BFI Black Frame Insertion (BFI)

What BFI is

Black Frame Insertion — also called backlight strobing on LCDs — is a display feature that reduces persistence blur by inserting a completely black frame between every lit frame, so the backlight (on LCD) or the pixels themselves (on OLED) go dark after every refresh. The technique is designed to emulate the impulse response of CRTs, where the image is shown briefly and then blanked, mimicking the CRT blanking period.

TV manufacturers ship BFI under proprietary names that hide the same underlying mechanism. LG calls its OLED implementation OLED Motion Pro, exposed inside the TruMotion sub-menu with off/low/medium/high settings. Sony's BFI control is the Clearness slider in Motionflow, and on models that include X-Motion Clarity, engaging Clearness activates that technology. Samsung exposes BFI inside Picture Clarity or Game Motion Plus depending on model.

Sony's X-Motion Clarity is a brightness-preserving variant that ties the strobe to the TV's local-dimming zones — each blink is individually controlled and its duration optimised, while brightness is boosted when needed, so the picture stays clear and smooth with virtually no loss in brightness. It is localised BFI combined with local dimming, not frame interpolation.

How BFI works

Modern LCD and OLED panels are sample-and-hold displays: each frame remains lit for the full frame duration. Because the eye smoothly tracks moving objects while the pixels stay static for that interval, the eye's motion smears the held image into perceived blur. Blur Busters formalizes this: the minimum motion-picture response time equals one frame duration on a sample-and-hold display — for example, 60 fps at 1000 px/sec yields 16.7 ms of persistence and 16.7 px of motion blur.

The Blur Busters Law quantifies the relationship: 1 ms of persistence equals 1 px of motion blur per 1000 px/sec of on-screen motion, and the relationship is linear in motion speed — at 3000 px/sec, 1 ms of MPRT generates 3 px of blur. BFI reduces blur by shortening the persistence interval, not by changing the source frame rate.

Implementation differs by panel type. On LCDs, BFI is typically achieved by strobing the backlight on and off in sync with each refresh. On OLEDs there is no backlight, so the pixels themselves must be rapidly turned on and off — feasible because OLED response times are far shorter than LCD's. OLED BFI generally works much better than LCD BFI thanks to the near-instant response times of the OLED panel, avoiding strobe crosstalk and ghosting.

The duty cycle — lit time vs dark time — sets how much persistence is removed and how much brightness is sacrificed. RTINGS' measurements of an aggressive OLED BFI mode show each cycle as roughly 2 ms lit followed by 14.67 ms of black at 60 Hz, and roughly 1.67 ms lit followed by 6.67 ms of black at 120 Hz; the exact duty cycle is implementation-specific and varies by panel and BFI strength setting. BFI looks similarly clean at the two refresh rates; the visible difference is brightness, not motion clarity.

When BFI helps and when it doesn't

Because the screen spends part of each frame interval dark, BFI inherently reduces perceived brightness. With simple every-other-frame insertion and the backlight fully off on the dark frame, brightness is effectively halved. Some implementations compensate by boosting the lit-frame brightness, so the real-world drop is often less than 50% but is never zero.

60 Hz BFI is more visibly flickery than 120 Hz BFI because 60 Hz strobing falls inside the human flicker-fusion range — the average rate at which humans stop reporting flicker is 60 Hz, but some viewers continue reporting flicker up to 90–100 Hz. That is why high-refresh (120 Hz+) panels handle BFI more comfortably than 60 Hz-only panels.

BFI and HDR pull in opposite directions. HDR mastering requires the panel to hit peak brightness for highlights, while BFI inherently dims the image, so many TVs disable BFI when an HDR signal is active. The brighter the content, the more noticeable the flicker becomes when BFI is engaged, compounding the problem.

A particularly effective pattern is a 120 Hz panel running BFI on 60 Hz content: each source frame is shown once and a black frame is inserted in the alternate slot, halving persistence without dropping the source frame rate. Blur Busters quantifies the gain — 120 Hz BFI on 60 fps removes about 50% of 60 Hz blur, and 240 Hz BFI on 60 fps removes about 75%.

BFI misconceptions

BFI does not increase the source frame rate and does not generate synthetic intermediate frames. A 60 fps source displayed with BFI is still 60 fps of actual motion — BFI only shortens how long each frame is visible. Frame interpolation is a separate technique that synthesizes new in-between frames; the two are sometimes combined but operate on different axes — persistence vs. frame count.

BFI is also not the same as PWM backlight dimming, even though both produce flicker. PWM modulates backlight brightness for dimming control; BFI deliberately blanks the screen for motion clarity. Many TVs do one without the other, so 'this TV uses PWM dimming' should not be read as 'this TV has BFI.'

OLED BFI and LCD backlight strobing are functionally similar — both shorten persistence by inserting dark intervals — but mechanically different. On LCD the backlight is strobed; on OLED there is no backlight to strobe, so the pixels themselves are turned off. The terms 'BFI' and 'backlight strobing' are often used interchangeably in casual writing, but the OLED implementation never involves a backlight.