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Julian

Must See for GH4 owners - Recovering Super Whites

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This might be obvious to some of you. It wasn't to me. By default the GH4 records in 16-255. So that's what I shot my video's in. Turns out, you have to do some stuff to recover the 'super whites', if you don't do it you end up with crushed highlights.

 

This guy took some original footage from Vimeo (yes, I'm flattered by the compliments I got on my cat ;)) and made a tutorial about it.

 

Awesome stuff, must see! The bad news, I have to re-edit all my videos and upload them again ;)

 

 

Also check out his website: http://www.florisliesker.nl/

This guy makes great stuff.

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I think the latter, because you will be able to record more highlight detail. You just have to make sure you actually use it, in post. This does make me wonder if using 0-255 makes sense to get more shadow detail.

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I wonder if this is true for GX7 as well, which is supposedly using the same sensor.

 

This has been debated before, but I think it is not the same sensor.

GX7 = Panasonic made.

 

I have strong reasons to believe the GH4 is Sony-based, like the GH3. Panasonic Europe told me it is based on the GH3, and NOT the sensor from the Panasonic PDF. Panasonic Japan told Andrew something else though.

 

But...

I tried opening the raw files from the GH4, there is no raw support in Adobe Camera Raw. What I usually do, and what usually works, is change the EXIF and make ACR think it is an older camera. This worked for example with the D4S (change it to D4), and all the Canon camera's (1200D, change to 650D or whatever).

 

So, I tried changing the camera type to GX7 in the exif, it wouldn't open the raw. When I changed the model type to GH3, it would let me open the GH4 raw. I think this pretty much proves the GH4 sensor is of the same origin as the GH3. Which is supposedly Sony.

 

Anyway, I think camera's with dont have luma settings record with the industry standard 16-235 settings. But it'd be interesting if someone could try.

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Geez, how long have we been discussing pulling down super whites in a 32bit float workspace, it really isn't anything new. Sorry but.... Any Sony cam like a NEX etc all 16 - 255, long discussed.

 

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But question is does the GH4 shoot 16 - 255 in a MOV or is it flagged fullrange so should be interpreted as 16 - 235, if someone would actually post a link to a freakin native file rather than some transcode it could be established. The GH3 h264 in a MOV was fullrange and flagged so, the GH3 AVCHD was 16 - 235 and didn't.

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Where? The Driftwood stuff has been transcoded and not native, titles added, fades at the end? Does the GH4 use MOV container or mp4? Can you provide a link to a native file straight off the camera, would you mind. Something that is clearly exposed to the right and clipping.

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Geez, how long have we been discussing pulling down super whites in a 32bit float workspace, it really isn't anything new. Sorry but.... Any Sony cam like a NEX etc all 16 - 255, long discussed.


For most people this is still a new and confusing thing. Though I know you have mentioned this many times in the past. I remember seeing some of those old discussions and not fully understanding it all. In fact I was thinking of starting a thread with some of my questions. But before I do that I will have a read of the old threads, so thanks for providing convenient links for those.

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Geez, I'm confused again... Looking at some of my clips on Vimeo and in Media Player Classic (and Premiere CC) I see differences both in the black and white levels. Now you mentioned it, I remember those old topics. I'm with Matt on not fully understanding the ins and outs of it...

 

But apparently the black levels are also a thing with Vimeo:

 

 

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hey julian--

 

i'm now starting to realize that this could be a problem with codecs on export from davinci or premiere, it looks like that's what most people are using. 

 

not really recovering super white info or making sure levels are "legal", but rather more like preventing a possible Y,CbCr screw up on export before upload to vimeo. this could also be based on render settings.

 

if you reimport your exported video, right after your export it for vimeo and see that it has changed at that stage, that would answer it. if it looks too bright on import and has the "super whites" above 235 straight from the camera, then the internal signal might not be getting to 255. this kinda makes sense if it's Y,CbCr internally.

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though something that has been discussed many times before, since this is a new camera I think it was good that Julian posted this.  I am familiar with the issue - particularly as a avchd user mac.  I wouldnt have expected it to show up on the gh4 but since it has, why not make a discussion about it.  eoshd is read by many - a lot of which might see the gh4 as their first dslr camera worth investing in for video use as well as stills.  I see the gh4 as being something that will be embraced by both pros and people with less knowledge about this type of thing.  

 

The number of videos I've seen shot by guys with Sony cameras using avchd that look digital and nasty is amazing - all because they are not aware of the issue and don't know how to rectify it.

 

I'd imagine this would be a good topic to start discussion about getting the most from footage shot on the gh4 - since the gamma tweek is one such process required in the signal chain 

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Ok, I found some native GH4 MOv's and they're not flagged full range ie: JPEG Levels, they are as Sony NEX etc 16 - 255 YCbCr. The 20 levels above 235 are superwhites, so it's upto individual whether to expose for 235 and let QT or whatever clip above that or expose to the right, capture into the 255 and pull down in post.

 

The black thing on Vimeo is not to do with Vimeo but to do with the limited range RGB signal chain from nvidia vid cards (as mentioned) plus effects of HW acceleration but both only when DVI is used. No problem over hdmi or SDI. DVI is crap anyway, 8bit RGB. And maybe wrong black level setting on the monitor if it's not auto sensed. All of which scale and rescale grey levels through the signal chain inducing increased banding.

 

Those using a decent or even reference monitor or who simply want better representation of the signal for grading and preview will be going 8/10bit hdmi YCbCr or better still SDI both from something like a Blackmagic Mini Monitor, using a 3D monitor LUT from calibration package and avoiding the issue every which way. DVI's fine for the NLE / Grading app interface where it doesn't matter but not for playback / review / grading of the image, no good.

 

As sunyata explains, 'legal' levels is an 8bit thing and related more to analog delivery & viewing, which is why you can pull the levels down in a 32bit workspace if you wish or let the decompressing codec / player clip for you at end of the signal chain. What's important is knowing if the clip is fullrange JPEG or normal range with supers and was it graded using a correct signal chain.

 

QT clips to 235 when using 8bit and so do some transcoders too, which is why native files get asked for not transcodes. Otherwise it's not unknown for people to download transcoded clipped files and talk BS about no highlight roll. :-)

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Ok, I found some native GH4 MOv's and they're not flagged full range ie: JPEG Levels, they are as Sony NEX etc 16 - 255 YCbCr. The 20 levels above 235 are superwhites, so it's upto individual whether to expose for 235 and let QT or whatever clip above that or expose to the right, capture into the 255 and pull down in post.

 

 

hey yellow, i'm fully retracting that previous statement based on your info here.. question: everything above 235 in the clips you found was reading as white? it seems like the internal signal could be 235 max no matter what you choose as the format.

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Don't know why it's too bad.. I love the sensor.

 

My last GH4 test video (now I have to wait for the camera that I ordered... :)).

This time I changed the White Output Levels to 235

 

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isn't this problem solved by encoding to ProRes in 5DtoRGB and choosing 701 and full range ?

 

that's what I've been doing with my G6 footage.

Depends on how your G6 native files were encoded in camera, when you know that you'll know if 701 & full range is correct or not.

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hey yellow, i'm fully retracting that previous statement based on your info here.. question: everything above 235 in the clips you found was reading as white? it seems like the internal signal could be 235 max no matter what you choose as the format.

 

For the GH4 the range is 16 - 255 luma ffmpeg gives me steady luma upto 255 and I believe it, QT Player, doesn't it clips to 235 when working at 8bit, Resolve using QT SDK I presume previews as it should clipped but data above can be pulled down, same with Premiere CS6.

 

For format and codec it's not so much what can be encoded into it, it's how it's interpreted by whatever 'make' of decompressing codec is used outputing it.

 

Is that what you mean?

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