As I'm a known authority here in Hz (cites in >35 papers) -- you have to track your eyes while you scroll a screen. It varies on the situation and screen, but a good test is TestUFO Panning Map Readability Test, or the TestUFO Ghosting test. Stationary gaze is not as noticeable.I don’t get it. I’ve never been able to tell a difference between 60hz and 120hz.
What I notice is LCD GtG throttles differences between Hz badly. The M1, while wickedly fast, is famously whispered hushly as one of the slower 120Hz LCDs, in terms of GtG speeds.
The approximate real-world differences in motionblur perceived by human eyes, for eye-tracking a smooth scroll/pan:
- Macbook Pro M1 ... about 1.1x motionblur difference between 60Hz and 120Hz on same display
- Macbook Pro M5 ... about 1.5x motionblur difference between 60Hz and 120Hz on same display
- OLED iPad Pro ... about 2.0x motionblur difference between 60Hz and 120Hz on same display
When you zero out GtG, the latter has the same amount of motionblur as 1/60sec shutter vs 1/120sec shutter, during eye-tracking a pan/scroll/etc. That's assuming eye-tracked pan having equivalent motionblur to a sports-panned photograph for the same motionspeed; as a reference scroll motionblur equality. Bigger screens (e.g. OLED iPad Pro) shows this more easily than small screens (e.g. iPhone) or slow screens (e.g. Macbook Pro M1)
GtG is pixel fading from one color to the next. It is like a slow moving camera shutter before/after refreshtime. You don't want a 10ms shutter movement before/after a 8.33ms shutter full-open time. Exhorbitantly slow GtG throttles Hz differences, even if GtG is slightly under a Hz. You need fast GtG (like an instant shutter) to eliminate GtG-derived blurring, and keep it pure MPRT blurring (eye tracked motionblur cannot be less than refreshtime on sample-and-hold, at GtG=0.0000).
Also, for those upgrading to future Hz, geometrics helps too (60Hz vs 240Hz at 0ms GtG is way more noticeable than 60Hz vs 120Hz at non-zero GtG -- you can have as much as almost 6-7x motionblur differential based on the combined Hz differential and the GtG being zeroed out). If any of you attend nuts and bolt supplier conventions like SID DisplayWeek, there is persistent rumors in the display panel manufacturing industry that Apple is moving to 240Hz OLEDs in a "Pro" model by year ~2028 for the even-further-improved scroll ergonomics.
Obviously, not everyone instantly notices, but GtG speeds and bigger Hz differentials, does amplify differences. The 480p-vs-8K effect, rather than 720p-vs-1080p, behaves very similarly in the temporal dimension during continuous medium-speed scrolls on big screens. Some people flick scroll with a fixed eye gaze rather than eye-tracking the scroll, and this makes the Hz differences less noticeable. Screens look different with stationary gaze vs moving gaze (there's a demo on TestUFO -> Green Menu -> Eye Tracking).
P.S. TestUFO 3.0 has launched. Display-P3 support has been added, and TestUFO is finally iPhone/iPad friendly too.
Last edited: