The refresh rate of the LED display is strictly defined as the number of times the display image is displayed in full grayscale in 1 second. The unit of measurement of screen image refresh rate is Hz.
When the refresh rate of the scanning display is seriously insufficient, it can be perceived by the human eye. (People can feel the flicker of the screen when the refresh rate is less than 240Hz). When using a high-speed shutter camera and a camcorder, it is very easy to capture black lines due to insufficient refresh rate of the display. The contradiction between grayscale and refresh rate on scanning screen is very obvious. At present, there are several driveing ICs for the embedded buffer and PWM core of the scanning screen, which are either costly or have a relatively serious afterglow, and cannot be widely promoted in the short term.
The gray scale of the LED display is implemented by weighting the subfield. The traditional control method is to implement all subfields of one row and then move to all subfields of the next row. This implementation will turn out black lines when photographing with a camera because the time spent on each line is too long, and the low visual refresh rate (equivalent to the line changing speed). The following picture shows an 8 scanning screen. The single cabinet 128*128 adopts the traditional method to achieve 14-bit grayscale and 300Hz refresh rate effect, and the exposure time of the Canon 7D camera is set to 1/1000 second.
The traditional control mode’s line changing speed is too slow, and will cause black lines when taking pictures. A more effective way is to divide all subfields to achieve a gray scale into multiple parts, first make a partial gray scale of the first line,then make the same partial gray scale of the next line. After one round of line wrapping is completed, implement next grayscale part. This can achieve to improve the visual refresh rate. The more parts of all subfields achieved in one gray scale, the higher the visual refresh rate that can be obtained.
At present, this technology is quite popular, and there is no black line while shooting with the camera. But it will produce an incomplete grayscale effect, commonly known as “sweat spot” or “watermark” effect. The following picture shows an 8-scan screen. The single cabinet 128*128 uses a 16-fold breakout way to achieve 14-bit grayscale and 3840Hz visual refresh rate effects. The exposure time of the Canon 7D camera is set to 1/1000 second.
The latest scanning screen control method
Through the upgrade and improvement of the control system, it is possible to ensure high gray scale and refresh rate at the same time, and still have excellent performance under high-speed shutter shooting.
