cru2323 wrote:Impulsive scanning technology reduces motion blur by regulating a monitor’s backlight between each scene. The conventional method to address this issue is to control the backlight from the center of the screen, but this may allow motion blur to remain in the upper and lower areas.
There are pros and cons.
Blur Busters used to be www.scanningbacklight.com
in year 2012 and we still have an old Scanning Backlight FAQ
that's still up.
While scanning backlights eliminate inconsistency in strobe crosstalk, they actually amplify screen-centre strobe crosstalk while dimming the top/bottom. This is because even if one part of the screen has an "ON" backlight section, a different part of the screen is usually not totally black -- there's often a lot of light leakage from the ON-segments to the OFF-segments. That produces strobe crosstalk (ehm, scanning backlight crosstalk). The big pro is it's completely uniform, top to bottom, because the scanning is out-of-phase of the LEDs, but no area of the screen has a completely-turned-off backlight.
As a result, strobe backlights are much easier to get lower-strobe-crosstalk if you are able to use large blanking intervals (extremely long pauses between refresh cycles).
For example, instead of a 120Hz refresh cycle refreshing in 1/120sec and a very brief time between refresh cycles -- you have a 120Hz refresh cycle scanning faster (e.g. 1/240sec) with a longer 1/240sec idle between refresh cycles. Most LightBoost/ULMB display internally scan-out in approximately 1/180sec (older displays) to 1/240sec (newer 240Hz monitors) before strobing the backlight. 144Hz ULMB refreshes in 1/240sec with the rest of the time being a pause between refresh cycles to let LCD GtG pixel response to complete as much as possible between refresh cycles.
Otherwise, you have not enough time for GtG to complete in darkness before strobe flash -- high speed video of a strobe backlight
... That's why strobe backlights often require a slightly lower Hz than the monitor's maximum Hz -- enough time to let pixels finish settling in dark.
This produces very low strobe crosstalk for the majority of screen, far less crosstalk than most scanning backlights. You need super-expensive locally-dimmed backlights (extremely good focussing on the screen with minimal diffusion of light leakage to the rest of the screen) to even achieve better than 10:1 to 50:1 contrast ratio between the off-sections and on-sections.
That is a 2%-intensity-ghosting strobe crosstalk for a scanning backlight. I've seen strobe backlights result in as little as ~0.1% strobe crosstalk intensity for screen centre, thanks to a strobe backlight's ability to be completely turned off between refresh cycles (letting more of LCD GtG complete in total darkness, never made visible by light leakage from a scanning backlight).
That said, better scanning backlights are coming though, in the upcoming new 4K120Hz locally-dimmed gaming monitors coming in 2018.