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Frame rate / refresh rate confusion?

  • I just purchased a new Samsung LED HDTV, with a 240 Hz refresh rate (I believe), and I SWEAR that the same TV shows I usually watch now seem much more "smooth" ... movements seem much more connected and seem to "flow." What I don't understand is ... if TV shows in the U.S. are generally filmed in no greater than 30 FPS ... then why am I getting a better quality on this TV? I've also read that the human eye can't really "detect" video being any more "smooth" beyond 60 FPS ... or a refresh rate beyond 60 Hz (forget which one) ... so wouldn't a screen with a refresh rate higher than 60 Hz provide the SAME video quality for any TV program of 30 FPS? Either way, why would I be getting a better video quality ("smooth like silk" motion) on this TV, simply because its refresh rate is high or something? Wouldn't the 30 FPS standard for U.S. TV shows be the "lowest common denominator" or "limiting factor?" So shouldn't the video look the same on any screen with a refresh rate 30 FPS or greater? There is a noticeable difference in video motion/smoothness between this new Samsung LED and my other HDTV, a Sony Bravia LCD (which I believe has a 120 Hz refresh rate). I thought there was almost no difference in quality between 120 and 240 Hz refresh rates ... so why is it so noticeable to me? Is it because a TV with a higher refresh rate than the video's actual FPS will "fill in" the missing frames with "fake" data (kind of like when you play SD video on an HD screen, and it automatically "upscales")? But if that is true, then how come you can still notice DROPPED FRAMES when playing a video game? Unlike TV and movies, video game frame rates are constantly changing depending on what is happening in the game and how the console is processing the data. But if a TV screen with a 240 Hz or 480 Hz refresh rate will simply "fill in" the space that is "missing frames," then how come you can still notice periods of dropped frames/lower FPS when playing games on a console? Shouldn't it be smooth throughout, albeit artifically? Would a game running on a 240 Hz screen look "smoother" during periods of frame rate drops, as opposed to if it were running on a 60 Hz screen during those same periods? It could also be that I have no clue what I'm talking about, this is all very confusing ...

  • Answer:

    Wow - big question. Video content in the U.S. comes in two flavors as far as frame rate goes - 30 Hz and 60 Hz (in Europe it's 25 and 50 Hz). 30 Hz video is interlaced, consisting of two "fields", one containing the odd-numbered lines and one containing the even-numbered lines. The field display rate is 60 Hz. 60 Hz video is non-interlaced, also called "progressive". Each 1/60 second, all the pixels of the frame are displayed. Refresh rate is mainly about flicker. When an video image is displayed at rates less than 50 Hz, the human eye/brain visual system can't blend the successive frames, resulting in a flickering picture. Interlaced systems depend on the fact that the two fields are so similar that they can blend OK. If you were to create a synthetic frame that had white odd lines and black even lines and displayed it in interlaced mode, it would flicker like crazy. Modern HDTVs use refresh rates beyond 60 Hz to smooth out some fast motion. Some of them do it by creating interpolated intermediate frames between the actual frames. Another reason is for dealing with movie content that is filmed at 24 Hz. 60 Hz systems have to resort to a trick called 3:2 pulldown to get the correct display rate. Odd frames get displayed 3 times, even ones two times. 120 and 240 Hz systems have the advantage that they are integer multiples of 24 Hz, allowing simple frame repetition to suffice. I'm not that familiar with gaming systems, but they still have to output at 60 Hz progressive, since that's all the TV can accept. I suspect that the dropped frames are a result of insufficient processing speed in the game console.

Kat Hillard at Yahoo! Answers Visit the source

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It's very common to confuse the refresh rate and the frame rate. However, the two have nothing to do with each other. Your set has a 240 hz refresh rate, which means the picture is reloaded (refreshed) on the screen 240 times per second. That's done by the TV itself, regardless of the incoming signal. The frame rate depends upon the incoming signal. It will usually have a frame rate of 24, 30, or 60 f.p.s. (or hz.), depending on its source, which means that 24, 30, or 60 still images are sent to the TV per second in order to form the picture. As for your questions about smoother video and dropped frames, there's no easy answer beyond the basics I've outlined above. This forum has seen every permutation of game console issue imaginable, often with no clear-cut answer. An Xbox or PS is a highly sophisticated device, as is a modern HDTV. When you connect the two together, there is a lot of opportunity for unexpected results.

kg7or

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