Picture-by-Picture (PBP) on Mac: Fix the Garbled, Stretched or Black-Barred Half

Updated 2026-10-16

Picture-by-picture (PBP) splits one monitor between two inputs — say a Mac on the left half and a PC on the right. On Mac, the Mac’s half often comes out garbled, stretched, or with black bars.

Why it happens

In PBP mode each input only gets half the panel, for example 1720×1440 on a 3440×1440 ultrawide. The Mac can only use resolutions listed in the monitor’s EDID, and many monitors don’t list the half-width mode on every input. macOS then sends the full-width signal or the nearest mode it knows, and the monitor squeezes, crops or garbles it.

On my own setup (CS385F, MacBook Air M5 over HDMI) the effect was very specific: at 3440×1440 @ 50 Hz and at 1600×1200 the lower half of the picture was garbled, 1680×1050 displayed cleanly, and adding a true 1720×1440 mode gave a correct, full-height picture.

Step 1: Rule out the simple things

• Make sure PBP is actually active on the monitor, and which input feeds which half.
• Try the monitor’s own PBP size or aspect setting if it has one. BenQ, for example, documents its 16:9 + 5:9 layout.
• Check the cable and port: the half-width mode still needs a link that can carry it.

Step 2: Check what macOS offers

Open System Settings › Displays, select the monitor, click Advanced… and turn on Show resolutions as list, then Show all resolutions. If the half-width resolution is not in the list, the monitor’s EDID doesn’t advertise it for this input — that is the problem.

Common PBP half resolutions

“Theoretical” means the size follows from the panel; I have not run it on that monitor. If you have, I’d like to hear how it went (see Contact).

Can macOS do it on its own?

No. There is no setting for custom resolutions, and on Apple silicon the old EDID override files are ignored. Older write-ups such as Kevin Hooke’s Samsung PBP post predate Apple silicon.

The fix: Display Fixes Pro

Display Fixes Pro is our menu bar app for exactly this. It identifies your monitor, adds the split resolution macOS leaves out (1720×1440 on the CS385F), offers to switch when you turn PBP on or off, and puts everything back after a reconnect, wake or restart. Restoring the monitor’s factory settings is one click.

It is free for 14 days, then $4.99 once. Download the free trial →

BetterDisplay Pro can also load a custom EDID on Apple silicon, with a general-purpose interface. If you already own it, it works too.

Limits

• Version 1.0 handles one monitor and 50/50 splits; three- and four-way splits are planned.
• The monitor’s EDID needs a free timing slot; if there is none, the app tells you.
• It relies on a private macOS API and can break after an update.