2016-01-26

recording and matching V-Log on the GH4 camera externally

The few things I blog here are mostly about making things.
However I DO have another hobby. Cinematography. Especially the technical aspects.
Currently I do use 2 Blackmagic Pocket Cinema Cameras and I have waited patiently for years to get a good deal on a non-EU GH4 or GH4R to combine 2 FullHD closeups (left and right interview subject/dialog participant/stage side) with a DCI 4K or UHD wide shot that acts as both wide and semi-wide by taking FullHD crops in post.

 Motivation

I'm finally going to get a GH4R with an external recorder.
Recording much on Blackmagic Pocket cameras, V-Log looks nice.
However there are some reports of issues it has. Many with 8bit 4:2:0 internal recording and sounding like they may go away with 10bit 4:2:2 recording.

Status: I did receive the GH4R and Ninja Assasin. However the Power Station is going to run late.
I'm not entirely disapointed about that, given the bug of the current Power Station mentioned below.

Reading material on V-Log

This is the text-list I have come up with so far to get a grip on this topic:

Very interesting read on VLog vs. Cinelike-D vs. Natural on the FH4 when using 10bit external recording and 8bit internal recording on the #GH4.

Linked to from this discussion:
http://www.eoshd.com/comments/topic/9431-v-log-l-captured-in-8-bit-vs-10-bit/

after reding this in-depth anylysis of the color-spaces:
http://forum.slashcam.de/gh4-aces-unterstutzung-vt127380.html
(better LUTs then the ones from Panasonic at the bottom of the thread.)

Some practical analysis of V-Log in 10bit here:
http://www.provideocoalition.com/v-log-l-on-the-gh4-don-t-panic

conclusions about V-Log

Record V-Log externally as compressing this huge dynamic range into 8 bit 4:2:0 MPEG leaves you with banding and green+magenta noise.
Maybe overexpose slightly when using V-Log to reduce noise in the shadows.
(8-bit ProRes seems to work well but...file size doesn't matter when recording to a hard disk/SSD-drive. anyway ) 
  • whenever possible but only recorded externally
  • priority on high dynamic range (e.g. lights at night)
  • high contrast situations (e.g. film noir)

For scenes with low dynamic range but important skin tones, "Natural" or "Cinelike-D"  seem to be called for.
  • when priority is on subtle skin tones 
  • when subtle gradients in the midtones are important (deep blue sky, rolling but bright fog)
  • hazy footage where focusing gets difficult (unless I can focus with a LUT and peaking on the recorder)
  • when recording internally

power everything

The Atomos Ninja Assasin for external recording comes with an Atomos Power station.
Aparently the Assasin drains batteries like crazy (not as crazy as the Blackmagic Pocket). So Atomos hands out larger batteries for the early adopters and makes a limited time deal for Power Stations to the later crowd.
It already includes the adapter to also power the GH4.

HOWEVER, numerous reports state that the Power Station has a few flaws in it's current firmware or hardware.
  • Same battery in Power Station lasts just half as long as directly plugged into the Ninja Assasin/Shogun 
  • Full Batteries in Power Station suddenly reported as empty
The voltage detection seems to be confused with the large power draw of the Shogun. It works fine with a small camera. My guess is that due to the power draw the voltage drops and thus the batteries are reported as empty way ahead of time.

matching cameras

Obviously I want to match the GH4 to the two BMPCC.
I found the color chart automatic matching in Davincy Resolve to be a great starting point.
However it does not match gain (white level 786 vs 1024), gamma (grey at 130 vs 250) and olive/green seems to be rendered differently (despite nothing non-green having any color cast at all).

The perfect way to go seems to be ACES "Academy Color Encoding System".
Yes, that's the Academy as in Academy Awards = Orcars.
Yes, Resolve V12 can convert footage into the camer-neutral XYZ color space using an IDT=input device transform.
Yes, there are IDTs for GH4 in V-Log and BMPCC in ProRes (Cinema DNG does not need an IDT as it contains all that transform information).
No, Resolve can not import IDTs and is limited to the few it has.
Choosing BMDFilm for the flat BMPCC and Sony SLog for the Panasonic V-Log gets you close.
However not as close as the color-chart.

Since I can't do this properly yet, I'll use it as a simply starting point whenever I can't have a color chart before/after the shot.
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