Why I Built a Custom Hybrid False Color LUT Builder (and Why You Need One)

If you’ve ever shot on a Sony FX3, A7S III, or even a cinema-line camera like the Venice, you’ve likely run into a frustrating trade-off: How do I accurately monitor exposure without ruining my ability to see the scene?

Standard False Color LUTs are a “rainbow mess.” They wrap your entire image in neon gradients, making it impossible to check white balance, judge skin tones naturally, or even pull focus comfortably. On the other hand, relying solely on a standard Rec.709 LUT is a guessing game for highlight retention and noise floors.

I wanted a better way. So, I built lut-builder.

The Problem: The “All-or-Nothing” Monitoring Trap

Most cameras don’t have built-in, customizable false color. To get it, you usually have to buy an external monitor or load a static .cube file. But these static LUTs have three major flaws:

1. They are rigid: You can’t change where the exposure bands sit.
2. They are distracting: They paint over the whole image.
3. They hide the “Real” Image: You can’t tell if your white balance is off because the “Green” exposure band is covering the actor’s face.

The Solution: A Hybrid, AI-Powered CLI Tool

I used AI to help me build a Python-based command-line tool that generates professional, standards-compliant .cube files.

The goal was simple: Hybrid Monitoring. My tool allows you to keep a Rec.709 base image (so you can see your colors and white balance) while overlaying “thin” or “razor” bands of false color only at the specific exposure stops you care about.

What makes this different?

• Precision Color Science: Unlike cheap LUTs that use fixed BT.709 approximations, this tool uses CIE Y luminance derived from your camera’s specific gamut matrix (S-Gamut3.Cine, V-Gamut, etc.). The stops you see are what the sensor actually sees.
• The “Hybrid” Edge: You can choose to have a monochrome base or a full Rec.709 base. This means you can see your exposure bands on top of a natural-looking image.
• Tailwind Integration: I integrated the Tailwind v4 palette, allowing you to pick professional, modern colors for your exposure bands using simple names or hex codes.
• Total Customization: You can define exactly how wide the bands are (from “Razor” to “Wide”) and exactly which IRE or Stop values they highlight.

How it Works

The script is a guided CLI experience. You just run uv run lut-builder (or use the double-clickable .bat and .command files I included for non-coders), and it walks you through:

1. Choosing your source (Sony, Panasonic, Canon, ARRI, RED).
2. Setting your target (Rec.709 or Rec.2020).
3. Defining your exposure bands (e.g., Middle Gray at 0 stops, Highlights at +2).
4. Exporting a .cube file ready for your monitor or NLE.

Built with AI, For the Community

This entire project was architected using AI to bridge the gap between complex mathematical transforms (scene-linear light decoding) and a user-friendly interface.

I’ve made it open-source because exposure shouldn’t be a premium feature. Whether you’re nailing the exposure on a skin tone or protecting your highlights in a high-contrast sunset, you should have a tool that works for your workflow—not one that forces you to look at a rainbow.

Check out the project and build your own LUTs here: https://github.com/Today20092/lut_builder

Ayoub is a creator focused on merging AI with cinematography tools to streamline the filmmaking process.