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Science: Blur Reduction Engineering (Strobe Backlights)

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Science: Blur Reduction Engineering (Strobe Backlights)

Postby Chief Blur Buster » 21 Apr 2017, 14:57

Advanced LCD Motion Blur Reduction Science:
The Challenges of Engineering a Strobe Backlight

You may already be familiar with "LightBoost" or "ULMB". There is also a new Motion Blur Reduction FAQ and already know that some displays have worse strobe crosstalk (double-image-effect) than other displays.

A video & picture is worth a thousand words! Here's a brand new diagram of proper quality strobing, to go with an existing high speed video.

(A) First, observe this below high speed video below. It is a high speed video of where the screen flashes rapidly between two colors, while displaying incrementing numbers. This high speed video is very educational to learn how an LCD refreshes.

phpBB [video]

(high speed video of an LCD panel refreshing. In both LightBoost and non-LightBoost modes)

By now, you've figured out that reducing motion blur on modern LCDs work very well with backlight flashing (aka strobe backlight) to eliminate motion blur. Some HDTVs (and a few expensive upcoming gaming monitors) use a 'scanning backlight' to do the same thing in a slightly different fashion.

(B) Next, here's a diagram of how to do proper backlight-based motion blur reduction on an LCD, and successfully bypass LCD GtG response limitations from becoming visible to eyes:


Now that you roughly understand how an LCD panel refreshes, you understand that only the fully-refreshed part of LCD (no double images) should be flashed.. Which means you can do one of two things:

(1) Use a global flash, all at once. This is possible on a cheaper LCD panel with edgelight/backlight.
This is done by: LightBoost / ULMB / BENQ Blur Reduction / BENQ Dynamic Acceleration / Samsung Blur Reduction / etc
....You need an LCD panel with a GtG much faster than the time period of a refresh cycle. Scan the LCD top-to-bottom faster so you have a longer idle period between refreshes (at the same refresh rate). The longer the idle period between refresh cycles, the less likely/visibly that the LCD GtG fade zone doesn't overlap into the next refresh cycle (weaker strobe crosstalk for top/bottom edges). Flash the LCD when the whole screen is simultaneously clearest.
Requirement: You can use existing cheaper LCD panels. Just do a fast scanout and do a long pause between refresh cycles. And use good overshoot-free overdrive. You're essentially trying to squeeze the whole LCD GtG response into the blanking interval between refresh cycles -- "that pause between scanouts".


(2) Use a scanning backlight with good optics.
Not widely done in computer monitors yet. This will be done by upcoming 4K 144Hz local-dimmed panels
....This can help slower LCDs, or push closer to GtG limits. You can even use reduced blanking intervals which makes crosstalk-free global-strobe impossible. Scanning backlights often require full-array backlights (which can have other benefits such as local-dimming and HDR capability, with higher contrast ratios). You flash a row of LEDs behind the fully-refreshed part of LCD, while keeping the "GtG wipe zone" in total darkness. You also need good full-array backlight optics to prevent leakage of light from the illuminated section into the dark section. By doing this, it is possible to reduce strobe crosstalk on slower LCD panels (or a fast LCD at even higher refresh rates, e.g. 240Hz TN with a theoretical FALD scanning backlight). Blur Busters originally launched as "" also has a very old (2012) Scanning Backlight FAQ.
Requirement: An expensive full-array backlight, although it can do double-duty for HDR and local-dimming (Potentially 1,000,000:1 contrast ratio in some cases). Good diffusion-free backlight optics to keep rest of panel as totally-black as possible, while flashing a different part of LCD. Very difficult. Dramatically raises cost of monitor. Already successfully used in some high-end HDTV sets. Only recently starting to arrive in gaming monitors, including the new "4K 144Hz" HDR-capable panels.

NOTE: Little known, but scanning backlights can also potentially reduce input lag over global-strobe backlights -- and potentially reduce some of the strobe-amplified VSYNC OFF microstutters (due to the time-delta inconsistency between LCD scanout and global-strobe, for top/center/bottom edges during VSYNC OFF).

For more reading, see:
Electronics Hacking: Creating a Strobe Backlight (Updated 2017).
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Science: Blur Reduction Engineering (Strobe Backlights)

Postby Chief Blur Buster » 21 Apr 2017, 15:48

This is currently posted on: | Facebook | Twitter ...

Feel free to share!

Also, feel free to contact your favorite monitor manufacturers too, so they can improve their Blur Reduction modes (Some of you already know which one don't do as good a job as others). Many of them already do a good job (especially the NVIDIA-derived technologies) but some could learn to do it better -- or license ULMB from NVIDIA. :)
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