Refresh Rate vs Scan Rate
Definition
Refresh rate and scan rate are two different figures in LED display specifications, and they are often confused. The video frame rate, typically 50 or 60 Hz, is the number of new images the processor receives each second. The refresh rate given in LED specifications, for example 1920, 3840 or 7680 Hz, is the number of times per second the LED drivers repeat their PWM output, and it determines how the wall behaves on camera. The scan ratio (1/8, 1/16 scan and so on) describes multiplexing, that is the number of pixel rows that share one driver channel and light in turn. Some suppliers use the term scan rate for the refresh rate. A higher scan ratio makes a high refresh rate harder to reach. For camera work, 3840 Hz is the figure commonly requested, and 7680 Hz for high-frame-rate shooting.
In the field
A wall that looks correct to the eye but shows bands or flicker on camera usually has a refresh rate too low for the shutter speed in use, or is not synchronised with the camera. Before panels are confirmed for broadcast or film, the supplier is asked for the refresh rate, the scan ratio, the processor model and whether genlock is supported.
Related lessons
Sources
- DOIT VISION, 1920Hz vs 3840Hz LED Screen Refresh Rate : 3840 Hz recommandé pour la captation caméra · doitvision.com
- Brompton Technology, ShutterSync : période de rafraîchissement scan-mux des dalles et période d'obturation · bromptontech.com
- Brompton Technology, Recreating Reality: Synchronisation Artefacts : bandes et scintillement à la caméra, genlock · bromptontech.com
- The Broadcast Bridge, Virtual Production For Broadcast: Video Wall Configuration : fréquences de rafraîchissement courantes des murs LED de 3840 ou 7680 Hz · thebroadcastbridge.com
- ROE Visual, Black Pearl BP2V2 : dalle de production virtuelle donnée jusqu'à 7680 Hz de rafraîchissement pour éviter les lignes de balayage à la caméra · roevisual.com