Thanks for the chime in!
I see this paper uses very different terminologies, scan-and-hold
I interpret it to mean equivalently as:
scan-and-hold display == sample-and-hold display
scan-and-erase display == impulse-driven display / strobed display / flicker / black-frame insertion
There's actually really a complete continuum between the two, as it's really a matter of adjusting duty cycle between the visible frames and the black period between frames (And how much blending there is --e.g. pixel transition effectds, phosphor decay effects, etc) though for new strobe-backlight gaming displays, they act essentially quite squarewave in "hold"/"erase".
BTW, on another topic but related, tilt artifacts caused by display scanning.
Higher refresh rates have less scan artifacts (tilting artifacts).
Technically, from a motion clarity perspective, it doesn't really matter if it's scanned top-to-bottom or flashed all at once (instantly). The main artifact difference is the tilting effect during horizontal motion (e.g. www.testufo.com/blurtrail
at Height->Full Screen on 60Hz LCD or CRT, will often show a tilting-line effect due to the finite speed of the top-to-bottom scan), and compress/stretch effect during vertical motion. A good paper about the tilting effects of scanned display is Charles Poynton's paper, Motion portrayal, eye tracking, and emerging display technology
. In addition, he has some illustrations that explains why we need to stick to sequential scanning because of the disjointed-scan effect (stationary tearline effect). He writes about the tilting effect caused by scanning on a LED marquee. This also applies to scanned displays (CRTs and LCDs).
Page 5 of Charles Poynton's Paper wrote:
This is another good reason of using higher refresh rates for non-strobed scanned displays -- at double the refresh rate, you get half the tilting effect for a specific motionspeed. I can still see the tilting effect at 120fps @ 120Hz at www.testufo.com/blurtrail
in non-strobed mode. All-at-once strobing does not create any tilting effect. That's why you will see the tilt effect when LightBoost is turned off, but the tilt effect disappears when you turn on LightBoost!
Also -- I have had at least two people suggest displays could refresh faster only where the eye is pointed at (e.g. random-access refreshing). This is a very good idea, and definitely should be tried. It may make the ultrahigh refreshrates and/or continuous-motion framerateless displays possible. However, the disjoints in refreshing synchronization will be very problematic for potential artifacts, for these very precise reasons already illustrated in Charles Poynton's paper.
Thusly, to avoid distortion effects, we're almost certainly to be stuck with various synchronized sequential-scanning or all-at-once presentation, for the most artifact-free motion. Otherwise we get disjoint problems caused by multi-scanning or random-access-refresh. Even simple things like interlacing creates venetian-blinds artifacts (Animation: www.testufo.com/interlace
). This, therefore, humankind (in the coming decades) may not have much choice but to refresh sequentially, and go for ultrahigh(quad-digit frame rates, e.g. 1000fps@1000Hz or similiar ultrahigh rates) or framerateless continuous-motion technology for the entire
display, to simultaneously solve the stroboscopic problem and the motion blur problem during ultrafast motion material (as discussed in earlier pages in this thread). Obviously, these may not be practical today or this decade, but may become more and more practical as time passes.Conclusion/TLDR:
- Scanning creates tilt effect on motion perpendicular to scan direction;
- CRTs and non-strobed LCD will have the scan tilting effect;
- Higher refresh rates / faster scanning will have less tilting effect;
- LightBoost (and similar strobe backlights) will not have the scan tilting effect;
- Multiscanning will create stationary tear-line artifacts;
- Interlacing will create venetian blind artifacts;
- Anything other than all-at-once presentation can cause motion distortions, in one form or another;
- Sequential scanning is the least-distorting method of scanning, short of doing all-at-once presentation.Interesting DIY Science on tilt effect of scanning: Load www.testufo.com/blurtrail on an iPad!. Pinch-zoom until the black animation with the moving line, just about fills the whole screen. You will notice the tilting effect of the moving line! Now rotate the iPad to all different 4 rotations, observe the tilt effect. You will see tilting in 2 orientations, and no tilting in 2 other orientiations. At least one apple iDevice I tried has landscape scanning (iPad 2), and a different apple iDevice I tried (Retina iPad Mini) has portrait scanning -- the tilting showed up only in portrait mode! Try this out now. (iPads worked best, since they can run the HTML5 animation at the proper synchronized 60fps@60Hz)