1440p HiDPI vs LoDPI on a native 1440p display: 144Hz cap, M4 performance, and subpixel rendering

[leonasdev]

Hi @waydabber,

First of all, thank you for this amazing tool! I’ve been reading through the BetterDisplay Wiki, specifically the "MacOS scaling, HiDPI, LoDPI explanation" and "Fully scalable HiDPI desktop" articles, which perfectly explained the 5K framebuffer and the supersampling/antialiasing effect for low/mid-PPI displays.

I successfully enabled HiDPI on my native 2K display, but I have a few advanced questions about optimization, refresh rate limits, and text rendering on modern Apple Silicon.

My Hardware Setup:

• Mac: Mac mini M4
• Monitor: 27-inch 2K (2560x1440), capable of up to 280Hz
• Connection: Thunderbolt 4

The Situation:
I can successfully select the 2560x1440 (HiDPI) option, but the maximum refresh rate available for this mode is capped at 144Hz. If I switch back to the native 2560x1440 (LoDPI) mode, I can perfectly select the full 280Hz.

I would love to hear your technical insights on the following:

1. HiDPI @ 144Hz vs LoDPI @ 280Hz: Which is recommended?
The Wiki mentions that rendering a 5K framebuffer for a 1440p display only creates a supersampling effect and has a performance impact. However, to my naked eye, the 1440p HiDPI mode actually looks slightly sharper and better than the native LoDPI. Given the power of the new M4 chip, is the performance/memory impact of running this 4x framebuffer negligible now? Would you recommend sticking to HiDPI @ 144Hz for the visual benefit, or is it technically "healthier" for the system to use LoDPI @ 280Hz?

2. Is the 5K framebuffer the direct cause of the 144Hz limit?
Why is the HiDPI mode capped at 144Hz while LoDPI can hit 280Hz? Is pushing a 5K framebuffer at 280Hz hitting a hard macOS software cap, an Apple Silicon GPU rendering bandwidth limit, or a Thunderbolt 4 protocol limitation?

3. Is subpixel rendering gone forever?
The Wiki clearly explains that Apple removed subpixel rendering because it is fundamentally incompatible with their current fractional bitmap scaling approach. Just out of curiosity, is there absolutely no way or workaround (third-party tools, terminal commands, or deep system tweaks) to bring back the legacy subpixel rendering algorithm for low-PPI displays on modern macOS?

Thank you so much for your time and for developing such a life-saving app for Mac users!

[leonasdev]

Just a quick follow-up with some macro-photography testing I did to compare the actual pixel sharpness.

I used the EIZO Monitor Sharpness Test patterns to compare the text rendering and scaling results across different OS and modes. My monitor is a GIGABYTE MO27Q28G (Tandem OLED).

Here are the macro-shots comparing Black on White vs. White on Black text:

OS / Display Mode	Black Text on White Background	White Text on Black Background
Windows (Native 1440p)
macOS (Native 1440p LoDPI)
macOS (BetterDisplay 1440p HiDPI @ 144Hz)

My observations from the test:
In terms of absolute pixel sharpness on this OLED panel for this specific test pattern, the result is:
Windows (Native 1440p) = macOS (Native 1440p LoDPI) > macOS (BetterDisplay 1440p HiDPI @ 144Hz).

This perfectly illustrates the Wiki's point that scaling a 5K framebuffer down to a 1440p display relies on averaging algorithms, which destroys the perfect 1:1 pixel mapping.

A quick note on Windows vs. macOS text clarity:
Although Windows and macOS LoDPI look identical in these specific EIZO macro shots, I strongly suspect the EIZO test pattern simply doesn't utilize Windows ClearType (Subpixel rendering). In actual daily usage across various applications, the text on Windows still feels significantly clearer and more legible to my eyes compared to macOS LoDPI.

I'm sharing these findings just to provide some visual context on the trade-offs I'm experiencing. I am still very eager to hear your technical insights on my original Question 2 (the exact bottleneck causing the 144Hz limit with the 5K framebuffer) and Question 3 (whether any subpixel rendering workarounds still exist for modern macOS) whenever you have the time. Thanks again.

[waydabber]

Nice comparison, thank you!

[waydabber]

Hi,

to your original questions:

1. I think you should trust your eyes and use whichever looks better. The M4 is completely fine rendering things at 5K and then downsampling it. For 3D applications like games of course you will see a clear difference, but for desktop work it doesn't really matter much.

2. Is the 5K framebuffer the direct cause of the 144Hz limit?
   Yes, as there is a framebuffer pixel clock limit as well. But you can try exceeding the 144Hz limit by selecting the desired 5K mode at 60-144Hz and then hold the SHIFT while opening the Refresh Rate menu and see if you have higher options there. If there is, you may try them. Not officially though but they may work.

3. Is subpixel rendering gone forever?
   Yes, it is gone forever I think.