How LED Screen displays an image
The flowchart below shows the sequence of processes that take place in order to display the desired image on a LED display.
So, overall, one row at a time is being displayed, but this process is done so fast, with speed much higher than human eye’s response time (which is >= 10ms) that all of the rows appear to be switched on / lit up. Hence, a complete image is formed on the display.
Larger the number of rows, higher the scan-time
As described earlier that one row of a display is switched-on at a time, so the Scan-rate of a display is the amount of time required to display data pixel on all the rows.
So, what if a LED display of resolution, e.g. 1024x768,768 rows. And the display controller starts from row 1 to row 768 to display one row at a time. The amount of time required for completing one-cycle, or more specifically the ‘Scan-time’, would increase very much and may get even higher than the Human eye’s response time. It would result in the rows of the display being noticed to be switching on & off. This effect can be termed as ‘flickering’. To compensate this increase in scan-time, one would suggest increasing the frequency at which data is clocked in, along with row selection. But this may lead to consequences in term of:
The solution is to limit the scanning to a specific number of rows. Commonly 1~16 rows in a matrix display are scanned. For additional sets of rows, additional ‘data group’ lines from the controller or LED display driver are connected to shift-in the data in parallel.
As described earlier that one row of a display is switched-on at a time, so the Scan-rate of a display is the amount of time required to display data pixel on all the rows.
So, what if a LED display of resolution, e.g. 1024x768,768 rows. And the display controller starts from row 1 to row 768 to display one row at a time. The amount of time required for completing one-cycle, or more specifically the ‘Scan-time’, would increase very much and may get even higher than the Human eye’s response time. It would result in the rows of the display being noticed to be switching on & off. This effect can be termed as ‘flickering’. To compensate this increase in scan-time, one would suggest increasing the frequency at which data is clocked in, along with row selection. But this may lead to consequences in term of:
- Increase in power consumption of the whole system, due to increase in frequency.
- Increase in hardware cost, due to increase in power supply and components required with higher frequency response.
- The brightness of the display might be affected by various undesired changes in other parameters.
- The control card or driver that drives the LED display to display an image may have limitations on scanning frequency.
- High scan time would lead to lower Frame-refresh rate.
The solution is to limit the scanning to a specific number of rows. Commonly 1~16 rows in a matrix display are scanned. For additional sets of rows, additional ‘data group’ lines from the controller or LED display driver are connected to shift-in the data in parallel.
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