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Frame Rate Drops in Low Light

When to use this article​

The camera frame rate drops, floats, or does not stay at the expected value, especially in a low-light environment.

Why frame rate changes​

Some cameras are designed for low-light applications. In automatic exposure mode, the camera may increase exposure time to preserve image quality. Longer exposure time reduces the maximum achievable frame rate.

Keep the frame rate more stable​

Use manual exposure mode when a constant frame rate is more important than automatic low-light compensation.

$ v4l2-ctl -d /dev/video0 --set-ctrl auto_exposure=1

You can also use VizionViewer or VizionCTL to change to AGC mode, which uses automatic gain control with manual exposure time.

Check the result​

Run a stream test and confirm the frame interval stays close to the expected value.

$ v4l2-ctl -d /dev/video0 --stream-mmap --stream-count=100

Image-quality tradeoffs​

  • Increasing gain in low light can add image noise.
  • If the scene is too dark, a constant frame rate may require additional lighting or a lower image-quality target.