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Refresh rate and gray scale analysis of led display

Aug. 29, 2021

                                             Refresh rate and gray scale analysis of led display


rental led screen for stage.jpg

 

With the development and application of indoor led display screens more and more, no matter in the command center, monitoring center or even the studio, you can see that led display screens are widely used. However, judging from the overall performance of the LED display system, can these displays meet the needs of users? Do the images displayed on these LED displays meet the human vision? Can these LED displays withstand the different shutters of the camera? The test of camera from different angles? These are all issues that need to be considered for LED display screens. Below we will analyze several major factors (including refresh rate, gray scale, etc.) that affect the LED display effect.


The refresh rate of the led display (visual refresh rate)

"Visual refresh rate" refers to the screen update rate, usually expressed in Hertz (Hz). Generally speaking, the visual refresh rate is above 3,000 Hz, which is a high-performance LED display. The higher the visual refresh frequency, the more stable the screen display, and the smaller the visual flicker. The low "visual refresh rate" of the led display screen has an impact in addition to horizontal stripes appearing during video and photography, but also images similar to tens of thousands of light bulbs flickering at the same time, which may cause discomfort when viewed by the human eye , And even cause damage to the eyes.


Although for the human eye, the visual refresh frequency of 60 Hz or more has been perceived as a continuous picture, but the higher the visual refresh frequency, the more stable the displayed image, and the less fatigue the human eye will feel. Nowadays, in high-quality video, in order to obtain more detailed images, such as wonderful playback or close-up photography, high-speed cameras above 1,000 Hz per second are used for shooting. At this time, for the LED display that will also be photographed, it is a big challenge to still be able to present continuous images (no black scan lines) or continuous color gradation under high-speed shutter.


The gray level of the led display


"Gray scale" refers to the color hierarchy of various colors between the darkest and the brightest. Generally speaking, the gray level is above 14 bits, that is, there are at least 16,384 color hierarchies. High-performance led display. If the number of gray levels is insufficient, the color level is insufficient or the gradient color level is not smooth enough, and the color of the video cannot be fully displayed. The LED display effect is greatly reduced. Some low-efficiency led display screens can already be detected with obvious color patch distribution under 1/500s shutter. If we increase the shutter speed, for example, 1/1,000s or 1/2,000s, the situation will be even worse. obvious.


What affects the refresh rate and gray scale of the LED display?


We know several core components of LED display screens, such as LED power supply, LED driver chip, led lamp beads, etc. For the refresh frequency and gray level of LED display screen, the LED driver chip directly determines the visual refresh rate of the LED display screen. , The performance of gray scale. Among the current LED driver chips, the highest new technology is "ScrambledPWM (S-PWM) technology". S-PWM technology is an improvement on the traditional pulse width modulation (PWM) technology, which disperses the time when an image is turned on. Into several shorter on-times to increase the overall visual update rate. To further explain, the S-PWM technology built into the new generation of LED driver chips can count once per frame (LED die ON→LED die OFF), and break it up into multiple counts on average. , And each divided aliquot can maintain the original On/Off ratio before being broken up.


S-PWM technology provides different counting modes, so it can increase the image refresh rate up to 64 times. If you change to S-PWM to increase the image refresh rate, you can easily increase the visual refresh rate by 64 times with a low-level clock (such as 5MHz), and it can reach more than 4,800Hz. Compared with general video, the refresh rate is at least 10 times higher, and it can also avoid the problems of high-frequency electromagnetic interference (EMIissue), over-voltage surge (Overshoot) and under-voltage surge (Undershoot).


The LED display of the S-PWM driver chip is photographed with a digital camera's high-speed shutter, but there is still no horizontal black scan line and color patch distribution. Its visual refresh rate and gray scale performance far surpass those of LED displays using traditional switch-type driver chips.


High-quality LED driver chip, built-in S-PWM technology, making the refresh frequency up to 3840Hz, gray level up to 16bit, in the case of high-speed shutter shooting, there will be horizontal black scan lines and color block distribution after the meeting.


Generally, for led display screens used for stage rental or live broadcasting or TV stations, Runbo uses ICN2153 high refresh chip to meet customer needs and ensure that the display screen is still in good performance when shooting with a shutter camera or mobile phone.


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