Zebras are a very useful way to measure exposure levels, whether that's skin tone levels or the brightness of a middle grey or white card. But, if you are going to use Zebras it's really important that you know exactly what it is that they are measuring because different gamma curves or different LUTs will have different brightness levels. Broadly speaking Zebras always measure what you see in the viewfinder regardless of any other settings, but there are some subtle difference when shooting with the CineEI mode as below.
On the FX3 and FX30 the Zebras always measure the image that you see on the LCD screen. So, if you are in the CineEI mode and you have a LUT on, the zebras will be measuring the level of the LUT. If using the default s709 LUT then skin tones will be around 60%, a white card 77-78% and middle grey 45%. If you are not using a LUT and are viewing the S-Log3 then the zebras measure the S-Log3 level in which case at the base exposure skin tones will around 50%, a white card 61% and middle grey 41% (for each stop brighter that you wish to expose S-Log3 add 8.5).
On the FX6 and FX9 in the CineEI mode the zebras always measure the image seen in the Viewfinder, regardless of what is set or being measured elsewhere. So if there is a LUT on in the viewfinder they measure the LUT, If using the default s709 LUT then skin tones will be around 60%, a white card 77-78% and middle grey 45%. If you are not using a LUT and are viewing the S-Log3 then the zebras measure the S-Log3 level in which case at the base exposure skin tones will around 50%, a white card 61% and middle grey 41% (for each stop brighter that you wish to expose S-Log3 add 8.5). On the FX6 and FX9 it is possible to have a LUT on for the VF (it will be measuring the LUT) while at the same time outputting without a LUT on the SDI/HDMI. As the cameras waveform measures the HDMI/SDI, in this case the Zebras will be measuring the Viewfinder LUT image while the waveform will be measuring the HDMI/SDI S-Log3 signal. This can be a little confusing as the levels in the VF can be different to the levels on the waveform depending on what is set for each. What the waveform is measuring is indicated just above the wave form display and the waveform measures the signal on the SDI/HDMI while the Zebras measure the Viewfinder image so whether this is the S-Log3 or the LUT is determined by the Viewfinder LUT setting.
The answer is bright, reflected whites. Nothing else matters. Skintones vary too much from person to person, and race to race. 18% gray is too dark and never found naturally. But white is all around us on white cards, chip charts, paper, clothing, clouds, cars, etc. It is always easy to find a white target.
I set Zebra2 (never Zebra1) for 72% and allow just a touch of zebras to appear in bright reflected whites. Done.
Couldn't be easier. And it works with all cameras.
But Zebra 2 on an FX9 and FX6 will show on anything at or above the point set. So with a scene with bright sky not only will there be zebras over your white target, there will also be zebras over the sky, shiny surfaces all over the place. This can be very confusing and hide issues in the highlight areas.
And why 72%? I'm assuming this is for S-Log3 as it would be too dark for most 709 type gammas. If you have S-Log3 white at 72% you are deliberately over exposing by 1.4 stops and with the recent cameras there really isn't any need to do this for every shot, it reduces the highlight range un-necessarily. There may be some shots where this is beneficial, but the whole point of CineEI is that you can alter your offsets on a scene by scene basis depending on what it is you are shooting.
The brightness of clouds varies immensely as more often than not they are not acting as a reflective surface but rather they are a part of your primary light source, so will more often than not be brighter than a white card or other reflective surface being illuminated by the light coming through those clouds. You should never rely on clouds as an exposure reference for the mid range. Most white cars are also a lot more reflective than 90% unless they have a matte paint job or are very dirty.
White is very useful especially if you avoid anything treated with brighteners or that have a specular reflectivity component such as nylon and man made fabrics. But you have to be very aware of exactly how bright the white target is when measuring conventional gammas and LUT's as the gamma roll off almost always starts at the equivalent of 90% reflectivity, sometimes just below. So, depending on exactly where the knee or roll off starts a white card exposed at 87% might be fine, but at 93% it will be well into the knee or roll off and it may be way too bright, it could be as much as a stop over with a strong roll off or knee. 95IRE with 709(800) is almost 1 stop over white. And this can be a big issue when you have grabbed a piece of paper or fabric of unknown reflectivity that is most likely treated with brightners or a shiny car that may be anywhere from 90% to 98% reflectivity. Where do you expose this when it will be well into the knee or roll off when exposed correctly? Middle grey doesn't have this issue. Light meters are calibrated for middle grey and the average brightness of most scenes will be the equivalent of middle grey. For these reasons middle grey is preferred by most cinematographers as it is extremely consistent, not affected by roll off's and is in the middle of most scenes. Grey cards are not expensive these days.
Well, that is a lot of stuff to respond to, but I will try to make myself understood.
First of all, the title of this thread (that you started) specifically says “CINE EI”, which basically means S-LOG3 on the newest cameras, such as the FX6 and FX9. I never said anything about LUTs or REC709, so I don’t know why you would think that my comments or advice regarding zebras would apply to anything other than S-LOG3. Please don’t put words in my mouth.
I agree that 72% would not work for a REC709 gamma. Gammas, other than LOG, do require a different Zebra2 level, which will vary depending on the chosen gamma and the DP’s exposure target – which is ultimately a creative decision. One DP may choose to expose a certain gamma at 80%, while someone else may choose 85%. Neither is right or wrong. But both of them can use my method to determine EXACTLY when they have hit their intended threshold, whatever that is.
72% won’t be appropriate for most monitor LUTs, either, but, then again, I never claimed it would be. I never said anything about LUTs in my earlier post. But for more than 10 years, in my books and videos, I have been providing recommended offset zebra values for many of the most popular monitor LUTs. My method of exposing with Zebra2 works just as easily with a monitor LUT, you just have to know what Zebra level to use that will put the underlying S-LOG recording at the proper level. Very simple.
In your hypothetical scene with a bright sky, you are correct that Zebra2 will show on everything above the threshold where it has been set, and that may very well include the bright sky and specular highlights from glass and chrome. No big deal. That is EXACLTY what makes Zebra2 superior to Zebra1.
If I set Zebra2 for 72%, then no zebras will be shown on anything that is under 72%.
Zebras will not appear until the exposure reaches exactly 72%.
And then they will continue to be visible on anything that is above 72%.
That is exactly how I want zebras to function. What I am looking for is just a touch of Zebra2 on bright reflected whites that are in the SAME lighting as the subject.
For example, if I’m shooting an interview, I will have the subject hold a white card directly in front of their face after all the lighting has been setup. I will adjust the exposure so there is just a hint of Zebra2 showing on the card, and then they can drop the card and we can roll. Not only does that method guarantee a perfect exposure, it also eliminates all guessing because the exposure is based on a (white) target of known reflectance, rather than someone’s face.
ZEBRA2 + WHITE CARD = INCIDENT LIGHT METER
By contrast, Zebra1, uses an aperture window. That means Zebra1 will start to appear earlier than the actual level that has been set, and then disappear again if the exposure rises beyond that window. For example, if I set Zebra1 for 72%, with the factory-default 10% aperture, Zebras will start to appear at 67% and then disappear again at 77%. Sloppy. There’s no precision with Zebra1, and it is too easy to overexpose without realizing it because Zebras are only going to show within that very narrow window. Changing the aperture to a narrower or wider window will just make the problems worse.
In your hypothetical situation with the bright sky, I agree that there may very well be zebras in the sky and on any specular hightlights from chrome, glass, etc. So what? If those things are not the subject of the scene, what difference does it make? Every camera has a limited dynamic range, so occasionally something has to be sacrificed when we have no control over the lighting. It is impossible sometimes, even for a Venice, to have everything in an outdoor, uncontrolled, shot exposed correctly.
So, if we have a shot where the main subject is a human being standing on the street, then it is that person who needs to be exposed correctly. And allowing for a little bit of Zebra2 on the person’s white clothing, or a nearby object in the same light, or even holding up a white card for a few seconds, is the perfect way to do it. This is especially true for documentaries, news, reality TV, etc. where the exposure must be set quickly and accurately.
In your hypothetical situation, the sky and specular highlights are secondary and do not matter. Why would I care if they have zebras on them? And why would that be “confusing” to you? BTW, the sky would be just as blown out with Zebra1. The difference would be that you won’t have any Zebras to tell you that it is blown out.
My choice of 72% for Zebra2 on the FX6 was not chosen at random. I arrived at that number after doing a lot of side-by-side testing with my Leader LV5330 waveform monitor, chip charts, real-world scenes, and Resolve Studio. Plus, that number has proven itself over and over again in two years of shooting with the FX6.
If you think 72% is too high, that is certainly your right, and you are welcome to expose however you want to. But I’ve done my own tests from 60% up to 85%, and I’ve determined that 72% consistently gives me the best results after grading in Resolve. I stand by the number.
You had me laughing out loud with your comments about you having issues with slight variations in bright white. Really? You think the slight differences between two different bright whites is important? It’s a fraction of a stop, at most, and easily compensated for in post. I can’t believe that someone who consistently tells people to expose for human faces (despite huge variations in skintone from race to race, and even between individuals within the same race) is suddenly concerned that the difference between something like a white shirt collar and a white piece of copy paper is just too much to deal with. Bright white is bright white. Slight differences, of only than a few IRE between different materials, won’t matter at all in post after grading.
You once wrote in another thread, “there isn't as much brightness variation between different skin tones as one might expect.” You have to be kidding, right? Think about two individuals, such as Jim Gaffigan and Chris Rock, and then tell me there isn’t much variation in skintone. Do you honestly think there is more variation between a standard white card and a sheet of white copy paper than what we see in those two faces? That’s absurd.
All things considered, Zebra2+White is a fast, easy, accurate, and nearly foolproof way to set exposure on the fly. It also easily understood and mastered by beginners who need some rules and guidelines to follow.
I hope that addresses your concerns about my methods.
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