Led display refresh rate and gray level analysis

- Jun 24, 2019-

With the development and application of indoor led display screens, LED display screens can be widely used in command centers, monitoring centers and even broadcast studios. However, from the overall performance of the LED display system, can these displays meet the needs of users? Can the images displayed by these LED displays conform to the human eye? Can these LED displays withstand different shutters of the camera? The test of different angles of camera? This is the problem that the led display needs to face the need to consider, the following powerful color will affect the LED display effect of several factors (including refresh frequency, gray level, etc.) to make an analysis.

        Led display refresh rate (visual refresh rate)

        "Visual refresh rate" refers to the rate of screen update, 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 rate, the more stable the picture display and the smaller the visual flicker. The low "visual refresh rate" of the led display screen affects the horizontal horizontal stripes in addition to the camera and photography. At the same time, images similar to tens of thousands of bulbs flash at the same time, which may cause discomfort when the human eye is watching. Even hurting the eyes.

        Although for the human eye, the visual refresh rate of 60 Hz or more has been perceived as a continuous picture, the higher the visual refresh rate, the more stable the displayed image, the less likely the human eye feels fatigue. In today's high-quality video, in order to get a more detailed picture, such as wonderful playback or close-up photography, they are all shooting at high speed cameras of 1,000 Hz or more per second. At this time, for an LED display that is also photographed, it is a great challenge to be able to present a continuous picture (no black scan line) or a continuous color scale under a high speed shutter.

        Led display gray scale

        “Grayscale” refers to the color hierarchy of various colors between the darkest and the brightest colors, with different variations. Generally, the grayscale is above 14 bits, that is, at least 16,384 color levels or more. 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 film cannot be fully displayed. The LED display effect is greatly reduced. Some low-performance LED displays can be detected with a clear color distribution under the 1/500s shutter. If we increase the shutter speed, for example, 1/1,000s or 1/2,000s, the situation will be even more obvious.

        What affects the refresh rate and gray level of the led display?

        We know several core components of LED display, such as LED switching power supply, LED driver chip, led lamp bead, etc. For the refresh frequency and gray level of LED display, LED driver chip directly determines the visual refresh frequency of LED display. , the performance of gray levels. Among the current LED driver chips, the newest technology is "ScrambledPWM (S-PWM) technology", which is a technology that improves the traditional pulse width modulation (PWM), which spreads the time of one image on. Several short on-times are added to increase the overall visual update rate. Furthermore, the S-PWM technology built in the new generation of LED driver chips can average the number of frames per frame (LED die ON → LED die OFF), and it is evenly divided into multiple counts. And each broken aliquot can maintain the On/Off ratio before the original is not broken.

        S-PWM technology provides different counting modes, so the image refresh rate can be increased up to 64 times. If you switch to S-PWM to improve the image refresh rate, you can easily increase the visual refresh frequency by 64 times and reach 4,800 Hz or more with a low-order clock (such as 5MHz). Compared with the general video refresh rate of at least 10 times higher, it can also avoid high frequency electromagnetic interference (EMIissue), overvoltage surge (Overshoot) and undervoltage surge (Undershoot).

        The LED display of the S-PWM driver chip is photographed with a high-speed shutter of a digital camera, and horizontal black scan lines and patch distribution are still not present. Its visual refresh rate and gray level performance far exceed the LED display using traditional switch-type driver chips.

        High-quality LED driver chip with built-in S-PWM technology, the refresh frequency is up to 3840Hz, the gray level can reach 16bit, and the camera will be in the case of high-speed shutter, and the horizontal black scan line and color block distribution will appear.