Why Does My Phone Security Camera Show Dark Rolling Bands Under Tube Lights? 50 Hz Power, Android's Anti-Banding Setting, and What Actually Fixes It
You point an old Android phone at the shop counter, start recording, and check the footage that evening. The picture is sharp and the colours are fine, but there are soft dark stripes across the frame, slowly crawling upward, like a television from the 1990s. In daylight they're gone. Under the tube light, every time. The phone isn't broken and the app isn't corrupting anything. The phone is…
The dark rolling bands seen on a phone security camera under tube lights are caused by the flickering of lights that are powered from the 50 Hz mains electricity supply. These lamps brighten and dim rapidly, and when a phone camera captures the image row by row, the alternating light causes horizontal bands of different brightness.
The camera's rolling shutter mechanism exposes and reads each row of the image sequentially, so if one row captures more of the bright phase of the flicker while the next row captures more of the dim phase, bands appear.
Android's camera system can help by using its anti-banding setting, CONTROL_AE_ANTIBANDING_MODE. This setting instructs the phone's auto-exposure system to only use exposure times that don't cause banding under a specific power frequency. The available modes include OFF (no antibanding), 50Hz (for 50 Hz power), 60Hz (for 60 Hz power), and AUTO (which adapts to the current illumination condition). By default, the phone will use either the 50Hz or 60Hz mode, depending on the country.
However, there are a few caveats to this solution. Not all phones support the AUTO mode or every antibanding mode. Additionally, if manual exposure control is enabled, the antibanding setting will not function. The manual exposure will overwrite the camera's anti-banding protection, causing the bands to reappear.
To fix the issue, users should ensure that the phone is set to the appropriate antibanding mode (50Hz or 60Hz) according to the local power supply frequency. If the phone does not have the AUTO mode or if it defaults to the wrong frequency, testing with different exposure times (10 ms, 20 ms, or 30 ms on 50 Hz power, and 1/120 s, 1/60 s, or 1/40 s on 60 Hz power) can help eliminate the bands.
Written by urgent.news from Dev.to's reporting — not their text. Machine-written — may contain errors; check the original before relying on it.
