thread: 120hz explained
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Old 01-25-2008, 09:51 PM   #1
stockstar1138 stockstar1138 is offline
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Apr 2007
Default 120hz explained

I already posted this in another thread, i put a lot of work into it and dont want to have it overlooked.

i have been hearing a lot of complaints about the 120hz tvs looking "too smooth" in the past i have complained about it to. i was ignorant to how these 120hz actually worked, below is a description on what is causing the "too smooth" look that people are complaining about and that these tvs do not have this problem if the settings are correctly set.


here is the problem you guys are seeing with the 120hz tvs.

they got these motion enhancer settings on and it tries to interpolate changes in the pictures for all 120 frames per second. in other words if i got 2 frames of a movie and the image of the move in one frame is here:



and the next frame is here

xxxxxxxxx

a tv that is set to display the native 1080p24 signal will do this (this is having motion settings set to low or off)

1st frame repeated 5x (24 x 5 = 120)








notice all similies are on the same spot horizontally on the screen as the same image is simply repeated 5 times in a row.

2nd frame
xxxxxxxxxx
xxxxxxxxxx
xxxxxxxxxx
xxxxxxxxxx
xxxxxxxxxx



the motion looks realitively smooth on the screen as all frames are repeated on screen an equal amount of times and the image is exactly how it is encoded vs. a 60hz tv will do this

1st frame





2nd frame
xxxxxxxxxxx
xxxxxxxxxxx

notice that all frames are not repeated equal amounts which creates uneven judder (note: judder is a natural part of 24p film, uneven judder, caused by a 3:2 pulldown is not). to arrive at this a hdtv does something called a 3:2 pulldown.

a 120hz tv with motion enhancers on is going to take a 1080p24 signal and display each frame 5 times, however instead of just displaying the image as encoded it is going to try to interpolate where the image will be at in between frames and is going to go like this
is

1st frame

xx
xxxx
xxxxxx
xxxxxxxx



2nd frame
xxxxxxxxxxx
xxxxxxxxxxxxx
xxxxxxxxxxxxxxx
xxxxxxxxxxxxxxxxx
xxxxxxxxxxxxxxxxxxx

with a 120hz tv with motion settings on "on" or high" every single frame (for 120 frames) will show a different image, even though the film should only be showing 24 different frames per second (each repeated 5 times) when being displayed at native 1080p24 signal. with motion enhancers on it will not repeat the native 1080p24 signal instead it will try to guess what the 4 frames would look like between what the blu-ray player is telling it to display. this is what gives it the ridiculous smoothness look. i hope this clears things up. nothing beats a native 1080p24 signal which you can get with a 120hz tv, but not a 60hz tv. all 120hz tvs should be able to have these motion enhancers turned off.

all those xxxxs were added as space fillers and mean nothing.

Last edited by stockstar1138; 06-11-2008 at 05:25 PM.
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