Some interesting science, which is pretty well covered (e.g.
Microsoft Research, Nokia, Sharp Labs, universities), is that motion blur is actually dictated by the length of time a refresh is displayed for, instead of the refresh rate.
That's why stroboscopic displays (flicker) such as CRT, plasma and LightBoost, have excellent motion quality. The flickers shortens the length of time a refresh is displayed for.
It's also precisely why long-time CRT users who have switched to 120 Hz LCD's (and gotten dissapointed) have noticed that CRT 75fps@75Hz produces much clearer motion than LCD 120fps@120Hz. That's because the CRT phosphor decays in less than 1/500th of a second, which is shorter than 1/120th of a second (Because LCD refreshes are continuously displayed for a whole refresh).
LightBoost strobes are 1/700th to 1/400th of a second (range of 1.4ms to 2.4ms), depending on the LightBoost OSD setting. The 1/700th of a second flickers of a frame produces less than 1/10th the motion blur of a standard 60 Hz LCD refresh. An LCD refresh is continuously shining, which is called "sample and hold".
On newer displays, motion blur is mostly caused by eye tracking, NOT pixel persistence
According to many research papers, including those in
Science & References here, motion blur is caused by eye tracking across a frame. Your eyes are always moving to track moving objects. The longer a frame is displayed for, the more eye tracking across the frame occurs (your eyes are in a different position at the beginning of a frame, versus end of a frame). That's why even sample-and-hold OLED displays have lots of motion blur (e.g. PS Vita has lots of motion blur) even though pixel response is nearly instantaneous. Even on LCD's (TN's especially) pixel persistence is already only a tiny fraction of of a refresh, so most motion blur is nowadays caused by eye tracking, instead of pixel persistence. The artificial stepping, caused by a finite framerate, produces opportunity for eye tracking to create a motion blur limitation that's not caused by pixel persistence.
Source:
Microsoft Research (and
many others)
The only way to reduce motion blur (caused by eye tracking) is to shorten the length of time that a frame is displayed for. This is accomplished by doing extra Hz (e.g. 240Hz, 480Hz, 960Hz...) or via extra black periods between refreshes (e.g. flicker displays like CRT, Plasma, LightBoost, black frame insertion, stroboscopic backlights, etc.) The bigger the black period and the smaller the refresh time period, the better it is for motion blur.
A medium persistence CRT display with 2ms phosphor decay would have the equivalent amount of motion blur to a theoretical flickerfree 500fps@500Hz LCD (2ms per continuously-shining refresh), which does not exist without motion interpolation (bad for games due to input lag). Who can buy a 500 Hz LCD and be able to run 500fps on it natively? You can't. As a result, it's cheaper from a GPU perspective to just simply shorten the frame samples without raising the framerate. Adding black periods between frames. That means flicker (stroboscopic effect of a black period between frames) is required to prevent the frames from being motion blurred as your eyes track across it. Now, you want a high enough refresh rate so the flicker is not noticeable (e.g. 120 Hz instead of 60 Hz).
Clearly, a frame being stroboscopically flashed for only 1/400th or 1/700th second (LightBoost 120 Hz) produces vastly clearer motion than frames displayed for a full 1/120th second (non-LightBoost 120 Hz LCD). This is very similar to CRT phosphor decay of 1-2ms, and results in several "It looks like a CRT" testimonials from long-time CRT users.
You need frame rate matching refresh rate, to prevent repeated refreshes from contributing to motion blur. When judder is too high frequency to detect, the judder blends into a motion blur (this is why 60fps@120Hz still looks less clear than 120fps@120Hz). LightBoost is hardware-limited to only function during high refresh rates (100-120Hz) so this enforces a high GPU requirement for best motion clarity. It's also why LightBoost doesn't help you very much if you're only running half the framerate of refresh rate; so for the "wow" LightBoost effect, you really need to run fps at least matching Hz, to make sure that your eye tracking trajectory follows the motion in the refreshes accurately.
Source:
Microsoft Research (and
many others)
Things that weaken a display's ability to eliminate motion blur
- Sample and hold (ala traditional LCD - creates eye-tracking-based motion blur)
- Pixel persistence (
finally solvable by turning off backlight while waiting for pixels to transition)
- Eye tracking (solved by reduce the amount of time a frame is displayed for)
- Judders/stutters/inconsistent frame rendertimes, eye tracking is less in sync with motion (get a better computer/GPU)
- Repeated refreshes via frame rates lower than refresh rate, eye tracking is less in sync with motion (get a better computer/GPU)
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