Black frame insertion demo. The flicker, shown honestly.
Strobing modes on monitors shorten how long each frame stays lit, inside one refresh, which is what reduces motion blur. A web page cannot do that: it can only draw a black frame at the same refresh rate, which halves the frame rate and sharpens nothing. So this shows the one thing software can show, the flicker, and you can skip it.
This check is visual: it draws movement or flicker on the screen, and you judge the result by eye, so a screen reader cannot describe it. The list under "What it measures" says in words what each one shows. If motion or flicker makes you unwell, or you have reduced motion switched on, you can leave it out: no other test on this site depends on it.
One check
- Black frame insertion
One check after another, with your progress along the top and a plain verdict on each. Nothing you show the camera or say into the microphone leaves this page.
In short
Black frame insertion demo: the answer first
A black frame insertion test shows what inserting a black frame does on a web page: the lower row is lit one frame in two, so it flickers at half your refresh rate and moves at half the frame rate. It is not sharper, and the page explains why a monitor's own strobe mode is.
Reading your result
- Flicker at half the rate
- At 60 Hz that is 30 Hz flicker, which most people see; at high rates it is above what most eyes notice.
- Half the light
- Half the frames are black, so the row is dimmer. Monitors raise the backlight in strobe mode to compensate.
- Why the monitor can do more
- Strobe modes shorten the flash inside one refresh and keep the frame rate. A page can only blank whole frames.
What it measures
Measured here, not assumed.
- What the row shows
- Flicker at half your refresh rate. The lower row is lit one frame in two, so its mark moves at half the frame rate and steps twice as far. It is not sharper; only a monitor's own strobe, which shortens the flash inside one refresh, can be.
- The cost
- Half the light, and flicker at half your refresh rate. At 60 Hz that is 30 Hz flicker, which most people see; at 240 Hz it is 120, which most do not.
- Why it is a menu option
- Monitor makers call it ULMB, ELMB, DyAc, MBR or 1 ms MPRT. They shorten the backlight flash within one refresh, keeping the frame rate, which is what a page cannot do.
If it fails
The usual failures, and what fixes each.
- It flickers badly
- That is expected at 60 Hz. Strobe modes are meant for high refresh panels, where the flicker is above what the eye sees.
- The lower row is too dim
- Also expected: half the frames are black. Monitors compensate with a brighter backlight in strobe mode.
- You want it in games
- Turn on the monitor's strobe mode in its menu; it is off by default. It usually disables variable refresh rate.
Where a browser stops
What it cannot tell you.
- This is a software imitation at the same refresh rate: it halves the frame rate and cannot shorten persistence. Only a monitor's strobing backlight sharpens.
- The flicker is real and can affect people with photosensitivity; the demonstration waits for a press and can be skipped.
- A page cannot measure your panel's strobe mode; this shows what strobing looks like, not what it does to blur.
Privacy
Nothing leaves this page.
The camera and microphone are read on this page and stopped as soon as they have been measured. The clip you can play back lives in the browser's memory and is discarded when you leave. The location check discards the position. The internet test sends random bytes to this site and nothing else. The result is stored nowhere unless you ask for it by email, and then only the fact that an email was sent is kept.
Questions
Black frame insertion demo, answered
- What is black frame insertion?
- Showing a black frame between real frames so each real frame is lit for less time. On a monitor or TV that is done inside one refresh, keeping the frame rate; a web page can only drop every other frame, which is why this is a demonstration of the flicker and not of the sharpness.
- Does black frame insertion reduce motion blur?
- A monitor's strobe mode does, in proportion to how much it shortens the lit time within one refresh. Software BFI at the same refresh rate does not: it halves the frame rate, so the mark steps twice as far and blurs the same.
- Why does it flicker?
- Because the screen is dark half the time. At high refresh rates the flicker is too fast to see; at 60 Hz it is not, which is why the demonstration warns and waits.
- Should I turn on ULMB, ELMB or DyAc?
- On a high refresh panel, for fast games, often yes; it is off by default and usually disables variable refresh rate. Try it and compare with the motion clarity test.
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