Light compensation for security cameras (WDR, BLC and HLC)

In this article, I talk about Light Compensation for security cameras.

The most popular technologies discussed in the articles are BLCWDR, and HLC.

Normal vs BLC vs WDR

You can find a clear explanation of the topic with good application examples.

By the end of the article, you can watch videos where I explain more about the  BLC, HCL, and WDR features for professional security cameras.

Why use light compensation?

The footage from a security camera must be as clear and crisp as possible to help identify an important event. The image should not be too bright or too dark in an ideal scenario, and features such as BLC, WDR, and HLC can help you.

Let's dive into the details..

BLC (Backlight compensation)

BLC is used to improve an image that is too dark by increasing the overall exposure to light. The foreground and the background will be exposed to more light, so there’s no double exposure, but only one.

BLC OFF

BLC OFF

BLC ON

BLC ON

Suppose your goal is to improve the images that are in the foreground, and you don’t care too much about the image background. In that case, BLC can be the right solution because it is a cheaper technology for backlight compensation.

WDR (Wide Dynamic Range)

WDR (Wide Dynamic Range) cameras can compensate for backlight issues.

With a camera pointing to an entrance, door, or window, you will notice parts of the image with an excess of light and other parts that are too dark. To obtain the correct image, the camera must compensate for this kind of situation.

Dark and Bright Area

In the window, you can see the excess of light with very bright areas, whereas, in particular inner regions, there are dark areas.

WDR can compensate for these different areas and balance them.

WDR technology works with different shutter speeds and allows more or less light to get into the camera by controlling the sensor's exposure to the light that is coming from the environment.

By using WDR, the camera shutter works as follows:

1. Works at a higher speed to expose the sensor to light for a short period of time

2. Works at a lower speed to expose the sensor to light for a longer period of time

3. Merge both captured images with different light exposure

WDR compensates for dark and brigth areas

By activating the WDR on the camera, the shutter will automatically expose the camera to light twice and merge them for a better result.

Over exposed image
Under exposed image

The first picture shows more indoor details while in the second picture you see the opposite effect with more outdoor details

WDR image

The merged image shows indoor and outdoor details from both light exposures performed by the camera with WDR.

The camera processing is intense because it has to merge two images into a third one. This technology costs more.

This variation between the darkest and brightest areas is the dynamic range. The greater the camera's ability to vary smoothly from one region to another, the more efficient it will be. You can find this information in the product catalog described in decibels (dB). The higher, the better.

Below is an example of the WDR information from a camera's catalog

WDR Information on a catalog

Be very careful when comparing the differences between cameras because some small details make a great difference in the footage quality.

Cameras that have true WDR are much more efficient than cameras that report having digital WDR.

True WDR and Digital WDR

True WDR works by capturing two images with different exposures to light and merging them into a third one, and therefore works more intensely but more efficiently. In contrast, the digital WDR works only with one image to make a digital exposure compensation.

A camera configured to work with 30FPS, using WDR will capture twice the frames (60) to deliver the final image.

True WDR concept

A camera configured to work with 30FPS, using digital WDR captures the same amount of frames (30) to deliver the final image.

Digital WDR Concept

Conclusion: cameras with True WDR are better but more expensive.

HLC (Highlight compensation)

HLC activates dynamic masks in some cameras with an excess of light. The masks follow the light movement, thus blocking the intense light.

HLC OFF ON

HLC OFF/ON

This feature varies depending on the camera model you are using.

The previous picture is from a Samsung camera, other models such as the Amcrest Night Color IP camera doesn't have the dynamic mask but can work on the overall image to reduce the spotlight glare.

Video:  What is backlight compensation

Please watch the video below for more information on backlight compensation.

Video:  What is WDR for security cameras

The video below shows more details about WDR technology.

Conclusion

BLC, WDR, and HLC are technologies that help reduce the contrast of light and improve the footage's overall quality. You can find this type of feature on most professional security cameras designed to work in harsh environments. 

I hope this article can help you; please share it with your friends.

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