Question about colour space and LUTS FX9

[JamieWelham]

I can't quite find the answer anywhere else so thought I'd ask the community re colour space and using LUTs on my Atamos Shinobi with FX9. I'm recently getting my head around working with LUTS.

 

If I choose to use S-Gamut3 as opposed to S-Gamut3.cine and I want to apply LUTs to my Atamos Shinobi, just for viewing purposes rather than to burn in, what kind of LUTs am I looking for?

 

It looks as though most slog3 LUTS are designed for S-Gamut3.cine but also when you download LUTS I'm slightly confused by the difference betweeen 'monitoring luts' (does that mean solely for monitoring purposes on monitor) and 'slog3 luts' (for example, Alexandru Don's LUT collection on the Sony site).

 

Any guidance hugely appreciated. Thanks

[joema]

Unfortunately, my team never uses S-Gamut3, only S-Log3/S-Gamut3.cine, so I don't have any experience with regular S-Gamut3. However, we do use an S-Log3-to-Rec.709 monitoring LUT on the Atomos Ninja V and Shogun 7 from our FX6 cameras. We use Alister Chapman's LUTs which are in various versions, including G1 and G2 variants with green correction and monitoring LUTs: https://www.xdcam-user.com/2018/08/new-venice-look-luts-version-3-includes-minus-green-luts-for-fs5-fs7-f55-a7s-a7r/alister-v-look-v3-s-log3/

On the FX6s we use only Cine EI mode and don't use any MLUTs, just monitor using waveform in S-Log3. We set exposure at 61% to 68% IRE on a 90% reflective white target using Zebra 2. That is the procedure recommended by Doug Jensen in his classes. I've seen countless operators try more complex procedures and they often get confused and make mistakes. Thanks, Doug, your advice has saved us many times!

Starting with Resolve 18.5, there are "RAW controls for XAVC," which requires Cine EI S-Log3 XAVC-I MXF files from the FX6 and FX9. This enables RAW-like corrections to white balance, tint and exposure in post. It's not equal to true RAW but it's very nice.

Here are some full-res TIFF frame grabs comparing extreme WB adjustment in FCP using ProRes RAW vs simultaneously-recorded FX6 XAVC-I using Resolve 18.5 "RAW controls for XAVC": https://www.dropbox.com/scl/fo/kr0x078460qichhgy5r8z/h?rlkey=mhc90mr03xgwc8tw4bnhsm2zx&dl=0

It works so well that we rarely use ProRes RAW from the FX6 cameras. We do use ProRes RAW on the DJI Ronin 4D because it has no equivalent to this adjustability without using RAW.

I don't think Resolve currently provides that feature for any other brand or camera -- only the Sony "cinema" series. I don't know who in Blackmagic and Sony negotiated that but it is a fantastic feature.

[joema]

Forgot to add: starting with Resolve Studio 18.5, it reads the EI (Exposure Index) data from the FX6 and FX9 and automatically applies that in post in the color page's RAW controls. Previously, an issue with the FX6/FX9 "ISO/gain" switch (in Cine EI mode, the L/M/H EI switch) on the FX6/FX9 was no NLE software could interpret it. Now Resolve does.

In Cine EI mode, the camera switch did two things: (1) Altered the *apparent* (not actual) exposure if using an MLUT, and (2) Wrote the selected EI data to the MXF file metadata.

However this meant if you never used EI and MLUTs, your L/M/H EI switch (and associated menu settings) might have been in any state.

Starting with Resolve Studio 18.5, it reads and automatically applies the L/M/H switch state -- even if you never used MLUTs. That alters the exposure slider in the RAW controls of Resolve's color page. E.g, say two years ago you pulled your FX6/FX9 out of the bag and something moved that switch. It made no difference unless you were using Cine EI mode *and* MLUTs. Now on Resolve 18.5+, whatever position that switch was two years ago now matters. 

It's not a big deal because the changes are "lossless" -- you just move the exposure slider in Resolve. But it could cause certain clips to suddenly appear in Resolve as over or under-exposed. 

My team still doesn't use MLUTs or the L/M/H ISO/gain switch. However, we have now programmed the FX6 Main Menu>Shooting>ISO/gain EI settings to 800 for all three switch positions in low base sensitivity and 12800 for all three switch positions in high base sensitivity. That means no matter what position the switch is in, it will not cause an exposure offset change in Resolve Studio. Again, those changes are easy to fix but this prevents it from surprising anybody in post for future clips.

[videosoul]

You are correct. Most LUTs designed for slog3 seem to be for sgamut3.cine

LUT creators should really specify!

When people say "monitoring LUTs" they usually mean 33-point or 17-point, as most cameras and monitors will only accept these. But grading LUTs should be 65-point for best quality.

https://www.4kshooters.net/2021/07/31/whats-the-difference-between-a-17grid-3d-lut-and-a-65grid-3d-lut/

FYI, if you haven't come across it, you can make your own LUTs with https://cameramanben.github.io/LUTCalc/ / https://apps.apple.com/gb/app/lutcalc/id1000409621?mt=12 (latest version is on the Mac App Store).