From: New Section in "Electronics Hacking: Creating a Strobe Backlight"
With nVidia’s G-Sync announcement, variable refresh rate displays are now a reality today. Refresh rates can now dynamically vary with frame rates, and it is highly likely that nVidia has several patents on this already. If you are a monitor manufacturer, contact nVidia to license this technology, as they deserve kudos for this step towards tomorrow’s perfect Holodeck display.
However, one additional idea that Mark Rejhon of Blur Busters has come up with is a new creative PWM-free-to-strobing dynamic backlight curve manipulation algorithm, that allows variable-rate backlight strobing, without creating flicker at lower frame rates.
It is obvious to a scientist/engineer/vision researcher that to maintain constant perceived brightness during variable-rate strobing, you must keep strobing duty cycle percentages constant when varying the strobe rate. This requires careful and precise strobe-length control during variable refresh rate, as the display now refreshes dynamically on demand rather than at discrete scheduled intervals. However, a problem occurs at lower framerates: Strobing will cause uncomfortable flicker at lower refresh rates.
Mark Rejhon has invented a solution: Dynamic shaping of the strobe curve from PWM-free mode at low framerates, all the way to square-wave strobing at high framerates. The monitor backlight runs in PWM-free mode during low refresh rates (e.g. 30fps@30Hz, 45fps@45Hz), and gradually become soft gaussian/sinewave undulations in backlight brightness (bright-dim-bright-dim) at 60fps@60Hz, with the curves becoming sharper (fullbright-off-fullbright-off) as you head higher in framerates, towards 120fps@120Hz. At the monitor’s maximum framerate, the strobing more resembles a square wave with large totally-black-gaps between strobes.
10fps@10Hz — PWM-free backlight
30fps@30Hz — PWM-free backlight
45fps@45Hz — PWM-free backlight
60fps@60Hz — Minor backlight brightness undulations (bright / dim / bright / dim)
80fps@80Hz — Sharper backlight brightness undulations (very bright / very dim)
100fps@100Hz — Starts to resemble rounded-square-wave (fullbright / fulloff)
120fps@120Hz and up — Nearly square-wave strobing like original LightBoost
This would be a dynamically variable continuum all the way in bewteen too, much like automobile CVT instead of discrete gears in automobile transmissions. You avoid flicker at lower frame rates, and you get full strobing benefits at higher frame rates.
Simpler algorithm variations are also possible (e.g. keeping a square wave, and using only pulsewidth / pulseheight manipulation to achieve the blending effect, but without curve-softening). This is included as part of my general idea of blending from PWM-free at lower refresh rates, to strobing at higher refresh rates. The trigger framerates may be different from the example above (or may even be adjustable via a user flicker-threshold setting), but the concept is the same.
If nVidia or any monitor manufacturer uses this idea (if no patent application dated before October 19, 2013 covers my invention), please give Mark Rejhon / Blur Busters appropriate due credit. It is realized nVidia has several patents, but none appears to be covering this additional improvement being suggested during combining strobing and variable refresh rates. As of this writing, research is being done on any prior art, to determine whether anyone dynamically considered blending from PWM-free to square-wave strobing. If anyone else already came up with this idea, already documented in a patent application prior to October 19, 2013, please let me know & due credit will be given here.