How to Fix LED Flicker and Banding in USB Cameras

When setting up a USB camera indoors, you may notice horizontal bands across the preview even though the document on the desk is stationary and the lighting looks steady. Sometimes the bands drift slowly across the image. In other cases, the entire picture becomes brighter and darker between frames, making text and labels harder to read.

Before replacing the camera, record the current settings and check the lighting. The relationship between exposure time and changes in light output is often a more useful starting point than switching to a higher-resolution module.

Why Cameras Record Flicker That Your Eyes Miss

Some LED lights vary in brightness because of their power supply or dimming method. Pulse-width modulation, or PWM, controls average brightness by rapidly switching the light on and off. Your eyes may not notice these changes, but a camera can record them during exposure.

A rolling shutter sensor exposes its pixel rows at slightly different times. If the light output changes while those rows are being exposed, some rows receive more light than others, producing bright and dark bands. The effect can become more noticeable at short exposure times. Basler’s lighting documentation describes how PWM lighting can cause brightness fluctuations and stripes in rolling shutter images.

Whole-image flicker and horizontal banding are related but distinct symptoms. Flicker is a change in brightness between frames; banding is uneven brightness within a single frame. Identifying which one you are seeing helps narrow down the next adjustment.

Check Whether the Lighting Is Responsible

Keep the camera and target in fixed positions, and use a sheet of white paper to make brightness differences easier to see. With the camera settings held constant, switch off the suspected light and test with a known stable light source.

If the bands disappear, focus on the original light’s driver and dimming method. For dimmable LEDs, test several brightness levels rather than checking only the maximum setting.

Where the camera supports it, temporarily disable automatic exposure and automatic gain, then hold both values constant. Otherwise, changes in illumination and the camera’s automatic adjustments can overlap, making it difficult to identify the cause.

Using the 50 Hz and 60 Hz Anti Flicker Settings

Anti-flicker settings generally restrict exposure choices to reduce flicker associated with the local mains frequency. Select the setting for the location where the equipment will operate, which may differ from the development site. Axis’s technical documentation explains these exposure modes.

LED dimming frequencies do not necessarily follow the mains frequency, however. If neither setting produces a clear improvement, investigate the light source rather than repeatedly switching between the two options.

Also check that the setting actually takes effect. An option appearing in the capture software does not, by itself, confirm that the module firmware supports the corresponding control.

Adjust Exposure for the Subject Being Captured

A longer exposure can sometimes reduce the visible effect of fluctuating light. This is worth testing when capturing stationary documents, while checking that text remains sharp and bright areas do not become overexposed.

Moving packages need a different approach. Extending exposure may introduce motion blur, so improving the stability and output of the lighting may be more practical. The aim is to provide enough light while keeping the exposure short enough for the movement.

Frame rate and exposure time also need to be checked separately. Changing from 30 fps to 25 fps does not automatically eliminate flicker. You still need to confirm how long each frame is exposed.

What to Confirm With Your Camera Module Supplier

When selecting USB camera modules for self-service terminals, document capture equipment, or indoor monitoring, ask whether manual exposure, gain, and anti-flicker controls are available. Test those controls with the operating system and capture application intended for the finished device.

For platform compatibility checks, see our guide to sourcing a USB camera module for kiosks and terminals.

If ambient lighting is difficult to control, consider adding a stable light source inside the device to reduce its dependence on external illumination.

Switching to a global shutter camera module does not guarantee flicker-free images. Although the rows share the same exposure period, different frames can still capture different amounts of light from a fluctuating source. Imatest’s explanation of flicker discusses this limitation.

What to Record During Prototype Testing

Use the same module and target for each test. Record the light source, dimming level, exposure time, gain, and frame rate, then save the original captures before and after each adjustment. Still images are useful for showing banding; a short video is better for showing flicker over time.

Share these records when you contact Sinoseen about your camera setup. They give the supplier a clearer basis for reproducing the issue.

Finally, repeat the test under the lighting conditions expected at the installation site. A clean image on an office workbench does not establish how the camera will behave under a different LED fixture or dimming setting.

Frequently Asked Questions

Q1:Why do LED lights cause horizontal bands in camera images?

Some LED lights fluctuate in brightness because of their power supply or dimming method. A rolling shutter camera exposes different rows at different times. When those rows receive different amounts of light, horizontal bands can appear even though the lighting looks steady to the eye.

Q2:Should I select 50 Hz or 60 Hz in the anti-flicker settings?

Start with the mains frequency at the equipment’s installation location. These settings can help with lighting fluctuations related to mains power, but they may not resolve banding from LEDs that use a different PWM dimming frequency. If neither setting helps, test another light source and check the exposure controls.

Q3:Will a global shutter camera eliminate LED flicker?

Not necessarily. A global shutter exposes all rows during the same period, avoiding the row-to-row timing difference that can cause banding under fluctuating light. However, brightness can still vary between frames. The light source and exposure settings still need to be tested together.

Q4:Can I reduce banding without replacing the camera module?

Often, yes. Start by testing a stable light source, checking the anti-flicker setting, and adjusting exposure while holding gain constant. A longer exposure may help with stationary subjects, but it can blur moving objects. Confirm that the module supports the required controls before deciding whether replacement is necessary.