This guide covers the S-Log2 workflow as it pertains to the Sony A7s, shot in S-Gamut color mode. We will learn:
- How to expose for S-Log2
- How to monitor exposure in S-Log2 using nothing but the camera
- How to match shots and grade in S-Log2
- Two ‘correct’ ways to expose, and which I prefer and why
The software I use are:
- Adobe Premiere Pro – to edit my sequence and to export to Youtube
- Adobe After Effects – my grading tool of choice, using Color Finesse 3
- Adobe Speedgrade – for the Annakotta (Elephant Fort) sequence
List of articles you need to read before watching the video
Before you watch the guide, or read about the wolfcrow system, please make sure we’re on the same page about the terminologies used. Otherwise it’s going to be tough viewing. Here are articles that will help you understand the terms as I define them:
- Full swing vs studio swing
- What is gamma?
- What is color space?
- What is color bit depth and a color model?
- What is middle grey?
- What is IRE?
- Driving Miss Digital – noise and signals
- What is a LUT?
- Adobe Premiere Pro articles
- Speedgrade articles
- What is the zone system?
- What is Slog2, from the A7s guide
- My Sony A7s review
- The Sony A7s preliminary guide
Also, please watch the fully graded Annakotta (Elephant Fort) sequence before you watch the workflow guide so I don’t put any thoughts into your head:
How to expose, monitor and grade S-Log2
Watch the entire thing if you can. It’s an hour long, but there was no faster way to explain how I arrived at the wolfcrow system. Here are some highlights, in case you feel like jumping ahead:
- 1:10 Two ways to expose for S-Log2! The ETTR system and the wolfcrow system
- 6:40 Problems with the ETTR system and why I don’t prefer it
- 8:00 Understanding the difference between RAW and S-Log2
- 11:00 Understanding S-Log2
- 13:50 How the Zebras in the Sony A7s works
- 17:40 How to use the Zone system to test for the usable Dynamic Range
- 26:30 What is the real “middle grey” for the Sony A7s?
- 29:18 How to expose for the best skin tones
- 32:12 The wolfcrow system of getting the right exposure with the Sony A7s
- 36:00 How to use nothing but the in-camera Zebra and meter for your exposures
- 42:42 When and how to use LUTs
- 49:40 wolfcrow system condensed
- 52:50 How to grade S-Log2 footage from the Sony A7s
Here’s the guide. Enjoy:
Notes, Errors and Omissions on the the Video
I recorded the video during the night to avoid traffic noise, so I have made a few slip ups. Here are the ones I caught at the time of publishing:
Errors and omissions:
Apologies for the voice and lack of eye contact. It was hard.
In my article on full swing vs studio swing, I define full swing correctly, as between 0-1024; yet in the video, I use the term ‘full swing’ to mean full swing+super whites, which is incorrect. Please be aware of the difference, and it doesn’t mean anything in practical terms. In the video, when I say full swing, I’m always referring to full swing+super whites. This is the entire range from -7 to 109 IRE.
I mention in the article that 2+ stops is the least noisy, though evidently that is incorrect. It was a slip up. The least noisy is ETTR, and the wolfcrow system is the next best thing.
During the chart after the 11:00 mark, I show how a one stop overhead makes the dynamic range 12 stops. That is incorrect, and was a mistake I made while speeding up post. The 12 stops of usable dynamic range includes the overhead, all the way to 109 IRE.
Some clarifications, in case things are not obvious:
2 stops over is the middle point. Following the Zone system analogy, it would be Zone V. Middle grey, then, will be at Zone III.
I did make some bold statements during the video, and here are the references for the same:
I say that Kodak film has a usable dynamic range of 12 stops. It is from a Kodak whitepaper (motion.kodak.com): Exposing Film. Some gems from it:
Generally speaking, the latitude of KODAK Color Negative Film is about 10-12 stops.
To obtain the best exposure, err on the side of over-exposure to create a “bullet-proof” negative. It’s better to provide too much information on the negative than too little.
The entire analog image chain is designed to accommodate a normal exposure, normal processing, and normal printing. In fact, the system is nearly foolproof and endlessly forgiving when everything operates under normal parameters.
Cinematographers usually operate very close to that line of normalcy. Small adjustments … can produce interesting outcomes that provide precise and repeatable control over a great number of image parameters.
This is the foundation of the wolfcrow system.
Always attempt to get the best latitude, grain, color and sharpness from the stock you’re using. A properly exposed negative will optimize all these characteristics. Once you understand the film’s limits and capabilities, you can be more confident while making tough, on-the-spot shooting decisions. Occasionally, you will deviate from the normal exposure.
Consistent exposure minimizes dependence on the laboratory’s ability to compensate; as exposure correction always results in a trade-off in some area of image quality.
About S-Log2, I mentioned it was designed for DI workflows. This is from S-Log: A new LUT for digital production mastering and interchange applications, by Hugo Gaggioni, Patel Dhanendra, Jin Yamashita, N. Kawada, K. Endo and Curtis Clark:
S-Log is a gamma function applied to Sony’s electronic cinematography cameras, in a manner that digitally originated images can be post-processed with similar techniques as those employed for film originated materials.
Shooting in S-Log will enable the cinematographer to decide the exposure value by using a light meter.
CMOS imagers respond to incoming light in a far more linear fashion than film, thus there are no “toes” or “shoulders”.
When shooting in S-Log, as distinct from ITU-R BT.709 (Rec. 709) video gamma, a color grading process (‘look management’) is mandatory…
About the relation of S-Log2 to white balance, and why it affects grading and the creation of LUTs, refer to Technical Summary for S-Gamut3.Cine/S-Log3 and S-Gamut/S-Log3, by Sony:
It [S-Log3] is more like a pure log encoding than S-Log2 to provide better log based grading.
S-Gamut needs color temperature setting to select color conversion matrix. S-Gamut3…does not depend on color temperature any more.
White point of S-Gamut is D65
S-Gamut is the color space when shooting S-Log2.
Mid exposure point or Zone V for the Sony A7s in S-Log2 mode
As mentioned in the video, the mid exposure point, or Zone V, for S-Log2 is 2 stops over. In other words, what should be middle grey should be overexposed by 2 stops:
How to expose for best quality
Unfortunately, areas at the ‘defined’ middle-grey (32% IRE) still suffer from color noise (click to enlarge):
The lowest level that eliminates color noise is IRE 40. For this reason, it is suggested to expose at 3 to 3 and 1/3rd stops over middle grey. This is the wolfcrow system.
The wolfcrow system, in a nutshell
Here is a simple list that tells you how to expose S-Log2 using the wolfcrow system:
- Choose the most important parts of your scene (skin tones, objects, whatever) that would traditionally be at middle grey (Zone V, to be precise). Using a spot meter, let these areas by 3 stops over the meter rating.
- If using a reflective light meter for lighting, calibrate your light meter to be 3 stops over the camera meter. Then you can light as usual.
- Keep the base exposure at about 60-70 IRE. You can use a waveform monitor (in full swing mode, important!) to show you this. If you don’t have access to a monitor, use the in-camera Zebra level of 70, which displays the 60-70 IRE range.
- Since white balance is critical, try to custom white balance each scene using a white card. If you’re in a run-and-gun setup, and know you can’t white balance for every shot, then use Auto White Balance (AWB), since this will give you the least amount of work during post production.
Can it be any simpler? No it cannot. Here’s a quick reference still from the video that shows all this in a nutshell:
When it comes to grading:
- Always grade in a 32-bit environment. Avoid NLE color grading when in doubt.
- A consistent middle point (Zone V) allows you to create LUTs easily. 1D LUTs for dailies and monitoring, and 3D LUTs to pass around during grading. No generic, third party or unofficial LUTs allowed.
- Begin primary grading by adjusting levels to correct for exposure inaccuracies (it happens, even when you’re perfect) for mid tones, then the necessary shadows. Look for noise.
- Finally, adjust gain for highlights. You can use levels, curves, exposure, gain or contrast to make these simple adjustments.
- Scene matching should be pretty easy if you’ve nailed white balance and Zone V exposure.
- Now grade to your heart’s content! Don’t worry about 8-bit. If you grade correctly, you will see zero banding. If you have exposed correctly, with no patches of underexposed color noise, you will see zero posterization. In case you do see issues, a little dithering will cure it.
The wolfcrow system vs ETTR
Finally, here’s a quick comparison chart between the two exposure methods. Both ETTR and the wolfcrow system are valid methods, though I prefer the wolfcrow system:
|Exposing to the Right (ETTR)||Least amount of noise possible||Can’t really expose using Zebras or the histogram, need a waveform monitor. 100+ zebra isn’t really ETTR.
Color grading is extremely hard, and ETTR for RAW does not work the same way as ETTR for S-Log2.
|The Wolfcrow System||Combines the advantage of ETTR (zero color noise) while maintaining maximum tonality and texture – the fundamental concepts of the zone system.
Provides a consistent Zone V point for easy color grading in post production – something that is mandatory with S-Log2.
One can use the in-camera meter and/or zebra to expose, without needing any external tools.
DPs can calibrate their light meters to a consistent level. You can light by eye!
|Due to inaccuracies in testing, zebras, meters, etc., individual operators must start experimenting with the Wolfcrow system and find their optimal exposure point. This is exactly how a DP would learn to use film. There is still a lot of subjectivity in exposure, which no system can cure.
One must always have an eye on clipping highlights, though that is the case for any exposure!
That’s it. I hope you have found this guide useful. Please share your experiments with the wolfcrow system, or any other exposure method for that matter. In the coming year, I’m going to be using the wolfcrow system with my Sony A7s.
Maybe you will too.