitor.  In the shot of that tilts down from the buildings to the people, it grades well, but theres still noise littered all over the blacks. Those same images shot with the Alexa would have had more head room for fixing.


Now Im not a hater, I actually love the GH4 is putting out on a well exposure image, like the car. i was actually able to recover clipped detail in the hood before I even began grading, pretty nice for an 8 bit codec! If i could get a truly log like starting point from the camera I'd love to see how far it can be pushed. And given how "bad" the tilt down shot was originally, i was very happy how far i could push it to something usable. 


Anyway, I love what panasonic is doing, and it looks like they have another winner, but lets not get crazy here people! :)


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Here are two quick grades.

I have a few issues with the footage so far:


1. Weird uneven green cast (might be the not perfect white balance combined with the compression).

2. The shadows are too far gone (a flatter picture profile might help with that).

3. I really don't like then lens (speedbooster)

4. The incamera sharpening


At this price, I'm preordering the camera even with these slight issues, but I think they can be solved for the most part.


I'm going to play around with the rest of the footage when I have more time.



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Yea, I hear your frustration. I think there is still some confusion about removing artifacts with some conversion workflow, but I don't want to  beat a dead horse. People will just need to get their hands on the footage (the source from camera footage) and give it a shot.


We had a studio that shall go nameless (but the name rhymes with Disney) once deliver footage to us as 8bit prores! So we "had" to work with it.. it took maybe 10x the amount of work because you can't it's more challenging to: camera track, planar track, color key, degrain.. it's just wrecked it's degraded once it goes to 8bit. the information is not there to recover, ever, not there... no matter what your subsampling scheme is.. for good... a black spot stays black, even if it goes from [0,0,0] black to [0.0] black .... it's still black! So when you grade that footage, those artifacts come back.


But I agree, it's interesting to see what Panasonic is doing. I kinda wish vendors were focusing more on nice 1080 though, less on selling 4k TV's. To be honest, 4k is about 2k too much IMO, unless you're making a movie.

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Okay, well that's great to know Sean, thanks. You realize I'm working on a show right now at 11:44PM Friday night and it's a bitch to track even with 10bit footage. btw, there were no planar trackers a decade ago. there is an unfortunate rule in CG, the faster the software gets, the more the clients want.. so what was accomplished a decade ago unfortunately is not what we have to do today. 


Before digital compositing artists used glass and motion control too... before that it was clay.. i think before that it was puppets?

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Okay, well that's great to know Sean, thanks. You realize I'm working on a show right now at 11:44PM Friday night and it's a bitch to track even with 10bit footage.


That's just the nature of tracking.  It's a lot better now than it was even five years ago and that was a lot better than 10 years ago.  It gets better as the software gets smarter.  Bit depth isn't a factor next to noise, focus, occlusion, color sub-sample (422, 420, 411, 311) or compression.  



btw, there were no planar trackers a decade ago.


I was going to suggest perhaps not commercially, but that's not true.  Before becoming Mocha, Imagineer System's Mokey was doing planar tracking in 2000.  ILM was using similar techniques as available in Mokey by the mid-late 1990s.

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This is really off topic, but yea, that's just wrong Sean. Bit depth is not a factor in pulling keys and in tracking?


No, not relative to other factors.  What's more likely to affect a key isn't the bit depth.  Bit depth is even less a factor in tracking.  I don't know how many ways to say it.  If you're having troubles it's not because of bit depth.

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Also, I don't know if this happened during transcoding or not (which is why you need to post the original files from the camera, please), but these are clearly upscaling artifacts:

attachicon.gifScreen Shot 2014-04-03 at 5.52.32 PM.png

attachicon.gifScreen Shot 2014-04-03 at 5.52.20 PM.png


Amem to original native camera files, transcoded from a new camera I don't understand personally, unless for playback on lower powered hardware, nor why 10bit when editing & grading apps will do the 4:4:4 BS when necessary, when transcoding important metadata can be lost, levels scaled, artifacts introduced through cheap chroma interpolation which is what 5DToRGB was all about I think, mitigating crap interpolation at the time, but is it still necessary now, only if on old outdated apps. Bad playback, such as Prores on Windows is shit whether via 32bit QT or ffmpeg using wrong color matrix on occasions, think DNxHD would have been better choice for Windows users. But gift horse and mouth.....



5DtoRGB isn't set up to do this at the moment, but I'm looking into adding this capability.


Maybe a modified denoiser to give 'cleaner' 8bit per channel in the MSB and plough the noise back in or certain amount as 8bit LSB, giving 16bit per channel, then range convert, 'organic' dither to 10bit etc. There are open source GPU assisted denoisers available.




Probably better than 4:2:0 to Cineform 10bit RGB

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I wasn't really discussing what is a bigger factor in tracking, bit depth vs film grain or chroma compression, because this is a forum on the GH4 camera... remember?


I don't really want to get into the details of what makes it easy to pull a good key.


With respect to the topic of cameras though, bit depth is the multiplier that all binary information will pass through, so it is important..

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You complained 8bit imagery made a laundry list of things not just hard but implied nearly impossible.  I'll give you exaggeration but the 8bits is not what makes any of the things you described harder.  "Perfect" tracking and clean keys are absolutely doable with 8bit imagery (this accounts for a majority of film work leading into the early '00s) if the material is good  and the actual factors that make either task something approaching easy are aligned in your favor.  All of the factors that actually make these tasks a pain will be equally bothersome no matter how many bits you throw at them.

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Anyway, more interesting than arguing over the importance of bit depth.. how about a test. I'll just illustrate the artifacts I'm referring to with a simple radial in Nuke..and some disco music.


I'm bored. Gimme a sec.

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I was there when we proved to a screening room full of film professionals that we could scan film at DD (creator of that software you're using), carefully construct an 8bit graded file from the scan and then output scan back to film to be intercut with only one filmmaker in attendance able to pick out any of the digital shots.   And our finals re-defined the transparency of digital effects. 


That's cool you're using Nuke.  I was maybe the first digital artist to final a Nuke composite on the first project it was ever used on because almost nobody else wanted to deal with it (mostly Flame, doing stellar 8bit tracking and keying).  Back then it was a compositing language.  The nodes came in v2 and I was one of the few artists giving the new version a go and sticking with it while Bill pushed out new versions daily that would totally screw your job mid render.

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Wow.. yea, so sad about DD. 


It is.  And R+H and I expect any day now SPI, at least their Culver facility.


But your disco demo doesn't really prove anything to me and the 4:2:0 part is completely irrelevant to the 8bit issue because it's going to have compression and the fact of color under-sampling way out ahead of bit depth ruining your day.  A poorly shot/lit GS is still a poorly shot/lit GS no matter the depth.  And being able to lift under-exposed footage several stops doesn't really give you better tracking performance.  


I'm doing that with RED Epic footage now, most of it at a noisy 1000iso, night and dimly lit interiors, and tracking is no better than with under-exposed or otherwise not ideal AVCHD footage.  Being able to raise my shadows by two stops or so  all the edges and features I need are just crawling with noise just like high ISO GH footage.   All the underlying problems making the process more difficult than we'd like it or than it should be aren't really bit depth related.  


That's 12/16bit raw -> EXR -> float workflow and none of what's holding you up with your footage is really any different.  I have to be prepared for each shot to break and be ready to step in to do what the software throws up its hands over.  Same as five years ago.  Same as ten years ago.  Same as twenty years ago.  That's just how it is.  It is a lot better now though, even though more folks take for granted our tools are pretty amazing now and act like they don't have to try and give us good material to work with.

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