Motion clarity and persistence blur
Most people assume motion blur on a monitor comes from slow pixels. On a modern fast panel it mostly does not. It comes from each frame being held perfectly still on screen while your eyes keep moving, and that is a different problem with a different set of fixes.
Two different blurs
When something moves on your screen and looks smeared, there are two independent causes, and they respond to completely different fixes.
| Type | Cause | Fixed by | Present on OLED? |
|---|---|---|---|
| Transition blur | Pixels take time to change colour | Faster panel, tuned overdrive | No |
| Persistence blur | Each frame is held still while your eyes move | Higher framerate, higher refresh, strobing | Yes, fully |
People who upgrade to OLED and are surprised there is still blur in fast motion are seeing the second one. It is not a defect; it is a property of holding an image on screen at all.
The persistence arithmetic
Persistence blur is simple to quantify. If a frame is displayed for time t and the object is moving at speed v across your screen, the object smears across a distance of v times t.
| Unique frames per second | Display time per frame | Blur width |
|---|---|---|
| 60 | 16.7 ms | 1.67% of screen width |
| 120 | 8.3 ms | 0.83% |
| 240 | 4.2 ms | 0.42% |
| 360 | 2.8 ms | 0.28% |
| 1000 (equivalent, via strobing) | 1.0 ms | 0.10% |
Note the crucial term: unique frames. A 480 Hz panel receiving 120 fps holds each unique image for 8.3 ms and has exactly the persistence blur of a 120 Hz panel. This is the single most important fact about motion clarity and it is almost never stated in a display review.
Strobing: the shortcut, and its price
Backlight strobing breaks the arithmetic above by making the display time shorter than the frame period. Instead of holding the image for the full 4.2 ms of a 240 Hz frame, the backlight flashes for perhaps 1 ms and is dark for the rest. Persistence blur drops by the same ratio.
Brand names vary: ULMB and ULMB 2 (Nvidia), DyAc and DyAc 2 (Zowie), ELMB (Asus), MPRT on some panels. The mechanism is the same.
| Cost | Severity | Notes |
|---|---|---|
| Reduced brightness | Significant | The backlight is off most of the time. Expect to lose half or more. |
| Visible flicker | Person-dependent | Some people see it immediately and get headaches; others cannot detect it at all. |
| Incompatible with VRR | Usually total | Most implementations require a fixed refresh rate. A few newer ones do not. |
| Double images if framerate drops | Severe when it happens | If your framerate falls below the strobe rate, frames get strobed twice and you see two of everything. |
| Crosstalk bands | Moderate | Imperfect timing leaves faint duplicate images, usually at the top and bottom of the screen. |
When strobing is the right call
You have a stable framerate at or above the strobing refresh rate, you are not flicker-sensitive, and you are willing to give up variable refresh. That combination describes a competitive player on a well-optimised older title, which is exactly the population that uses it. If your framerate fluctuates or you play modern demanding games, VRR plus a high framerate is the better setup.
The practical hierarchy
- Raise framerate. Reduces persistence blur and latency simultaneously, works everywhere, no side effects.
- Raise refresh rate, once framerate can feed it. Same benefit, requires the frames to exist.
- Move to OLED. Removes transition blur entirely, leaving only persistence.
- Strobing. The largest single reduction in persistence blur, with the longest list of caveats.
Related reading
- Refresh rate, and why unique frames are the unit.
- Response time for the other blur.
- Variable refresh, which strobing usually excludes.
Frequently asked questions
What is persistence blur?
The smearing you see when tracking a moving object on a sample-and-hold display. Your eyes move smoothly to follow the object, but the image sits still for the whole frame period, so the object's light sweeps across your retina. The amount of smear is proportional to how long each frame is displayed.
How do I reduce motion blur on my monitor?
Three ways, in order of preference: raise your framerate (each unique image is held for less time), raise your refresh rate if your framerate can feed it, or use backlight strobing, which shows each frame in a brief flash instead of holding it. Strobing is the most effective and has the most side effects.
What is backlight strobing or black frame insertion?
The backlight is switched off between frames so each image is shown as a brief pulse rather than held continuously. This drastically reduces persistence blur, because the light exists for only a fraction of the frame period. The costs are lower brightness, visible flicker for some people, and incompatibility with variable refresh on most implementations.
Is ULMB or DyAc worth using?
If you have a stable framerate at or above the strobing refresh rate and you are not sensitive to flicker, the motion clarity improvement is large and immediately visible. If your framerate fluctuates, the strobe and frame timing desynchronise and you get double images, which is worse than the blur you were fixing.
Does OLED remove motion blur?
It removes the pixel transition component entirely, which is a large improvement. It does not remove persistence blur, because OLED is still sample-and-hold. A 240 Hz OLED and a 240 Hz perfect LCD have identical persistence blur; the OLED just does not add smearing on top of it.