ScepticMatt wrote:Relying on anecdotal evidence is a slippery slope, and should only be used in lieu of more solid evidence. All too often selection bias, preference, placebo or self-fulfilling prophecy ruin the cogency of the results.
Agreed as that case may be, it's still a strong enough indicator that new scientific research needs to be done on these modern display phenomenons, under these new, modern variables.
ScepticMatt wrote:Looking a bit more into it, so far inability to accommodate could be the explanation for eye strain and fatigue caused by screen blur.
Here is a study showing the effects of out of focus screens:
http://www.cs.sfu.ca/CourseCentral/820/ ... ort-09.pdf
Any idea what additional research keywords for "motion blur" I could look for?
For the purposes of searching science papers -- most specifically, in terms of terminology, it is not really "screen blur", but motion blur created by tracking eyes on high persistence displays; "persistence" (used in mainstream media) is essentially a synonym around here for the "sample-and-hold" effect (used in science papers). So essentially, it's 'perceived' motion blur since it only occurs when your eyes are moving across a display (like looking at UFO #1 and UFO #2 at
http://www.testufo.com/eyetracking ...)
Industry people are calling it "persistence", but the reused term "persistence" (as applied to strobe backlights and pulsed OLEDs) is more or less a synonym to the "sample-and-hold" and "hold-type" terminology used in several of these older papers. Longer hold, longer persistence, so for the purposes of science, these terms are equal, as the media & the science paper uses different terminology. However, these papers only describe the motion blur reduction benefits, and not the flicker-versus-blur tradeoff.
On Google Scholar, there's a bunch of old science papers (many 2005-ish and older) that contains information on
"hold-type displays", "MPRT pursuit camera", "sample-and-hold effect", "MPRT", "moving picture response time" (MPRT), "LCD motion blur", but almost all of them come from the pre-strobe-backlight era. Some of the papers are linked from
http://www.blurbusters.com/references while others you can find in Google Scholar. The animation that I designed at
http://www.testufo.com/eyetracking also demonstrates this too -- Your eyes don't move like digital stepper motors; your eyes move continuously while tracking moving objects (give or take some eye saccades), but the frames are static. The longer frame is static for, the more opportunity it is blurred across your retina as you're tracking your eyes continuously across a finite-framerate display (much like taking a photo while a camera is moved around, e.g. the sample-and-hold effect is a motion blur equivalence to a camera shutter - e.g. eye tracking on a 60Hz sample-and-hold display, creates the same amount of motion blurring as panning a 1/60sec shutter camera across real-world imagery). There is a close relationship between motion blur and the frame rate on a sample-and-hold display.
On sample-and-hold displays (0ms transition), minimum motion blur is one frame length
...(e.g. 60Hz = 1/60sec = 16.7ms persistence = 16.7ms of motion blur = MPRT 16.7ms)
On strobed displays (squarewave), minimum motion blur is the strobe length
...(e.g. 1/1000sec flash at any refresh rate = 1ms persistence = 1ms of motion blur = MPRT 1ms)
For fast-persistence displays (where GtG is insignificant) and for squarewave impulses (strobe backlights), this perfect equivalence (in milliseconds) occurs:
"persistence" == "MPRT" == "moving picture response time" == "hold time" == "sample-and-hold time"
The media uses "persistence", while science papers often use "sample-and-hold" or "MPRT", but you can consider these two terms equivalent when it comes many examples of modern displays.
Other variables (e.g. slower GtG, phosphor decay, etc) will fuzzy this up, but as displays have become faster and more squarewave, these correlations are immediately observed when playing with fast sample-and-hold displays (e.g. 1ms LCD, OLED) as well as strobe-backlight displays or fast-impulse displays (pixel impulses that resemble squarewave), I haven't yet met a display that behaved this way (under high speed camera) that diverged away from this formula. Strobing isn't always perfectly squarewave, and LCD transitions aren't perfectly squarewave but even non-strobed modern LCD displays are already starting to resemble squarewave pixel transitions (Just view
http://www.testufo.com/#test=eyetrackin ... eckerboard on any modern faster 1ms or 2ms 60Hz TN LCD, and you'll see the checkerboard pattern effect of pixel transitions starting to resemble more squarewave. That's because 1-2ms GtG is only a tiny fraction of the 16.7ms refresh cycle. Tracking eyes (or camera) essentially mapping the GtG pixel transition as a motion blur trail, and the sharper the GtG transitions are, the sharper the checkerboard boundaries are in this checkerboard illusion. But when you try to view this TestUFO checkerboard illusion on an older LCD, it becomes more gaussian/sinewave when you view the same animation, such as 10-year old monitors, and stops resembling a near-perfect checkerboard pattern as it does on several modern 120Hz/144Hz monitors). Displays that show a near-perfect checkerboard in this test, tend to also very accurately follow the Blur Busters Law formula. Consequently, I've been very reliably able to predict the amount of a motion blur a display will produce, just by measuring strobe length of a strobe-backlight display. Would love to see more research being done in this direction.
It was only around 2011-2012 when LCDs could compress GtG transitions into a fraction of a refresh cycle to an extent necessary to make pixel transitions (GtG) a far more insignificant factor than persistence. That was the necessary ingredient necessary to make active shutter stereoscopic 3D practical, and highly efficient low-persistence abilities via motion blur reduction strobe backlights. I'm not sure if there are any science papers written since 2011 that clearly covers this, since motion blur of LCDs underwent a huge leap forward in clarity. This would be a new era of displays.
The persistence of a sample-and-hold display is equal to the refresh period -- e.g. (1/Hz)ms -- which means 60Hz LCDs have 16.7ms of persistence. So during 1000 pixels/second motion, you've got 16.7 pixel steps between frames. But your eyes (assuming motionspeeds where eyetracking is still relatively accurate) have continuously moved along the motion vector, by that equal distance; smearing a static frame about 16.7 pixels of motion blur. This motion blur effect form perseffect is clearly witnessed at
http://www.testufo.com framerate comparision on a 120Hz monitor. 60fps has half the blurring of 30fps, and 120fps has half the blurring of 60fps. This leads to the simple equation,
1ms of persistence (pixel visibility time) translates to 1 pixel of motion blurring during 1000 pixels/second motion, assuming squarewave persistence (e.g. strobe backlights, sample-and-hold on fast LCDs, rolling-scan OLEDs such as Sony Trimaster), framerate == stroberate == refreshrate, consistent motion, and motionspeed well within eye tracking ability (motionspeeds where minor eye saccades not major blurring factor). I am not currently aware of any science paper that confirms this formula that I have reliably confirmed repeatedly with all major brands of strobe backlights; the motion blurring observed is very consistent with the photodiode oscilloscope strobe length. In the past, most displays were too slow and persistence not squarewave (e.g. phosphor decay, plasma subfields, DLP temporal dither, etc), but with strobe backlight displays, the formula I've discovered (Blur Busters Law) of 1ms persistence = 1 pixel of blurring during tracking 1000 pixels/second motion -- which appears pretty accurate both for human vision and for pursuit camera observations. I've written about this formula at
http://www.blurbusters.com/lightboost/10vs50vs100 and hinted upon this in the older
http://www.blurbusters.com/faq/60vs120vslb ... These are not real science papers, but articles written for high-end mainstream. However, it would be lovely to see a researcher/scientist take upon studying of this and creating a peer reviewed paper (If any is reading -- obviously, I certainly would be happy to help out -- mark[at]blurbusters.com).
When sitting arm's length away from 24" display, 1080p motion running at 960 pixels/second is a close number to 1000 pixels/second but is a number still divisible by 30, 60 and 120, providing a very convenient test case, a motion speed that is relatively accurately trackable by most human users (eye saccades minor enough that you can still count the number of pixels in the TestUFO alien single-pixel eyes, during ~1ms strobing, when the UFO is moving horizontally at 960 pixels/second -- so at this motionspeed, eye saccades aren't a limiting factor to ability to detecting individual pixels). In this situation, adjusting persistence from 60Hz non-strobed (16.7ms persistence = ~16 pixels blurring at 960pps), 120Hz non-strobed (8.3ms persistence = ~8 pixels blurring at 960pps), LightBoost 100% (2.4ms persistence = ~2 pixels blurring at 960pps), LightBoost 10% (1.4ms persistence = ~1 pixel blurring at 960pps), so adjustable-persistence displays such as LightBoost monitors are excellent potential researcher tools in showing the relationship between persistence and motion blur (1ms persistence = 1 pixel of motion blur during 1000 pixels/second) assuming consistent motion of framerate equalling refreshrate and accurate tracking? The formula applies
to both human eye and to tracking cameras (pursuit camera).
-- Any other papers you've found, based on search terms I've suggested, that are new enough to cover strobe backlight behavior?
-- Any scientific paper on any adjustable-persistence displays?
-- Any scientific paper on fast-response displays where GtG/transition/pixel movement is an insignificant factor and persistence is the dominant factor of motion blur? (e.g. squarewave transitions)
-- Any scientific paper that contains/confirms the simple persistence formula (or a derivative thereof) that I've discovered, 1ms persistence = 1 pixel of motion blur during 1000 pixels/second? (I've begun to call this a Blur Busters Law, due to its reliably repeatable observations on strobe-backlight monitors).