understanding tv refresh rate

Understanding TV Refresh Rate

Can't understand what the refresh rate of your new TV means, exactly? This Buzzle article will explain everything you need to know about TV refresh rates.

Know When To Stop
When buying a new HD TV, remember that a refresh rate of 120 Hz is enough for pretty much anything current filming technology can throw at it. If you don't need a 3D TV, any more than 120 Hz is just overkill.
TVs are judged on a variety of criteria. Its screen size, its resolution, and of course, its price. When it comes to old cathode ray tube (CRT) television, these criteria are enough to determine whether a TV is a good buy. But in the days of LCD, plasma, and HD, a new criterion has emerged that has become increasingly important in the market race to grab the customer's attention and wallet―the refresh rate. Refresh rates can be confusing if you are not acquainted with the basic mechanics of how a television set works, but it is actually quite a simple concept. Refresh rate is the rate at which the pixels on a screen are capable of changing their color. This is completely independent of the picture that the device receives, but refers to how the picture is displayed by that particular device. The refresh rate is measured in Hertz, the unit of frequency. If a TV with interlaced resolution (1080i etc.) has a refresh rate of 60 Hz, its pixels change 30 times per second. If a TV with progressive resolution (720p, 1080p, etc.) has a refresh rate of 60 Hz, its pixels change 60 times every second. Refresh rate becomes especially important when fast motion images, as seen in sports, are to be displayed. In order to show any video, a TV needs to constantly change the color of its pixels according to the incoming data. The higher the refresh rate, the smoother the projection of motion becomes. If the refresh rate can't keep up with the incoming data, the TV can't change the pixels fast enough to accommodate it, which results in 'judder'. This is why early LCD TVs suffered severely from motion blur. This becomes a particularly prickly issue when it comes to broadcasting films on television.
Refresh Rate and Film
The standard frame rate for films is 24 frames per second (fps). The glitch occurs when these 24 frames are to be projected through the 30 flashes of the interlaced pixels. Videos are thus converted to 30 fps through a process known as 2:3 pulldown. Essentially, the 24 frames are stretched and redistributed to cover 30 frames instead of the original 24. For TVs with a refresh rate of 60 Hz and a progressive resolution, the 24 frames are converted into 30 and then interlaced into 60 to fit the refresh rate. Though this allows a film to be played on television, these conversions render the film imperfect, and result in film judder.
Refresh Rates That are More Than 60 Hz
24 fps films can't fit on a 60 Hz screen, since 60 is not a multiple of 24. This problem can be overcome if the refresh rate is 120 or 240, both multiples of 24. But even though the TV can refresh its pixels at such a high rate, it can't change the frame rate of the incoming data. Thus, TVs with higher refresh rates create extra frames between those provided by the source. These frames are created by comparing and extrapolating information from successive source frames, and calculating the 'in-between' version. This reduces film judder, and creates a seamless transition between the existing frames. However, many, including yours truly, deem this duplicated smoothness worse than the judder that results when the fps in the source and the refresh rate of the TV don't match. The duplicated frames often make the output seem unreal, and can be a worse put-off than the judder! But of course, this is a matter of perception and taste, and is a personal choice. When buying a new HD TV, stay informed about its refresh rates and how it affects viewing quality. If you want to buy a 3D TV, get a TV with a refresh rate higher than 120 or 240, but otherwise, as highlighted before, a refresh rate of 120 Hz or even 60 Hz is more than enough.

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