O texto em si:
Barry Green was responding to tests done by Matthew Allard at newsshooter on vlog for the DVX2000 where he had a lot of clipping. Not the exact same thing, but valuable exposure information below:
"I woke up this morning realizing what I had missed -- sorry for not catching this earlier. What this means is: USER ERROR. Mr. Allard didn't understand how VLOG works, and so (I am 99% certain) he grossly overexposed the images he was testing -- and yes grossly overexposed images will clip, of course they will.
VLOG is like other LOGs, but VLOG-L is not displayed like other cameras' LOG curves, and you can't judge exposure exactly like you would with other LOG curves. VLOG-L is designed to match the VariCam's VLOG, but it can only represent up to 12 stops. Full VLOG is designed to handle 16 stops.
Now, where this comes into play is keenly represented by Allard's statements about the built-in waveform monitor and false color. Those tools WILL NOT show clipping, because in VLOG-L all the brightness levels are remapped, and the absolute clip point happens at about 79 IRE.
While you let that sink in, I'll try to explain a bit further. Users are well-trained that middle gray (18% reflectance) is normally exposed at around 50-55 IRE, and that "broadcast safe" or "studio" white (90% reflectance) is at 90 IRE. And that chroma clipping is usually happening at any brightness level over 100, and that absolute clipping is taking place at 109.
THIS IS NOT HOW VLOG-L WORKS.
In VLOG-L, middle gray should be exposed at 42 IRE (well, actually, 41.7, but that's a little hard to narrow down on the camera's built-in waveform monitor). This is similar to how other LOG curves work, although a little higher.
In VLOG-L, 90% reflectance white should be exposed at 61 IRE. This is similar to, but a little lower than, other LOGs. CLOG should record 90% white at 62.7 IRE, SLOG records it at 65.3 IRE.
And this is where things change. In SLOG and CLOG, they use the range on the wavefrom from ~64 IRE on up to 109 IRE to represent the "superwhites". And that's how it would work on full VLOG too. But VLOG-L is an abbreviated curve that doesn't have the additional stops in highlights over white (the "superwhites").
In VLOG, on a VariCam, the absolute clip point happens at about 14 stops in. On the DVX200, it happens at 12 stops in, at 4 stops over middle gray. This chart shows how VLOG is mapped, and I added some green lines to show where VLOG-L cuts off.
The important thing to get here is -- VLOG-L is designed to use the same LUTs as VLOG, so they didn't modify the shape or IRE representations from VLOG. And because of that, the maximum brightness that a DVX200 can deliver, in VLOG-L, ends up at 79 IRE.
You cannot make the waveform monitor clip. You cannot make an external monitor show "false color" clipping. If you pointed the DVX200 (in VLOG-L) at the sun, with the iris wide open, the maximum exposure you'll see is 79 IRE. It is impossible to get the DVX200's zebras (at 80%, in VLOG-L mode) to show up. It cannot generate those higher stops, because those are reserved for >12 stops of dynamic range in full VLOG.
So -- yes, if you're used to looking at the waveform from other cameras, you'd think that the DVX200 wasn't clipped when the peaks were at 80 IRE. But they would be, they'd be horribly clipped.
I knew this would bite people in the butt, and I've asked the factory for a couple of ways to address this, including remapping the waveform monitor so that in VLOG mode it shows nothing above 80. I have also asked them to consider a different, VLOG-based gamma that is designed specifically for this sensor, that remaps the superwhites into the full range at 80 and above. Either approach would help cinematographers use it, because frankly, it's different and so far nobody can be expected to intuitively know how to use it because ... this is the first camera that has it.
In short, if you're using the waveform monitor with VLOG-L:
Blacks go at 7.3 IRE Middle gray sits at 42 IRE 90% white sits at 61 IRE Absolute clip is at 79 IRE
You cannot use "false color" with VLOG-L as it won't show the proper values. Unless you press the "REC 709 LOG" user button, which overlays a REC 709 gamma on the monitor output -- if you do that, then yes you'd see traditional waveform values on your external monitor, and you'd easily see that the image was grossly clipping."