Closely related to the concept of temporal rate is refresh rate, which is the number of pictures a display shows per second. Although temporal rate is often measured in frames per second (fps) or hertz (Hz), refresh rate is typically measured only in Hz.
As discussed in the TV Broadcast Formats article, television is usually transmitted at either 50Hz or 59.4Hz depending on what part of the world you are talking about. So, for many years, TVs simply had a refresh rate of 50Hz for the 50Hz countries and 59.94Hz for the 59.94Hz countries. However, this is no longer the case.
The 3-3-3 Plan for Understanding Refresh Rate
There are three general principles that are crucial to understanding refresh rate. These are:
Given these principles, a refresh rate other than the default 50Hz or 59.94/60 Hz offers the following possible benefits:
Finally, there are a few times when the "refresh rate" of a display is not really the refresh rate, at least in the traditional sense. The reality is that, traditionally speaking, 240Hz is the highest refresh rate available in displays today. Instances of this "fudging" are:
Judder & Cadence
As already mentioned, some HDTVs will let you turn off smoothing for 24p video but leave it enabled for non-24p material. But how, exactly, would you go about this? Although it varies somewhat between the different TVs, take a look at the picture below :
The above picture shows the "Auto Motion Plus 120Hz" menu for the Samsung UNB6000 series of HDTVs. The "Blur Reduction" option controls how much smoothing is used for non-24p video, while the "Judder Reduction" option controls how much smoothing is used for 24p video. Setting the "Judder Reduction" to 0 causes each frame of 24p material to be shown 5 times (120/24 = 5), thus allowing you to view movies without that pesky 4% speedup or 3-2 pulldown [8 page 2].
But wait a minute - what the heck is judder, anyway? Believe it or not, there are actually two very different definitions of judder. On the one hand, judder can refer to the unevenness caused by the 3-2 pulldown process. On the other hand, judder can refer to the stuttering and choppiness that is inherently part of anything recorded at a mere 24fps . If someone is talking about dejudder or judder reduction, that person is most likely discussing a smoothing system in a display designed to reduce the 2nd type of judder. This is particularly true if the term judder reduction is used since 3-2 pulldown cannot be "reduced" - it is either there or it isn't.
Another term you might find thrown around is cadence. Basically, if someone says that a display preserves the cadence of film, it is just a fancy way of saying that a display can show movies without using a 4% speedup or 3-2 pulldown.
Flicker-Free Refresh Rates
For film projectors, which run at either 48Hz or 72Hz, 48Hz is adequate for removing flicker, although 72Hz may be needed for some people .
For CRT TVs and plasmas, 59.94/60Hz is, for the most part, good enough .
For CRT computer monitors, it is generally agreed that at least an 85Hz refresh rate is needed to remove flicker , although some like myself may need a higher refresh rate such as 90Hz. This means that for both flicker-free and cadence-correct viewing on a CRT computer monitor, 96Hz would be required for 24p, 100Hz would be required for 50i/p, and 120Hz would be required for 60i/p.
The response time of a display is how long it takes any given pixel to change from one color to another color. It is not really an issue for CRTs or plasmas, but it is for LCDs.
The response time for a display is measured in milliseconds (ms), which is one-thousandth of a second. At a bare minimum, the response time of a display should be the duration of each frame, i.e. a 60Hz display should have a response time of at least 16ms (1000/60 = 16.6). However, an LCD will still benefit from a lower response time. This is because the change from one pixel color to another pixel color will produce colors that were never in the original video, i.e. a pixel will be gray during the time it changes from white to black or black to white. A lower response time minimizes the appearance of these changes.
Panel Self-Refresh (PSR) & Selective Refresh (SR)
On Feb. 7, 2011, the Video Electronics Standards Association (VESA) announced the approval of Embedded DisplayPort (eDP) 1.3, which is used in laptops and other products with embedded displays .
One interesting feature of eDP 1.3 is PSR, which allows the computer to stop sending frames to the display if the video doesn't change. This is turn reduces power consumption and can save on battery life [23 page 25].
Although PSR is a step in the right direction, the ideal would be to use SR. In SR, only changed information is sent from the computer to the display. This would further reduce power consumption and could also improve game performance. For instance, consider the example of the computer game StarCraft II. When used at high frame rates, this game caused problems for some computer users. The solution to this problem that was posted by Blizzard, the company that makes the game, was to limit the frame rate  . However, if there was a video interface in use that used SR, the need to limit the frame rate would be greatly reduced if not entirely eliminated, thus giving better game performance. Additionally, the game would be able to generate more frames with SR than without SR due to freed up power.
So, is there any plug that uses SR? Although the creators of the Digital Visual Interface (DVI) plug, which was approved on Apr. 2, 1999 [26 page 1], commented that SR would be possible over DVI [26 page 8], this never came to be. On Apr. 18, 2004, VESA approved the Digital Packet Video Link (DPVL) standard that could provide SR "utilizing conventional digital monitor interfaces" [27 page 1], but this standard has yet to see widespread use.
However, there may still be hope for the use of SR. On Sept. 10, 2012, VESA announced the upcoming release of eDP 1.4, which allows for "a new partial-frame update capability for Panel Self Refresh (PSR)" among other things. This is basically SR. Embedded DisplayPort 1.4 "is anticipated to be released in October 2012, and utilized in commercial products as early as 2014" .
The most recent advance in the area of refresh rate has been NVIDIA's G-SYNC technology. The main benefit of G-SYNC is that it allows for displays to have a variable refresh rate . As a bonus, G-SYNC displays will also have a strobing backlight mode to reduce motion blur . You can read more about G-SYNC here.
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