OLED has been regarded as a Holy Grail for eliminating motion blur. Unfortunately, the portable Playstation Vita and Samsung Galaxy S3 have lots of motion blur during fast scrolling animations.
Why?
The answer lies in sample-and-hold. OLED is great in many ways, but some of them are hampered by the sample-and-hold effect. Even instant pixel response (0 ms) can have lots of motion blur due to the sample-and-hold problem. Some newer OLED’s use impulse-driving in order to eliminate motion blur, but not all of them do.
Your eyes are always moving when you track moving objects on a screen. Sample-and-hold means frames are statically displayed until the next refresh. Your eyes are in a different position at the beginning of a refresh than at the end of a refresh; this causes the frame to be blurred across your retinas:
(Source: Microsoft Research)
Vertical axis represents position of motion. Horizontal axis represent time.
Middle image represents flicker displays, including CRT and LightBoost.
Right image represents sample-and-hold displays, including most LCD and OLED.
The flicker of impulse-driven displays (CRT) shortens the frame samples, and eliminates eye-tracking based motion blur. This is why CRT displays have less motion blur than LCD’s, even though LCD pixel response times (1ms-2ms) are recently finally matching phosphor decay times of a CRT (with medium-persistence phosphor). Sample-and-hold displays continuously display frames for the whole refresh. As a result, a 60Hz refresh is displayed for a whole 1/60th of a second (16.7 milliseconds).
(Source: Microsoft Research)
Motion blur occurs on the Playstation Vita OLED even though it has virtually instantaneous pixel response time. This is because it does not shorten the amount of time a frame is actually visible for, a frame is continuously displayed until the next frame. The sample-and-hold nature of the display enforces eye-tracking-based motion blur that is above-and-beyond natural human limitations.
Solution to Motion Blur
The only way to reduce motion blur caused by sample-and-hold, is to shorten the amount of time a frame is displayed for. This is accomplished by using extra refreshes (higher Hz) or via black periods between refreshes (flicker).
Some experimental OLED televisions now shorten frame sample lengths by strobing the pixels, and/or motion interpolation (extra refreshes). Motion interpolation can interfere with video games due to input lag. Fortunately, impulse-driving (flicker) is video game friendly.
This is why many HDTV displays now use motion interpolation and high refresh rates, as well as using scanning backlights. In addition, some new 120 Hz gaming computer monitors now have a strobe backlight feature such as LightBoost, which allows these LCD’s to have less motion blur than sample-and-hold displays (including the PS Vita OLED).
One big problem to overcome first, is that impulse-driving require a lot of brightness to compensate for extra black period between refreshes. OLED has historically had brightness problems, however, researchers are continually improving this.
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References
This list of scientific references help you gain a better understanding of how eye-tracking creates motion blur on sample-and-hold displays:
“Temporal Rate Conversion” (Microsoft Research)
Information about frame rate conversion, that also explains how eye tracking produces perceived motion blur on a sample-and-hold display, including explanatory diagrams.
“Correlation between perceived motion blur and MPRT measurement”
by J. Someya (SID’05 Digest, pp. 1018–1021, 2005.)
Covers the relationship between human perceived motion blur versus Motion Picture Response Time (MPRT) of the display. This also accounts for motion blur caused by eye tracking on a sample-and-hold display, a separate factor than pixel persistence.
“What is needed in LCD panels to achieve CRT-like motion portrayal?”
by A. A. S. Sluyterman (Journal of the SID 14/8, pp. 681-686, 2006.)
This is an older 2006 paper that explains how scanning backlight can help bypass much of an LCD panel’s pixel persistence.
“Frame Rate conversion in the HD Era”
by Oliver Erdler (Stuttgart Technology Center, EuTEC, Sony Germany, 2008)
Page 4 has very useful motion blur diagrams, comparing sample-and-hold versus impulse-driven displays.
“Perceptually-motivated Real-time Temporal Upsampling of 3D Content for High-refresh-rate Displays”
by Piotr Didyk, Elmar Eisemann, Tobias Ritschel, Karol Myszkowski, Hans-Peter Seidel
(EUROGRAPHICS 2010 by guest editors T. Akenine-Möller and M. Zwicker)
Section “3. Perception of Displays” (and Figure 1) explains how LCD pixel response blur can be separate from hold-type (eye-tracking) motion blur.
“Display-induced motion artifacts”
by Johan Bergquist (Display and Optics Research, Nokia-Japan, 2007)
Many excellent graphics and diagrams of motion blur, including impulse-driven and sample-and-hold examples.
“Flicker Fusion”
by Stephen Macknik, Barrow Neurological Institute (Scholarpedia)
Background information that relates to how flicker becomes a continuous image (applies to CRT and to scanning backlights).
“Temporal Resolution”
by Michael Kalloniatis and Charles Luu, Webvision (University of Utah)
Background information that relates to human vision behavior and how multiple flicker events, over a short interval, blends together.
More references can be found in Science & References.
Other Reading
- High Speed Video of LCD versus CRT.
- High Speed Video of traditional LCD refreshing in action. (Sample-and-hold)
- High Speed Video of LightBoost stroboscopic backlight. (Impulse-driving)
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