A7s low light strategy - how to address a noisier image in 4K via Shogun?

[Nicholas Natteau]

I just received the Atomos Shogun yesterday and I'm trying to figure out how to deal with what seems to be significantly more noise when recording 4K via the Shogun as opposed to 1080p within the Sony A7s.

I understand that by recording 4K there will be more noise in the image since there is no in-camera noise reduction to speak of as would be the case with internally recorded A7s 1080p footage. But apart from using software like Denoiser 2 or Neat Video, what would be some other ways to deal with increased noise in 4K?

I 've read that with the A7s, even 25,000 ISO looks great and certainly usable when shooting 1080p.
But what about recording in 4K in low light? Thank you in advance.

 

[Erik Wittbusch]

If you don't need the DR of SLog2, you can avoid SLog2 by using
cine4 instead.

You can try to overexpose your footage by 1-1,5 stops. This leads to
overexposed footage, that will be brought down in post and therefore
the noise will be brought down a s well.

This is what we do on our bigger cinecams (F5/55, FS7) as well, but in an
easier way, as this is already implemented in cineEI mode.

 

[Ebrahim Saadawi]

1-Neat video. Applying neat video will recover the in-camera noise reduction advantage.
2-Shoot with fast primes at wide open aperture, making you use lower ISO number.
3-Expose to the right: over expose your image to just before clipping the highlights, then bring exposure down in post.
4-Avoid S-log2 since it starts at 3200ISO as you can get a cleaner image at lower ISO values, if the scene requires more than 3200 anyway, S-Log is fine.
5-Downscaling to 1080p for 1080p delivery decreases noise a lot.

 

[stevedocmaker]

Can you post some samples?

 

[Nicholas Natteau]

Thank you very much for your help everybody. I just realized that I was shooting in APS_C crop mode. Now that I reverted to full frame, it's definitely less noisy.

My concern now is the ugly skin tones I'm getting. I absolutely love this camera for it's low light sensitivity, but I'm having a terrible time getting good skin tones out of the A7s shooting in S-Log 2 with S-Gamut profile. Please see the frame grabs below in which skin tones seem to take on a yellowish or greenish complexion. The skin texture in my tests also doesn't look that detailed. Here I'm lit by a single Ikan IFB576 LED light color balanced to 5600K as is the A7s. Lack of detail in skin texture may be because I over-exposed skintones by +2 stops (skintones were at 65-70 IRE on the Atomos Shogun) according to Alistair Chapman's method:

http://www.xdcam-user.com/2014/08/e...-on-the-sony-a7s-part-one-gamma-and-exposure/



These crops were from 4K Apple Pro Res LT files. My skin tone results were similar in 4K Pro Res and in camera at 1080p.

I wish now that I hadn't sold my Canon 1DC last year, as I was able to get fantastic looking skin tones out of that camera shooting in 4K cinema log. And it seems in retrospect to have been a lot easier to color correct than S-log2. I'll do some more tests later today or tomorrow by trying out PP4 instead.

 

[Ebrahim Saadawi]

We're all still experimenting with S-Log2 as non-professional colourists :lipsrseal

Here's a small chat among noobs:

http://www.eoshd.com/comments/topic/7737-a7s-slog2-is-really-really-flat/

 

[ade4all]

If you use s gamut you must then apply specific luts which deal with s gamut colour otherwise you'll have colour issues

 

[toxotis70]

You have two options for good color...
1) dont shoot with sgamut.... Try cinema or pro , or rec709

2) shoot in sgamut profile but you have to use a proper lut to bring back the right colors from sgamut to rec709 color space.
sgamut is not only amuch wider color profile but a twisted one.... So the colors you see in sgamut are not the final colors.

 

[jurny]

1) buy back 1DC
http://www.eoshd.com/comments/topic/7726-canon-1d-c-vs-sony-a7s-4k-dynamic-range-preview/
2) shoot with slog2 sgamut and use Filmconvert

 

[stevedocmaker]

There are several threads about getting the best color out of this camera. I've yet to find anyone that likes s-gamut. But even if you try some of the others you'll need to make some adjustments. In my experience, Canon profiles are dialed in for skin tones, the color modes on this camera are not, but good results can be achieved.

 

[Nicholas Natteau]

Thanks again everyone. I see what you mean stevedocmaker. It's true that the Canon profiles are very flattering to skin tones. Personally, I've never been able to achieve better skin tones than with the C300 and 1DC. I'm not sure what it is, but even though they're not as sensitive to low light as the A7s, the texture they display in skin tones is really beautiful. But I'm not at all giving up on the A7s as I've seen this camera deliver stellar results. I guess it requires a lot more expertise than I possess, so I'll keep trying to get it right. Thank you all again for the tips and links.

 

[stevedocmaker]

As a starting place you might try color mode cinema, with the following color depth settings: R+3, G+1, C+5, M-3 (blue and yellow at 0). This is very accurate across the spectrum (much more accurate than anything you can get out of a C100). From there you can tweak skin tones in post with a secondary CC. I've used this in conjunction with C100 interview footage and was very pleased with the results.

I hope you can post some Shogun footage (especially frame grabs with a 1:1 crop). I'm very interested to see what 4K can look like with this recorder.

 

[caseywilsondp]

If you check the link Ebrahim posted i think you can see that you can get good skin tones even in slog2 by following his instructions. Notably adjusting your mid tones by adding some magenta and some blue back in. Also if you light with LEDs know that much of the time your skin tones will skew even further from what's considered "normal" as they have a more limited spectral range than standard film lights.

 

[Nicholas Natteau]

Thank you both. Steve I'll be sure to try those and post some clips later in this thread. Casey I'll do some tests with non LED lights as well.

I just got hold of the Shogun two days ago. I shot 4k in Pro Res and LT and was very pleased with the compression in LT. I really couldn't tell the difference with Pro Res regular which is great because whereas Pro Res is around 450 Mbps, LT will give you 330 Mbps. A single 240GB Sandisk SSD gives me 60 min in regular pro res, and 90 in LT. I haven't shot anything in HQ yet.

Besides its stellar low light performance, one reason I migrated to the A7s and external recorder was actually because of the 1DC's MJPEG 500 Mbps codec. Though I love the image quality out of the 1DC, I was looking for a lower 4K compression rate. Of course there's the GH4's 100 Mbps which is great but not my ideal choice when it comes to shooting talking head interviews. I prefer to use the GH4 for other situations. But I'm really looking forward to what Canon has in store for 4K this year. Since no camera is perfect at everything, for 4k work right now, I plan to use the A7s for low light, the GH4 for landscape and outdoor shooting, and the 1DC for talking head interviews.