Aha, generic questions about double frame effect; which I'm very familiar with.
The answer to your question is different depending on whether the display is sample-and-hold (most LCD's) versus impulse-driven (CRT, and most plasma's).
Originally Posted by Butmuncher
Thanks Mark for your reply.
Do you think its the " duplicated " frames that i'm seeing as a double trailing image instead of a low pixel response time.
Double trailing images is caused by the frame being repeated two times, which can occur with any of the following:
(1) (common...) Running at half the framerate (e.g. 30fps at 60Hz) on an impulse driven display (CRT, plasma, or scanning backlight) -- the most common cause
(3) (common...) Running 60fps on certain scanning backlights that does two impulses per refresh (e.g. less aggressive scanning backlight modes that reduce flicker in exchange for less motion blur elimination)
(2) (rare............) Running 60fps on an LCD display that has a backlight flickering at 120Hz PWM dimming (pulse-width-modulation technique of dimming a backlight) -- normally this should be a higher frequency;
(4) (sometimes) Running 60fps on certain plasma displays that does two bona-fide impulses per refresh (e.g. clusters of plasma subfield refreshes tightly time-coupled with each other. Ideally, it should be all clustered into only one cluster of subfield refreshes with lots of black time in between refresh). Most modern plasmas either just spread the subfield refreshes throughout the entire refresh; while better plasmas try to cluster the subfield refreshes more tightly over a tinier time period (for better motion resolution).
This applies to other multiples, like a frame being repeated three timesOn an old Samsung 226BW with a CCFL backlight with a 180Hz PWM dimming, especially at half brightness setting, I can see triple trailing images at 60Hz refresh (The math is 180/60 = 3) This is seen in situations such as moving a smooth-fluidity gaming mouse on a black background, while tracking eyes on the fast moving mouse pointer.
There's allways a second image following the first, some sets i've had have been very good and have had only a tiny distance between the 2 images, some sets though especially the high range ones have had the second image too far apart, looks awfull it does
For motion running at the same speed, this can be caused by impulses being further apart, versus closer together. Most commonly, frame repeats are spread evenly. For example, 30fps at 60Hz, the trailing image is 1/30th of a second behind. The double image is very far apart in this case.
In other cases, where the double image is close together, can be caused by:
(1) Certain plasma displays that tries to cluster subfield refreshes relatively close together, sometimes the clustering of subfield refreshes causes the brightness peaks two times very closely-spaced together. This essentially leads to what looks like a repeated frame that is extremely, extremely close together.
(2) Scanning backlights. It can also happen with scanning backlights that strobe a backlight segment two times in quick succession (But not quick enough to be undetectable).
Am i correct in saying that a 60hz panel with a 60fps source would have less blur than a 200hz panel running 60fps without interpolation on if the 2 panels was exactly the same apart from refresh rate?
Only if it's an impulse driven display, and the impulse time is the same. CRT at 60fps@60Hz is smoother looking than 60fps@120Hz, for example (this is because 60fps@120Hz leads to a repeated frame; adding to the motion blur effect).
For LCD displays that have continuous backlights, and with motion interpolation disabled (and backlight is non-PWM, non-scanning), 60fps@60Hz looks the same as 60fps@120Hz. Because the display is continuously shining, there is no difference between a repeated frame or keeping displaying the same refresh. Assuming the response time is the same. There can be other effects, such as differences in pixel response speed (for 60Hz versus 120Hz) and differences in input lag, but if all other variables are the same, there's no difference.
For LCD displays that have non-continuous backlights and with motion interpolation disabled (PWM dimming, or scanning backlights), the answer gets more complex - if the PWM frequency stays the same (e.g. PWM stays at 240Hz, for example, even if 60Hz or 120Hz refresh), then there's no difference, either. For scanning backlights, it depends on how the scanning backlight operates (single strobe or multiple strobes per spatial display point per refresh). The sequential scanning backlights that emulate the CRT the most (one strobe per spatial display point per refresh) will behave the same as CRT -- 60fps@60Hz will look better than 60fps@120Hz(signal refresh, not backlight refresh or interpolated rate), for example, in terms of motion fluidity. In reality, scanning-backlight displays that are able to accept and display a 120Hz native input refresh (for 2D PC signal), are rare -- at the moment.
As interpolation sorts out the trailing image it means to me possibly that i may not be going back to a lcd 3dtv for gaming.
I could but then i'd have to buy the same 3dtv for a 3rd time which was a lg 47ld950 / 920.
Interpolation will solve the trailing image problem by a large part, but at the cost of major input lag. This is okay if you're not an online gamer or competitive, but caveat emptor about the input lag if you use motion interpolation with computers and games -- many people find the latency annoying. However, it *does* make motion look much better in fluidity.