Causes and solutions of color cast in surveillance images

Common reasons

1. White balance not calibrated: Most common. The color temperature of different light sources varies greatly (sunlight is about 5500K, Incandescent lamps are about 2800K, fluorescent lamps are about 4000K), and the automatic white balance is prone to misalignment under mixed light sources.
2. ICR dual filter switching problem: Switch to the infrared cut filter during the day and remove it at night to improve sensitivity. If the switching is stuck or the threshold is improper, there will be a reddish/purple color cast during the day and a color cast at night.
3. Mixed light sources: White light, yellow light, and green light (such as LED screens) exist simultaneously in the same picture. Automatic white balance is difficult to balance.
4. Through tinted glass or film: It will change the overall color temperature.
5. Mismatch in fill light color temperature: Warm light and cool white light are mixed.
6. Cable/interface problems: Common in analog systems, poor network cable contact may also cause color abnormalities.

Processing method

Manual white balance calibration steps

1. Under actual lighting conditions (do not turn on the lights temporarily).
2. Place a piece of white paper or white cardboard at the monitoring target location.
3. Let the white paper fill the center area of the picture.
4. Execute "White Balance → Manual/One-click Calibration" in the camera menu.
5. Save and observe the actual footage, fine-tuning if necessary.

Prevention suggestions

• Unify the color temperature of the light source in the same area to avoid mixing hot and cold colors.
• Use a fill light with a higher color rendering index (Ra), Ra ≥ 80, which is closer to the true color.
• Avoid large-area single-color wall reflections (such as green walls and yellow walls) in the picture, which will mislead the white balance.
• It is recommended to turn on the true color restoration mode in important forensic areas (such as the checkout counter).