Scan Lines - Visible lines in the camera capture
Scan lines are dark or light lines that can scroll through the LED display, or show as static lines. They are visible when recording footage of the LED wall with a camera while the two are not timed together properly.
Note - If you can see scan lines with the naked eye, this is a tile refresh rate issue - too low. Please contact LED tile manufacturer for more info.
Scan line causes:
- If lines are static: Scan lines result from the sync being at different offsets when comparing the LED display and the camera sensor. This is the relation between the LED refresh cycle (multiplexing) and the camera sensor charging.
- If lines are rolling: The scan lines result from a refresh rate / sync mismatch between the LED display and the camera sensor. Think 59.94Hz versus 60.00Hz for example. This would causing the times to slowly drift over time causing the appearance of rolling bars throughout the screen.
Example of static horizontal scan lines.
Example of static horizontal scan lines.
Example of rolling horizontal scan lines (when viewing from camera, this bar scrolls).
Recommended Troubleshooting Steps
When using a camera with an LED wall, both the camera and the wall must be in sync.
- Step 1: Check that External Sync on the HELIOS is activated, and that there is a matching sync signal with the same rate as the content. Make sure that the camera recording frame rate is set to exactly that same rate (screenshot below).
- Step 2: If scan lines are still visible, adjust the Sync Delay (Input > NanoSync). Start with microsecond (us) movements and then move to smaller units as needed.
If adjusting the Sync Delay in a multi-camera set up, keep in mind that the HELIOS is moving time the same for all cameras. If scan lines are still appearing in other camera views, use the sync generator to offset these individually. - Step 3: If scan lines are still visible, adjustments can be made via GhostFrame slices. You can add black subframe slices to help improve image quality. For example, in the below screenshot the charge time of the sensor was determined to be occurring during slices 4 and 5. Turning those to black resolved the scan line issue because the LEDs are not emitting light during that time.
- Step 4: If scan lines are still visible, adjust the shutter angle/shutter speed of the camera. The User should make the shutter angle smaller/shutter speed faster.