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Frame frequency and refresh rate

          Frame frequency and refresh rate

Visual time characteristic

One of the characteristics of human visual is limited resolution of observation movement, independent screen in a series of discrete visual residual effect may look the same as continuous. First film and later television are use this characteristic, namely in a series of images little chnage (frames) fast switching caused by the effect of movement.

Generating visual reality there are two requirements: First, the image reproducing speed must be sufficient to ensure operation between frames transition very smooth; secondly, to reproduce the speed must also be sufficient to cover the residual visual flicker when the refresh switching generated.

Frame frequency

Frame frequency Definition: the frequency of the screen updates.
In earlier films, there are 16 films per second. Later changed to 24.
In the history of world television development, the use of a frame frequency is 25 and 30. Only M manufactured using 30 frames per second, which includes the United States and Japan M-NTSC, Brazil M-PAL and the like. Later in the development of color television in the United States, Japan and other countries using the M-NTSC requiring separate pan, 30Hz frame frequency be changed to 29.97Hz.

Refresh rate
Refresh rate definition: is the number of repetitions for monitor display data per second

Movement Continuity
Since the movie frame rate is 24 frames / sec, and therefore often looks somewhat jitter, especially a large object moves quickly to the viewer. For example, movie which only 16 frames per second , if not technical processing, the film will shake so calendar harm. In order to reduce flicker, the light may additionally be interrupted in the process of projecting the one frame twice, with such a picture was more refreshed twice, so 24 frames / sec per reproduce the movie 48 times, that is refreshing frequency is 48. Under the premise of not increasing the number of films to get good results. However, when only 16 per movie screen refresh In each film twice, refresh frequency becomes 32, it can still be observed noticeable flicker. To this end, to refresh each piece change to three times, and thereby gaining a refresh rate of 3 × 16 = 48Hz, but this can only be changing the flashing of its reproduction, and does not change the sense of continuity of its action. Later, people will be 16 frames per second of footage per second speed of 24 to release, so do not blink, but the action becomes fast.

When LED large screen display and refresh rate are determined, still feel some flicker region (even a slight flicker), other regions have not, then the light emission brightness of these areas must be relatively centered. Emitting large screen are using pulse width modulation, the duty cycle of the light-emitting close to half / half area of flashes occurring may be greater than the minimum luminance and regional approaches close to the peak brightness.

In addition, even the big screen refresh rate constant peak brightness must also take different scanning method, which effect may be different.

                                                        Translator: Eva
                                                        12th. Sept. 2016

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