Low-level dithering & display-signal control (DisplayPort + HDMI) for AMD GPUs on Linux
RedControl talks directly to the AMD display engine (DCN) through UMR — the User Mode Register debugger — to control things no desktop settings panel exposes: per-pipe spatial/temporal dithering, color truncation, and the display stream encoder itself (DisplayPort and HDMI). Built for flicker-sensitive users, display tinkerers, and anyone who needs to know (and change) exactly what signal their AMD GPU is putting on the wire.
git clone <this-repo-url> RedControl && cd RedControl
./install.shinstall.sh verifies Python/Tkinter, installs umr (the one required dependency) for your distro — or builds it from source — adds an app-menu launcher, and offers to launch. Prefer to do it by hand? See Requirements.
- 🎛️ Dithering Control — enable/disable spatial and temporal dithering, RGB noise, highpass/frame random, with per-depth and per-mode settings on every output (HDMI, DisplayPort, eDP, DVI)
- ✂️ Color Truncation — force a static signal by truncating/rounding to 6/8/10/12 bpc instead of dithering
- ⇄ Signal panel — live view of the DIG encoder driving each output: link type (DisplayPort, HDMI, or HDMI-over-DP++), pixel encoding (RGB/YCbCr) and the color depth actually on the wire. Force
DP_COMPONENT_DEPTH(DP, 6–16 bpc) orHDMI_DEEP_COLOR_DEPTH(HDMI, 8–16 bpc) instantly — no modeset required; HDMI changes auto-revert in 15 s unless confirmed - 🎨 Color / Depth — max bpc, colorspace (BT.709/opRGB/BT.2020), RGB range (full/limited) per connector
- 🖥️ Multi-Monitor — CRTC-based pipe mapping; each display configured independently
- 🎮 Multi-GPU — automatic detection and switching between AMD GPUs
- 🔄 Settings Persistence — per-monitor auto-save/restore
- ⏱️ Safe Mode Changes — resolution/refresh changes ask for confirmation and auto-revert after 15 s if the screen goes blank
- 💾 VRAM Vendor Detection — Samsung / Hynix / Micron shown next to the GPU name
- 🚀 System Tray — minimize to tray with quick actions
- 📋 Command Log — every register write is logged as the exact
umrcommand, so you can reproduce or script anything the GUI does
AMD's driver enables temporal dithering in situations where it can cause visible flicker, eye strain, or headaches for sensitive users — and there is no official switch to turn it off on Linux. RedControl gives you that switch, per output, at the register level, plus the DisplayPort-side depth control to pair with it (e.g. force a clean static 8 bpc signal with no dithering at all).
All AMD GPUs with a DCN (Display Core Next) display engine:
- RDNA 1: Navi 10, 12, 14 (RX 5000 series)
- RDNA 2: Navi 21, 22, 23, 24 (RX 6000 series)
- RDNA 3: Navi 31, 32, 33 (RX 7000 series)
- APUs: Renoir, Cezanne, Rembrandt, Phoenix (Ryzen 4000–7000 integrated graphics)
Tested on: CachyOS (Arch Linux), Cinnamon on X11, with an RX 6600 (RDNA 2) and Radeon 780M (RDNA 3 / Phoenix APU). Other AMD GPUs share the same DCN display engine and should work, and other distros/desktops should too — but only the above is verified. X11 is recommended; the xrandr-based controls (resolution, refresh, scaling, Broadcast RGB) need X11, though core dithering and the DP/HDMI signal panel also work on Wayland. Reports from other setups welcome.
- Linux with the
amdgpudriver (X11 session recommended; core dithering + DP signal features also work on Wayland) - Python 3 with Tkinter
- UMR (User Mode Register debugger)
- Optional:
python3-pil,pystray(tray icon),vulkan-tools(better GPU names)
# Arch Linux
yay -S umr-git
# Ubuntu/Debian
sudo apt install umr
# From source
git clone https://gitlab.freedesktop.org/tomstdenis/umr.git
cd umr && mkdir build && cd build
cmake .. && make && sudo make installpython3 redcontrol.py # normal launch
python3 redcontrol.py --tray # start in system tray
python3 redcontrol.py --debug # verbose console outputRun as a normal user — UMR calls go through sudo, and the app can set up passwordless access for the exact commands it needs (menu: Auto-Start → Passwordless Access).
Open Signal (DP / HDMI) in the sidebar for any monitor:
- Live Signal shows which DIG encoder drives the output (auto-matched via the DIG frontend's source CRTC), whether the link is DisplayPort or HDMI/TMDS — including HDMI carried over a DP++ port through a passive adapter — the pixel encoding, and the color depth actually on the wire. Also: HDMI deep color & TMDS clock state, active lanes, DP link rate/lane config, the source framebuffer format (is your compositor 8-bit or 10-bit?), driver color-LUT activity (GAMCOR/shaper/output gamma), DSC compression state, VRR range, and a true refresh rate measured from the GPU's frame counter.
- Force Link Depth writes the encoder's depth field directly (
DP_COMPONENT_DEPTHon DP,HDMI_DEEP_COLOR_DEPTH/ENABLEon HDMI). Every force goes through a Keep/Revert dialog that auto-reverts in 15 s if unanswered. Pin (auto-reapply) keeps a forced depth alive: a watchdog reapplies it whenever the driver resets the register on a modeset or monitor sleep/wake. - Why no 6 bpc on HDMI: DisplayPort defines an 18-bit link format; HDMI's minimum is 24-bit RGB. For 6-bit output on HDMI, use Truncate → 6-bit or 6-bit spatial dithering — the wire stays 8 bpc but only 6 bits carry content.
RedControl writes GPU registers directly. All writes are non-persistent (a reboot or modeset restores driver defaults), but a forced depth or encoding the sink can't handle may blank the screen until you revert. Use at your own risk.
MIT — see LICENSE.