60 hertz vs. 120 hertz Refresh Rate?

[wuvhandles]

Hi. Is there any real difference between 60 herts and 120 hertz on the new tvs?
I saved over 1000 on my aquos LC46D62U by getting the regular model (which i assume is 60 hertz, or else they would advertise 120).
And when I say difference, I mean to our eyes, (not just on paper )

When I watch hockey in HD, it looks super crisp to me. I mean I can't complain. I have a 46inch tv and I sit about 10-11 feet away.

When I watch SD though, thats different, the closer I sit, the more I notice pixelization during fast moving pictures. Would more hertz give SD a better picture? Or would it not matter?
Please reply, thanks!

[reddfoxx]

Quote:
A Television with a 60hz refresh rate represents complete reconstruction of the screen image 60 times every second. As a result, this also means that each video frame (in a 30 frame per second signal) is repeated twice every 60th of a second.

If you have a TV with a 120hz refresh rate that is 1080p/24 compatible (1920 pixels across the screen vs 1080 pixels down the screen, with a 24 frame per second rate). The TV ends up displaying 24 separate frames every second, but repeats each frame according to the refresh rate of the TV. In the case of 120hz each frame would be displayed 5 times within each 24th of a second.

The whole thing boils down to the concept of separate frames vs repeated frames. In the case of frame rate vs refresh rate calculations, repeated frames are not considered separate frames as the information in the repeated frames is all identical. It is when you move to a frame with different information that you have to count it as a new frame.

You can find more info here: hometheater.about.com/od/televisionbasics/qt/framevsrefresh.htm

[grog]

The issue is with displaying film-based material on progressive (digital) displays. A display operating at 60 Hz refreshes its image 60 times per second (i.e. it can display 60 unique images per second). 120 Hz is obviously double that. Here's why that is significant.

Film is shot using 24 frames per second whereas video is shot using 30 or 60 frames per second. For the video it's no problem displaying this smoothly on a display that operates at 60 Hz because the number of video frames divide evenly into the display's refresh rate. e.g. If the video you're displaying has 30 frames per second you simply display each frame twice. However, if your source is film with 24 frames per second you can't directly map the film frames to the display frames. To get around this they use a technique called 3:2 pulldown. In a nutshell, 3:2 pulldown is an algorithm that displays some of the frames 3 times and some of them twice in order to map the film's 24 fps to 30 fps. The downside of 3:2 pulldown is it introduces motion artifacts. This is mostly noticeable in fast moving scenes or pans - you may see blurriness, choppiness, etc.

This is where 120 Hz refresh rates come in. 120 Hz is nice because 24 fps film or 30 or 60 fps video all divide evenly into the refresh rate of the display so you no longer need to use 3:2 pulldown. There's a good article here that goes into a lot more detail about 3:2 pulldown: http://www.dvdfile.com/news/special_...2_pulldown.htm

To answer your specific questions, HD hockey looks great and smooth because it's shot in video so no need to do any 3:2 pulldown. There shouldn't be any difference between a 60 Hz display and a 120 Hz display for video sources (assuming all other components of the display are equal). It won't make any difference for SD either. SD looks like crap because it's SD, plain and simple. The difference would be with film based material. If you have a film based source and a Blu-ray or HD DVD player capable of outputting 1080p/24 then you will get an optimal picture with a 1080p/24 display running at 120 Hz because it won't need to do any 3:2 pulldown.

http://www.digitalhome.ca/forum/showthread.php?t=17869

[wuvhandles]

Thanks so much Grog for your reply.
Now I'm reassured that I made the right decision at the time to purchase my tv (especially now that it went up $300 in price for the same model :-D
I don't plan on getting hd dvd's or blue ray discs, even if I had a high end player. Just not my thing (I burn all my movies off movie central, etc, for personal use).

[mart242]

If you don't see the difference, keep what you have.

To me, fast action looks really bad and not smooth on LCD at 60Hz. 120Hz is a bit better, but I hate the pixelation effect so I went with a plasma. (same for my projector, I went with a DLP because I could not stand the screen door effect)

[grog]

If everything else about the display is equal there's no reason that 120 Hz should look any different than 60 Hz for video-based content. You aren't displaying any more information with a 120 Hz refresh rate. At best the source content will be have 60 frames per second so you just display the exact same frame twice if displaying on a 120 Hz display.

However, odds are everything else isn't equal with with a 120 Hz display vs a 60 Hz display. The 120 Hz display will likely have a higher quality panel with a better response time. Response time is how quickly a pixel can "change" from one colour to another. In older LCDs this response time was in the 20-30 ms range so fast moving scenes would be particularly bad because the pixels couldn't even keep up with the refresh rate (at 60 Hz the frame is being redrawn every ~16 ms). Newer displays are much better with response times of just a few milliseconds but it can still be perceptible.

Bottom line - you may very well see a difference in quality between a 60 Hz and a 120 Hz display for video-based material but that difference isn't because of the refresh rate. It's because of differences in panel quality or perhaps other components of the display, just like two displays with the same refresh rate can have very big differences in quality.