pulling key in davinci resolve for slog2 a7s footage

[komlope]

Hi,

 

I got my a7s a few weeks ago and I'm still in the process of getting oriented. I managed to get by most challenges but seem to be getting completely stuck on this one.

 

I'm trying to stick with shooting slog2 and sgamut for now to see how far I can push the camera in it's "most native" mode. I can do some basic grading using LUTs etc to get back a nice natural looking image. However, when trying to push the footage beyond that and apply a look to it, it just falls apart.

 

More specifically, I've tried various ways of pulling a key in secondary color correction but it is just not clean or smooth. It picks up various stuff from other parts of the image and I can't work with it. I tried using power windows in all sorts of combinations including tracking. However, whatever I try it allays ends up somewhat messy and awkward. So at this point I'm ready to conclude that I'm hitting the limits of grading 8 bit footage. There just isn't enough data there to be efficient or even workable for more involved grading. I understand that this is very image specific, still I think what I'm trying to accomplish is reasonable.

 

What are your experiences? How do you pull key/grade 8 bit footage? Keep in mind that I'm pretty new to color grading and videography in general.

 

Thanks

[Snowfun]

Hi,

I'd be tempted to take this to the Blackmagic forum (lots of Resolve specific expertise) and/or eoshd.com (lots of grading experience).

But be prepared for the obvious comments about 8 bit...

Would be interesting to know the outcome.

Tim

[brettfrey]

Simple, basic rules about shooting s-Log gamma. Only use this setting (PP7) if you intend to color grade.

 

1) Custom white balance every scene you shoot. Go neutral right down the middle. And seriously, set on AWB if you cant remember.

 

2) Set ISO to 3200 and leave it there. Never shoot s-Log gamma at anything but 3200. If you want to explore high ISO video that's gradable, use PP6 Cine2 gamma. ISO 20,000 looks acceptable to me.

 

3) S-Log gamma has no black floor. Shoot at 2-stops over exposed, ALWAYS. Set your EV at +2 if it helps. Effectively it makes s-Log gamma (PP7) ISO 800. When you reset a solid black level in post (pull down 2-stops) you will have a correct exposure and no noise in the lower zones.

 

4) Record with an external device (Odyessey 7Q+ or  Atomos Ninja). Generally you will have a significantly more robust file to work with (compared with XAVC-S), and more importantly these machines are doing the heavy lifting and prevent the camera from over heating. Added benefit is you can use LUT's that are corrected for 2-stops over in s-Log gamma so you can pre-visualize your photography.

[JayPFilm]

Does anybody have any good LUTS for slog that they can recommend that I can use in Premiere?

[brettfrey]

I keep about 120 LUT's in my Odyessey 7Q+ and I find that I use Alister Chapman's set most often. I particularly like the "A7s Filmic2 2-over" cube the most. You can down load the series free here:

http://www.xdcam-user.com/2014/08/set-of-20-cube-luts-for-the-sony-a7s/

 

Also spend some time on his site. He has a lot to teach about A7s and exposure.

http://www.xdcam-user.com/2014/08/exposing-and-using-slog2-on-the-sony-a7s-part-one-gamma-and-exposure/

 

Another savant of these matters is Wolfcrow. Another very worthy read.

http://wolfcrow.com/

[komlope]

Thanks for the reply brettfrey. I'm actually following all the step you listed very closely. Except for the external recorder. I don't want to invest in that at this point. (Also I believe that the a7s caps hdmi output at 8bit, so I'm not sure how much that would help.)

 

I did a lot more experimentation and reading since my original post and pretty much came to the conclusion that I'm hitting the limits of 8 bits footage. I still like the camera and enjoy s-log but I'll have to get my footage close to the final look and accept the limitations of how far I can push it in post. Especially when it comes to secondary grading and HSL keying.

Thanks!