What does the refresh frequency and gray level of the led display mean?
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 the LED display screen is widely used. However, judging from the overall performance of the LED display system, can these displays meet the needs of users? Can 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 different camera angles? These are all issues that need to be considered for LED display screens. Below, I will analyze several major factors (including refresh rate, gray level, 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 the 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 to the human eye, the visual refresh frequency of 60Hz 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 pictures, 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 screen that will also be photographed, it is still a big challenge to still be able to present continuous images (no black scan lines) or continuous color gradation under high-speed shutter.
What affects the refresh frequency and gray level of the LED display?
We know several core components of the LED display, such as LED switching power supply, LED driver chip, LED lamp beads, etc. For the refresh frequency and gray level of the LED display, the LED driver chip directly determines the visual refresh frequency of the LED display , 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, as shown in the figure below.
S-PWM technology provides different counting modes, so it can increase the image refresh rate up to 64 times. If you switch 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 with S-PWM driver chip is photographed with a high-speed shutter of a digital camera, but there is still no horizontal black scan line and color patch distribution (as shown in the figure below). Its visual refresh rate and gray scale performance far surpass those of LED displays using traditional switch-type driver chips.
The high-quality LED driver chip, built-in S-PWM technology, makes the refresh frequency up to 3840Hz, the gray scale can reach 16bit, and the video is taken under the condition of high-speed shutter, and there will be horizontal black scanning lines and color patch distribution after the meeting.
