How to avoid the overexposure of image?

VIGI Security Manager
Updated 06-30-2020 02:54:57 AM 1302
This Article Applies to: 

The overexposure of surveillance images can be roughly divided into over-exposure during the day and overexposure at night. The overexposure in the daytime is basically caused by the backlight of the scene, while the overexposure at night is caused by the over-intensity of the infrared reflected light of the object.

Note: Please make sure the lens is clean.

Overexposure in the daytime

The light reflected from the counter is relatively strong, making the counter very bright and unclear


The camera will overexpose in the presence of bright light directed or reflected into the lens. Overexposure will lead to unclear details. During installation, we need to consider scenarios and avoid direct light or strong reflections. If it is unavoidable, we need to adjust the image parameters to alleviate the overexposure.

Step 1: We take the overexposure area as the exposure target and do backlight compensation (BLC), so that the IPC takes the overexposure area as the target to reduce the overall light input. The overexposure area in the figure is near the center, and we set BLC area to be center.

Step 2: After we enable BLC, the IPC reduces the overall light input, so the surroundings will become darker. We can increase the brightness of the surroundings by wide dynamic range (WDR).

Step 3: We can fine-tune brightness and contrast to display the best image.

The following picture shows the adjusted result. (BLC area in center + WDR + brightness 60, contrast 40.) As you can see, the area of counter is clearer. You can further adjust the parameters according to your own image quality.



Overexposure at night

Overexposure due to being next to the wall is quite obvious, as shown below.


When the camera is installed next to the wall, if the angle is too biased towards the wall, the infrared light reflected back from the wall will be too strong, and the wall will be overexposed. If the wall is overexposed, the camera will reduce the shutter exposure time to maintain the overall average brightness of the screen, so that the other part of the screen will be too dark.

Step 1. Adjust angle to reduce the area of overexposed objects in the picture.

Without affecting the monitoring, make the wall area in the picture as small as possible. Firstly, the effective monitoring area can be increased; secondly, if the overexposure area of the wall is reduced, the exposure time of the camera will be increased, and the monitoring image will be clearer.


Step 2. Set BLC area to make dark areas brighter

You can increase the exposure time of the camera by setting the BLC area of the camera. Although the wall or reflective obstacles may be brighter, the effective monitoring area can be seen more clearly.


Step 3. Enable WDR to balance the brightness

Increase WDR can strengthen the details in the dark, and monitoring effect in night vision is better.

Note: Too high WDR will increase the noise in the night vision picture. WDR should be properly increased.

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