External Display Control on macOS (No Third-Party GUI Apps)

Overview

macOS doesn't natively expose controls for third-party displays, but most modern displays
support DDC/CI — a protocol that lets software send commands directly to display hardware:
brightness, contrast, volume, input source, color temperature, power, and more.

This skill is split into a setup section (below) and per-control reference files.
Once set up, jump to the reference file for the control you need.

Reference Files (read after setup)

File	Controls covered
INLINECODE0	Brightness — scripts, keyboard shortcuts, cron presets
INLINECODE1

Contrast — tips for color-mode lock |

Step 0 — Identify Your Setup

What Mac chip?

uname -m   # arm64 = Apple Silicon | x86_64 = Intel

How is your display connected?

Cable	Apple Silicon	Intel
USB-C / Thunderbolt	✅ Full DDC support	✅ Full DDC support
DisplayPort

✅ Works | ✅ Works |

If you're on Apple Silicon with HDMI and can't switch cables → jump to Software Fallback.

Step 1 — Install the Right Tool

Apple Silicon → m1ddc

Intel → ddcctl

Homebrew not installed?
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Step 2 — Quick Smoke Test

Verify DDC is working before scripting anything:

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No change? → See Software Fallback below.

Multiple displays? Target a specific one:

m1ddc display list              # find index
m1ddc display 2 set luminance 60
ddcctl -d 2 -b 60               # Intel equivalent

Step 3 — Set Up Shell Scripts

All controls work as one-line shell commands. Create a ~/scripts/ folder
and save scripts there so Automator, cron, and keyboard shortcuts can call them.

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Always use full binary paths in scripts — Automator and cron don't load your shell PATH:

• - Apple Silicon: INLINECODE9
• Intel: INLINECODE10

See each references/*.md file for ready-to-paste scripts per control.

Make scripts executable after creating them:

chmod +x ~/scripts/*.sh

Step 4 — Keyboard Shortcuts (Automator)

Works for any script. Do this once per action you want to bind to a key.

1. 1. Open Automator → New Document → Quick Action
2. "Workflow receives" → no input in any application
3. Add Run Shell Script → paste the full script path (e.g. /Users/yourname/scripts/brightness-up.sh)
4. Save as e.g. Brightness Up
5. System Settings → Keyboard → Keyboard Shortcuts → Services → General
6. Find your Quick Action → assign a shortcut (e.g. ⌃⌥↑)

If the shortcut doesn't fire: System Settings → Privacy & Security → Automation → grant access.

Step 5 — Time-Based Presets (Optional)

Use cron to switch display settings automatically at certain times:

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See references/color-temperature.md for ready-made day/night scripts.

Software Fallback (No DDC Support)

If your display doesn't respond to DDC (TVs, budget displays, DisplayLink docks),
use macOS Gamma table control to dim the image in software:

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As a script (~/scripts/brightness-soft.sh):
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⚠️ Software dimming changes appearance only — no power saving, slight colour shift at
low values. Hardware DDC is always preferable when available.

Troubleshooting

References

• - m1ddc (Apple Silicon): https://github.com/waydabber/m1ddc
• INLINECODE21 (Intel): https://github.com/kfix/ddcctl
• DDC/CI HDMI block on Apple Silicon: https://github.com/MonitorControl/MonitorControl#readme