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Compression issues with S-log 3 footage low light

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Brad Bores
Compression issues with S-log 3 footage low light
on Apr 15, 2016 at 2:29:01 pm

I am working on a music video and I am attempting a vintage creamy/hazy look by flattening the blacks heavy in the curves on 2nd node. First node is color corrected with Impulz slog 3 LUT and minor tweaks. I am pretty happy with the results when I watch in playback with davinci and when exporting a pro-res version. The issues arise when exporting the h.264 version for upload to web. I am getting serious compression chunks and ugly grey and black separation in areas that look completely black with little detail in the pro res.

This was my first shoot on A7s2 at Slog3 and have since learned that Slog 3 is terrible in low light. Also my first time working in Resolve so double learning curve going on. Since this project was more of an experiment with the camera at this point I want to be able to pull of this look while salvaging the final layoff. I know I can crush the blacks super heavy but don't want that overall look for the entire video. If there is a way to isolate just the areas with the issue and pull out/darken that information that the compression is processing I think it would solve the problem.

I have attached a still for reference (link below). It really only shows up heavy when the monitor is turned all the way up.


Thanks!


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Brad Bores
Re: Compression issues with S-log 3 footage low light
on Apr 15, 2016 at 2:33:51 pm
Last Edited By Brad Bores on Apr 15, 2016 at 2:35:39 pm

also just to note I have exported the h.264 at highest settings, 20,000 kbs per second, tried a 2 pass vbr at 20 kbs from premiere, tried Mpeg streamclip to no avail.



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Brad Bores
Re: Compression issues with S-log 3 footage low light
on Apr 15, 2016 at 2:45:59 pm

last note I have used Neat Video as well

Here is a reference picture from Resolve showing the lack of details that show up from compressing



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Chris Wright
Re: Compression issues with S-log 3 footage low light
on Apr 15, 2016 at 3:53:27 pm

luts aren't smart. they don't know what you want all the time. there was also rumours that impulse luts had quality issues from being below 64 cube quality etc. you'd get better quality tweaking your slog3 without a lut with simple levels input/output black/white acting as a precontrast limiter for brightness/contrast filter. if you upload with a DnxHD codec, youtube will look perfect.


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Brad Bores
Re: Compression issues with S-log 3 footage low light
on Apr 15, 2016 at 4:41:39 pm

Thanks for the advice. I will give it a go manually. as far as exporting a DNXHD codec what exact dnx format do you recommend? I have never worked with that codec before. Is there a specific one for controlling data limits to export for web?

Thank you!


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Brad Bores
Re: Compression issues with S-log 3 footage low light
on Apr 15, 2016 at 4:42:45 pm

also fyi this was shot on sony a7s2 XAVC S HD 2k


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Chris Wright
Re: Compression issues with S-log 3 footage low light
on Apr 15, 2016 at 10:58:15 pm

the regular 8 bit one should be fine as youtube is 8 bit anyway. Gives slightly better results than h.264 and colors don't shift.


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Brad Bores
Re: Compression issues with S-log 3 footage low light
on Apr 16, 2016 at 12:35:00 pm

exporting a DNXHD is giving me a .mxf which will not upload to youtube. It also does not allow any bandwidth control to keep the file small enough to upload. I was under the impression that h.264 is the only route to youtube and vimeo.


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Chris Wright
Re: Compression issues with S-log 3 footage low light
on Apr 18, 2016 at 4:58:24 am

try the free 3rd party handbrake tool from your previous intermediate file. it should look good on youtube.


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Bruce Greene
Re: Compression issues with S-log 3 footage low light
on Apr 24, 2016 at 6:26:16 pm

I see this on Slog2 on a Sony A7rII recorded in camera. I think, if you look closely, the artifacts are in the original recording. Over exposing by one stop helps a lot, but you loose the lowlight advantage.

The only cure I can think of is to record to an external recorder, preferably in 10 bits or higher with a non GOP codec like prores.

Varicam/Steadicam Owner
Los Angeles, CA
http://www.brucealangreene.com


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Chris Wright
Re: Compression issues with S-log 3 footage low light
on Apr 24, 2016 at 9:35:51 pm

that might indeed be the problem, where there's artifacting, but crushing the blacks with a contrasty lut isn't going to help. neatvideo assigned to just shadows might fix it some. Make sure you only use 32bpc effects.


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Marc Wielage
Re: Compression issues with S-log 3 footage low light
on Apr 25, 2016 at 1:30:55 am

Very dense blacks are a huge challenge for any compression engine. My response would be to try to go for an image hosting site that has less compression. Vimeo Pro might possibly be a solution.

If you put up some test signals with just a black screen or various shades of gray, you'll often see the same problems. These are known compression artifacts. Compression is evil.

There are also issues with 8-bit video in general from DSLRs, but if what you see on your own display is good, and it got a lot worse online, clearly the problem is the online compression. Whether you can change your own compression method would be a question of experimentation.


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