For this discussion, SI-2K log is output = Log base 90 (input*89+1).

http://cineform.blogspot.in/2007/09/10-bit-log-vs-12-bit-linear.html

V-Log -> linear, exposure comp., linear -> Rec.709

As best I can tell, that banding is present in the 8-bit source file. It's worse in the first second: I skipped past that.

and my previous V-Log L test images

Downloadable sample of GH4 V-Log-L footage, shot in 4K at 24p, recorded with internal 8-bit H.264 encoder:

https://drive.google.com/file/d/0BzXpNy2MdkE6N19Ld0h6c2Qyems/view

Here's a screenshot of a sample frame, along with its waveform. Notice the black pedestal at 10 IRE and the highlight peak at close to 79 IRE, both consistent with V-Log-L proper exposure guidelines:

For the novices among us I think this technical talk is getting too far into the weeds. I don't believe anyone is being educated by this back and forth at this point. What i'd like to know is how are we going to be successful in exposing our cameras using V-Log L? can we successfully get predictable results using the tools in camera or will we need to use other means? How should we use Zebra's or Histogram etc to get the right exposure?

Light can be quantified as luminous exposure, measured in lux seconds. (equal to illuminance multiplied by the exposure period) You can relate it to the camera's output, for example, by saying that at a certain ISO setting, a certain luminous exposure produces a certain output value.

ISO matters because in a camera log mode, the ISO setting changes the mapping between raw sensor values and the output log space. The mapping is not constant. And the sensor gain is different in log mode compared to in a display-referred mode, for the same ISO setting. And not every ISO setting is available in log mode. A camera log color space isn't just another gamma curve.

I really suggest reading Larry Thorpe's Canon Log white paper: http://learn.usa.canon.com/app/pdfs/white_papers/White_Paper_Clog_optoelectronic.pdf

and also Jeremy Selan's Cinematic Color white paper: http://cinematiccolor.com/

I do not know that is "brightness of the exposure", it is just raw sensor values.

Light. Photons. Before the sensor produces raw sensor values, there is light falling on the sensor. That light can be quantified, and related to the camera's output.

ISO is not fiction. It defines the relationship between the brightness of the exposure on the camera's sensor and the output values. And it totally matters when you decide how you are going to expose and how to set the ISO. Are you using a light meter? Are you using the camera's built-in exposure meter? Are you using a monitor LUT? Are you looking at a histogram or false color display? You need to know how your camera maps into the output range, and the performance of each part of the output range for each ISO setting. Where does it clip? Where in the shadows does noise become apparent? Where does color accuracy suffer? These things are not just properties of the sensor. They change when you change the ISO setting.

Extended highlight range is not marketing speak. It's a very real property of the camera's behavior, which you need to understand when you're shooting.

It is just software thing, sensor is linear device (well, almost) who does not care or know about it :-)

As soon as you dump all IRE, middle gray and such, it will be much simpler and closer to reality.

We just have sensor(linear)->ADC(still linear)->raw(linear)->processing (log, Rec 709, anything)

All this complex stuff is introduced on processing step.

@balazer

A typical camera clips at 3.5-4 stops above middle grey.

https://en.wikipedia.org/wiki/Middle_gray

"Middle grey" is not an absolute reference point, in sRGB terms, it's defined as 50% of the maximum brightness, which is the highlight clipping point of the image sensor. The "extended" terminology used to refer to the additional 4-stops of V-Log range compared to 12-stop V-Log-L is an artifact of how Panasonic chose to scale the highlight clipping point of each camera's image sensor. In the Varicam's V-log profile, highlight clipping is scaled down to about 90% of the top of the 16-stop V-Log range. In the DVX200's V-log-L profile, highlight clipping is scaled down to about 72% of the top of the 16-stop V-log range. In both cases, the full range of highlight sensitivity is recorded from each sensor, it is just scaled differently in 16-stop V-Log versus 12-stop V-Log-L. The chart below shows how this scaling works. (Note that in this chart IRE scaling is not quite the same as percentages, since 100% = 109 IRE.)

In short, the "extended 4-stop highlight range" terminology is marketing-speak, it is not a physical property of the image sensor. All cameras capture the full linear highlight range of the image sensor up to the point of clipping. An internal tone curve is then used to manipulate that data into ranges tailored for a variety of professional and consumer purposes.

Have you verified this yourself, or are you relying on the early tests done by other people?

I'm relying on reports of Panasonic's DVX200 and GH4R Beta testers, who IMO, have the tools and track records to know what they're talking about.

With V-Log-L on the DVX200 (and presumeably on the GH4R) "proper" exposure is highly unintuitive. The maximum output level of the sensor is scaled down to 79 IRE, and there's no way to capture anything but white in the 80-109 IRE range. That means you have to expose your highlights to fit within 79 IRE rather than the 100-109 IRE range you're used to with the other built-in profiles.

Well, USE TOOLS Luke, as I said, it is super simple. As for lack of information in upper values - it is just Panasonic engineers utter failure.

@Vitaliy_Kiselev

Another strange point is that you need some super special way to check footage during shooting for proper exposure.

With V-Log-L on the DVX200 (and presumeably on the GH4R) "proper" exposure is highly unintuitive. The maximum output level of the sensor is scaled down to 79 IRE, and there's no way to capture anything but white in the 80-109 IRE range. That means you have to expose your highlights to fit within 79 IRE rather than the 100-109 IRE range you're used to with the other built-in profiles.

Yes, so long as you tune things after first processing the log footage through a precalibrated LUT. If you use an uncalibrated LUT or just eyeball it without a LUT, you're basically using the log curve as a subjective flavoring, like any other tone curve.

Again - underexpose footage and you will get underexposed result with this LUT.

LUT is just method to define function, and you can repeat such LUT using set of transforms. So, best way to supply any footage transformation is to use multiple tunable nodes (hence the approach used in serious grading apps).

Another strange point is that you need some super special way to check footage during shooting for proper exposure, while it is simple if you use proper tools present even in cheap monitors and many cameras (false color will do as well as even zebra if you can set the level of it).

As you claim, any exposure mismatch between the footage and the LUT could be easily corrected by adjusting the gain of the footage before feeding it into the LUT. But that would require manual calibration of post production levels, and Panasonic's engineers wanted to avoid that complication.

I did not say anything like this. I just said that you will get usual underexposed footage, as always.

And you do not need any calibration, as you can just tune things looking at proper tools if you need to change how footage looks.

My math example was intended not to reflect workflow, but to show that interval definition of LOG function does not mean anything.

They instead enforce the proper V-Log-L exposure level at the time of recording, producing a turnkey workflow that requires no technical understanding of the process on the part of the user.

Well, technical understanding and grading skills are required if you are shooting such things as LOG and raw.