Inspired by Ed Lachman’s EL Zone, using the camera as a spot meter is really interesting for us DITs.
I had a couple issues with the EL Zone:
– The 14 stops Dynamic Range (I wanted the clipping points)
– The color schemes (Not a fan of green for under exposed)
What’s the base for it?
To turn our picture into stops, we will base our research on the DCTL made by Diode Film. Here is his nice tutorial on it https://www.youtube.com/watch?v=iXrR0CMFNZY
Everything is amazingly well explained in his video, but we will just need to add a CST from our camera color space to LINEAR, and then add a DCTL. Once this is done, we should have a nice False Color color coded by T Stop.
We can (and will!) modify this DCTL to add stops above and under to have our clipping point where we want them depending on the camera we’re using.
1D LUT VS 3D LUT
Why is 1D LUT better than 3D LUT in that case?
A 1D LUT (we’re going with 10bits), is just 1024 values turned into 1024 other values, with no interpolation, this will allow us crisp edges compared to a 3D LUT that uses interpolation between values.
Also 3D LUT interpolation doesn’t work great with grey, it
The input image also needs to be black and white, if it’s not, you will have some color artefacts, as shown in the ISSUE part of this post.
All of this is nicely explained in the Pomfort False Color creator (Which uses a 1D LUT system): https://kb.pomfort.com/livegrade/color-grading-features/false-color-mode-in-livegrade/
Here’s a quick comparison of 3D lut vs 1D LUT. That’s a shot with a lot of well separated brightness. In real conditions, 3D LUT is really hard to use for False Color.
Changing the DCTL for our cameras:
This is where testing needs to be done, but the base DCTL gives us 6 stops over and 6 stops under. We’re going to try and have our clipping points in our false color.
Here’s the classic dynamic range distribution for our most used cameras (at base ISO!)
Sony Venice 1: +6 / – 9
Arri ALEV3 sensors: +7.5 / -7.0
Arri ALEV4 sensors: +9.3 / -7.5.
LOG SONY VENICE 1
DCTL WITH STOPS -9/+6
Sony Venice classic False color
We can see that with our modified DCTL, we’ve got our high clipping points. Our low ones, due to the linear encoding (not much values at the bottom), isn’t as perfect, but we can adjust our bottom stops to match the official false color if needed.
How to setup in Resolve
If you’ve never used a DCTL before, copy the .dctl files in your Resolve LUT folder (/Library/Application Support/Blackmagic Design/DaVinci Resolve/LUT), restart resolve.
Add an OpenFX DCTL and select your DCTL in the list.
NODE #1
Monochrome
NODE #2
CST to Linear
Input: Camera Colorspace / Gamma (LOG)
Output: Camera Colorspace / Linear
Tone mapping: None
NODE #3
DCTL (OpenFX)
How to export a 1D LUT?
Resolve unfortunately can’t export a 1D LUT natively. We can’t convert a 3D LUT into a 1D without loosing all our colors and precisions (even with tools like Lattice). But thanks to Thatcher Freeman who coded some nice Fusion Fuses, allowing us to export 1D LUT from Fusion page.
Here’s how we do it, in this repository we need 2 fuses:
– LUT Cube Creator 1D : https://github.com/thatcherfreeman/utility-dctls/blob/main/Fuses/LUT%20Cube%20Creator%201D.fuse
– LUT Cube Analyzer 1D : https://github.com/thatcherfreeman/utility-dctls/blob/main/Fuses/LUT%20Cube%20Analyzer%201D.fuse
Copy the .fuse’s here: ~/Library/Application Support/Blackmagic Design/DaVinci Resolve/Support/Fusion/Fuses
In Fusion, shift+space bar to search for tools, select all the following nodes:
NODE #1
LUTCubeCreator1D: 1024
NODE #2
CST to Linear
Input: Camera Colorspace / Gamma (LOG)
Output: Camera Colorspace / Linear
Tone mapping: None
NODE #3
[[DCTL]]
NODE #4
LUTCubeAnalyzer1D: Export 1D LUT
The LUT Cube Creator creates a 1 pixel x 1024 pixel wide image with a scale from black to white, the CST adjust that scale from our camera color space to linear, our DCTL applies some color per brightness, and then we export with LUT Cube Analyser. You can see on the right viewer the visual representation of our False Color.
In Fusion, we can now clearly see how 1D LUT color scheme:
Links
Here’s a small link to all the DCTL/Files I did. Terribly sorry for this badly written article and badly organised files.
https://drive.google.com/drive/folders/1730gMiqiSJwkM9T-QsAcB8GgY-R2t07h?usp=sharing
ISSUES:
BLACK AND WHITE INPUT
Without a Black and White input, there is some weird color artefacts coming in. You can see some pink going into some colors.
What’s next?
Try all this theory on set first, thanks to Tom from Omniscope, the version 1.10.139 accepts 1D LUT import, which can make a project like that very useful for all the DITs.
Making a script to streamline all this would be nice too. Instead of having to enter the code and add RGB values to every stop manually.
