thatoneguy wrote: ↑19 May 2024, 21:53
Is this the case with Quest 2/3 too? I thought those were using some faster switching LCDs.
Apples vs bananas.
Quest 2/3 is strobed.
I wasn't talking about strobed LCDs.
When I compared non-strobed 1000Hz sample hold LCD versus 480Hz sample and hold OLED I meant flickerless sample-and-hold 1000Hz LCD versus flickerless sample-and-hold OLED -- with no BFI and no strobe backlight.
The impulsing method for LCDs is backlight flashing, and OLEDs is black frame insertion. They achieve the same end goal (in theory). LCD is throttled by crosstalk (GtG0->100% longer than a refresh cycle), while OLED is throttled by refresh rate limitation (since BFI has to be delivered like a refresh cycle to a non-PWM-driven OLED)
Also...The art of a strobe backlight is "Cram LCD GtG In The Blanking Interval In Total Darkness Between Strobe Flashes". Strobe crosstalk is the remnant LCD GtG unfinished by the time the backlight flashes again. But Quest 2/3 achieves nigh near perfect zero crosstalk, due to superlative overdrive tuning.
Quest 2/3 are impulse-driven LCDs (strobe backlight) with giant-budget (Facebook $$) overdrive tuning that managed to squeeze LCD GtG into the dark period of a strobed refresh cycle.
At 90Hz and 0.3ms pulse width flash (1/90sec = 11ms) that gave Facebook a budget of up to ~10ms to try to hide LCD GtG0%->100% in total darkness between LCD scanouts. In reality, no LCDs can global-refresh, so you have to subtract scanout latency from that. Faster scanout latency (from large VT's or QFT) can give more time for LCD to settle in total darkness before being flashed visible. Quest 2/3 alsouses an internal variant of the Large Vertical Total trick (bottom of
www.blurbusters.com/xg2431 ...) to create a large VBI, as LCD GtG is initiated on last pixel in a time-delayed offset relative to LCD GtG on first pixel (high speed videos at
www.blurbusters.com/scanout ...) -- not all pixels refresh at the same time, and that's a problem for global strobe flash. However, the problem was solved on Quest 2/3, completely hiding the LCD GtG in total darkness between flashes.
As a reminder to forum readers (for squarewave GtG=0 displays impulsed versus sample-and-hold):
- Eye tracking motion blur is frametime on sample and hold (flickerfree).
- Eye tracking motion blur is pulsewidth on impulsed (strobed).