Sharp HiDPI ("Retina") text on 14–16" portable monitors connected to a Mac. Free, open source, menu bar only.
한국어 설명서: docs/manual-ko.md
Plug a 16" 2560×1600 portable monitor into a MacBook and macOS offers two kinds of settings:
- 1280×800 HiDPI – sharp, but everything is huge.
- 1680×1050, 1920×1200, … – a comfortable size, but not HiDPI. macOS draws 1680×1050 pixels and the monitor stretches them to 2560×1600, so text looks blurry.
What you actually want is "looks like 1680×1050" rendered at 3360×2100 and scaled down to the panel, which is what MacBooks do on their own screens. On monitors below 4K, macOS on Apple Silicon offers only one HiDPI mode (half the panel resolution) and nothing larger than the panel, and the old display-override plist trick no longer works there.
You don't need this for 4K monitors: macOS already offers 1920×1080 HiDPI on them.
Requires macOS 13 or later. Built and tested on Apple Silicon; the universal build also runs on Intel Macs but is untested there.
- Download
PortableHiDPI.zipfrom Releases and double-click it to unzip. - Drag
PortableHiDPI.appinto your Applications folder. - Double-click it. macOS blocks the first launch because the app is not notarized (that needs a paid Apple Developer account). Click Done.
- Open System Settings › Privacy & Security, scroll down to "PortableHiDPI" was blocked, click Open Anyway and confirm with your password or Touch ID.
- A display icon appears in the menu bar. The app has no Dock icon.
Steps 3–4 can be replaced by one Terminal command:
xattr -dr com.apple.quarantine /Applications/PortableHiDPI.app
- Connect the monitor and click the menu bar icon.
- Monitor Size – pick your monitor's diagonal. Many portable monitors report a wrong size (the one tested here claims to be 27"), and the size decides which resolution gets the (recommended) mark.
- Pick a resolution, e.g. 1680×1050 HiDPI (recommended). The monitor blinks for a second and comes back sharp. Pick a larger number if text is too big, a smaller one if it's too small.
- Optional: Refresh Rate (60 / 120 Hz, on monitors that support it) and Launch at Login.
The choice is remembered per monitor and re-applied whenever you reconnect it.
To start the app again after quitting: open it from Applications, or search "PortableHiDPI" in Spotlight (⌘ Space).
Targets the same text size as a MacBook's built-in screen (about 125 points per inch).
| Panel | 14" | 15.6" | 16" | Example models |
|---|---|---|---|---|
| 1920×1080 | 1504×846 | 1600×900 | 1600×900 | Most 15.6" FHD portables |
| 1920×1200 | 1504×940 | 1600×1000 | 1600×1000 | Lenovo ThinkVision M16 |
| 2240×1400 | 1504×940 | 1680×1050 | 1680×1050 | Lenovo ThinkVision M14d |
| 2560×1600 | 1504×940 | 1680×1050 | 1680×1050 | ZEUSLAP P16K, LG gram +view, ASUS MB16QHG |
| 2880×1800 | 1504×940 | 1680×1050 | 1680×1050 | 16" OLED portables |
| 3840×2160 | macOS default | macOS default | macOS default | macOS already offers 1920×1080 HiDPI |
Models are examples; check your monitor's panel resolution.
| Symptom | Fix |
|---|---|
| Black borders around the picture | Menu › Re-apply (fix black borders or blur) |
| Blurry again after waking from sleep | Wait ~3 seconds (it re-applies automatically), else Re-apply |
| An extra "PortableHiDPI …" display in System Settings › Displays | Expected: that's the virtual display. Change resolution from the menu bar app, not there |
| HDR is off | Limitation of mirroring. Choose Off when you need HDR |
| Link-hand or text cursor disappears near the right/bottom edge | Handled by the app (see below). If the copy is the wrong size, Match Cursor Size |
| Anything else odd | Quit – the monitor goes back to its previous mode |
Turn off Launch at Login, quit, and move the app to the Trash. To also remove saved settings: defaults delete io.github.subbak2.PortableHiDPI.
- Creates a virtual display offering the HiDPI mode you picked (1680×1050 at 2x = 3360×2100), with CoreGraphics'
CGVirtualDisplay. - Makes the real monitor mirror the virtual display.
- Sets the real monitor back to its panel resolution (2560×1600). Joining a mirror set makes macOS drive the panel at the virtual display's 3360×2100, which the monitor's scaler shrinks with black borders. The app re-checks this after every display change.
- The GPU renders at 2x and scales down to the panel, like a MacBook's "More Space" setting, so text stays sharp.
Quitting or choosing Off removes the virtual display and restores the monitor's previous mode. Nothing is installed system-wide and no admin password is needed. Before sleep the virtual display is removed, and it's recreated about 3 seconds after wake (mirroring across sleep is fragile in macOS).
- No network access: the app makes no connections and opens no ports. The only link is the "About" menu item, which opens this page in your browser.
- No admin password, no special entitlements, no system files changed. Settings live in the app's own preferences (
io.github.subbak2.PortableHiDPI). - No data collection or analytics.
- The release is ad-hoc signed and not notarized (no paid Apple Developer ID). Build it yourself from source if you prefer.
- Download only from this repository's Releases. Each release lists the zip's SHA-256; check it with
shasum -a 256 PortableHiDPI.zip.
CGVirtualDisplay is undocumented. It has shipped in every macOS since 11 and other display tools rely on it too, but Apple can change or remove it without notice.
| If a macOS update… | What happens | What you do |
|---|---|---|
| removes the classes | The app still launches (they are weak-linked), the menu says "Not supported on this macOS version", nothing is applied | Wait for an update, or delete the app |
| changes their behavior | Enabling fails with an error and the setting is not retried on reconnect | Choose Off or quit |
| makes mirroring misbehave | Black borders, blur or a black external screen | Re-apply, unplug the monitor, or quit |
App Store review rejects private APIs, so this app will only ever be distributed here.
The app can't damage hardware or brick the Mac. It only creates a virtual display and changes display modes for the current login session; nothing is written to firmware, system files or the monitor.
Safeguards built in:
- The built-in screen is never touched, so you always have a working display.
- Display changes are made "for this session" only. Logging out or restarting always returns every display to the setting chosen in System Settings.
- If the app is quit, crashes or is force-quit, macOS removes the virtual display and the monitor returns to its previous mode.
- If the previous run died while applying a setting, the next launch does not auto-apply (safe start). Hold Shift while launching for the same.
- If the private API is missing, the app turns itself off instead of crashing.
If the external screen ever goes black or wrong, in order:
- Menu › Re-apply, or Off
- Quit the app from the menu bar (on the built-in screen)
- Unplug the monitor and plug it back in
- Log out or restart. To keep the app from starting at login once, hold Shift on the login screen when you click Log In
- Reset saved settings:
defaults delete io.github.subbak2.PortableHiDPI
Rendering at 2x and scaling down costs some GPU time. Measured on one setup (MacBook Pro M1 Max, macOS 27, 16" 2560×1600 monitor at 1680×1050 HiDPI, 60 Hz, idle desktop, GPU "Device Utilization" from ioreg):
| GPU utilization | |
|---|---|
| HiDPI on | about 5–6% |
| HiDPI off | about 0.3% |
With no external monitor connected, the app just sits in the menu bar: CPU stays at about 0% (0–1% in 5-second samples) and it submits no GPU work, so leaving it running costs nothing noticeable.
On battery that means somewhat shorter battery life while an external monitor is connected; the exact amount depends on your Mac, resolution and what's on screen (video and scrolling cost more than a still desktop). If battery matters more than sharp text, choose Off while unplugged. To measure watts on your own Mac: sudo scripts/measure-power.sh.
While mirroring, macOS keeps the real monitor's own desktop area at its native HiDPI size (1280×800 points for a 2560×1600 panel), smaller than the virtual display (1680×1050). The arrow cursor shows everywhere, but cursors that apps switch to (the link hand, the text I-beam) disappear in the strip outside that area: roughly the right and bottom quarter.
PortableHiDPI draws a copy of the cursor there, in a click-through window, only when the cursor is not the arrow. It matches your Pointer size setting (System Settings › Accessibility › Display); after changing it, choose Match Cursor Size in the menu.
Because it's drawn by an app rather than the hardware, that copy can trail the mouse by about a frame, and it checks the cursor shape every 0.1 s, so hand ↔ arrow switches can lag by up to 0.1 s. It costs a few % CPU only while the pointer moves in that strip, and nothing elsewhere.
- While mirroring, HDR is not available and the monitor runs SDR.
- 120 Hz through a mirrored virtual display can feel choppy on some setups; use 60 Hz if it does.
- Rendering at 2x costs some GPU time and memory (a 3360×2100 frame buffer); see "GPU and battery use".
/Applications/PortableHiDPI.app/Contents/MacOS/PortableHiDPI --list # monitors and options
/Applications/PortableHiDPI.app/Contents/MacOS/PortableHiDPI --inches 16 --apply 1680x1050 # set and run
/Applications/PortableHiDPI.app/Contents/MacOS/PortableHiDPI --apply off
--inches and --apply act on the first external monitor and then keep the app running.
git clone https://github.com/subbak2/PortableHiDPI.git
cd PortableHiDPI
scripts/build-app.sh # build/PortableHiDPI.app and build/PortableHiDPI.zip
python3 scripts/make-diagram.py # redraw docs/images (needs rsvg-convert for PNG)
Needs Xcode command line tools (Swift 5.9+). No Xcode project.
- BetterDisplay – full-featured display manager (free tier + Pro).
- DeskPad – virtual display shown in a window, handy for screen sharing.
PortableHiDPI does one thing: sharp text on a portable monitor, with nothing else to configure.
MIT