How can 60 frames per second be displayed with 25ms pixel response LCD-TV?

[reader]

Video gurus,

I need your comments on the following:

While shoppoing for LCD TV, I saw the specs:

1. 25ms pixel response time - means (1000/25 = 40) - a
pixel can be switched on/off 40 times per second?

2. 1280x720p at 60 frames - means 60 frames per second
(progressive)

Where does extra (60 - 40 = 20 ) 20 times switching of the pixel
come from?

I appreciate your comments .... please enlighten me.

 

[Walter Mitty]

Video gurus,

I need your comments on the following:

While shoppoing for LCD TV, I saw the specs:

1. 25ms pixel response time - means (1000/25 = 40) - a
pixel can be switched on/off 40 times per second?

2. 1280x720p at 60 frames - means 60 frames per second
(progressive)

Where does extra (60 - 40 = 20 ) 20 times switching of the pixel
come from?

I appreciate your comments .... please enlighten me.

It doesn't : and is why you can get tearing. Google for more.

 

[Bob Myers]

Video gurus,

I need your comments on the following:

While shoppoing for LCD TV, I saw the specs:

1. 25ms pixel response time - means (1000/25 = 40) - a
pixel can be switched on/off 40 times per second?

2. 1280x720p at 60 frames - means 60 frames per second
(progressive)

Where does extra (60 - 40 = 20 ) 20 times switching of the pixel
come from?

I appreciate your comments .... please enlighten me.

 

[Bob Myers]

Video gurus,

I need your comments on the following:

While shoppoing for LCD TV, I saw the specs:

1. 25ms pixel response time - means (1000/25 = 40) - a
pixel can be switched on/off 40 times per second?

No, not really. It depends on just what definition of
"response time" is being used. Very often, the quoted
response time spec is actually the sum of the turn-on and
turn-off times. It also, in any case, may be the time required
to turn from full-on to full-off, which can be considerably
different from the time required to transition between
intermediate "gray levels." (That time might be shorter, or
it might be longer - considerably longer! - that the full
white/black transition time.) And most LC technologies
require a longer transition time in one direction that the other.
So the bottom line is that these specs, at least as published
in a good deal of the information/advertising aimed at the
end user, may be difficult to compare or to translate
directly into frame-rate capability.

2. 1280x720p at 60 frames - means 60 frames per second
(progressive)
Right.


Where does extra (60 - 40 = 20 ) 20 times switching of the pixel
come from?

Nowhere, and in fact a good number of panels spec'ed at
"25 ms" response times will show smearing or other artifacts
when operated at these rates with rapidly moving imagery.
However, note that the response time does NOT restrict the
rate at which new frames can be written into the panel. Most
LCDs these days are run at at LEAST a 60 FPS rate; whether
or not moving objects appear as you'd like them to is another
matter altogether.

Look at it this way - let's say I can throw baseballs to you
at the rate of one per second, and you can catch them that
fast. That doesn't mean, though, that you'll have time to
read the labels on each one.

Bob M.

 

[Not Gimpy Anymore]

No, not really. It depends on just what definition of
"response time" is being used. Very often, the quoted
response time spec is actually the sum of the turn-on and
turn-off times. It also, in any case, may be the time required
to turn from full-on to full-off, which can be considerably
different from the time required to transition between
intermediate "gray levels." (That time might be shorter, or
it might be longer - considerably longer! - that the full
white/black transition time.) And most LC technologies
require a longer transition time in one direction that the other.
So the bottom line is that these specs, at least as published
in a good deal of the information/advertising aimed at the
end user, may be difficult to compare or to translate
directly into frame-rate capability.


Nowhere, and in fact a good number of panels spec'ed at
"25 ms" response times will show smearing or other artifacts
when operated at these rates with rapidly moving imagery.
However, note that the response time does NOT restrict the
rate at which new frames can be written into the panel. Most
LCDs these days are run at at LEAST a 60 FPS rate; whether
or not moving objects appear as you'd like them to is another
matter altogether.

Look at it this way - let's say I can throw baseballs to you
at the rate of one per second, and you can catch them that
fast. That doesn't mean, though, that you'll have time to
read the labels on each one.

Bob M.

Here is an analogy I like better, FWIW
Your car suspension has a parallel connection of spring
and "damper" (shock absorber) at every wheel (typically).
If I take an assembly of that combination and test it on
an impact machine, I discover that it takes about 100 mS
(not a real #) for it to go from full compression to full extension.
I can hit that combination with a "hammer" every 100 mS and
it will transition the full range of extension.
But if I hit it more frequently (higher frequency = less time
between hits), say every 80 mS, then it will not have reached its
full extension before I hit it again.
In that condition, I may actually measure the amplitude of
the motion and say it is (X)% of "full scale". The assembly
still works, but does not reach "full performance".
In a LCD display (or any type) that has a response time
(the time it takes to do a full transition) slower than the refresh
time (the TIME between each "impact"), the result is less than
full amplitude "intensity". It is necessary in this case to think
about time, instead of frequency.

Help?

NGA